Comparative Morphology and Generic Classification of Catfishes of the Trichomycterus Lineage (Siluriformes: Trichomycteridae) ^†

Abstract

Recent genomic phylogenies have generated new robust classifications of actinopterygian fishes, making possible greater nomenclatural stability, but genus-level classifications of groups like the diverse catfish subfamily Trichomycterinae are still unclear, containing ill-defined paraphyletic taxa. The focus of the present study is the Trichomycterus Lineage (TL), a clade with great morphological diversity, containing about 170 species widely distributed in South America, occurring in the most important biodiversity hotspots of the world, such as the Atlantic Forest, Cerrado, and the Tropical Andes. Most species are small, but at least one reaches about 400 mm of total length, being used as food and depicted in pre-Hispanic Andean ceramics. Based on a comparative morphological analysis, mainly using osteological characters, supported by concordant genomic phylogenies, a new classification at the genus level is here provided. Many morphological features delimiting TL genera seem to be related to ecological adaptations. Nine genera are here recognised of which five are new. Recognition of the new genera will allow easier descriptions of new species and consequently better biodiversity estimates.

1. Introduction

Genomic phylogenies have provided unprecedented and robust information on the internal relationships of Actinopterygii fishes, the largest group of vertebrates in the world, leading to structural changes in their classification [1]. These changes tend towards more stable phylogenetic classification systems over time, fundamental for a better understanding of biodiversity and, consequently, for its conservation. New classification proposals range from new arrangements for orders and families (e.g., [1,2,3]) to intrafamilial revisions at the genus level (Refs. [2,4,5] as examples of Neotropical groups). However, the genus-level classification of some groups continues to have very low phylogenetic resolution, including paraphyletic genera with ambiguous or uninformative diagnoses.

With about 340 valid species [6] occurring in a vast region between southern Central America and southern South America, trichomycterine catfishes (Trichomycteridae: Trichomycterinae) are an example of genus-level classifications that still have an unsatisfactory resolution [7,8]. For many years, the vast majority of trichomycterines were allocated in a single paraphyletic genus, Trichomycterus Valenciennes, 1832, whereas others were included in monotypic genera that were described based on their unique characteristics of the external morphology without considering their relationships (see [8,9] for a recent overview). In recent decades, advances in the taxonomy of the group have resulted from greater depth studies on morphology [10,11,12,13,14,15,16] and phylogenetic relationships [7,8,9,17,18,19,20], but there are still important gaps to be filled.

The two main milestones on the way to resolving the historical taxonomic problems of Trichomycterinae were studies supporting its monophyly [7,12,17,18] and the establishment of the identity of the type species of Trichomycterus, Trichomycterus nigricans Valenciennes, 1832 [21]. Previously, Trichomycterinae was considered a paraphyletic group [22], and T. nigricans was mistakenly identified [23]. Trichomycterus was then restricted to a monophyletic group endemic to eastern South America, containing the type species of the genus and sister to a clade comprising other genera (i.e., Cambeva Katz, Barbosa, Mattos & Costa, 2018 and Scleronema Eigenmann, 1917) from eastern South America [18]. However, the many other species of other lineages formally allocated in ‘Trichomycterus’ remain with an uncertain status [8].

Phylogenetic studies have corroborated two more inclusive monophyletic groups of Trichomycterinae, both with wide geographical distribution in South America [7,8,19], the Eremophilus Lineage and the Trichomycterus Lineage [7]. The Eremophilus Lineage (EL) comprises Eremophilus Humboldt, 1805, a monotypic genus from the Andean region of Colombia; Bullockia Arratia, Chang, Menu-Marque & Rojas, 1978, a monotypic genus from trans-Andean Chile; Hatcheria Eigenmann, 1909, and Silvinichthys Arratia, 1998, two genera with poorly defined boundaries, endemic to the southern Andes region; Ituglanis Costa & Bockmann, 1993, endemic to a vast area including northern, eastern, central, northeastern, and southeastern South America; and Oreiadoglanis Costa & Katz, 2025, endemic to central South America [7,8]. Another likely member of EL is Rhizosomichthys Miles, 1943, a monotypic genus from the Colombian Andes, supposedly extinct since the 1920s [14]. In addition, numerous species allocated in ‘Trichomycterus’ from western and northwestern South America belong to different EL clades [8].

The Trichomycterus Lineage (TL), the focus of this study, includes a lineage from eastern South America comprising three genera, Cambeva, Scleronema, and Trichomycterus (the CST clade [15]), with 164 valid species, corresponding to about 50% of all trichomycterines, and two unnamed lineages from western South America, with at least about 10 species, presently allocated in ‘Trichomycterus’ [7,19]. Species of TL occur in most South American tropical river basins and typically inhabit mountain rivers and lakes, but some lineages are found in lowland fast-flowing streams [18]. The great majority of TL taxa are endemic to areas within biodiversity hotspots, including the Atlantic Forest of eastern South America, the savanna-like Cerrado and the Tropical Andes. They are small, usually reaching between about 50 and 120 mm of standard length (SL), but one species, Scleronema auromaculatus Costa, Sampaio, Giongo, de Almeida, Azevedo-Santos & Katz, 2022, does not surpass 40 mm of total length [9], and at least one species, ‘Trichomycterus’ rivulatus Valenciennes, 1846, reaches about 400 mm of total length and is used as food by people from the Lago Titicaca region [24], having been depicted in Incaic ceramics, thus revealing an old local socio-cultural importance [25].

The CST clade concentrates most of the trichomycterine phylogenetic studies (e.g., Refs. [8,9,18,20] and included references). Cambeva and Trichomycterus have a larger number of species (64 and 89, respectively), and although both genera are recovered as monophyletic in all molecular analyses (e.g., [7,16,18]), they have not yet been diagnosed by exclusive morphological characteristics or a combination of external morphological features, making their identification without molecular data difficult. Scleronema comprises 10 species in three lineages differing from each other by numerous morphological characters [9,26]. One of these lineages (i.e., subgenus Plesioscleronema Costa, Sampaio, Giongo, de Almeida, Azevedo-Santos & Katz, 2022) exhibits great morphological similarity with a lineage of Cambeva (i.e., the Cambeva variegata group; [27]) that occurs in the same region (upper Rio Paraná drainage, southeastern Brazil), generating difficulties in discerning the two genera with diagnoses currently available. The western South American lineages have poorly defined boundaries and scarce available information about the morphology of included species (see results below).

The first objective of this study is to conduct a comparative morphological analysis based on a large sample of all known TL lineages, searching for informative characters diagnosing TL clades. The second objective is to provide a new classification at the genus level reflecting the phylogeny of the group, allowing better identification of TL genera and reducing the number of incertae sedis species in Trichomycterinae.

2. Materials and Methods

This study was based on the examination of 154 nominal species of TL and many still undescribed species, representing all lineages and 91.6% of all nominal species of TL herein recognised (i.e., 168 species). A list of examined specimens appears in Appendix A; lists of other non-TL Trichomycterinae examined appear in Costa et al. [16,27]. In species lists after diagnoses, * indicates species that were not examined in this study; morphological data about these species were taken from the literature.

Osteological preparations followed Taylor & Van Dyke’s protocol [28]. Osteological illustrations were made using a Zeiss Stemi SV 6 stereomicroscope (Microscope Centra, Willow Grove, PA, USA) with camera lucida. The osteological nomenclature primarily follows that described in Costa [15], which was based on previous studies [29,30,31,32,33,34,35,36,37]. Modifications were those proposed by Kubicek [38] based on developmental osteology of siluroids. As observed in this study, variations in the number of branchiostegal rays among trichomycterine taxa only occur through addition or subtraction of the anterior rays. The posterior rays, which are the first to appear in developmental series [38], always remain in the same position and maintain approximately the same shape, supporting recognising them as homologous in different taxa. Consequently, numbering rays starting from the most anterior backward, as is commonly done (e.g., Refs. [14,38,39]), may result in using different numbers for the same homologous posterior ray in cases when addition or subtraction of anterior rays occurs. To maintain numbering always associated with the same homologous rays (same position and shape), here numbering is done from the most posterior ray (i.e., ray 1) forward (Figure 1).

The nomenclature of the pores of the cephalic latero-sensory system followed the proposal of Arratia & Huaquin [40], which basically followed the nomenclature of cephalic canals described by Northcutt [41], with some modifications to optimise the recognition of homologous pores. In Trichomycteridae, except for the basal trichomycterids Copionodontinae and Trichogeninae, the cephalic latero-sensory system has a considerable reduction in canals and pores, making it difficult to recognise pore homology. Among the basal trichomycterid groups, the cephalic laterosensory system of Trichogenes longipinnis Britski & Ortega, 1983, represents the least reduced system pattern among the Trichomycteridae. This pattern is here considered plesiomorphic for trichomycterids due to its great similarity in both position and number of pores with representatives of the family Diplomystidae [40], a basal group of Siluriformes [42], which in turn represents the latero-sensory morphology compatible with the generalised pattern of other teleost fishes (e.g., [43,44]). Thus, the pore pattern exhibited by T. longipinnis and diplomystids is here used as a basic standard to infer pore homologies within Trichomycterinae. On the other hand, uniquely Nematogenys inermes (Guichenot, 1848), often supported as the sister group to a clade comprising all other Loricarioidei [28,45], has a larger number of pores and is not used here as a model for pore nomenclature.

The infraorbital canal of Trichomycterinae is reduced and is represented by two segments separated by a wide interspace, each with two infraorbital pores (io pores), thus differing from the continuous canal with eight or nine pores in T. longipinnis and diplomystids. The anterior-most pore of the anterior segment is positioned near the snout, externally near the anterior nostril, internally close to the lacrimal bone canal, and the posterior pore is situated slightly posterior to the lacrimal, near the posterior nostril (Figure 2A,E,F). These pores correspond in position to pores io1 and io2 of diplomystids (figures 4B, 6 and 8A in [40]) and not to pores io1 and io3 as proposed by Arratia & Huaquin [40]. The posterior segment comprises two pores externally near the posterior portion of the orbit, internally close to the pterotic (Figure 3), corresponding to pores io8 and io9 of diplomystids, not io10 and io11 as in Arratia & Huaquin [40], who based their nomenclatural model on the autapomorphic pattern of N. inermes.

The most common morphological pattern of the supraorbital canal in Trichomycterinae, also present in basal lineages of Trichomycteridae (e.g., T. longipinnis) and thus considered the plesiomorphic condition for Trichomycteridae, is a continuous canal with only three supraorbital pores. The most anterior pore is located near the snout tip, externally adjacent to the anterior nostril, internally above the anterior portion of the autopalatine (Figure 2A,B,D–F). The median pore is adjacent to the posterior nostril and located above the anterior portion of the lateral ethmoid (Figure 2A,F). The most posterior pore is located at the level of the posterior portion of the orbit and internally associated with the frontal canal at the level of the anterior fontanel (Figure 3). These pores correspond in position, respectively, to pores s1, s3, and s6 of diplomystids, thus corroborating the nomenclature proposed by Arratia & Huaquin [40]. However, in different lineages of Trichomycterinae, the supraorbital canal is secondarily broken into two segments in its median region, with each segment having a pore at the extremity of each fragment (Figure 2B,D,E) instead of a single s3 pore in the median portion of a continuous canal. Therefore, in the interrupted canal pattern, there is one pore more than in the general plesiomorphic continuous pattern. The additional pore is here interpreted as a duplication of the pore located in the median position where the fracture occurs, the s3 pore. In these cases, it would not be appropriate to name the additional pore by its relative position as in other non-trichomycterid catfishes (i.e., s4 in [39]), since it would not be homologous to the pore of the same name in other catfish lineages. The median pores are here called s3A and s3B following a similar interpretation on canal breaking made by Gosline [46] for Cyprinodontiformes. The pores associated with the postorbital canal are here called po1 and po2, following Bockmann & Sazima [47].

The classification here proposed is according to molecular phylogenies that are concordant and complementary among themselves, including the analysis using genomic ultra-conserved elements by Ochoa et al. [7], which constitutes the most comprehensive analysis of Trichomycteridae and the one with the highest support values at all nodes, and other phylogenetic trees generated by multigene datasets [8,9,16,19,20]. The classification followed a subordinate phylogenetic trajectory according to Figure 4. Each subsection of results begins with a brief introduction containing data on phylogenetic position and diagnostic character states (sense Sereno [48]), justifying the delimitation of taxa in the new proposed classification, followed by formal taxonomical accounts containing diagnoses, included taxa, and geographical distributions. The diagnoses are objective and include character states that occur in all members of each diagnosed group. Characters with ambiguous states or incomplete distribution among species of monophyletic units herein focused on were not included in diagnoses.

3. Results

3.1. The Trichomycterus Lineage (TL)

The Trichomycterus Lineage supported in Ochoa et al. [7] comprises taxa exhibiting high morphological diversity. No unique character state was found to diagnose TL. In addition to the absence of those character states uniquely diagnosing EL genera (see below), each TL genus is diagnosable by either unique morphological features or by unique combination of character states (see diagnoses below). TL comprises a single diverse sublineage endemic to eastern South America, the CST clade, and two sublineages endemic to western South America, the Western Trichomycterus Sublineages (WTSs).

The genera of TL are distinguished from other trichomycterine genera by the following: caudal peduncle not distinctively slenderer than the anterior portion of the trunk (vs. distinctively slenderer in Bullockia and Hatcheria [49,50]); dorsal-fin base relatively short, slightly longer than the anal-fin base, with the distal margin nearly straight to slightly convex (vs. dorsal-fin base relatively long, twice longer or more than the anal-fin base, distal margin slightly concave in Bullockia and Hatcheria [49,50]); having the anal-fin origin at a vertical approximately through the middle of the dorsal-fin base or posterior to it (vs. through the dorsal-fin base or immediately posterior to it in Ituglanis and Silvinichthys [11]); two or four infraorbital pores (vs. six in Bullockia [40]); having the supraorbital canal when continuous with three pore pairs and the lateral line canal of the trunk with one to three pores (vs. supraorbital always continuous and with five pore pairs and the lateral line canal of the trunk with four to seven pores in Bullockia and Hatcheria [40]); the absence of a thick layer of adipose tissue between the skin and the body musculature and the absence of two pillow-like masses of adipose tissue on the nape (vs. presence in Rhizosomichthys [14]); the absence of a conspicuously perforated skin surface of the body by pores of ampullary organs (vs. body skin surface highly perforated by pores of ampullary organs in Silvinichthys [11]); having 33–41 vertebrae (vs. 43 or 44 vertebrae in Eremophilus); having a laterally directed sphenotic process (Figure 3; vs. anteriorly directed in Ituglanis (figure 3 in [10]); the absence of a robust osseous ridge on the dorsolateral surface of the autopalatine and absence of a crescent-shaped transverse crest on the supraoccipital (vs. presence of both structures in Rhizosomichthys (figures 9 and 10 in [14]); the absence of a sharp posteroventral process on the lateral ethmoid (vs. presence in Eremophilus [51]); autopalatine never with a deep rounded concavity on the medial margin of the autopalatine (vs. always with a peculiar deep rounded concavity on the medial margin of the autopalatine in Ituglanis (figure 6 in [10]); and the metapterygoid never with a rounded dorsal margin to form an approximately semicircular structure (with a rounded dorsal margin to form an approximately semicircular structure in Ituglanis (figure 4 in [10]).

3.2. The CST Clade

This clade is supported in all molecular analyses [7,9,16,17,18] but not corroborated by unique morphological character states. It comprises the greatest diversity of trichomycterines in both number of species and external morphological features (e.g., Figure 5A–D).

Included taxa. The CST clade contains two more inclusive clades, each distributed in a vast region of eastern South America: the CS clade and the T clade (Figure 4), as described below.

3.3. The CS Clade

The CS clade contains different lineages exhibiting a great diversity of morphological patterns and occupying a wide geographical area [7,9,16,17,18,20]. Despite the great morphological divergence found among included lineages, this clade is here corroborated by a series of morphological character states that are unique among taxa of TL: skin surface between opercular and interopercular odontode patches continuous with the branchial membrane (Figure 5A–C; vs. separated by a skin fold or crests forming a gap, Figure 5D–F); the posterior nostril orifice smaller than the anterior nostril orifice; the largest axis of the opercular patch of odontodes horizontally aligned (Figure 5A–C; vs. slightly perpendicularly aligned, Figure 5D–F); the distal extremity of the branchiostegal ray 3 not distinctively widened, about as wide as the extremity of neighbouring rays (Figure 1A–C; vs. branchiostegal ray 3 extremity distinctively wider than neighbouring rays, Figure 1D,E); dorsal process of the interopercle with a rudimentary or absent laminar bone expansion overlapping the ventral portion of the preopercle, resulting in a nearly flat dorsal profile of the process (Figure 6A–C; vs. with a well-developed laminar bone expansion, dorsal profile convex, Figure 6D–F); quadrate narrow, with a deep concavity in its anteroventral margin (Figure 6A–C; vs. relatively broad, concavity moderate or absent, Figure 6D–F); the parapophysis of the first free vertebra with a process projecting over the dorsal surface of the adjacent rib (Figure 7H; vs. without that process, Figure 7G); and the articulation zone between the frontal and the supraoccipital comprising numerous, small prominent undulations (Figure 3A,B; vs. weak or no undulation, Figure 3C–E).

Other morphological features consisting of potential synapomorphies of the CS clade but that cannot be used as diagnostic features by homoplastically occurring in a few taxa of other TL lineages or being variable in taxa of the CS clade include the following: a rudimentary or absent coracoid supra-lateral process, occurring in all species of the CS clade (Figure 8A–C; vs. well-developed, Figure 8D), but variably developed or sometimes absent in other lineages of TL (e.g., Figure 8E); undulating margin of jaw suspensorium bones (Figure 6B,C), a condition inconspicuous or absent in some Cs clade members (Figure 6A); absence of a curved expansion on the posterior region of the posterior ceratohyal (Figure 1A–C, vs. presence, Figure 1D,E), which is also absent in some lineages within the genus Trichomycterus (e.g., subgenera Cryptocambeva Costa, 2021 and Paracambeva Costa, 2021).

Included taxa. The CS clade comprises two monophyletic groups, the C clade and the S clade (Figure 4).

3.4. The C Clade

This clade has been always corroborated as monophyletic [7,17,18,20] and is presently represented by a single nominal genus, Cambeva, not diagnosable by unique morphological features [15] but consistently differing from the S clade by a combination of morphological features (see diagnosis below). Molecular phylogenies [17,18,20] have concordantly supported four monophyletic groups: the Cambeva clade alpha that contains two subclades, the Cambeva iheringi species group and the Cambeva variegata species group, the Cambeva clade beta, and the Cambeva clade gama.

The Cambeva iheringi species group and the C. variegata species group have been supported as sister taxa (e.g., [20]), but no potential morphological synapomorphy shared by them was found. On the other hand, these two groups greatly diverge morphologically and are geographically disjunct. The Cambeva iheringi group is endemic to an area of south-eastern Brazil encompassing the upper Rio Tietê drainage of the upper Rio Paraná basin and coastal basins between the Rio Ribeira de Iguape and rivers draining into the northern extremity of the Baía de Paranaguá (Figure 9B). Species of the Cambeva iheringi group possess an exceptionally long sesamoid supraorbital, unique among TL taxa (Figure 2A), and a typical pelvic bone morphology, in which the anterior processes are situated near its medial margin (Figure 7A), not closer to the lateral margin as in other lineages of the C clade (Figure 7B) and most taxa of the S clade (Figure 7C,D).

The C. variegata species group inhabits an area comprising the Rio Grande drainage of the upper Rio Paraná basin and the upper course of the Rio São Francisco basin, southeastern Brazil (Figure 5C). This group is easily distinguished from other C clade lineages by having a skin crest similar to an adipose fin on the dorsal margin of the caudal peduncle, which is shared with all taxa of the S clade (see below). In both the C. variegata species group and in the S clade this crest is well-developed and similar in shape and position, thus not confirming Bockmann at al.’s [39] assumption that it would be well-developed in Scleronema (=S clade of the present study) and rudimentary in the C. variegata species group. The C. variegata species group shares other morphological characteristics with the S clade that are not present in any other lineage of the Cambeva clade, including both external (i.e., supraorbital canal interrupted, Figure 2B) and osteological features (premaxilla morphology, Figure 2B).

The Cambeva clade beta and the Cambeva clade gama together form a diversified monophyletic group supported in molecular phylogenies (e.g., [20]) occurring in a vast region of southern Brazil and in an adjacent area of Argentina (Figure 9A). Taxa belonging to this monophyletic group share reduced paired fins, with the pelvic-fin bases being medially placed in close proximity or in contact, besides having osteological character states unique among taxa of the Cambeva-Scleronema clade, including a large metapterygoid (Figure 6A) and a small coracoid (Figure 8A). Species of this clade typically have a high number of branchiostegal rays (8–10), but a few species have seven rays (e.g., Cambeva alphabelardense Costa, Feltrin & Katz, 2022, and Cambeva pascuali (Ochoa, Silva, Costa e Silva, Oliveira & Datovo, 2017), and eight rays may be present in some species of other genera of the CS clade.

The morphological divergence found among lineages of the Cambeva clade, mainly regarding the similar general appearance of the Cambeva variegata group with members of the S clade (see below), impedes a clear morphological identification of Cambeva among other TL genera. To improve classification with diagnosable genera, new genera are described here for the C. variegata species group and its sister group, the Cambeva iheringi species group (i.e., Pseudocambeva gen. nov. and Pericambeva gen. nov., respectively), and the genus Cambeva is restricted to the clade containing the Cambeva clade beta and the Cambeva clade gama (see below).

Included taxa. Three genera, Cambeva, Pericambeva gen. nov., and Pseudocambeva gen. nov.

Cambeva Katz, Barbosa, Mattos & Costa, 2018, new usage

Cambeva Katz et al. [18]: 560 (original description; type species: Pygidium davisi Haseman, 1911).

Diagnosis. Cambeva differs from the remaining genera of the CS clade by having the pelvic-fin bases medially in close proximity or in contact (vs. separated by an interspace), a hypertrophied metapterygoid in specimens above about 60 mm SL (Figure 6A; vs. metapterygoid small to moderate in length, Figure 6B–F), branchiostegal rays anteriorly extending to about the middle of the hyoid bar (Figure 1A; vs. slightly anteriorly surpassing the ventral cartilage of the hyoid bar, Figure 1B–E), and a relatively small coracoid (Figure 8A; vs. relatively large, Figure 8B–F). Cambeva is also distinguished from Pseudocambeva gen. nov. by the absence of a skin crest similar to an adipose fin on the dorsal margin of the caudal peduncle (vs. presence); by having the supraorbital canal continuous (vs. interrupted); the pelvic fin tip barely or not reaching the anus (vs. surpassing the urogenital papilla); and the premaxilla not distally terminating in a narrow extremity and from Pericambeva gen. nov. by having a shorter sesamoid lacrimal, shorter to slightly longer than the longitudinal length of the autopalatine excluding the posterolateral process (vs. distinctively longer).

Included species. Fifty-three species: Cambeva alphabelardense Costa, Feltrin & Katz, 2022, Cambeva atrobrunnea Costa, Feltrin & Katz, 2024, Cambeva balios (Ferrer & Malabarba, 2013), Cambeva barbosae Costa, Feltrin & Katz, 2021, Cambeva betabelardense Costa, Feltrin & Katz, 2022, Cambeva brachykechenos (Ferrer & Malabarba, 2013), Cambeva biseriata Costa, Feltrin, Mattos, Dalcin, Abilhoa & Katz, 2023, Cambeva botuvera Costa, Feltrin & Katz, 2021, Cambeva castroi (de Pinna, 1982), Cambeva crassicaudata (Wosiacki & de Pinna, 2008), Cambeva chrysornata Costa, Feltrin, Mattos, Dalcin, Abilhoa & Katz, 2023, Cambeva cauim dos Reis, Ferrer & da Graça, 2021, Cambeva cubataonis (Bizerril, 1994), Cambeva davisi (Haseman 1911), Cambeva diatropoporus (Ferrer & Malabarba, 2013), Cambeva diabola (Bockmann, Casatti & de Pinna, 2004), Cambeva diffusa Costa, Feltrin & Katz, 2021, Cambeva duplimaculata Costa, Feltrin & Katz, 2021, Cambeva flavopicta Costa, Feltrin & Katz, 2020, Cambeva galactica Costa, Feltrin & Katz, 2024, Cambeva gamabelardense Costa, Feltrin & Katz, 2022, Cambeva grisea Costa, Feltrin & Katz, 2021, Cambeva guaratuba Costa, Feltrin, Mattos, Dalcin, Abilhoa & Katz, 2023, Cambeva guareiensis Katz & Costa, 2020, *Cambeva horacioi dos Reis, Frota, Fabrin & da Graça, 2019, *Cambeva igobi Wosiacki & de Pinna, 2008), Cambeva imaruhy Costa, Feltrin & Katz, 2021, Cambeva longipalata Costa, Feltrin & Katz, 2021, Cambeva luteoreticulata Costa, Feltrin & Katz, 2024, Cambeva mboycy (Wosiaski & Garavello, 2004), Cambeva melanoptera Costa, Abilhoa, Dalcin & Katz, 2022, Cambeva naipi (Wosiaski & Garavello, 2004), Cambeva notabilis Costa, Feltrin & Katz, 2021, Cambeva orbitofrontalis Costa, Feltrin & Katz, 2021, Cambeva perkos (Datovo, Carvalho & Ferrer, 2012), Cambeva panthera Costa, Feltrin & Katz, 2021, *Cambeva papillifera (Wosiaski & Garavello, 2004), Cambeva pascuali (Ochoa, Silva, Costa e Silva, Oliveira & Datovo, 2017), Cambeva pericoh Costa, Feltrin & Katz, 2021, Cambeva piraquara dos Reis, Wosiacki, Ferrer, Donin & da Graça, 2023, *Cambeva plumbeus (Wosiaski & Garavello, 2004), Cambeva podostemophila Costa, Feltrin & Katz, 2023, Cambeva poikilos (Ferrer & Malabarba, 2013), Cambeva rotundipinna Costa, Feltrin & Katz, 2024, Cambeva stawiarski (P. Miranda-Ribeiro, 1968), Cambeva taroba (Wosiaski & Garavello, 2004), Cambeva tourensis Costa, Feltrin & Katz, 2023, Cambeva tropeira (Ferrer & Malabarba, 2011), Cambeva urubici Costa, Feltrin & Katz, 2021, Cambeva ventropapilata Costa, Feltrin, Mattos, Dalcin, Abilhoa & Katz, 2023, *Cambeva ytororo (Terán, Ferrer, Benitez, Alonso, Aguilera & Mirande, 2017), and Cambeva zonata (Eigenmann, 1918).

Geographical distribution. The Rio Paraná system between the Rio Paranapanema and upper Rio Uruguai basin in Brazil and Argentina and smaller coastal basins of southern Brazil between the Rio Ribeira de Iguape basin and the Lagoa dos Patos system (Figure 9A).

Pericambeva gen. nov.

LSID:urn:lsid:zoobank.org:act:D5CFFD3B-9146-4100-A7AD-106A9ABD2AA5

Type species. Cambeva difficilis Costa, Feltrin & Katz, 2024.

Diagnosis. Pericambeva is distinguished from the other TL genera by having a long sesamoid lacrimal, its length distinctively longer than the longitudinal length of the autopalatine excluding the posterolateral process (Figure 2A; vs. shorter to slightly longer, Figure 2B–F). Pericambeva also differs from other genera of the CS clade by having the anterior processes of the pelvic bone situated nearer the medial margin of the bone (Figure 7A; vs. nearer the lateral margin, Figure 7B–D). Pericambeva also differs from Cambeva by having the pelvic-fin bases medially separated by a broad interspace (vs. in close proximity or in contact), a moderately sized metapterygoid (vs. hypertrophied, Figure 6A), branchiostegal rays anteriorly just surpassing the ventral cartilage of the hyoid bar (vs. anteriorly extending to the middle of the hyoid bar, Figure 1A), and a relatively large coracoid (vs. relatively small, Figure 8A) and from Pseudocambeva gen. nov. by the absence of a filament at the tip of the first pectoral-fin (vs. presence), absence of a skin crest similar to an adipose fin on the dorsal margin of the caudal peduncle (vs. presence), a continuous supraorbital canal (Figure 2A; vs. interrupted, Figure 2B), a shorter pelvic fin, its extremity barely reaching urogenital papilla (vs. relatively long, surpassing urogenital papilla), and the premaxilla not distally terminating in a narrow extremity (vs. distally terminating in a narrow extremity, Figure 2B).

Etymology. From the Greek prefix peri (near) and cambeva (a popular name for trichomycterines in southeastern Brazil and also a trichomycterine genus), an allusion to the geographical proximity between the new genus and the genus Cambeva. Gender feminine.

Included species. Four species: Pericambeva difficilis (Costa, Feltrin & Katz, 2024) comb. nov., *Pericambeva guaraquessaba (Wosiacki, 2005) comb. nov., Pericambeva iheringi (Eigenmann, 1917) comb. nov., and Pericambeva tupinamba (Wosiacki & Oyakawa, 2005) comb. nov.

Geographical distribution. Upper Rio Tietê drainage and coastal basins between the Rio Ribeira de Iguape basin and river basins associated with the northern portion of the Baía de Paranaguá (Figure 9B).

Pseudocambeva gen. nov.

LSID: urn:lsid:zoobank.org:act: F92D593B-C398-4486-895B-32DE660AAFFA

Type species. Trichomycterus variegatus Costa, 1992.

Diagnosis. Pseudocambeva is distinguished from all other genera of the CS clade by having a broad lateral process of the pterotic (Figure 3A; vs. narrow, Figure 3B,C). Pseudocambeva is also distinguished from other genera of the C clade by the presence of a skin crest similar to an adipose fin on the dorsal margin of the caudal peduncle (vs. absence), having the supraorbital canal interrupted (Figure 2B; vs. continuous, Figure 2A), a relatively long pelvic fin, its extremity surpassing urogenital papilla (vs. shorter, barely or not reaching urogenital papilla), and the premaxilla distally terminating in a narrow extremity (Figure 2B; vs. not distally terminating in a narrow extremity, Figure 2A); from Cambeva by having the pelvic-fin bases medially separated by a broad interspace (vs. in close proximity); and from Pericambeva by the absence of the anterior infraorbital canal (Figure 2B; vs. presence, Figure 2A) and the presence of a filament at the tip of the first pectoral-fin (vs. absence).

Etymology. From the Greek pseudes (false) and cambeva (a popular name for trichomycterines in southeastern Brazil and also a trichomycterine genus), referring to its greater morphological similarity with genera of the S clade than to the genus Cambeva, in which their species were previously classified. Gender feminine.

Included species. Seven species: Pseudocambeva babilonica (Costa, Azevedo-Santos & Katz, 2025) comb. nov., Pseudocambeva capetinga (Costa, Azevedo-Santos, Uzeda & Katz, 2025) comb. nov., Pseudocambeva concolor (Costa, 1992) comb. nov., Pseudocambeva damnata (Costa, Azevedo-Santos, Ottoni, Vilardo & Katz, 2024) comb. nov., Pseudocambeva capitoliensis (Costa, Azevedo-Santos, Uzeda, Vilardo & Katz, 2025) comb. nov., Pseudocambeva occidentalis (Costa, Azevedo-Santos & Katz, 2025) comb. nov. and Pseudocambeva variegata (Costa, 1992) comb. nov.

Geographical distribution. Rio Grande drainage of the Rio Paraná basin and upper Rio São Francisco basin, southeastern Brazil (Figure 9C).

3.5. The S Clade

The S clade, previously considered as a single genus, Scleronema, is supported as monophyletic in all molecular analyses [7,9,16,17,18]. Three lineages have been supported within the S clade: Plesioscleronema, until now considered as a subgenus, and the Scleronema minutum and Scleronema operculatum species groups of the subgenus Scleronema [9,39]. Only one exclusive morphological character state was confirmed here for the S clade, consisting of the first free vertebra being more posteriorly directed, making them closer to the vertebral centra and overlapping them in a ventral view (Figure 7H).

Bockmann et al. [39] considered the presence of a skin crest similar to an adipose fin on the dorsal margin of the caudal peduncle as a synapomorphy of the S clade. However, a similar skin crest is also present in Pseudocambeva (see above) and in Trichomycterus rubbioli Rizzato & Bichuette, 2012, a basal taxon in its genus (Costa et al., unpublished), possibly comprising an ancestral condition for the CST clade, not a synapomorphy of the S clade. All taxa of the S clade also have a very short interopercle, making its dorsal process proportionally broader (Figure 6B,C), but a short interopercle is present in some species of Cambeva (e.g., Cambeva naipi (Wosiaski & Garavello, 2004)), making this character state unsuitable for use in diagnoses.

The monotypic Plesioscleronema has been always supported as sister to a clade containing the remaining taxa of the S clade [9,39]. Plesioscleronema is endemic to a small area of the Rio Paranaíba drainage of the Rio Paraná basin, uplands of south-eastern Brazil (Figure 9A), separated by about 1000 km from the distribution area occupied by the clade comprising the other lineages of the S clade (the Parascleronema-Scleronema subclade, Figure 9B,C) in the lowlands of southern Brazil and adjacent areas of Argentina, Paraguay, and Uruguay [9] and markedly differs from other taxa of the S clade in both the external morphology and osseous traits (see below). The great morphological divergence between Plesioscleronema and the clade comprising the other members of the S clade supports recognition of Plesioscleronema as a separate genus.

Two unique character states of the caudal skeleton described by Costa et al. [9] for Plesioscleronema, the presence of a broad hemal spine on the preural centrum 2, its width about twice or slightly more than twice the width of the anteriorly adjacent hemal spine (figure 5L in [9]), and the uroneural separated from the dorsal hypural plate by an interspace (figure 5L in [9]), are here confirmed as autapomorphies for the monotypic Plesioscleronema. Another supposedly unique character state, the presence of an expansion on the posterodorsal portion of the quadrate directed towards a concavity on the anterior outgrowth of the hyomandibula (figure 5L in [9]), is similar to the condition found in small specimens of other S clade lineages (Figure 6B), therefore not useful to diagnose Plesioscleronema. The anterior dorsocranial fontanel of Plesioscleronema that is rudimentary or absent contrasts with the well-developed fontanel in other members of the S clade and basal taxa of the C clade as well as in Trichomycterus, supporting the condition as autapomorphic for the monotypic Plesioscleronema, although there is an absence or extreme reduction of cranial fontanels homoplastically occurring in Cambeva (e.g., [52,53]).

The two other lineages of the S clade, the Scleronema minutum species group and the Scleronema operculatum species group [26], together form a clade corresponding to the genus Scleronema in Ferrer & Malabarba [26] and subgenus Scleronema in Costa et al. [9] and Bockmann et al. [39]. This clade is supported in molecular analyses (e.g., [9]) and corroborated by a series of unique morphological character states. These two species groups have highly overlapped distribution areas (Figure 9B,C) but greatly diverge in morphological features. Only the Scleronema operculatum group exhibits the main diagnostic features used by Eigenmann [54] to diagnose Scleronema, including ‘opercle with a long dermal flap’ (Figure 5C) and ‘maxillary barbel with a large osseous base (i.e., maxillary bone, Figure 2D)’. The great morphological divergence exhibited by these two lineages (see below), both in external and osteological features, justifies their obvious separation into two genera. Scleronema is here restricted to the two nominal species of the Scleronema operculatum group, thus restoring the original delimitation of Scleronema as proposed by Eigenmann [54,55]. A new genus (Parascleronema gen. nov.) is described below to contain all species of the Scleronema minutum group.

Unique character states previously described as synapomorphic for the Parascleronema-Scleronema clade and herein corroborated include the following: the presence of a fleshy keel on the posterior margin of the basal portion of the maxillary barbel (Figure 5B,C; previously described as a fleshy flap at the base of the maxillary barbel, e.g., [39]); an arched pectoral fin as a consequence of a distinctively short first ray, followed by progressively longer rays [9]; a reduced number of ventral principal caudal-fin rays (five vs. six, [39]); the presence of hypertrophied odontodes on the posterior portion of the opercular and interopercular patches of odontodes (figure 5g,h in [9]); maxilla elongate (Figure 6B,C); the presence of a prominent nerve canal on the autopalatine surface, close to the articulation for the lateral ethmoid (Figure 2C,D; modified from [26]); the autopalatine articulatory socket for vomer advancing medially, making it mostly located under the mesethmoid (modified from [26]; vs. not or slightly under vomer); and the metapterygoid elongated and slightly curved (Figure 6B,C, modified from [9]).

New unique character states corroborating the Parascleronema-Scleronema clade are as follows: a reduced number of principal anal-fin rays (i.e., six, vs. seven to nine); the basal portion of the maxillary barbel distinctively broad, abruptly tapering distally (Figure 5B,C); and the anterior-most pore of the lateral line of the trunk situated below the opercle (Figure 6B,C; vs. posterior to opercle, Figure 6A,D–F).

Species of the Parascleronema-Scleronema clade typically have six branchiostegal rays [39], instead of seven to ten as in other members of TL. However, specimens of most species may have a seventh ray, which when present is small and not directly attached to the hyoid bar. The reduction in the number of branchiostegal rays is considered here as a synapomorphy of this clade, but it is not useful to diagnose it due to the occurrence of the small seventh ray in Plesioscleronema and some species of Pseudocambeva. The narrow and sharply pointed lateral process of the parurohyal occurring in all species of the Parascleronema-Scleronema clade is not found elsewhere among species of the CS clade, except in Cambeva panthera (Costa, Feltrin & Katz, 2021). A similar condition was also observed in Trichomycterus mimonha (Costa, 1992), thus impeding it from being used as diagnostic. In addition, the absence of a laminar osseus expansion on the posterior portion of the autopalatine, ventral to the articular facet for the lateral ethmoid described by Costa et al. [9] and confirmed by Bockmann et al. [39] as synapomorphic for this clade is here refuted. This condition does not occur in larger specimens of both species of the Scleronema operculatum group (i.e., genus Scleronema in the present sense) and is therefore not diagnostic for the new genus (see below).

Scleronema in the present sense is diagnosable by 12 character states that are unique among trichomycterines. Unique character states previously described and here confirmed include the following: opercular odontode patch membrane posteriorly elongated, forming a distinctive skin flap [54] (Figure 5C), and a hypertrophied maxilla, its length about three to four times the length of the premaxilla (modified from [54], Figure 2D). The presence of a broad dark grey to black bar on the posterior portion of the caudal fin present in both species of Scleronema [26] (here confirmed) distinguishes Scleronema from the other taxa of the S clade, supporting it as a synapomorphy of this genus, but a similar colour pattern occurs in some species of Cambeva [56], although this condition is useful to distinguish Scleronema from the other taxa of the S clade.

Firstly described character states uniquely found in Scleronema among TL taxa include the following: the presence of a skin fold on the dorsal surface of the premaxillary barbel base (Figure 5C); the maxillary barbel base abruptly terminating in a narrow and short barbel filament antero-laterally directed (Figure 5C); a short nasal barbel, not or barely reaching the anterior naris, with its extremity abruptly narrowing distally (Figure 5C); orbits medially in close proximity, projecting above the dorsal surface of the head (Figure 5C); a distinctive narrowing in the anterior portion of the neurocranium (Figure 3B); a long thin osseous rim on the lateral margin of the pterotic, just anterior to the lateral process, supporting ligaments connecting it to the lateral surface of the opercle (Figure 3B); a compact preopercle, posteriorly widening (Figure 6C); and the postero-medial cleithrum extremity distinctively widened (Figure 8C). Species of Scleronema also have a broad pelvic bone (Figure 7D), contrasting with the narrower pelvic bone of other taxa of the S clade (Figure 7C), but this condition is variable in the C clade and T clade.

The new genus described below, corresponding to the Scleronema minutum species group [26], exhibits three character states that are unique among trichomycterine taxa: the presence of a long tooth, slightly curved to the mouth inside, at the corner of the distal extremity of the premaxilla, contrasting with other premaxillary teeth that are shorter and nearly straight (Figure 7L); the absence of a laminar osseous expansion on the posterior portion of the autopalatine, ventral to the articular facet for the lateral ethmoid (Figure 5D in [9]); and the presence of a short process on the proximal extremity of the fourth ceratobranchial, close to the articular cartilage (Figure 7F).

Included taxa. The genera Parascleronema gen. nov., Plesioscleronema and Scleronema.

Parascleronema gen. nov.

LSID: urn:lsid:zoobank.org:act: B0D91992-E6E9-448C-AA19-3DA339334DCA

Type species. Trichomycterus minutus Boulenger, 1891.

Diagnosis. Parascleronema is distinguished from all other genera of TL by having an elongate, slightly curved tooth at the corner of the distal extremity of the premaxilla (Figure 7L; vs. tooth on the distal extremity of the premaxilla not differing from other premaxillary teeth) and the presence of a process on the proximal extremity of the fourth ceratobranchial (Figure 7F; vs. absence, Figure 7E). Parascleronema is also distinguished from Scleronema by the absence of a skin fold on the dorsal surface of the premaxillary barbel base (Figure 5B; vs. presence, Figure 5C); the opercular odontode patch membrane not posteriorly elongated to form a distinctive skin flap (Figure 5B; vs. elongated, forming a distinctive skin flap, Figure 5C); a nasal barbel moderate in length, gradually narrowing distally (Figure 5B; vs. short, not or barely reaching the anterior naris, abruptly narrowing distally, Figure 5C); the anterior portion of the neurocranium not distinctively narrowed (like in Pseudocambeva, Figure 3A; vs. distinctively narrowed, Figure 3B); the absence of a long thin osseous rim on the lateral margin of the pterotic (vs. presence, Figure 3B); a moderately lengthened maxilla (Figure 2C; vs. hypertrophied, its length about three to four times the length of the premaxilla, Figure 2D); an elongate preopercle, not distinctively widening posteriorly (Figure 6B; vs. compact, posteriorly widening, Figure 6C); and the absence of a broad dark grey to black bar on the posterior portion of the caudal fin (vs. presence). Parascleronema is also distinguished from all other genera of TL, except Scleronema, by having the following: a fleshy keel on the posterior margin of the basal portion of the maxillary barbel (Figure 5B,C; vs. absence, Figure 5D–F); six principal anal-fin rays and ten principal caudal-fin rays (vs. seven and eleven, respectively); the basal portion of the maxillary barbel distinctively broad, abruptly tapering distally (Figure 5B,C; vs. basal portion never so broad, with gradual narrowing distally, Figure 5D–F); an arched pectoral fin as a consequence of a distinctively short first ray, followed by progressively longer rays making the first ray distinctively shorter than other rays (vs. pectoral fin subtriangular, first ray never distinctively shorter than other rays); the anterior-most pore of the lateral line of the trunk situated below the opercle (vs. away from opercle, at a vertical through the middle portion of the pectoral-fin base); the presence of hypertrophied odontodes on the posterior portion of the opercular and interopercular patches of odontodes (Figure 6B,C; vs. absence, Figure 6A,D–F); a prominent nerve canal on the autopalatine dorsal surface, close to the articulation for the lateral ethmoid (Figure 2C,D; vs. absence, Figure 2A,B,E,F); the posteromedial extremity of the autopalatine extending ventrally under the mesethmoid (vs. laterally in contact with the mesethmoid); and the lateral process of the vomer rudimentary and posteriorly directed (vs. well-developed, posterolaterally directed).

Etymology. From the Greek prefix para (resembling) and Scleronema, a nominal trichomycterine genus, of which the name means hard thread, referring to the hard base of the maxillary barbel (Eigenmann, 1917). Gender neuter.

Included species. Seven species: Parascleronema carijo (Bockmann, Ferrer, Rizzato, Esguícero, Duboc & Ingenito, 2023) comb. nov., *Parascleronema guapa (Ferrer & Malabarba, 2020) comb. nov., Parascleronema ibirapuita (Ferrer & Malabarba, 2020) comb. nov., Parascleronema mate (Ferrer & Malabarba, 2020) comb. nov., Parascleronema milonga (Ferrer & Malabarba, 2020) comb. nov., Parascleronema minutum (Boulenger, 1891), and *Parascleronema teiniagua (Ferrer & Malabarba, 2020) comb. nov.

Geographical distribution. Lower Río de La Plata system in Brazil, adjacent areas of Argentina, Paraguay, and Uruguay and coastal basins of southern Brazil, including those associated with the Lagoa dos Patos system (Figure 9B).

Plesioscleronema Costa, Sampaio, Giongo, de Almeida, Azevedo-Santos & Katz, 2022, new usage

Plesioscleronema Costa et al. [9]: 87 (original description, as a subgenus of Scleronema Eigenmann, 1917; type species: Scleronema auromaculatum Costa, Sampaio, Giongo, de Almeida, Azevedo-Santos & Katz, 2022, by monotypy and original designation).

Diagnosis. Plesioscleronema differs from the other genera of the S clade, Parascleronema and Scleronema, by the anterior dorsocranial fontanel that is absent or rudimentary (vs. well developed); the presence of a broad hemal spine on the preural centrum 2, its width about twice or slightly more than twice the width of the anteriorly adjacent hemal spine (figure 5L in [9]; vs. only slightly wider or equal in width); having the uroneural separated from the dorsal hypural plate by an interspace (figure 5L in [9]; vs. in contact); the absence of a fleshy keel on the posterior margin of the basal portion of the maxillary barbel (vs. presence); having seven principal anal-fin rays and eleven principal caudal-fin rays (vs. six and ten, respectively); the basal portion of the maxillary barbel moderately wide and gradually narrowing distally (vs. basal portion distinctively broad, abruptly tapering distally); the anterior-most pore of the lateral line of the trunk posterior to the opercle, at a vertical through the middle portion of the pectoral-fin base (vs. situated under the opercle); the absence of a distinctive canal on the dorsal surface of the autopalatine, close to the bone articulation with the lateral ethmoid (vs. presence); the posteromedial extremity of the autopalatine laterally in contact with the mesethmoid (vs. extending ventrally under the mesethmoid); the lateral process of the vomer well-developed, postero-laterally directed (vs. rudimentary and posteriorly directed); and posterior interopercular odontodes not distinctively broader than other interopercular odontodes (vs. distinctively broader).

Included species. A single species, Plesioscleronema auromaculatum (Costa, Sampaio, Giongo, de Almeida, Azevedo-Santos & Katz, 2022).

Geographical distribution. Rio Paranaiba drainage, Rio Paraná basin, southeastern Brazil (Figure 9B).

Scleronema Eigenmann, 1917

Scleronema Eigenmann [54]: 691 (original description; type species: Scleronema operculatum Eigenmann, 1917, by monotypy and original designation).

Diagnosis. Scleronema is distinguished from all other trichomycterine genera by the presence of a skin fold on the dorsal surface of the premaxillary barbel base (Figure 5C; vs. absence); the maxillary barbel base abruptly terminating in narrow and short barbel filament antero-laterally directed (Figure 5C; vs. never a similar barbel morphology); a short nasal barbel, not or barely reaching the anterior naris, abruptly narrowing distally (Figure 5C; vs. never a similar morphology); the opercular odontode patch membrane posteriorly elongated, forming a distinctive skin flap (Figure 5C; vs. never elongated); orbits medially in close proximity, projecting above the dorsal surface of the head (Figure 5C, vs. never so close, not projecting dorsally); a strong narrowing in the anterior portion of the neurocranium (Figure 3B; vs. weak narrowing, Figure 3C–E); a long thin rim on the lateral margin of the pterotic, just anterior to the lateral process, supporting ligaments connecting it to the lateral surface of the opercle (Figure 3B; vs. rim minute or absent, Figure 3C–E); a hypertrophied maxilla, its length about three to four times the length of the premaxilla (Figure 2D; vs. never hypertrophied); a compact preopercle compact, posteriorly widening (Figure 6C; not widening posteriorly, Figure 6A,B,D–F); and the medial cleithrum extremity distinctively widened (Figure 8C; vs. not distinctively widened, Figure 8A,B,D–F). Species of Scleronema are also distinguished from other trichomycterines of the S clade by the presence of a broad dark grey to black bar on the posterior portion of the caudal fin (vs. absence).

Included species. Two species, Scleronema macanuda (Ferrer & Malabarba, 2020) and Scleronema operculatum (Eigenmann, 1917).

Geographical distribution. Rio Uruguai basin in Brazil, adjacent areas of Argentina and Uruguay, and coastal drainages of southern Brazil and Uruguay including the Lagoa dos Patos system (Figure 9C).

3.6. The T Clade

This clade includes a single genus, Trichomycterus (sensum strictum, see introduction above), with intrageneric lineages exhibiting relatively high morphological diversity [15]. The T clade is distinguished from its sister group, the CS clade, by a series of morphological features that are unique for this clade. The present comparative analysis also indicated osteological character states unique for Trichomycterus, including the morphology of the last proximal radial of the dorsal and anal fins, the dorsal process of the interopercle, and the supraoccipital (see below). Most species of Trichomycterus also differ from other TL trichomycterines in possessing a sharply pointed metapterygoid, but this condition is not present in all congeners, thus not serving to diagnose the genus.

Trichomycterus Valenciennes, 1832

Trichomycterus Valenciennes in Humboldt and Bonpland [57]: 348 (original description; type species: Trichomycterus nigricans Valenciennes, 1832, by monotypy and original designation).

Diagnosis. Trichomycterus differs from other TL genera by having a bifid process on the subdistal portion of the last proximal radial of the dorsal and anal fins (Figure 7K; vs. process without a bifid termination, Figure 7I,J); a rounded expansion on the dorsal margin of the dorsal process of the interopercle, causing a bird-like lateral profile (Figure 6D; vs. absence of that expansion, Figure 6A–C,E,F); and a sinuous anterior portion of the supraoccipital (Figure 3C; vs. not sinuous, Figure 3A,B,D,E). Trichomycterus is also readily distinguished from other genera of the CST clade by having the skin surface between opercular and interopercular odontode patches separated from the branchial membrane by a skin fold (Figure 5D; vs. continuous, Figure 5A–C); the posterior nostril larger than the anterior nostril; the largest axis of the opercular patch of odontodes slightly perpendicularly aligned (Figure 5D; vs. horizontally aligned, Figure 5A–C); and the distal extremity of the branchiostegal ray 3 distinctively widened than other rays (Figure 1D; vs. branchiostegal ray 3 extremity not distinctively wider, Figure 1A–C).

Included species. Ninety species: Trichomycterus adautoleitei Costa, Azevedo-Santos & Katz, 2023, Trichomycterus albinotatus Costa, 1992, Trichomycterus alternatus (Eigenmann, 1917), Trichomycterus altipombensis Costa, Katz, Vilardo & Mattos, 2022, Trichomycterus anaisae Katz & Costa, 2021, Trichomycterus antiquus Costa, Fentrin, Mattos & Katz, 2024, Trichomycterus araxa Costa, Mattos, Sampaio, Giongo, de Almeida & Katz, 2022, Trichomycterus argos Lezama, Triques & Santos, 2012, Trichomycterus astromycterus Reis, de Pinna and Pessali 2019, Trichomycterus auroguttatus Costa, 1992, Trichomycterus bahianus Costa, 1992, Trichomycterus barrocus Reis & de Pinna, 2022, Trichomycterus brucutu Reis & de Pinna, 2022, Trichomycterus berthalutzae Costa, Barbosa & Katz, 2024, Trichomycterus brasiliensis Lütken, 1874, Trichomycterus brigadeirensis Costa, Katz and Vilardo, 2023, Trichomycterus brunoi Barbosa & Costa, 2005, Trichomycterus caipora Lima, Lazzarato & Costa, 2008, Trichomycterus candidus (P. Miranda-Ribeiro, 1949), Trichomycterus caparaoensis Costa, Barbosa and Katz, 2023, Trichomycterus caratinguensis Costa, Katz and Vilardo, 2023, Trichomycterus castelensis Costa, Katz and Vilardo, 2023, Trichomycterus caudofasciatus Alencar & Costa, 2004, Trichomycterus claudiae Barbosa & Costa, 2005, Trichomycterus coelhorum Costa, Azevedo-Santos & Katz, 2023, Trichomycterus diamantinensis Costa, Feltrin, Mattos & Katz, 2024, Trichomycterus espinhacensis Costa and Katz, 2023, Trichomycterus fabioheppi Costa, Barbosa & Katz, 2024, Trichomycterus fuliginosus Barbosa & Costa, 2005, Trichomycterus funebris Katz & Costa, 2021, Trichomycterus garbei Costa, Azevedo-Santos & Katz, 2023, Trichomycterus gasparinii Barbosa, 2013, Trichomycterus giarettai Barbosa & Katz, 2016, Trichomycterus giganteus Lima & Costa, 2004, Trichomycterus goeldii Boulenger, 1896, Trichomycterus humboldti Costa & Katz, 2021, Trichomycterus illuvies Reis & de Pinna, 2022, Trichomycterus immaculatus (Eigenmann & Eigenmann, 1889), Trichomycterus ingaiensis Katz & Costa, 2021, Trichomycterus ipatinga Reis & de Pinna, 2022, *Trichomycterus itacarambiensis Trajano & de Pinna, 1996, *Trichomycterus itacambirussu Triques & Vono, 2004, Trichomycterus itatiayae A. Miranda-Ribeiro, 1906, Trichomycterus jacupiranga Wosiacki & Oyakawa, 2005, Trichomycterus jequitinhonhae Triques & Vono, 2004, *Trichomycterus landinga Triques & Vono, 2004, Trichomycterus largoperculatus Costa & Katz, 2022, Trichomycterus lauryi Donin, Ferrer & Carvalho, 2020, Trichomycterus listruroides Costa, Katz & Azevedo-Santos, 2023, Trichomycterus longibarbatus Costa, 1992, Trichomycterus luetkeni Katz & Costa, 2021, Trichomycterus macrophthalmus Barbosa & Costa, 2012, Trichomycterus macrotrichopterus Barbosa & Costa, 2005, Trichomycterus maculosus Barbosa & Costa, 2010, *Trichomycterus maracaya Bockmann & Sazima, 2004*, Trichomycterus mariamole Barbosa & Costa, 2005, Trichomycterus melanopygius Reis, dos Santos, Britto, Volpi & de Pinna, 2020, Trichomycterus mimonha Costa, 1992, Trichomycterus mimosensis Barbosa, 2013, Trichomycterus mirissumba Costa, 1992, Trichomycterus mutabilicolor Costa, 2022, Trichomycterus nigricans Valenciennes, 1832, Trichomycterus nigroauratus Barbosa & Costa, 2008, Trichomycterus novalimensis Barbosa & Costa, 2005, Trichomycterus pantherinus Alencar & Costa, 2004, Trichomycterus paquequerensis (P. Miranda-Ribeiro, 1943), Trichomycterus pauciradiatus Alencar & Costa, 2006, Trichomycterus paulence (Eigenmann, 1917), Trichomycterus pirabitira Barbosa & Azevedo-Santos, 2012, Trichomycterus potschi Barbosa & Costa, 2003, Trichomycterus pradensis Sarmento-Soares, Matins-Pinheiro, Aranda & Chamon, 2005, Trichomycterus puriventris Barbosa & Costa, 2012, Trichomycterus quintus Costa, 2020, Trichomycterus reinhardti (Eigenmann, 1917), Trichomycterus rubiginosus Barbosa & Costa, 2005, Trichomycterus rubbioli Bichuette & Rizzato, 2012, Trichomycterus ruficaudatus Costa, Mattos, Amorim, Gago & Katz, 2025, Trichomycterus sainthilairei Katz & Costa, 2021, Trichomycterus santaeritae (Eigenmann, 1918), Trichomycterus saquarema Costa, Katz, Vilardo & Amorim, 2022, Trichomycterus saturatus Costa, Katz & Azevedo-Santos, 2023, Trichomycterus septemradiatus Katz, Barbosa & Costa, 2013, Trichomycterus tantalus Reis, Vieira & de Pinna, 2022*, Trichomycterus tete Barbosa & Costa, 2011, Trichomycterus travassosi (Miranda Ribeiro, 1949), *Trichomycterus trefauti Wosiacki, 2004, Trichomycterus uberabensis Costa, Azevedo-Santos & Katz, 2023, Trichomycterus vermiculatus (Eigenmann, 1917), Trichomycterus vinnulus Reis & de Pinna, 2022, and Trichomycterus vitalbrazili Vilardo, Katz and Costa, 2020.

Geographical distribution. River basins of eastern Brazil, between Rio Paraguaçu and streams draining the northern portion of the Baía de Paranaguá, including the upper and middle Rio Paraná and Rio São Francisco basins (Figure 9A).

Remarks. The genus Trichomycterus was divided into six subgenera by Costa [15]. With the inclusion of numerous taxa and more morphological variation recorded in recent years, limits of those subgenera will be revised elsewhere.

3.7. The Western Trichomycterus Sublineages

Two sublineages of TL from western South America have been recognised in molecular phylogenies. The first one, the Andean Trichomycterus Lineage (ATS), is supported in different molecular phylogenies as a sister to the CST clade [7,8,16,19] and includes taxa both from cis- and trans-Andean areas. The second lineage, the Pacific Trichomycterus Lineage (PTS), is supported in the most taxon-inclusive analysis by Ochoa et al. [7] as a sister to all other TL taxa and includes at least two species from the coastal Pacific river basins.

No apomorphic features shared by ATS, PTS, and other TL genera were found to corroborate the relationships strongly supported by molecular data [7]. On the other hand, two features shared by members of both ATS and PTS are unique among trichomycterine genera: the posterolateral process of the autopalatine is slightly curved (Figure 2E,F; vs. straight, Figure 2A–D), and the coracoid anteriorly terminates in a long keel (Figure 8E,F; vs. anterior keel short when present, Figure 8A–D).

3.8. The Andean Trichomycterus Sublineage (ATS)

The Andean Trichomycterus Lineage was supported by Ochoa et al. [7] as a sister to the CST clade, based on two species collected in the upper Amazon basin, Central Andes of Peru. They were identified as ‘Trichomycterus’ quechuorus (Steindachner, 1900) and ‘Trichomycterus’ cf. oroyae (Eigenmann & Eigenmann, 1889). These two nominal species have similar general appearance (e.g., head weakly flattened dorso-ventrally, nearly rounded in dorsal view; small eye), which was recognised by Eigenmann [55] when placing them together in its identification key. However, whereas specimens of ‘Trichomycterus’ cf. oroyae used by Ochoa et al. [7] were collected in the same area of the type locality of ‘T.’ oroyae (i.e., Río Mantaro drainage), therefore confirming its identification as belonging to this species, specimens of ‘T’. quechuorus were collected in the Río Urubamba basin, Río Paucartambo drainage, cis-Andean region, therefore distant from the type locality of ‘T’. quechuorus in the trans-Andean region of Arequipa, making species identification improbable. A similar species occurring in the Río Paucartambo is ‘Trichomycterus’ megantoni Fernández & Chuquihuamani, 2007 [58], but the present examination of photographs of the specimens identified as ‘T’. quechuorus and used in Ochoa et al. [7] have clearly shown that this species it not ‘T’. megantoni but another closely related species from the same drainage, apparently still undescribed and herein also examined. The present examination of ‘T’. megantoni, ‘T’. oroyae, and the unidentified species from the Río Urubamba basin revealed some unique morphological features shared by these three species, including structures in the region involving the opercular and jaw suspensorium apparatus, which are diagnostic for a new genus, Mauri gen. nov. (see below).

Fernandez et al. [19] also found phylogenetic support for a monophyletic ATS sister to the CST clade using a different approach (multigene analysis instead of ultraconserved elements as in Ochoa et al. [7]). In this analysis, ATS included that species identified as ‘T’. quechuorus using DNA sequences extracted from the same material used in Ochoa et al. (2020), five undescribed species from Bolivia, ‘Trichomycterus’ rivulatus Valenciennes, in Cuvier & Valenciennes, 1846, from the Lago Titicaca basin, ‘Trichomycterus’ spegazzinii (Berg, 1897) and ‘Trichomycterus’ roigi (Arratia & Menu-Marque, 1984) from the high Andean drainages of northern Argentina. Morphological structures of ‘T’. roigi illustrated in its original description (figures 4A and 9A in [59]) and an illustration of ‘T.’ rivulatus (figure 41 in Baskin [28]) clearly show unique features shared by ‘T’. megantoni, ‘T’. oroyae, and the unidentified species from the Río Urubamba basin, justifying their inclusion in the new genus described below.

Mauri gen. nov.

LSID: urn:lsid:zoobank.org:act: 36D853E1-A508-4CB2-BDCD-AE2AFEAF35D9

Type species. Trichomycterus megantoni Fernández & Chuquihuamani, 2007.

Diagnosis. Mauri differs from all other trichomycterine genera by a series of structures in the region involving the opercular and jaw suspensorium apparatus, externally including two longitudinally converging skin crests between the opercle and the interopercle (Figure 5E; vs. no skin crest on the opercular region, Figure 5A–D,F) and internally including a shortened longitudinal axis of the quadrate (Figure 6F; vs. never a similar morphology, Figure 6A–E); the presence of a distinctive keel in the middle portion of the lateral surface of the hyomandibula (Figure 6F; vs. absence); a short and anteriorly widened preopercle (Figure 6F; vs. never a similar morphology, Figure 6A–E); a prominent anterodorsal expansion of the dorsal process of the interopercle (Figure 6F; vs. never a similar expansion, Figure 6A–E); a relatively long interopercular odontode patch, with long internal odontodes (Figure 6F; vs. interopercular odontode patch and internal odontodes never so long, Figure 6A–E); and a uniquely elongated opercle (Figure 6F; vs. longitudinal axis of the quadrate not shortened, preopercle never anteriorly expanded, dorsal process of the interopercle never with a prominent anterodorsal expansion, Figure 6A–E).

Etymology. Mauri is a generic popular name for species of this new genus in the Andes of Bolivia and Peru. The origin of the name is unknown, possibly derived from the Quechua or Aymara languages. Gender masculine.

Included species. Five species: Mauri megantoni (Fernández & Chuquihuamani, 2007) comb. nov., Mauri oroyae (Eigenmann & Eigenmann, 1889) comb. nov., *Mauri rivulatus (Valenciennes, 1846) comb. nov., *Mauri roigi (Arratia & Menu-Marque, 1984) comb. nov., and Mauri sp.

Geographical distribution. Lago Titicaca and Andean tributaries of the Río Amazonas and Río Paraguay basins between central Peru and northern Argentina (Figure 9C).

Remarks. Fernández & Chuquihuamani [58] diagnosed M. megantoni by the presence of ‘interopercle thickened integument’, indicated by an arrow in the ventral border of the interopercular patch of odontodes (figure 2 in [58]) and a ‘foramen frontal-supraoccipital reduced’. Examination of paratypes of this species (MUSM 3115) did not reveal any distinctive morphological feature in the ventral border of the interopercular patch of odontodes and confirmed an extreme reduction of dorsal cranial fontanels (Figure 3D). In the other members of Mauri, both dorsal cranial fontanels are well-developed as in most other trichomycterine taxa.

3.9. The Pacific Trichomycterus Sublineage (PTS)

PTS was supported as a sister to a clade comprising all other taxa of TL [7], including ‘Trichomycterus’ punctulatus (Valenciennes, 1846) from the Pacific coastal basins of eastern Peru, ‘Trichomycterus’ cf. knerii (Steindachner, 1882) from the Ecuadorian Amazon, and ‘Trichomycterus’ cf. taenia (Kner, 1863) from the western slope of the Ecuadorian Andes. Specimens of ‘Trichomycterus’ cf. knerii and ‘Trichomycterus’ cf. taenia used to extract DNA by Ochoa et al. [7] and collected in areas of great trichomycterine diversity were not available for study, thus it was not possible to confirm their identity. The coordinates of the material identified as ‘T.’ punctulatus, the only group occurring in that region of Peru (i.e., coastal Pacific river basins crossing deserts of central Peru), confirms its identity. Examination of material of ‘T.’ punctulatus and a closely related species from the same region revealed apomorphic character states unique among TL taxa, including a peculiar subconical head morphology, superficially remembering the Asiatic cypriniform Dojo loach (Misgurnus anguillicaudatus (Cantor, 1842)) and other details of the cephalic morphology, diagnosing a new genus, Eremoglanis gen. nov., described below.

Eremoglanis gen. nov.

LSID: urn:lsid:zoobank.org:act: 492399DB-EC3C-4AFB-B68E-43884B38AE48

Type species. Trichomycterus punctulatus Valenciennes, 1846

Diagnosis. Eremoglanis is distinguished from all other trichomycterine genera by having a relatively deep head, subconical, with eye situated laterally (Figure 5F; vs. never a similar head morphology, eye situated laterodorsally or dorsally on head, Figure 5A–E); the presence of a deep skin fold separating opercular-interopercular skin and branchial membrane (Figure 5F; vs. skin fold superficial or absent); and a rudimentary posterior nostril membrane (Figure 5F; vs. well-developed, Figure 5A–E). Eremoglanis is also distinguished from all other members of TL, except Trichomycterus, by having a single median S6 pore (Figure 3E; vs. paired S6 pore, Figure 3A,B,D).

Etymology. From the Greek eremos (desert) and glanis, name of uncertain origin used by Aristotle for a catfish and frequently used to compose generic names in Siluriformes.

Included species. Two species: Eremoglanis punctulatus (Valenciennes, 1846) comb. nov. and Eremoglanis sp.

Geographical distribution. Pacific coastal river basins, Peru (Figure 9A).

3.10. Key to Identification of TL Genera Using External Morphology

1A. No longitudinal skin crest between opercle and interopercle; head subtrapezoidal or sub-rectangular in dorsal view ………………………………………………………. 2

1B. Two longitudinal converging skin crests between opercle and interopercle (Figure 5E); head rounded in dorsal view ………….…………………………………….. Mauri

2A. Head flattened, with eye situated laterodorsally or dorsally on head (Figure 5A–E); posterior nostril membrane well-developed (Figure 5A–E) ………………….………. 3

2B. Head subconical, with eye situated laterally on top of head (Figure 5F); posterior nostril membrane rudimentary (Figure 5F) …………………………………….. Eremoglanis

3A. Skin surface between opercular and interopercular odontode patches continuous with the branchial membrane; posterior nostril smaller than the anterior nostril; opercular patch of odontodes horizontally aligned (Figure 5A–C) …………………………………… 4

3B. Skin surface between opercular and interopercular odontode patches separated by a skin fold forming a gap; posterior nostril larger than the anterior nostril; opercular patch of odontodes slightly perpendicularly aligned (Figure 5D) ……… Trichomycterus

4A. A fleshy keel on the posterior margin of the basal portion of the maxillary barbel (Figure 5B,C); pectoral fin arched, first ray short, followed by progressively longer rays; five ventral principal caudal-fin rays; six principal anal-fin rays; anterior-most pore of the lateral line of the trunk situated below the opercle ………………………………………… 5

4B. No fleshy keel on the posterior margin of the basal portion of the maxillary barbel; a subtriangular or rounded pectoral, first ray never distinctively shorter than other rays; six ventral principal caudal-fin rays; seven to nine principal anal-fin rays; anterior-most pore of the lateral line of the trunk situated posteriorly to the opercle …………………… 6

5A. Opercular odontode patch membrane posteriorly elongated, forming a distinctive pointed skin flap (Figure 5C); a skin fold on the dorsal surface of the premaxillary barbel base (Figure 5C); maxillary barbel base abruptly terminating in narrow and short barbel filament antero-laterally directed (Figure 5C); no distinctive tooth at the corner of the distal extremity of the premaxilla; a broad dark grey to black bar on the posterior portion of the caudal fin ………………………………………………………………. Scleronema

5B. Opercular odontode patch membrane short and rounded (Figure 5B); no skin fold on the dorsal surface of the premaxillary barbel base (Figure 5B); maxillary barbel base not abruptly terminating in narrow and short barbel filament antero-laterally directed (Figure 5B); a long tooth, slightly curved to mouth inside, at the corner of the distal extremity of the premaxilla (Figure 7L); no broad dark grey to black bar on the caudal fin …………………………………………………………………….……………. Parascleronema

6A. Anterior section of the supraorbital canal present ………………………………. 7

6B. Anterior section of the supraorbital canal absent …………………. Plesioscleronema

7A. Pelvic-fin bases medially separated by a broad interspace …………………… 8

7B. Pelvic-fin bases medially in close proximity or in contact ………………… Cambeva

8A. No skin crest similar to an adipose fin on the dorsal margin of the caudal peduncle; supraorbital canal continuous; anterior section of the infraorbital canal present; pelvic fin extremity barely or not reaching urogenital papilla ………………………. Pericambeva

8B. A skin crest similar to an adipose fin on the dorsal margin of the caudal peduncle; supraorbital canal interrupted; anterior section of the infraorbital canal absent; pelvic fin extremity surpassing urogenital papilla ……………………………………. Pseudocambeva

4. Discussion

4.1. Morphological Diversity in the CST Clade

The present study provided a series of new data on the morphology of lineages of the CST clade previously supported only by molecular data or a few morphological synapomorphies. Whereas the T clade exhibits a moderate morphological diversity, supporting a classification containing a single genus, Trichomycterus, with six subgenera [15], the CS clade exhibits the most remarkable morphological diversity among TL members, justifying the six genera herein recognised. At least part of this morphological diversity is coincident with ecological specialisations like semi-fossorial habits and psammophily, as below discussed.

Among the two main clades included within the CS clade, the C clade and the S clade exhibit different patterns of morphological diversification. Field studies indicate that species of Cambeva, the most diverse lineage of the CS clade, occur in a wide range of fluvial environments from mountain rivers at about 1,325 m asl [53] to lowland streams slightly above sea level [56]. Even occupying this broad range of habitats, all species of Cambeva share some reduction of paired fins, including reduction of osseous fin support (i.e., a small coracoid, see results above), occurring with four independent evolutionary events of pelvic fin loss [20]. In addition, the largest vertebrae counts among taxa of the CST clade occur in Cambeva (i.e., 40–42 vs. rarely having more than 37 vertebrae).

Tendencies toward fin reduction and increasing of vertebrae number are typical of species with fossorial or semi-fossorial habits [60,61,62,63], occurring independently in other trichomycterid lineages (i.e., microcambevines and glanapterygines [62,64] and the trichomycterine subgenus Cryptocambeva Costa, 2021 [15]). Most species of Cambeva live associated with gravel bottom of streams, being frequently found buried under pebbles, whereas some other species have been found buried into plant debris deposited on stream banks, in amphibious plants in marginal areas with strong currents, or even specifically within dense mats of Podostemaceae plants (e.g., [20,65,66,67]). A possible exception is Cambeva crassicaudata (Wosiacki & de Pinna, 2008) supposedly having pelagic habits [68].

The greatest morphological shift among lineages of the CS clade occurs in the S clade. Field observations have indicated that Plesioscleronema auromaculatum, from the uplands of southeastern Brazil, is found associated with areas of fine gravel and sand bottom [9]. A similar condition is found in the upper land genus Pseudocambeva, a basal lineage of the C clade, therefore presumably a plesiomorphic condition for the S clade. Contrastingly, in the lowland sister genera Parascleronema and Scleronema, included species are always found associated with sandy substratum [26], being considered the only true strict psammophilic taxa [39]. Some morphological features uniquely shared by Parascleronema and Scleronema are typical of psammophilic species of other trichomycterid subfamilies. The paired fins are elliptical and relatively large in these genera, a condition frequently found in other psammophilic taxa [69], including species of the microcambevine subgenus Pterocambeva Costa & Katz, 2021 [62,70]. The basal portion of the maxillary barbel is broad (Figure 5B,C) and associated with an elongated maxillary bone that is approximately straight (Figure 2C,D), conditions also occurring in other psammophilic taxa, including the microcambevine genus Microcambeva Costa & Bockmann, 1994 [62] and the sarcoglanidine genus Stauroglanis de Pinna, 1989 [71].

Scleronema concentrates the most noteworthy morphological features among TL taxa, only paralleled by those traits present in specialised psammophilic trichomycterids. The hypertrophied maxillary bone (Figure 5C), not found elsewhere among trichomycterines and which has induced Weitzman & Myers [72] and de Pinna [71] to consider Scleronema as closely related to Amazon sarcoglanidines, is present in a few psammophilic trichomycterids non trichomycterines [28,73]. Similarly, the peculiar position of eyes that are dorsally placed and medially close to each other is a condition often occurring in psammophilic teleost fishes [69], including Stauroglanis as an example among trichomycterids [74]. Some morphological traits uniquely occurring in Scleronema among trichomycterids, including the presence of a long skin flap on the posterior margin of the opercle, a skin fold on the dorsal surface of the premaxillary barbel base, and a minute anterolaterally directed maxillary barbel filament (Figure 5C), still have their function unknown and may also be related to psammophily.

4.2. Distribution Patterns of WTLs

The distribution of TL genera illustrates historical biogeographical patterns where the Andes occupy a pivotal role, as recently discussed [8]. With an estimated origin in Central Andes during the late Eocene (about 50 Ma), TL occupies a large portion of South America, with the known distribution areas of the western and eastern lineages separated by a broad geographical gap. This intermediate area without known records of TL taxa nearly corresponds to an extensive flooded lowland region between eastern Bolivia, central-western Brazil, and northwestern Argentina. The only trichomycterine occurring in this region with uncertain generic status is ‘Trichomycterus’ dali Rizzato, Costa-Jr., Trajano & Bichuette, 2011, a troglomorphic species from central-western Brazil [75], never included in molecular phylogenies. However, examination of a specimen of this species did not reveal any characteristics allowing it to be placed in any TL group.

According to a recent time-calibrated phylogeny [8], the split between the Mauri lineage and the CST clade occurred during the Eocene (about 40 Ma), supporting an ancient origin for WTLs. Mauri, as delimited here, includes at least four nominal species (see above) occurring in a large Andean region extending over 1000 km between central Peru and northern Argentina, whereas Eremoglanis includes at least two species from Pacific river basins crossing an arid region of central Peru (Figure 9A,C). Data on species of WTLs is nearly limited to the few morphological data presented in their original descriptions, and the number of species in each genus is probably higher since many incertae sedis species in the region are poorly known and are presently allocated in ‘Trichomycterus’ (e.g., [76]). According to Fernandez et al. [19], five undescribed species from Bolivia belong to the same lineage of the herein described genus Mauri. Furthermore, in the distribution area of Mauri, there are some nominal species that are probably valid but that have been synonymised based on superficial comparative analysis without a detailed morphological study (e.g., Ref. [77], based on morphometric data), contributing to the low taxonomic resolution of Andean trichomycterines.

5. Conclusions

Previous studies have shown a positive relationship between the delimitation and formal description of monophyletic genera with the increased recognition and formal descriptions of new species, a fundamental step for biodiversity estimates and more consistent conservation strategies [8]. Therefore, the classification proposed here tends to improve the taxonomy of Trichomycterinae, facilitating the recognition of new species and their conservation. This step is particularly important, since the greatest majority of species from the nine genera delimited here occur in the most important biodiversity hotspots of the world, such as the Atlantic Forest, Cerrado, and the Tropical Andes [78], thus contributing to a better understanding of the global biodiversity.