3.1. Taxonomic Account
Phylum Gastrotricha Metschnikoff, 1865.
Order Macrodasyida Remane, 1925 [3
] (Rao & Clausen, 1970) [48
Family Turbanellidae Remane, 1926 [49
Remane, 1927 [7
sp. 2—Todaro & Rocha [34
Examined material: Holotype. Photographs of an adult specimen, collected on 9th November 2017 from Praia do Cachadaço, in the Trindade district in the municipality of Paraty, Rio de Janeiro State, Brazil (23°21′15.8″ S 44°43′41.5″ W). Bare sand of 30 cm depth had the following sediment characteristics: mean = 1.4111 phi (medium sand), SD = 0.8137, skewness = −0.8573, kurtosis = 4.4435, and median = 1.3215.
The specimen was observed alive with a compound microscope, but due to the fragility of the organisms, it was inadvertently destroyed during the study and is no longer available [50
]. The holotype is illustrated in Figure 2
(according to the International Code of Zoological Nomenclature, 2017: Article 73, Recommendation 73G, in Declaration 45), and photos are available at the Museum of Zoology, University of Campinas, Brazil, under the accession number ZUEC GCH 61.
Paratypes. Photographs of five adult specimens (adults), collected on 9th November 2017 from Praia do Cachadaço, in Trindade district in the municipality of Paraty, Rio de Janeiro State, Brazil. The specimens were observed alive with a compound microscope, but due to the fragility of the organisms, physical specimens were inadvertently destroyed during the study and are no longer available [50
]. Photographs of each specimen are available at the Museum of Zoology, University of Campinas, Brazil, under accession numbers ZUEC GCH 62–66.
From the type locality, ten specimens were prepared for SEM and from locations sampled between 2002–2003 [34
], two specimens are shown in Figure 4
and Figure 5
Etymology: The specific name refers to the triple caudal cone.
Diagnosis: The body is strap-shaped, and its length ranges from 417 to 480 μm. It has a large terminal mouth with a diameter ranging from 13.3 to 17.4 μm. The buccal cavity is heavily cuticularized, and it has a head with noticeable peribuccal swelling and ventral papillae. The pestle organ is absent. The pharyngo-intestinal junction (PhJIn) is between U34 and U38, and the distance of the pharyngeal pores from PhJIn varies from 20.2 to 27.1 μm. Epidermal glands are arranged in a single column on each side. There are five to six anterior adhesive tubes (TbA) on each side, all occurring on fleshy hands. There are two accessory adhesive tubes (“dohrni” tubes) of unequal length per side (the longer tube maximum length is 33.8 μm and the shorter is 19.4 μm). There are six posterior adhesive tubes (TbP) per side, the outermost being the longest. Dorsal adhesive tubes (TbD), ventral adhesive tubes (TbV), ventrolateral adhesive tubes (TbVL), and lateral adhesive tubes (TbL) are absent. In the posterior region, body tapering occurs gradually to the caudal base, and the caudum has three caudal cones, one medial and two laterals. Paired testes extend into sperm ducts, which turn anteriorly at U65 and fuse in a mid-ventral pore at U53. The frontal organ is at U71. About 20–30 epidermal glands are distributed along both lateral body margins.
The description is based on both the holotype and ten paratypes (see Table 2
). The body is strap-shaped and 417 μm in total length. The head bears noticeable lateral peribuccal swelling (U03) and a pair of papillae ventrally but no pestle organ; the cephalic region is delimited by a neck constriction 34.1 μm wide (U05). Body tapering occurs gradually to the caudal base, and the caudum bilobed has three caudal cones (U96). Widths at the outer oral opening, neck constriction, mid-pharynx, PhJIn, mid-intestine, furcal base, and their locations along the body length are: 16.4, 37.1, 25.2, 22.2, 19.7, and 33.0 μm at U0, U05, U20, U37, U64, and U93, respectively. Epidermal glands are arranged along the body in one column per side of 30 glands, which vary in size (1.6–4.7 μm in diameter).
Adhesive tubes: There are five or six anterior adhesive tubes (TbA) per side, all of which occur on fleshy hands that insert at U15. The innermost, mimicking a thumb, is the shortest, while the second from the inner side is the longest. Accessory adhesive tubes (“dohrni” tubes) are posterolaterally directed, and there are two per side of unequal length (the longer tube is 14 μm and the shorter is 9 μm) at U17. Dorsal adhesive tubes (TbD), ventral adhesive tubes (TbV), ventrolateral adhesive tubes (TbVL), and lateral adhesive tubes (TbL) are absent. There are six posterior adhesive tubes (TbP) per side, the outermost being the longest. The distance between the external TbP is greater than the width of the body’s caudal base.
Ciliation: The cephalic region has ciliary patches and circumcephalic rows in the mouth. Ventral locomotor cilia are arranged in two longitudinal bands that trace the lateral body sides and join posteriorly near the anal opening. Additional sensory bristles are organized in lateral, dorsolateral and dorsal columns.
Digestive tract: The mouth is terminal and surrounded by the mouth ring, composed of a strengthened cuticle; buccal cavity (6.4 μm wide and 19.1 μm long) mug shaped with walls heavily cuticularized. The pharynx is 142 μm in length and 22.6 μm in wide (U30), with pharyngeal pores near the base at about U33 and PhJIn at U37; the intestine is straight and the anus ventral is at U85.
Reproductive tract: It is hermaphroditic, with paired testes from U52 to U67, which extend into two sperm ducts at U60, turning anteriorly and fusing in a mid-ventral pore at U90. The frontal organ at U70 is vesicular and filled with bundled spermatozoa; the caudal organ is absent; the paired ovaries are at U68, and mature egg dorsal (to the intestine) occurs at U60.
3.1.1. Variability and Remarks on General Morphology
Seven additional adult measured specimens showed six TbP per side and three caudal cones, meaning that these traits are rather constant within and among the investigated populations. On the other hand, the number of TbA is slightly variable but not related to the size of the animal; in fact, one of the specimens attaining a maximum length of 480 µm (Figure 5
) possessed only five TbA per side while another attaining 332 µm in total length had six TbA.
3.1.2. Taxonomic Remarks
Currently, there are 23 described species belonging to the genus Paraturbanella
]. The new species bares closest resemblance to five species: P. africana
Todaro, Dal Zotto, Bownes & Perissinotto, 2017 [17
]; P. teissieri
Swedmark, 1954 [19
]; P. sanjuanensis
Hummon, 2010 [23
]; P. solitaria
Todaro, 1995 [31
]; and P. xaymacana
Dal Zotto, Leasi & Todaro, 2018 [33
], showing similar body and head shape, as well as peribuccal swelling [33
The species Paraturbanella tricaudata sp. nov. is considered new because it has three caudal cones, while the others have just one cone; moreover, the arrangement of the reproductive system, and in particular the location of the male pore, in combination with the extension and anatomical positioning of the testes is unique among congeneric species (two sperm ducts at U60 turning anteriorly and fusing in a mid-ventral pore).
3.1.3. Phylogenetic Analyses
The final alignment of the combined dataset yielded 3525 positions (1693 in 18S rDNA and 1832 in 28S rDNA). The parsimony analysis yields only one most-parsimonious tree with 4626 steps (Figure 7
Parsimony and Maximum Likelihood analyses yielded congruent topologies. In both analyses the phylogenies showed that the family Turbanellidae (both supported by very high bootstrap value - 100) and the genera Turbanella and Paraturbanella were monophyletic (Parsimony: Turbanella with good bootstrap values - 85; Maximum Likelihood: both genera supported by very high bootstrap value, respectively 100 and 99) and sister groups.
The phylogenetic position of Paraturbanella tricaudata
sp. nov. was not stable in both analyses. The new species appeared as the sister-group of Paraturbanella
sp. and both species were closely related with P. pallida
in Maximum Parsimony analysis (Figure 7
). However, Paraturbanella tricaudata
sp. nov. was sister-group of P. pallida
and both species were closely related with Paraturbanella
sp. in Maximum Likelihood analysis (Figure 8
3.1.4. Conclusive Remarks
The majority of marine gastrotrich sampling sites are in the Northern Hemisphere [51
], while in tropical countries the investigated areas are very scattered [14
]. The Brazilian coast is poorly sampled, although it shows a high diversity of marine gastrotrichs, according to current literature [5
]. In terms of knowledge of Turbanellidae diversity from Brazil, there are at least four candidate species to be formally described (one Turbanella
species and three Paraturbanella
species) from the north coast of São Paulo State [34
The Brazilian coast represents a potentially important area for the discovery of new species, and it is worth noting that this region is of particular interest in the study of marine meiofauna and the diversity of Gastrotricha, as recorded in previous studies [2
]. We emphasize the importance of investigating new geographic areas in order to improve our understanding of morphological diversity and the species richness of gastrotrich species.
Finally, the inclusion of new sequences of data concerning Paraturbanella tricaudata
sp. nov. and the use of distinct phylogenetic approaches did not change the scenario found by Todaro et al. [44
], Kolicka et al. [13
], and Garraffoni et al. [4
]. However, it is important to highlight that the low number of Turbanellidae species sequenced (from two of the six genera) may result in misleading the phylogenetic relationships within this clade.