A Review of the Genus Serratella Edmunds, 1959 in China with Description of a New Species (Ephemeroptera: Ephemerellidae)

Simple Summary Mayflies in the Holarctic genus Serratella Edmunds (Ephemeroptera: Ephemerellidae) are common aquatic insects in some places. Their nymphs can live in a variety of aquatic habitats, ranging from wide rivers to narrow creeks, and their imagos sometimes occur in mass emergences. Thus, Serratella species are common in aquatic insect collections. However, both their immature and imaginal stages are difficult to identify based on morphology because of confused generic definitions and poor species descriptions. This situation is especially bad in China. Historically, fifteen species have been reported from this country, but more than half of them (eight) have been moved to other genera. The remaining seven, including species both endemic to China and species also occurring elsewhere in the Palearctic region, have never been compared and studied systematically. The present paper provides detailed figures and diagnostic characters of five species (one of the other two is excluded from this genus; one is synonymized) and a new species from Western China. This is the first comprehensive and detailed study of Serratella diversity in China, which provides valuable information and character candidates to identify the genus and helps understand its phylogenetic position in the family. Abstract Species in the genus Serratella Edmunds, 1959 from China have never been compared and photographed systematically. Six valid Chinese Serratella species are recognized and revised in this paper. Among them, the imagos of S. brevicauda Jacobus et al., 2009 are unknown; the nymph of this species has a stout, strong body, with remarkably short caudal filaments and maxillary palpi. In contrast, only the imago stage of Serratella fusongensis (Su and You, 1988) (=Serratella longipennis Zhou et al., 1997, syn. nov.) is known; it has relatively long penes with small dorsal projections. The nymphs of S. setigera Bajkova, 1967 have small abdominal tergal spines but distinct, stout, blunt bristles on the spines, and the apexes of the male penes are round and shallowly divided. The fourth species, S. acutiformis sp. nov., which was collected from Western China, has sharp penial apexes (imagos) and large abdominal spines (nymphs). Unlike the former four species, S. ignita (Poda, 1761) and S. zapekinae Bajkova, 1967 has sub-quadrate penes without prominent dorsal projections. The nymph of S. ignita has lateral hair-like setae on the caudal filaments, while the nymph of S. zapekinae lacks such setae but has pairs of tubercles on the head and pronotum. Some characters used in the generic delineation of the genera Ephemerella Walsh, 1862 and Serratella, such as nymphal maxillary palpi and hair-like setae on caudal filaments as well as features of the imaginal penes and forelegs, are varied in Chinese species. However, all species in this paper have bifurcate ventral lamellae of gill VI. Our work highlights a need for further comparative systematic study of the genera Serratella, Ephemerella, and another related genus Torleya Lestage, 1917.


Introduction
The ephemerellid taxon Serratella was established originally as a subgenus of Ephemerella Walsh, 1862by Edmunds in 1959, who designated Ephemerella serrata Morgan, 1911 [2] as the type species to include a morphologically diverse group of North American and Eurasian species (type species of Ephemerella: Ephemerella excrucians Walsh, 1862 [3], designated by Eaton in 1868 [4]), nearly half of which have been moved to other genera since then. Jacob [5] provided a study of European species, but almost all of the species subsequently were moved to other genus groups. Despite this problematic taxonomic past, Serratella is now widely regarded as a genus containing just under 20 species globally, based on the generic definition by Jacobus and McCafferty [6]. However, this proposal was not followed by some researchers. For example, Bauernfeind and Soldán [7] adopted a different understanding of this taxon, leaving a common and widely distributed species, Ephemerella ignita (Poda, 1761) [8], outside Serratella; Kluge [9,10] suggested that this genus is close to Torleya Lestage, 1917 [11] or even just a subgenus of the latter. Edmunds [1] previously suggested that the two genera may eventually prove to be inseparable. It is believed here that with more detailed descriptions of more species, some of the dust raised around Serratella will be cleared.
In the past decade, thousands of Serratella specimens have been collected from all over China. In 2021, four males, five females, and some subimagos of a new species were reared from mature nymphs. In addition, the seldom collected species S. fusongensis You, 1988 andS. longipennis Zhou et al., 1997 were also found, but only in the stages previously known. The species S. xiasimaensis You, 1987 was depicted with four-segmented forceps in the original figures [14], and its holotype and paratypes cannot be located currently; thus, it is not included in our present study. So, six species are compared here. We emphasize that this is a regional study for China, and it includes only species recorded from this area. Conclusions and diagnoses are applicable only to this geographic area. However, their detailed characters may provide some insights into the systematics of the genus Serratella.

Materials and Methods
The nymphs were collected using hand nets. Some imagos and subimagos were reared from mature nymphs in a plastic container covering a nylon net indoors. The associations between imagos and nymphs were also confirmed by their COI sequences (GenBank accession numbers: OP737501, OP737502, OP737503).
All specimens were examined under a stereo microscope (Mingmei Photoelectric, MZ81, Guangzhou, China) and photographed with a digital camera (Single Lens Reflex, Guangzhou, China). Some small structures, such as mouthparts, claws, and gills, were placed on temporary slides with ethanol to be observed and photographed under a microscope camera (Nikon Eclipse 50i, Tokyo, Japan). Eggs were dissected from mature female nymphs and photographed with a scanning electron microscope (Apreo 2S, Thermo Fisher Scientific Company, Waltham, MA, USA). All structures except eggs and gills were preserved in alcohol after the photographs were taken.
The materials mentioned in this study were deposited in the Mayfly Collection, College of Life Sciences, Nanjing Normal University (NNU), China.
The specimens were stored in ethanol (around 85%). We used the morphological species concept.

Serratella Acutiformis Zhou sp. nov.
Distribution: China (Sichuan, Yunnan). Description of nymph ( Figure 1A-C and : Body length 6.0-7.0 mm, caudal filament length 5.0-6.0 mm, terminal filament slightly longer than cerci; body coarse, pale, gray to brown, washed with various tan to dark dots and markings ( Figure 1A); whole dorsal surface covered with very tiny brown to dark particle-like protuberances rarely present on abdomen ( Figure 1B).
Antennae pale, with tiny hair-like setae on scapes, pedicels, and articulations of flagella. Dorsal surfaces of frons and genae with transverse row of brown to dark dots, shapes of them irregular; genae slightly expanding forwards, making anterior margin of head semi-round, with dense hair-like setae. Vertex rough, with three pairs of blunt protuberances of different sizes ( Figure 2B).
Labrum slightly asymmetrical (five individuals checked for this feature), right half slightly longer than left one ( Figure 2C), width ca. 2.0× length, leading margin with shallow anteromedian emargination; free margins and dorsal surface with hair-like setae, ventral surface with two tufts of sub-median setae. Mandibles with long hair-like setae on outer margin and surface, outer incisor with three blunt denticles, inner incisor with two small and acute denticles ( Figure 2D,E); prostheca represented by tuft of plumose setae and strong spine; mesal margin near mola of left mandible with row of long hair-like setae. Maxillae with three apical blunt canines and two distinct dentisetae, series of bristles near dentisetae ( Figure 2F); tuft of bristles on apex; outer and inner margins of maxillae with hair-like setae; three-segmented maxillary palpi about half of upper half maxillae in length, with very sparse hair-like setae ( Figure 2G); length ratio of three segments of maxillary palp from base to apex = 1.0:0.5:1.25, segment I broader than segments II and III; cardo also with setae. Labial palp moderately developed with three segments ( Figure 2H), both segments I and II with setae on outer margin, segment III with distinct shorter and sparser setae, length ca. 3.0× width; length ratio of them from base to apex = 1.0:0.8:0.5; both dorsal and ventral surfaces of glossae and paraglossae with dense hair-like setae; glossae long and oval, with distinct convex apex, length ca. 2.0× width; width of paraglossae 2.0× that Labrum slightly asymmetrical (five individuals checked for this feature), right half slightly longer than left one ( Figure 2C), width ca. 2.0× length, leading margin with shallow anteromedian emargination; free margins and dorsal surface with hair-like setae, ventral surface with two tufts of sub-median setae. Mandibles with long hair-like setae on outer margin and surface, outer incisor with three blunt denticles, inner incisor with two small and acute denticles ( Figure 2D,E); prostheca represented by tuft of plumose setae and strong spine; mesal margin near mola of left mandible with row of long hair-like setae. Maxillae with three apical blunt canines and two distinct dentisetae, series of bristles near dentisetae ( Figure 2F); tuft of bristles on apex; outer and inner margins of maxillae with hair-like setae; three-segmented maxillary palpi about half of upper half maxillae in length, palp from base to apex = 1.0:0.5:1.25, segment I broader than segments II and III; cardo also with setae. Labial palp moderately developed with three segments ( Figure 2H), both segments I and II with setae on outer margin, segment III with distinct shorter and sparser setae, length ca. 3.0× width; length ratio of them from base to apex = 1.0:0.8:0.5; both dorsal and ventral surfaces of glossae and paraglossae with dense hair-like setae; glossae long and oval, with distinct convex apex, length ca. 2.0× width; width of paraglossae 2.0× that of glossae. Lingua with subparallel lateral margins ( Figure 2I), surface with tiny hair-like setae; apical margins of superlinguae with long hair-like setae. Thorax brown, with brown to dark maculae ( Figure 3A); pronotum with straight anterior, lateral and posterior margins; surface of pronotum coarse, one pair of protuberances apparent. Anterolateral angles of mesonotum at same level of lateral margin of pronotum, with very shallow crease nearby. Coxa of fore-and midlegs with larger, blunter dorsal plates than hindlegs ( Figure 3B,D). Femora of all legs with three dorsal brown bands at base, middle, and sub-apex respectively, basal one-third of tibiae brown, basal and apical brown bands on tarsi ( Figure 1A). Forefemora with three spines and a row of hair-like setae on outer margin ( Figure 3B), subapical band of spine-like setae present, inner margin with very tiny hair-like setae; fore tibiae with hair-like setae on inner and outer margins, additional row of spine-like setae on dorsal margin, tuft of bristles on inner  Abdomen dark-brown, terga I-V pale ( Figure 1A,B). All terga with stout spine-like setae on lateral margins ( Figure 1B); terga I-II with hair-like setae on posterior margins, tergum II with additional spine-like setae on posterior margin; terga III-VIII each with a pair of acute median spines extending backwards and upwards into distinct spur-or hornlike structures ( Figure 1B,C), larger progressively from anterior to posterior; spines on tergum VIII distinctly larger and more widely spaced than anterior pairs ( Figures 1B and  4A). All spines of abdomen with additional stout, blunt, bristle-like setae ( Figure 4A),   Thorax brown, with brown to dark maculae ( Figure 3A); pronotum with straight anterior, lateral and posterior margins; surface of pronotum coarse, one pair of protuberances apparent. Anterolateral angles of mesonotum at same level of lateral margin of pronotum, with very shallow crease nearby. Coxa of fore-and midlegs with larger, blunter dorsal Insects 2022, 13, 1019 7 of 21 plates than hindlegs ( Figure 3B,D). Femora of all legs with three dorsal brown bands at base, middle, and sub-apex respectively, basal one-third of tibiae brown, basal and apical brown bands on tarsi ( Figure 1A). Forefemora with three spines and a row of hair-like setae on outer margin ( Figure 3B), subapical band of spine-like setae present, inner margin with very tiny hair-like setae; fore tibiae with hair-like setae on inner and outer margins, additional row of spine-like setae on dorsal margin, tuft of bristles on inner apex; whole surfaces of tarsi with hair-like setae, some additional spine-like setae on inner margin; length ratio of femora:tibiae:tarsi = 1.0:0.9:0.6. Middle legs and hind legs similar to forelegs in color and structure pattern but without subapical band of spine-like setae ( Figure 3C,D), margins with more and longer spine-like and hair-like setae. Length ratio of femora:tibiae:tarsi of midleg = 1:0:0.8:0.6, ratio of hindleg = 1.0:1.0:0.6. Mid-and hindlegs with patellar-tibial fusion sutures. Tarsal claws of all legs similar, apex hooked ( Figure 3E), with three subapical setae and seven basal denticles of different sizes.
Abdomen dark-brown, terga I-V pale ( Figure 1A,B). All terga with stout spine-like setae on lateral margins ( Figure 1B); terga I-II with hair-like setae on posterior margins, tergum II with additional spine-like setae on posterior margin; terga III-VIII each with a pair of acute median spines extending backwards and upwards into distinct spur-or horn-like structures ( Figure 1B,C), larger progressively from anterior to posterior; spines on tergum VIII distinctly larger and more widely spaced than anterior pairs ( Figures 1B and 4A). All spines of abdomen with additional stout, blunt, bristle-like setae ( Figure 4A), those setae also on posterior margins of terga VIII and IX, forming comb-like structures along with spines and their associated setae.
Gills III-VI similar, with dorsal lamella sub-quadrate and with trilobed markings ( Figure 4B,C); ventral lamella divided into two clusters of lobes. Gills VII membranous, much smaller than others, ventral lamella comprised of several lobes ( Figure 4D).
Caudal filaments with dark-brown base, fading to apex ( Figure 1A). Articulations of basal half alternately with distinct spine-like bristles and hair-like setae but articulations of apical half with both kinds of setae ( Figure 4E); apical half of terminal filament with additional hair-like setae on both sides, while apical half of cerci with mesal fringes only.
Description of male imago ( Figure 5A-G and Figure 6A-C): Body 8.0 mm, caudal filaments ca. 9.0 mm. Body brown, with pale sutures, and one pair of median pale dots on mesothorax. Compound eyes contiguous with reddish upper portion but dark lower portion; ocelli with dark bases.
Description of egg ( Figure 7): Length 150-160 μm, width 100-120 μm. Drum-like in shape, with one polar cap; surface with scattered attachment structures; micropyles present.  Figure 4C). In males, this new species is similar to S. fusongensis and S. setigera in having a relatively straight segment II of the genital forceps, nearly round segment III; dorsal projections on penes ( Figure 6); and subequal foretibiae and tarsi ( Figure 5C). It is a definite Serratella species according to the definition of this genus provided by Jacobus and McCafferty [6] and Bauernfeind and Soldán [7].  Figure 4C). In males, this new species is similar to S. fusongensis and S. setigera in having a relatively straight segment II of the genital forceps, nearly round segment III; dorsal projections on penes ( Figure 6); and subequal foretibiae and tarsi ( Figure 5C). It is a definite Serratella species according to the definition of this genus provided by Jacobus and McCafferty [6] and Bauernfeind and Soldán [7].
Our new species can be distinguished from other Chinese species by the following characters. In the nymph, it has distinct abdominal spines on terga III-VIII ( Figure 1B,C) and moderately developed maxillary palpi ( Figure 2F,G) (longer than those of S. brevicauda but shorter than those of other species (Figure 8)). Its paired tergal spines have denser distributions of bristle-like setae ( Figure 4A). Furthermore, the apical halves of its caudal filaments have lateral hair-like setae ( Figure 4E), and its head with three pairs of protuberances is also useful with respect to identification (Figure 2A,B). The male imago has longer foretibiae than tarsi ( Figure 5C), acute penial apexes, and ventrally visible subapical projections on the dorsal sides of the penes ( Figure 6A-C).
The nymph of Serratella setigera is somewhat similar to this new species in having abdominal spines on terga III-VIII, but the spines of the former are much shorter ( Figure 1K,L). Dissimilarly, S. setigera has no protuberances on the head and pronotum, nor lateral setae along caudal filaments ( Figure 9E), but has more setae covering its nymphal body ( Figure 1J). Moreover, the two species have different imaginal penes (Figure 6A-C,G-I). and moderately developed maxillary palpi ( Figure 2F,G) (longer than those of S. brevicauda but shorter than those of other species (Figure 8)). Its paired tergal spines have denser distributions of bristle-like setae ( Figure 4A). Furthermore, the apical halves of its caudal filaments have lateral hair-like setae ( Figure 4E), and its head with three pairs of protuberances is also useful with respect to identification (Figure 2A,B). The male imago has longer foretibiae than tarsi ( Figure 5C), acute penial apexes, and ventrally visible subapical projections on the dorsal sides of the penes ( Figure 6A-C). The nymph of Serratella setigera is somewhat similar to this new species in having abdominal spines on terga III-VIII, but the spines of the former are much shorter ( Figure  1K,L). Dissimilarly, S. setigera has no protuberances on the head and pronotum, nor lateral setae along caudal filaments ( Figure 9E), but has more setae covering its nymphal body ( Figure 1J). Moreover, the two species have different imaginal penes (Figure 6A-C,G-I).
The nymphs of this new species resemble S. brevicauda in having strong bodies (Figure 1A,D) and lateral setae on caudal filaments ( Figures 4E and 9C). However, the latter species has obviously shortened tails ( Figure 1D), distinctive maxillary palpi ( Figure 8C), and apical segments of labial palpi ( Figure 8D). The terga have shorter and blunter spines ( Figure 1E,F). The imagos of the latter are still unknown.
On the other hand, the males of the new species are similar to S. fusongensis in penial shape ( Figure 6A-F). However, the penes of the latter species are more narrowly divided, and the dorsal subapical projections are smaller, which cannot be seen in the ventral view ( Figure 6D-F). The nymphs of S. fusongensis are still unknown.
In contrast to the penes of S. acutiformis sp. nov., which has divided apexes and distinct dorsal projections ( Figures 5G and 6A-C), the penes of S. ignita ( Figure 10E-G) and S. zapekinae ( Figure 10H-J) have no prominent dorsal projections and are sub-quadrate in shape. Although the nymphs are similar with respect to the labial palpi ( Figures 2H and  8H,P), the new species has a shorter apical segment of the maxillary palp ( Figures 2G and  8G,O), and larger abdominal spines than the latter two species ( Figure 1C,I,O). In addition, the outer sides of the cerci of the new species S. acutiformis sp. nov. have no hair-like setae  Figure 4E), though these setae are present on the cerci of the species S. ignita ( Figure 9D). The caudal filaments of S. zapekinae have no lateral hair-like setae ( Figure 9F). Furthermore, nymphs of both S. acutiformis sp. nov. and S. zapekinae have protuberances on their heads and pronota, but the former species has three pairs of protuberances on the head ( Figure  2B), while the latter has one pair only ( Figure 9A). According to Edmunds [1] and Allen and Edmunds [32], the North American Serratella species have no lateral hair-like setae on their caudal filaments and their penial apexes are very blunt. The European Serratella species in the book of Bauernfeind and Soldán [4] is similar to the American ones.
On the other hand, the males of the new species are similar to S. fusongensis in penial shape ( Figure 6A-F). However, the penes of the latter species are more narrowly divided, and the dorsal subapical projections are smaller, which cannot be seen in the ventral view ( Figure 6D-F). The nymphs of S. fusongensis are still unknown.
In contrast to the penes of S. acutiformis sp. nov., which has divided apexes and distinct dorsal projections ( Figures 5G and 6A-C), the penes of S. ignita ( Figure 10E-G) and S. zapekinae ( Figure 10H-J) have no prominent dorsal projections and are sub-quadrate in shape. Although the nymphs are similar with respect to the labial palpi ( Figures 2H  and 8H,P), the new species has a shorter apical segment of the maxillary palp ( Figures  2G and 8G,O), and larger abdominal spines than the latter two species ( Figure 1C,I,O). In addition, the outer sides of the cerci of the new species S. acutiformis sp. nov. have no hair-like setae ( Figure 4E), though these setae are present on the cerci of the species S. ignita ( Figure 9D). The caudal filaments of S. zapekinae have no lateral hair-like setae ( Figure 9F). Furthermore, nymphs of both S. acutiformis sp. nov. and S. zapekinae have protuberances on their heads and pronota, but the former species has three pairs of protuberances on the head ( Figure 2B), while the latter has one pair only ( Figure 9A).

Serratella brevicauda
Serratella brevicauda : Zhou, 2013: 181 [29]; Zhou et al., 2015: 229 [25]. Distribution: China (Yunnan, Shaanxi). Descriptions: See Jacobus, Zhou, and McCafferty, 2009 [24]. Diagnosis: This species was described using nymphs only. Its nymphs have remarkedly reduced caudal filaments ( Figure 1D), maxillary palpi ( Figure 8A-C), and apical segment of the labial palpi ( Figure 8D). In addition, the bodies of this species are very stout and strong, and their caudal filaments have lateral setae on the apical half ( Figure 9C). However, its maxillae are similar to other species in the present paper, and its nearly oval head shape is also similar to that of the new species S. acutiformis sp. nov.
Descriptions: See Su and You, 1988 [15], or Zhou et al., 1997 [18]. Diagnosis: The males of this species can be differentiated by the longer penes which, further, have smaller apical projections ( Figure 6D-F). The tip of the penis in some individuals extended inwards to form a small dorsal projection. The two penes are almost fused in full length, with a broad V-shaped emargination between them.
Remarks: We examined the holotypes of two species, S. fusongensis and S. longipennis, and found that they are conspecific. In the original pictures, Su and You [15] showed or concentrated on the division between the two penes, while Zhou et al. [18] focused on their apical projections. These inaccurate illustrations caused some misunderstandings, and this synonymy is the result.
Based upon its penes, this species might be a member of the genus Torleya, like Torleya mikhaili Tiunova, 1995 [34]. Its exact status will be clarified when the nymph can be described.

Discussion
This detailed research allows us to make some generalizations about the genus Serratella in China. All known Chinese Serratella nymphs share the following combination of characters that distinguish them from other ephemerellid genera: ventral lamella of gill VI deeply cleft; gills III not operculate, nor distinctly semi-operculate; tarsal claw with only a single row of denticles, in which the most distal denticle is not very much larger than the rest; and abdominal terga with paired posteromedial projections that are situated subparallel to one another. A tentative diagnosis can be made for those Chinese Serratella species with male imagos that have been described: genital forceps segment II is somewhat compressed, with a slight apical twist; and the penes have dorsolateral projections and/or obvious spine-like setae variously situated laterally and/or in the apical cleft. Eggs are not consistently distinguishable from all other Ephemerellidae genera, but they usually have a smooth chorion and often have a nipple-shaped polar cap.
Edmunds [1] separated the genus Serratella from Ephemerella using imaginal dorsal penial projections and the nymphal setae pattern of the caudal filaments, the former genus having projections on penes but lacking lateral setae on nymphal tails. However, the Chinese species, including S. acutiformis sp. nov. and S. brevicauda, show a mix of these characters, having setae on both the articulations and lateral sides of the caudal filaments ( Figures 4E and 9C), and the penes of S. acutiformis sp. nov. have dorsal projections ( Figure 6C). On the other hand, the Chinese species in the present study also show that, when present, the size of dorsal penial projections is variable, with those of S. fusongensis being small ( Figure 6E) and those of S. acutiformis sp. nov. being larger ( Figure 6B); two of the species lack prominent projections altogether. So, in order to clarify the exact relations between Palearctic and Nearctic Serratella species (the latter group containing the type species of the genus), more direct and detailed comparisons of species within the genus and with species in other genera are needed, which may result in modifications to the definition of the genus Serratella.
Jacob [5] suggested that Serratella nymphs have reduced maxillary palpi and no lateral hair-like setae on caudal filaments and that imaginal penes have dorsal projections. In contrast, Ephemerella was said to have hair-like setae on tails, maxillary palpi relatively well developed, and male imagos with penes lacking dorsal projections. Based on these characters, he put the species E. ignita in the genus Serratella. Using the same characters, on the contrary, Bauernfeind and Soldán [7] retained this species in the former genus. Furthermore, Edmunds [1] and Allen and Edmunds [32] realized that some species of Ephemerella and Serratella have spines on the lateral margins of the penes (such as Serratella serrata Morgan, 1911 [2]), but Bauernfeind and Soldán [7] defined the genus Serratella without spine on penes. For the same reasons mentioned above (these characters are variable and Chinese species show intermediate states between them), we think we should consider other candidate characters to separate those two genera.
Kluge [10,11] and Jacobus and McCafferty [6] adopted the character of gills VI to delimitate the genera Serratella and Ephemerella. Serratella has a deeply cleft ventral lamellae of gill VI, while Ephemerella lacks this deep cleft. Given this, the species E. ignita was included in the genus Serratella. This kind of classification allows not only a compromise with respect to some of the apparently paradoxical characters described above but it also retains both S. ignita and S. zapekinae, whose penes are extremely similar to each other but different from those of other Serratella species, in the genus Serratella. Therefore, it is followed in the present study.
Unfortunately, this classification causes another problem. Both the genera Serratella and Torleya have similar gills VI, and their males usually have dorsal penial projections and similar forceps. Further, the gills III of many Torleya species are not enlarged, such as those of Torleya mikhaili Tiunova, 1995 [34], which is a key character used to separate them, originally by Edmunds [1]. Kluge [10,11] regarded those two genera as one, and Edmunds [1] did express reservations about their distinctiveness. A comprehensive and comparative study of these species and a few in some other genera is needed to resolve problems regarding identification and classification globally. At this moment, however, when we consider just the Chinese materials, we see that the nymphs of Torleya have more hair-like setae but fewer and smaller abdominal tergal spines than those of Serratella, and the male imagos have slight differences in the apical segments of their forceps. Data Availability Statement: All data are available in the paper.