Trichorhina amplitelson Campos-Filho, Carpio-Díaz & Borja-Arrieta, n. sp.

(Figs 2D; 19-21)

urn:lsid:zoobank.org:act: 4B96C1B2-5207-4F38-A125-40AAEB620903

TYPE MATERIAL. — Holotype. Brazil • ♂; Caverna do Jabuti, Curvelândia, state of Mato Grosso; 15°33’56.2”S, 57°59’20”W; 324 m a.s.l.; 29.IX.2017; J. E. Gallão, R. Machado & A. Chagas-Jr leg.; LES 27989.

Paratypes. Brazil • State of Mato Grosso: 9 ♂ (one with parts in micropreparations), 12♀ (one in micropreparations); same data as holotype; LES 27990 • 1 ♂; same data as holotype; LES 27991 • 1♀; Gruta do Isopoda cave, Sítio Bom Jesus, Mirassol do Oeste; 15°35’23.1”S, 58°00’22.4”W; 30.IX.2017; J. E. Gallão, A. Chagas-Jr & R. Machado leg.; LES 27992 • 2 ♂, 5 ♀; Caverna Labirinto, same municipality and state as previous; 15°32’50”S, 58°01’29.28”W; 234 m a.s.l.; 20.IX.2017; same collectors as previous; LES 27993 .

ETYMOLOGY. — The name of the new species refers to the wide shape of the telson, typical of this species.

DESCRIPTION

Maximum body length: ♂ 2.8 mm, ♀ 3.5 mm. Animal without body pigments (Fig. 2D). Body (Fig. 19A) slightly convex and robust. Dorsal surface covered with fan-shaped scale-setae (Fig. 19B). One line of noduli laterales per side, inserted close to posterior margins and more or less at same distance from lateral margins, d/c and b/c coordinates as in Figure 19C, D, respectively. Cephalon (Fig. 19E, F) with lateral lobes triangular, protruding frontwards; suprantennal line slightly concave, frontal line absent; eyes composed of four or five ommatidia. Pereonite 1 epimera directed frontwards, pereonite 2-7 epimera pointing backwards (Fig. 19A). Pleon (Fig. 19A, G) with outline continuous with that of pereonite 7; epimera of pleonites 3-5 falciform, directed backwards; telson trapezoidal, almost as wide as long, distal portion slightly narrower than proximal portion, apex broadly rounded. Antennula (Fig. 19H) of three articles, distal article longest with several aesthetascs inserted apically and sub-apically. Antenna (Fig. 19I) when extended posteriorly surpassing posterior margin of pereonite 1; flagellum with two articles, second article about twice as long as first, bearing two lateral aesthetascs, apical organ short with long free sensilla. Mandibles with molar penicil dichotomized consisting of up to eight branches, left mandible (Fig. 19J) with 2+1 penicils, right mandible (Fig. 19K) with 1+1 penicils. Maxillula (Fig. 19L) inner branch with two subequal penicils, distal portion rounded; outer branch with 3+4 teeth simple. Maxilla (Fig. 19M) with setose and bilobate apex; outer lobe about three times as wide as inner lobe, distal margin rounded. Maxilliped (Fig. 19N) basis rectangular bearing sparse setae; endite subrectangular, medial seta surpassing distal margin. Uropod (Fig. 20A) protopod and exopod grooved on outer margin bearing glandular pores, exopod slightly longer than endopod, endopod inserted proximally. Pereopod sternal setae with cleft apex; pereopod 1 with antennal grooming brush reaching median margin of carpus; dactylus with long inner claw, ungual seta simple, dactylar seta simple surpassing outer claw.

Male

Pereopods 1 and 7 (Fig. 20B, C) without sexual dimorphism. Genital papilla as in Figure 20D. Pleopod 1 (Fig. 20E) exopod subovoid, about twice as broad as long; endopod about three times as long as exopod, distal part acute. Pleopod 2 (Fig. 20F) exopod triangular, outer margin concave bearing short setae; endopod flagelliform longer than exopod. Pleopod 3 and 4 exopods as in Figure 20G, H, respectively. Pleopod 5 exopod (Fig. 20I) triangular, outer margin slightly convex bearing short setae.

REMARKS

The genus Trichorhina comprises about 70 species distributed in tropical and subtropical areas of the globe (Schmalfuss 2003; Boyko et al. 2008). The genus was morphologically re-defined by Carpio-Díaz et al. (2018). Molecular data contradict its monophyly within Platyarthridae (Javidkar et al. 2015, 2017). The members of the genus exhibit reduced size, body pigments and/or ommatidia are reduced or absent, the dorsal surface is covered with fan-shaped scale-setae, and the pereopods are short, bearing sternal fringes of setae (see Campos-Filho et al. 2014, 2015b, 2016). The dorsal scale-setae reduce the adhesion of microparticles facilitating the movement of the animals in non-consolidated substrates. Several species of the genus occur in caves and until more sampling outside caves is made, they are considered to be troglophile.

To date, 35 species of the genus are known from Brazil, of which eight are recorded from subterranean environments, i.e. T.acuta Araujo & Buckup, 1994, T. anhanguera Campos-Filho, Araujo & Taiti, 2014, T. cipoensis Campos-Filho, Bichuette & Taiti, 2016, T. curupira Campos-Filho, Araujo &Taiti, 2014, T. guanophila Souza-Kury, 1993, T. kaingangi Campos-Filho, 2015, T. pataxosi Campos-Filho, Bichuette &Taiti, 2016, and T. yiara Campos-Filho, Araujo & Taiti, 2014 (Campos-Filho et al. 2018a for complete references).

Trichorhina amplitelson Campos-Filho, Carpio-Díaz & Borja-Arrieta, n. sp. is easily distinguished from all the previously mentioned species in the wide shape of the telson. Only T. acuta has eyes composed of four ommatidia; however, the new species differs in having the molar penicil of the mandibles composed up to eight branches (vs six in T. acuta), outer endite of the maxillula with teeth apically simple (vs two apically cleft in T. acuta) (see also Araujo & Buckup 1994).

In a broader comparison, T. aethiopica Arcangeli, 1941, T. giannellii Arcangeli, 1929, T. hospes Silvestri, 1918, T. minima Schmalfuss & Ferrara, 1978, T. paraensis Souza-Kury, 1997, T. silvestrii Arcangeli, 1936, and T. vandeli Rioja, 1955, also have eyes composed of four ommatidia. As common within Oniscidea, most of the characters used in taxonomic descriptions until the middle of the 20th century were generic, and comparisons were not presented. Trichorhina amplitelson Campos-Filho, Carpio-Díaz & Borja-Arrieta, n. sp. differs in having colorless body (vs grey-brownish in T. aethiopica), cephalon with lateral lobes well-developed (vs slightly developed in T. hospes and T. paraensis), telson trapezoidal (vs triangular in all the above mentioned species), antenna with apical organ short (vs elongated in T. paraensis), mandibles with molar penicil dichotomized and composed of eight branches (vs simple in T. hospes and T. paraensis, three branches in T. silvestrii, several branches in T. vandeli), maxillula outer endite with all teeth apically simple (vs two cleft in T. hospes, T. paraensis, T. silvestrii, and T. vandeli), maxilla outer lobe wider than inner lobe (vs subequal in T. hospes), and male pleopod 1 exopod sub-ovoid (vs heart-shaped in T. minima and T. vandeli, subquadrangular in T. paraensis) (Silvestri 1918; Arcangeli 1929, 1936, 1941; Rioja 1955; Mulaik 1960; Schmalfuss & Ferrara 1978; Souza-Kury 1997).

Within Oniscidea, the morphology of the mouth parts is relatively stable among congeneric species (see Schmidt 2002, 2003). In most cases, few variations can be observed, such as the apical shape of the teeth of the outer endite of maxillula, and relative width of the lobes of the maxilla. Nevertheless, in T. micros and T. minutissima as described by Budde-Lund (1913), the outer teeth on the outer endite of the maxillula are pectinate, a character state not observed in the remaining members of the genus. This shape of teeth is considered to be plesiomorphic and it is present in other genera of Oniscidea, e.g., Ligia, Alboscia Schultz, 1995, Benthana Budde-Lund, 1908, Ctenoscia Verhoeff, 1928, and Paractenoscia Taiti & Rossano, 2015 (Philosciidae) (see Leistikow 1997, 2001b; Schmidt 2008; Taiti & Rossano 2015; Campos-Filho et al. 2015a, 2020). Therefore, these two species of Trichorhina need to be revised in order to clarify their taxonomy.