Orientogidiella reducta, Sidorov & Reddy & Shaik, 2018

Sidorov, Dmitry, Reddy, Yenumula Ranga & Shaik, Shabuddin, 2018, Groundwater amphipods (Crustacea, Malacostraca) of India, with description of three new cavernicolous species, Zootaxa 4508 (3), pp. 403-426 : 406-411

Orientogidiella reducta , new species

Figures 2A , 3–5

Diagnosis. Slender, small-sized amphipods of typical bogidiellid habitus (sexual dimorphism pronounced, i.e., males slightly larger than females; uropods I and II sexually dimorphic with inner rami bearing 1 modified apical spine each in males); coxal plates shallow (wider than deep); posterodistal corners of pleonal plates I–III acute; antenna I longer than antenna II; accessory flagellum of antenna I reduced, 1-articulate; molar of mandible greatly reduced; palp of maxilla I reduced, 1-articulate; propodus of gnathopod I distinctly larger and stouter than that of gnathopod II; pereopods V and VI relatively short (especially pereopod V) with dense row of fine setae on anterior margin of merus (article IV) and with stocky carpus (article V) armed with conspicuous groups of strong spines; pereopods II–VI with coxal gills. Large males 5.5–6.5 mm, largest female 5.0 mm.

Material examined. Holotype MNHN-IU- 2018-47. INDIA: ♂ 5.5 mm, Borra caves, cave-pool sediments, 18.280278, 83.038611, elevation ca. 705 m, Andhra Pradesh state, coll. Shabuddin Shaik, 17 th June 2013 . Paratypes MNHN-IU- 2018-48: 2 ♂♂ measuring 6.5 mm each, 3 ♂♂ measuring 6.0 mm each, 1 ♂ 5.5 mm, ca. 3.5 mm fragment, 1 ♀ 5.0 mm, oostegites undeveloped; same data as for holotype .

Etymology. The specific epithet reducta (Latin) is an adjective, meaning 'reduced'.

Description of holotype MNHN-IU- 2018-47. GENERAL BODY MORPHOLOGY ( Figs 2A , 3A , 5A, B, F ). Body unpigmented (whitish in color), smooth, setose with fine setae. Head longer than deep and longer than first pereon segment; rostrum indistinct, interantennal lobe irregularly rounded apically; eyes absent. Pleonal plates I– III lacking setae/spines on ventral margins; posterior margins convex, bearing 2 or 3 thin setae; posterodistal corners acute. Telson subquadrate with apical margin roundly convex, width to length ratios 1:0.6, bearing 2 strong, notched spines, accompanied by 3 penicillate setae subapically. ANTENNAE ( Figs 2A , 3B, C ). Antenna I about 35% of body length; primary flagellum of 12 articles, each article with 2–6 setae, aesthetascs present on 10 distal articles; ratios of peduncular articles 1–3 1:0.6:0.3; proximal article of peduncle with 2 simple spines on ventral margin; accessory flagellum small, 1-articulate. Ratio of lengths of antenna I to antenna II is 1:0.8; flagellum of antenna II of 5 articles, last one minute, each of other articles sparsely setose; peduncular article 4 slightly longer than article 5; flagellum ca. 30% shorter than peduncle (articles 4+5); last 2 peduncular articles with short spines and setae; gland cone short. MOUTH PARTS ( Figs 3 D–I). Labrum subtrapezoidal, as long as broad, epistome broadly roundish. Inner lobes of paragnath absent; outer lobes closely spaced, apices somewhat narrowly rounded and finely setose; mandibular process narrow. Left mandible: incisor with 5 teeth, lacinia mobilis consisting of 2 finely denticulate plates of similar size; row of 4 densely plumose spines (1 of them long) between lacinia and molar process; molar vestigial, conical, bearing 3 plumose spines. Right mandible: incisor with 5 teeth, lacinia mobilis with 5 teeth, row of 4 plumose spines (1 of them long) between lacinia and molar process; molar similar to that of left mandible; mandibular palp article 2 about 25% longer than article 3; palp article 1 without seta, article 2 with 2 long setae on inner margin; distal article narrow, with 1 long seta on apex. Maxilla I palp reduced, 1- articulate, with 2 long setae of equal length on apex (palps symmetrical); outer plate with 7 serrate spines; inner plate with 2 plumose setae. Maxilla II inner plate broader than outer one, with 4 apical setae of varying size; outer plate bearing 4 simple setae apically. Maxilliped outer plate short, evenly rounded apically, with 2 naked sub-apical spines and 2 long lateral setae in distal part; inner plate broad, with 2 short apical spines (1 of them finely serrate) and 1 stiff naked seta, 1 seta located medially on small pedestal; palp 4-articulate; article 2 longest, expanded, distinctly convex on inner margin, with 11 long simple setae in 2 rows along inner margin; article 3 narrow, bearing 2 sets of long setae apically and on medial face; article 4 about as long as preceding article, slightly curved and tapering distally, with 1 dorsal seta and 2 setae at base of nail; inner margin pubescent, nail sharply pointed, 0.25× length of pedestal. Lateralia with 15 strong, pectinate spines. COXAL PLATES AND GILLS ( Figs 2A , 4 A–G). Coxal plates I–VII wider than long, free, not overlapping one another, coxa VI largest; coxal plates V–VII semicircular, narrow posteriorly, bearing 1 stiff seta. Coxal gills oblong, stalked on coxae II–VI. GNATHOPODS I AND II ( Figs 2A , 4A, B ). Gnathopod I basis short, broadest medially, with 1 short seta on distoposterior corner; merus with 4 stiff setae on distoposterior margin, posterior surface spinose; carpus triangular, with 2 setae of equal length on narrowly rounded spinose distoposterior lobe; propodus prominent, swollen, ca. 1.5× longer than broad, palmar margin slightly convex, nearly 1.5× longer than posterior margin, palmar angle indistinct, armed with 3 strong spines and 1 long seta; anterior margin with 1 seta, and a group of 2 setae anterodistally; palm armed with 12 stiff, tiny notched setae along inner and outer faces; dactylus falcate, about 50% length of propodus, with 3 shallow serrations, accompanied by thin 1 seta on inner face and 2 short setae on outer face, demarcation of nail indistinct. Gnathopod II basis sublinear, with 1 short seta on distoposterior corner; ischium posterior surface spinulose with 1 posterodistal seta; merus with 1 stiff posterodistal seta; carpus sub-triangular, with 16 thin subequal setae on broadened, spinulose ventral lobe, 1 set of long setae distally on medial face; propodus small, nearly 0.3× shorter than propodus of gnathopod I; palmar margin straight, shorter than posterior margin; palmar angle distinct, armed with 2 strong spines and 1 long seta; anterior margin with 1 seta, anterodistal group with 3 setae; palm armed with 2 stiff, tiny notched setae, accompanied by 2 long setae along inner and outer faces; dactylus similar to that of gnathopod I. PEREOPODS ( Figs 2A , 4 C-G): lacking lenticular organs. Pereopods III–IV subequal, bases fusiform (especially PIII), each with 1 stiff seta on anterodistal margin; dactyli ca. 0.4× length of corresponding propodi. Pereopod V very short, only about 33% length of pereopod VII and 70% length of pereopod VI; basis broad, 0.5× broad as long, posterior margin with 3 notched spines and 1 seta; merus with a dense row of fine setae anteriorly; carpus (article 5) short and stocky, armed with conspicuously strong lateral spines; propodus (article 6) longer and narrower than carpus, with 5 apical spines; dactylus (article 7) 0.4× length of corresponding propodus. Pereopod VI length 0.3× body length; basis broad, length to width is 1:0.5; posterior margin with 3 notched spines and 1 seta; anteriorly 3 notched spines and 2 setae; merus armed like that of pereopod V; carpus armed more profusely than that of pereopod V; propodus with 5 lateral and 4 apical spines; dactylus about 0.33× length of corresponding propodus. Pereopod VII ca. 45% longer than pereopod VI, basis subrectangular, ca. 50% longer than wide, both anterior and posterior margins bearing notched spines; carpus longer than merus; propodus with 1 group of 3 short spines and 1 long stiff seta apically; dactylus ca. 40% length of corresponding propodus. PLEOPODS AND UROPODS ( Figs 2A , 5 A–E). Pleopods I–III subequal; peduncular articles linear, in ratios 1:1:0.8, with 2 retinacula each; inner ramus absent; outer ramus 3-articulate, fringed with long, plumose setae at distal end of each article. Uropod I peduncle without basofacial spine; with 2 dorsolateral spines and distally with 1 very strong dorsomedial spine; exopodite to endopodite length 0.8:1; endopodite length 0.6× peduncle; rami straight, each armed with 4 strong apical spines (1 of them simple, much larger); endopodite with 1 modified apical spine (large, bowed, tapered to sharp point, with tiny serration on upper surface). Uropod II peduncle with 1 dorsolateral spine and 1 strong dorsomedial spine distally; exopodite to endopodite length 0.8:1; endopodite a little shorter than peduncle; rami straight, each armed with 4 spines apically (1 of them simple, much larger) and endopodite with 1 modified sub-apical spine. Uropod III (single appendage was found separately in vial): long, with peduncle only about half length of rami, armed with 2 notched spines apically; rami subequal, armed with singly inserted 4 or 5 lateral and 3 apical spines (1 of them long).

Variation. Not observed.

Sexual dimorphism. Female 5.0 mm long, oostegites (brood plates) weakly developed, very small and present on pereopods II–V (non-setose in the material examined); uropods I and II lacking modified spines; in all other characters similar to male.

Distribution and ecology. Orientogidiella reducta gen. n., sp. n. is known only from its type locality (see Fig. 1 ). A bathynellacean syncarid, Habrobathynella borraensis Ranga Reddy, Shaik, and Totakura, 2014 , was also collected from the same locality ( Ranga Reddy et al. 2014). Interestingly, clusters of some extremely small eggs (or cysts?) were found under each of the pleonal or epimeral plates in the so-called "epimeral pockets" (used here as a conditional name for the cavity between lower free margin of epimera and the lateral margin of abdomen; see Fig. 5A ).

Remarks. Orientogidiella reducta gen. n., sp. n. most closely resembles O. indica ( Holsinger et al. 2006) comb. n., but can be distinguished from the latter by (character states of O. indica comb. n. in parentheses): palp of maxilla I reduced, 1-articulate (normal, 2-articulate); inner lobes of paragnath absent (present); defining angle of gnathopod II armed with 2 strong spines and 1 long seta (spines absent); merus (article 4) of pereopods V and VI with dense row of fine setae on anterior margin (bearing 4 or 5 spines); posterodistal corners of pleonal plates I–III acute (corners of plates I and II indistinct, sub-rounded, plate III acute); and inner ramus of uropod II in males bearing 1 modified spine (modified spines absent).

Figures

FIGURE 1. Height map of India showing geographic distribution of subterranean amphipods. Question mark (?) indicates collections of undescribed specimens of Bogidiella sp. reported in Holsinger et al. (2006). Asterisk (*) indicates new sample sites.

FIGURE 2. Habitus of examined specimens: (A) Orientogidiella reducta gen. n., sp. n., holotype MNHN-IU-2018-47, male, 5.5 mm; (B) Bogidiella hindustanica sp. n., holotype MNHN-IU-2018-50, female, 2.75 mm; (C) Indoniphargus subterraneus sp. n., holotype MNHN-IU-2018-52, female, 5.2 mm.

FIGURE 3. Orientogidiella reducta gen. n., sp. n., holotype MNHN-IU-2018-47, male, 5.5 mm: (A) head; (B) antenna I; (C) antenna II; (D) mandible, right; (E) mandible, left; (F) paragnaths (=lower lip); (G) maxilla I; (H) maxilla II; (I) maxilliped. Scale bars 0.1 mm.

FIGURE 4. Orientogidiella reducta gen. n., sp. n., holotype MNHN-IU-2018-47, male, 5.5 mm: (A) gnathopod I; (B) gnathopod II; (C) pereopod III; (D) pereopod IV; (E) pereopod V; (F) pereopod VI; (G) pereopod VII. Scale bars 0.2 mm.

FIGURE 5. Orientogidiella reducta gen. n., sp. n., holotype MNHN-IU-2018-47, male, 5.5 mm: (A) pleonal plates I–III and pleopods I–III; (B) urosome; (C) uropod I; (D) uropod II; (E) uropod III; (F) telson. Scale bars 0.2 mm.