Indoniphargus subterraneus, 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 : 414-420

Indoniphargus subterraneus , new species

Figures 2C , 9–12

Diagnosis. Stocky, small-sized amphipod of typical austroniphargid habitus (sexual dimorphism marked, i.e.,

males smaller than females, dorsal surface weakly spinose, gnathopods and uropod II sexually dimorphic); remarkably shallow coxal plates III and IV (posterior excavation of coxal plate IV indistinct); antenna II shorter than antenna I, with long gland cone; body of mandibles large, with well-developed palp, molar process with transverse ribs and strong, pectinate spiniform seta ("damper seta"); gnathopods I and II dissimilar in size and armament; carpus of both gnathopods (article 5) elongate and swollen, posterior margins of articles covered with fine soft hairs; pereopods III–VII relatively short and spinose, pereopod VI longest; thoracic segments covered with fine hairs dorsally, but abdominal segments spiny; posterodistal corners of pleonal plates I–III roundish; telson deeply cleft, 2 apical spines on either lobe; coxal gills of pereopods II–VI stalked. Largest male 4.0 mm, female 5.2 mm.

Material examined. Holotype MNHN-IU- 2018-52. INDIA: ♀ 5.2 mm, oostegites developed, non-setose, Kapiladevi caves, cave-pool sediments, 19.532333, 78.995028, elevation 324 m, Telangana state, coll. Shabuddin Shaik, 12 th May 2013. Paratypes MNHN-IU- 2018-53: 2 ♂♂ measuring 4.0 mm each, 5 juveniles; same data as for holotype. Accompanying fauna: Bogidiella hindustanica sp. n. ( Amphipoda : Bogidiellidae ) described above.

Etymology. The specific epithet subterraneus (Latin) is an adjective, meaning 'underground'. Gender masculine.

Description of holotype MNHN-IU- 2018-52. GENERAL BODY MORPHOLOGY ( Figs 2C , 9A , 11A, H ). Body whitish, semitransparent in preserved specimens, stout, lacking dorsal cuticular elements, but densely covered with thin setae and curved spines. Head as long as first pereon segment; rostrum indistinct; interantennal lobe rounded, inferior antennal sinus shallow; eyes absent. Pleonites and urosomites bearing stiff, curved and distally notched setae on dorsal surface; urosome segments distinct; urosomite I bearing 2 strong spines on ventral margin. Pleonal plates I–III with roundish posterodistal corners, each bearing 2 or 4 notched spines; 5–7 stiff notched setae on posterior margin; ventral margins of plates unarmed; plates II and III with lateral groups of spines. Telson about 0.25× longer than broad, deeply cleft; lobes tapered distally, bearing 2 apical notched spines each. ANTENNAE ( Figs 2C , 9B, C ). Antenna I ca. 55% of body length, and 2.0× longer than antenna II; ratios of peduncular articles 1–3 1:0.7:0.5, article 1 with a few notched spines on ventral margin; primary flagellum with 18 articles, each article with 2-4 short setae, aesthetascs present on each of 12 distal flagellar articles; accessory flagellum short, 2-articulate. Antenna II (flagellum short due to some malformation): gland cone long; peduncular article 5 longer than article 4, both articles bearing sparse notched spines along dorsal and ventral margins; flagellum about 30% shorter than peduncle (articles 4+5), consisting of 6 articles with sparsely covered thin setae; calceoli absent. MOUTH PARTS ( Figs 9 D–K). Labrum sub-quadrate with fine setae on apex. Paragnath outer lobes rounded, mandibular process narrow, inner lobes absent. Mandibles sub-equal: right mandible incisor process with 6 teeth, lacinia mobilis consisting of 2 finely denticulate plates of similar size, and a row of 4 serrate spines between lacinia and molar; triturative molar process bearing strong, pectinate spiniform seta (see Fig. 12 ) at upper distal corner and opposite short, plumose gnathobasic seta; incisor of left mandible with 7 teeth, lacinia mobilis with 5 teeth; a row of 4 serrate spines between lacinia and molar process; molar similar to that of right mandible; mandibular palp article 2 twice as long as palp article 3; proximal palp article without setae; article 2 with a group of 4 plumose setae on subterminal margin; distal article short, with a group of 10 E-setae (1 of them very long) on distal half. Maxilla I inner plate narrow, with 2 plumose setae, outer plate with 9 multi-toothed spines (first two of them bifid); palp relatively long, both asymmetric; distal palp article with 6 strong spines and 1 simple seta each on apical and sub-apical margins (left maxilla I, Fig. 9H ); or 4 finely plumose setae (right maxilla I, Fig. 9I ). Maxilla II with both plates narrow, apical margin of outer plate with 24 simple setae of varying size and occurring in 2 rows; inner plate lacking oblique row of setae but bearing 1 long, plumose seta apicomedially and 16 short simple setae in 2 rows on apical margin. Maxilliped: inner plate oblong, narrow, with 3 strong spines and 2 naked setae apically, 4 plumose setae on inner ventral face; outer plate sub-ovoid, with a row of 6 strong, knife-like spines and 3 groups of paired simple setae along outer margin; palp article 2 sub-linear, with a row of about 10 thin setae along inner ventral face and 1 elongate apicolateral seta; article 3 narrow, with a subtle pubescent bulge on posterodistal lobe, 3 long setae on distal margin, and a row of 4 long simple setae medioventrally; article 4 (distal) shorter than article 3, curved, with 1 dorsal seta and 2 setae at base of nail; inner margin pubescent, nail slender, sharply pointed and slightly shorter than pedestal. COXAL PLATES, OOSTEGITES AND GILLS ( Figs 2C , 10 A–G). Coxal plates I–IV dissimilar in shape being somewhat square or rectangular, slightly overlapping one another, and each with a sparse row of short setae along ventral margin; coxal plates V and VI with distinct anterior lobes, posterior margin bearing 1 seta each; coxal plate VII rather large, semilunar, with 2 setae on posterior margin; each of plates II–VI bearing single coxal gill each with long stalk. Sternal gills absent. Oostegites II–V not well developed. GNATHOPODS I AND II ( Figs 2C , 10A, B ). Gnathopods almost similar, subchelate, but gnathopod II somewhat larger than gnathopod I; surface of posterior margins with peculiar patches of pilosity; basis (article 2) with 2 short setae on anterior and 3 long setae on posterior margins; carpus (article 5) stout, sub-triangular, anterior angle bearing 1 seta, 2 groups of long, stiff setae on subventral margin; propodus (article 6) sub-rectangular, bearing a group of 3 setae on antero-distal corner, 1 or 3 long setae along on subventral margin; palm twice shorter than posterior margin, somewhat oblique and beveled, with cutting margin rugous, palmar margin with 2 short setae along outer and inner faces, palmar angle indistinct but armed with 4 distally notched spines along with 2 long setae; dactylus strong, crescent-shaped, nail long, 0.4× of total length of dactylus, 1 seta on anterior margin, inner margin smooth, with a group of setules. PEREOPODS ( Figs 2C , 10 C–G). Pereopods III and IV sub-similar, without any obvious peculiarities; bases narrow, with short, stiff setae on both margins. Pereopods V̄VII subsimilar; length ratios 5:6:7 is 0.7:1.0:0.9. Pereopod VI length 0.5× body length. Bases of pereopods V–VII narrowed distally, posterior margins slightly expanded, but postero-distal lobes indistinct; marginal serration with short, stiff notched setae posteriorly and with 6–10 notched spines anteriorly; merus, carpus and propodus strongly spinose, especially in pereopod VII; dactyli relatively short, about 0.3× of propodus length, inner margin with 1 stiff seta at hinge. PLEOPODS AND UROPODS ( Figs 2C , 11 B–G). Pleopods I–III sub-equal, each with 2 coupling setae (retinacles); peduncular articles naked; outer rami larger, with 7–8 articles each, inner rami slender, consisting of 5 articles, both rami fringed with long, plumose setae. Uropod I heavily spinose with strong, curved, distally notched spines; protopodite with 4 robust, basofacial spines, 5 dorso-lateral spines, 5 dorso-medial setae and 1 very large corner spine; endopodite as long as protopodite, each with 3 spines on outer margin, accompanied by short plumose setae; exopodite as long as endopodite, bearing 5 spines along lateral margin; rami fringed with long plumose setae on inner margins and armed with 5 spines apically and sub-apically (one of them very large). Uropod II exopodite 0.2 as long as protopodite and slightly shorter than endopodite; protopodite and rami armed sub-similar to those of uropod 1. Uropod III parviramus/dispariramus; endopodite vestigial, scale-like, 50% of as protopodite length, fringed with 1 medial and 1 apical plumose setae; exopodite 1-articulate, 0.6 as long as protopodite, with 5 sets of distally notched spines on outer margin and with a dense row of 10 plumose setae accompanied by 2–3 short spines along inner margin and 3 distally notched apical spines.

Variation. Not observed.

Sexual dimorphism. Two damaged, apparently subadult males, both without antennae, some pereopods differing from those of female, and habitus smaller and more slender and sparsely covered with spines and setae; gnathopods sub-similar, gnathopod propodi with a clearly emergent palmar angle and bearing only 2 mid-palmar spines; peduncle of uropod II heavily armed bearing 3 additional groups of paired spines on ventral face.

Distribution and ecology. Indoniphargus subterraneus sp. n. is known only from its type locality (see Fig. 1 ).

Remarks. An enigmatic I. indicus ( Chilton, 1923) collected in a coalmine and springs of north-eastern India ( Fig. 1 ) was reported in several previous publications (see Straškraba 1967), which has now necessitated a comparative study of this species with I. subterraneus sp. n. First of all, it must be underscored that the differences observed by us, though not numerous, are indeed significant. A distinctive feature of I. indicus is the clear reduction in the size of coxal plates, which is typical of stygomorphic forms; also, I. subterraneus sp. n. can be distinguished from I. indicus mainly by the following features (character states of I. indicus in parentheses): gland cone of antenna II long, tip reaching about half of peduncular article 4 (short, not reaching); posterodistal corners of pleonal plates roundish (rectangular), and telson without dorsolateral spines (with 2 spines). At the same time, we must admit that some features of I. indicus (e.g., number of spines on outer plate of maxilla I, absence of the oblique row facial setae on maxilla II, mittenform propodi of gnathopods, a number of retinacles, etc.) are somewhat different from those mentioned in the previous publications, thus warranting a more detailed morphological study of the species. Further, we propose to treat the genus Indoniphargus Straškraba, 1967 , as belonging to the family Austroniphargidae Iannilli, Krapp, and Ruffo, 2011 sensu Iannilli et al. (2011) (see Discussion below).

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 9. Indoniphargus subterraneus sp. n., holotype MNHN-IU-2018-52, female, 5.2 mm: (A) head; (B) antenna I; (C) antenna II; (D) mandible, right; (E) mandible, left; (F) labrum (=upper lip); (G) paragnaths (=lower lip); (H) maxilla I, left; (I) palp of right maxilla I; (J) maxilla II; (K) maxilliped. Scale bars 0.1 mm.

FIGURE 10. Indoniphargus subterraneus sp. n., holotype MNHN-IU-2018-52, female, 5.2 mm: (A) gnathopod I; (B) gnathopod II; (C) pereopod III; (D) pereopod IV; (E) pereopod V; (F) pereopod VI; (G) pereopod VII. Scale bars 0.1 mm.

FIGURE 11. Indoniphargus subterraneus sp. n., holotype MNHN-IU-2018-52, female, 5.2 mm: (A) pleonal plates I–III; (B– D), pleopods I–III; (E) uropod I; (F) uropod II; (G) uropod III; (H) telson. Scale bars 0.1 mm.

FIGURE 12. Scanning electron micrographs of mandibles of Indoniphargus subterraneus sp. n., holotype MNHN-IU-2018- 52, female, 5.2 mm: (A) right mandible, anterior part; (B) molar process of the same mandible, lateral view; (C) surface of a pectinate ''damper seta'' (detail from Fig. 12B); (D) molar process of left mandible, median view; (E) surface of a pectinate ''damper seta'' (detail from Fig. 12D).