Potamiscus mima, Pati, 2021

Pati, Sameer Kumar, 2021, Two new species of freshwater crabs of the genus Potamiscus Alcock, 1909 (Brachyura: Potamidae) from Nagaland, northeastern India, Nauplius (e 2021006) 29, pp. 1-14 : 10-13

publication ID	https://doi.org/ 10.1590/2358-2936e2021006
DOI	https://doi.org/10.5281/zenodo.10911702
persistent identifier	https://treatment.plazi.org/id/C8692D2D-FFDD-FFB3-FEBC-E345AC30FC73
treatment provided by	Felipe
scientific name	Potamiscus mima
status	sp. nov.

Treatment

Potamiscus mima View in CoL sp. nov.

( Figs. 2G–L View Figure 2 , 3E–H View Figure 3 , 4D–F View Figure 4 )

Zoobank: urn:lsid:zoobank.org:act:F2462728-23EC-448E-AAF5-E64286258BCD

Type material. Holotype: adult male ( CW 42.65 mm, CL 33.82 mm, CH 22.16 mm, FW 9.83 mm), Mima, Kohima District , Nagaland, India (25.591°N 94.110°E), altitude 2105 m a.s.l., 6 July 2017, coll. Apeyo ( ZSI-WRC C.1954) GoogleMaps . Paratypes: adult male ( CW 44.94 mm, CL 34.27 mm, CH 23.29 mm, FW 11.08 mm) and adult female ( CW 43.04 mm, CL 33.27 mm, CH 22.98 mm, FW 10.57 mm), same data as holotype ( ZSI-WRC C.1955); adult male ( CW 38.87 mm, CL 31.01 mm, CH 20.91 mm, FW 10.11 mm) and adult female ( CW 41.51 mm, CL 31.57 mm, CH 22.55 mm, FW 10.46 mm), same data as holotype ( ZSI-WRC C.1956) GoogleMaps .

Additional material. 6 males ( CW 39.60–52.50 mm, CL 31.37–40.61 mm, CH 20.76–26.59 mm, FW 10.22–12.18 mm), same data as holotype ( ZSI-WRC C.1957) GoogleMaps ; 7 females ( CW 35.41–44.11 mm, CL 28.06– 34.40 mm, CH 19.77–24.07 mm, FW 8.92–11.23 mm), same data as holotype ( ZSI-WRC C.1958) GoogleMaps .

Diagnosis. Carapace large( CW <53mm), subovate, broad ( CW /CL = 1.3), moderately deep ( CH /CW = 0.5–0.6); dorsal surface gently convex in frontal view; anterolateral margins cristate; frontal margin narrow (FW/CW = 0.25); epigastric cristae distinct, slightly anterior to postorbital cristae, groove separating it from latter barely visible; postorbital cristae distinct, sharp, not confluent with epibranchial tooth; external orbital angle triangular, with relatively short outer margin, subequal in length to inner margin; epibranchial tooth distinct, with distinct cleft; cervical grooves indiscernible; suborbital margin separated from supraorbital margin by external orbital angle ( Figs. 2G–I View Figure 2 , 4D, E View Figure 4 ). Third maxilliped exopod with vestigial flagellum ( Fig. 2J View Figure 2 ). Chelipeds rugose, asymmetrical, with broad inner distal major tooth on carpus ( Figs. 2G–I View Figure 2 , 4D, E View Figure 4 ). Ambulatory legs relatively stout (P3 merus approximately 2.8 times long as broad), short, generally glabrous ( Figs.2G–I View Figure 2 , 4D, E View Figure 4 ). Suture between male S2/S3 distinct as shallow, narrow groove, reaching lateral margins; suture between male S3/ S4 visible as shallow depression, running from edge of sternopleonal cavity to lateral margins ( Fig. 2I, K View Figure 2 ). Male sternopleonal cavity relatively long, reaching to imaginary line joining medial part of cheliped coxae ( Fig. 2I, K View Figure 2 ). Male pleon narrow, triangular, with gently concave lateral margins; somite 2 broader than somite 1; somite 6 trapezoidal, distinctly broad, with straight lateral margins ( Fig. 2I, L View Figure 2 ). Male telson as long as pleonal somite 6, with strongly concave lateral margins ( Fig. 2I, L View Figure 2 ). G1 relatively slender, with terminal segment bent outwards at angle of about 30° from longitudinal axis, tip narrow, reaching to pleonal locking tubercle or beyond, not touching suture S4/S 5 in situ; flexible zone large; terminal segment sinuous, slender, subconical, long, approximately 0.4 times combined length of flexible zone and subterminal segment, distal third gently curved, dorsal flap distinct but low, broadly rounded; subterminal segment sinuous ( Figs. 2K View Figure 2 , 3E–G View Figure 3 ). G2 slightly longer than G1, approximately 1.1 times length of G1; distal segment long, approximately 0.6 times length of basal segment ( Fig. 3G, H View Figure 3 ). Vulvae on S6 relatively closely located, ovate, large, occupying two-thirds length of S6, anterior margin touching suture S5/S6 with mesial end reaching close to suture S4/S5 ( Fig. 4F View Figure 4 ).

Description of male holotype. Carapace transversely subovate,broaderthanlong( CW /CL=1.3),moderately deep ( CH /CW = 0.5); dorsal surface gently convex in frontal view, glabrous, smooth except for frontal region, epigastric cristae, postorbital cristae, branchial regions and posterolateral margins; anterolateral surface gently inf lated in frontal view; anterolateral margins convex, granular, distinctly emarginated at distal quarter, raised, separated from anterolateral surface by distinct groove; posterolateral margins rugose, converging posteriorly, joining with gently concave posterior margin; front trapezoidal, anterior portion strongly def lexed, divided into 2 rectangular, rugose lobes; frontal margin concave medially, narrow (FW/ CW = 0.25); epigastric cristae distinct, rugose, slightly anterior to postorbital cristae, groove separating it from latter barely visible; postorbital cristae distinct, sharp, not confluent with epibranchial tooth; external orbital angle triangular, with gently convex, short outer margin, subequal in length to inner margin; epibranchial tooth distinct, blunt, positioned above level of postorbital cristae, cleft distinct; postorbital region concave; branchial regions gently inflated, strongly granular anterolaterally; cervical grooves barely visible; mesogastric groove deep, narrow, long, extending into frontal region, bifurcated posteriorly; H-shaped groove visible; subhepatic region highly rugose; suborbital region smooth except for few low granules, glabrous; suborbital margin concave, cristate, with few very low granules, not joining with supraorbital margin; pterygostomial region smooth except for anteriorly located low granules; frontal medial triangle incomplete, with dorsal margin only, lateral margins indiscernible; epistome posterior margin with well-developed, triangular medial tooth, outer parts sloping downwards laterally ( Fig. 2G–I View Figure 2 ).

Eyes smaller than orbital space; eye stalk short, narrow; cornea moderately large, pigmented ( Fig.2H View Figure 2 ).

Antennules long, folded in longitudinally narrow fossae; antennae very short, reaching slightly beyond base of eye stalk ( Fig. 2H View Figure 2 ). Mandibular palp 3-segmented; terminal segment simple, undivided. First, second maxillipeds each with long flagellum on exopod. Third maxillipeds cover most of buccal cavity when closed; ischium subrectangular, longer than broad, with broad, moderately deep, oblique medial groove; merus subpentagonal, broader than long, depressed; exopod slender, distally narrow, longer than ischium, reaching proximal quarter of merus, with vestigial f lagellum, approximately 0.2 times merus width ( Fig. 2H–J View Figure 2 ).

Chelipeds rugose, asymmetrical, right chela larger ( Fig. 2G–I View Figure 2 ). Major chela with 4 or 5 large, blunt teeth on each finger, small gape when fingers closed; dactylus slightly rugose, gently curved, moderately stout, longer than upper margin of palm, with 3 or 4 distinct but low dorsal granules on proximal third; palm slightly longer than high, with widely spaced, distinct granules on outer-, upper- and lower surfaces; carpus rugose, sunken anteromedially, with stout, sharp, triangular inner distal major tooth and low, moderately sharp sub-basal tooth; merus rugose on outer surface, lacking subterminal spine ( Fig. 2G–I View Figure 2 ).

Ambulatory legs moderately stout (P3 merus approximately 2.8 times long as broad), short, P3 longest, generally glabrous; merus (P2–P5) elongate, lacking subdistal spine; propodus (P2–P5) moderately stout; dactylus (P2–P5) gently recurved, slightly longer than propodus, with short, sharp chitinous spines on margins ( Fig. 2G–I View Figure 2 ).

Thoracic sternites generally smooth and glabrous; S1 and S2 completely fused; suture S2/S3 distinct as shallow, narrow groove, reaching lateral margins; suture S3/S4 visible as very shallow depression, running from edge of sternopleonal cavity to lateral margins; suture S4/S5, S5/S6, S6/S7 shallow, narrow, medially indiscernible; suture S7/S8 laterally indiscernible, only visible towards sternopleonal cavity but interrupted by longitudinal groove between S7 and S8, lacking transverse ridge ( Fig. 2I, K View Figure 2 ). Pleonal locking mechanism with prominent tubercle on submedial part of S5 ( Fig. 2K View Figure 2 ). Sternopleonal cavity deep, long, reaching to imaginary line joining medial part of cheliped coxae ( Fig. 2I, K View Figure 2 ).

Pleon narrow, triangular, with gently concave lateral margins; somite 1 rectangular, narrower than somite 2; somite 2 almost rectangular, with strongly convex lateral margins; somites 3–5 trapezoidal, with converging lateral margins; somite 6 trapezoidal, broader than long (proximal width approximately 1.8 times medial length), distinctly longer than preceding somites, almost equal in length to telson, with straight lateral margins ( Fig. 2I, L View Figure 2 ). Telson triangular, broader than long (proximal width approximately 1.4 times medial length), with strongly concave lateral margins, apex narrow, round ( Fig. 2I, L View Figure 2 ).

G1 moderately stout, with terminal segment bent outwards at angle of about 30° from longitudinal axis, tip narrow, reaching to pleonal locking tubercle in situ; flexible zone large; terminal segment sinuous, slender, subconical, long, approximately 0.4 times combined length of flexible zone and subterminal segment, distal third gently curved, dorsal flap distinct but low, broadly rounded; subterminal segment sinuous, distal quarter narrow, broad at base ( Figs. 2K View Figure 2 , 3E–G View Figure 3 ). G2 slightly longer than G1, approximately 1.1times length of G1; distal segment gently curved, subcylindrical, long, approximately 0.6 times length of basal segment; basal segment stout at proximal third, appearing ovate ( Fig. 3G, H View Figure 3 ).

Paratypes. The male paratypes ( ZSI-WRC C.1955, 1956) are similar to the holotype in both external morphology and gonopod structure. The only exception is the G1 tip of the smaller male paratype ( ZSI-WRC C.1956) that reaches beyond the pleonal locking tubercle, but never touches suture S4/S5. The G 1 tip only reaches to the pleonal locking tubercle in the holotype and the larger male paratype. The female paratypes ( ZSI-WRC C.1955, 1956) have no differences in non-sexual character states with the holotype. The female paratypes have a narrowly ovate pleon that covers the thoracic sternum except for S1, S2, and lateral edges when closed ( Fig. 4E View Figure 4 ). In the female paratypes, pleonal somite 1 is the shortest; pleonal somites 2–5 are progressively longer; and pleonal somite 6 is the longest, much broader than long, almost equal in length to the telson, with convex lateral margins ( Fig. 4E View Figure 4 ). The female telson is broadly ovate, much broader than long, with convex lateral margins and round apex ( Fig. 4E View Figure 4 ). The vulvae on S6 are close to each other ( VD /SW = approximately 0.1), ovate, large, occupying two-thirds the length of S6, deep, anterior margin touching the suture S5/S6 with the mesial end reaching close to the suture S4/S5, and completely covered by a soft operculum ( Fig. 4F View Figure 4 ).

Etymology. The species is named after the type locality, Mima, a large village in the Kohima District of Nagaland State, India. Used as a noun in apposition.

Remarks. Potamiscus mima sp. nov. is strikingly similar to three Indian congeners ( Po. chizami sp. nov., Po. palelensis , and Po. tumidulus ) and a species from Myanmar ( Po. whitteni ) due to the presence of a slender, subconical, sinuous, gently outwardly curved, and relatively long terminal segment of the G1, which measures about 0.4 times the combined length of the flexible zone and subterminal segment and possesses a distinct but low dorsal flap ( Fig. 3A–C, E–G View Figure 3 ; cf. Mitra and Waikhom, 2019: figs. 2A, B, E, F, 4A–C for Po. palelensis ; Ng et al., 2020: fig. 3D for Po. whitteni ; personal observation for Po. tumidulus ). Potamiscus mima sp. nov. and Po. whitteni are readily distinguishable from Po. chizami sp. nov., Po.palelensis , and Po. tumidulus by their relatively narrow male pleon ( Fig. 2I, L View Figure 2 ; cf. Ng et al., 2020: figs. 2A, B, 3A for Po. whitteni ) (vs. relatively broad male pleon, Fig. 2C, F View Figure 2 ; cf. Mitra and Waikhom, 2019: fig. 1C for Po. palelensis ; personal observation for Po. tumidulus ) and the relatively more slender G1 terminal segment ( Fig. 3E–G View Figure 3 ; cf. Ng et al., 2020: fig. 3C–F for Po. whitteni ) (relatively more stout G1 terminal segment, Fig. 3A–C View Figure 3 ; cf. Mitra and Waikhom, 2019: figs. 2A, B, E, F, 4A–C for Po. palelensis ; personal observation for Po. tumidulus ). On the other hand, Po. mima sp. nov. is distinct from Po. whitteni by its gently convex dorsal surface of the carapace ( Fig. 2H View Figure 2 ) (vs. distinctly convex dorsal surface of the carapace; cf. Ng et al., 2020: fig. 1D), a barely visible groove between epigastric- and postorbital cristae ( Figs. 2G View Figure 2 , 4D View Figure 4 ) (vs. distinct groove between epigastric- and postorbital cristae; cf. Ng et al., 2020: fig. 1A–C), the separation of the suborbital margin from the supraorbital margin by the external orbital angle ( Fig. 2H View Figure 2 ) (vs. conf luent suborbital- and supraorbital margins; cf. Ng et al., 2020: fig. 1D), the broader male pleonal somite 2 than somite 1 ( Fig. 2L View Figure 2 ) (vs. equally broad male pleonal somites 1, 2; cf. Ng et al., 2020: fig. 3A), the strongly concave lateral margins of the male telson ( Fig. 2I, L View Figure 2 ) (vs. gently concave to almost straight lateral margins of the male telson; cf. Ng et al., 2020: figs. 2A, B, 3A), and the straight G1 tip ( Fig. 3E, F View Figure 3 ) (vs. upcurved G1 tip; cf. Ng et al., 2020: fig. 3D, F).

In addition to the narrow male pleon and the slender G1 terminal segment, Po. mima sp. nov. is easily separated from Po. palelensis by its stouter ambulatory legs, P3 merus approximately 2.8 times long as broad ( Figs. 2G View Figure 2 , 4D View Figure 4 ) (vs. relatively slender ambulatory legs, P3 merus approximately 3.7 times long as broad; cf. Mitra and Waikhom, 2019: fig. 1A) and the gently curved distal third of the G1 terminal segment ( Fig. 3E, F View Figure 3 ) (vs. distinctly curved distal third of the G1 terminal segment; cf. Mitra and Waikhom, 2019: figs. 2A, B, 4A, C).

Furthermore, Po. mima sp. nov. is differentiated from Po. tumidulus in many characters of the carapace, including postorbital cristae, external orbital angle, epibranchial tooth, suture between the male S3/S4, and male sternopleonal cavity (see Remarks for Po. chizami sp. nov.).

Potamiscus mima sp. nov. and Po. chizami sp. nov. can be distinguished from each other as compared in the remarks for Po. chizami sp. nov.

Potamiscus mima sp. nov. need not be confused with some similar looking Indian species (viz., Po. annandali and Po. decourcyi ) due to its less bent (curved outwards at an angle of about 30° from the longitudinal axis of the G1) and relatively slender G1 terminal segment, which possesses a low but distinct dorsal flap ( Fig. 3E–G View Figure 3 ). In addition to lacking a dorsal flap, Po. annandali and Po. decourcyi have a G1 terminal segment that is strongly bent (curved outwards at an angle of about55° from the longitudinal axis of the G1) and relatively stout (cf. Bott, 1970: pl. 38, fig. 28 for Po.annandali ; personal observation for Po. decourcyi ).

Geographical distribution. Potamiscus mima sp.nov. is only known from Mima village in Kohima District of Nagaland, northeastern India.