Badistemon fulvum, Mitra & Monica & Waikhom, 2020

Mitra, Santanu, Monica, Thingbaijiam & Waikhom, Mema Devi, 2020, A new species of freshwater crab of the genus Badistemon Yeo & Ng, 2007 (Decapoda: Brachyura: Potamidae: Potamiscinae) from Manipur State, India with the reassignment of Potamiscus pealianus (Wood-mason, 1871), Zootaxa 4838 (4), pp. 475-490 : 476-482

publication ID	https://doi.org/ 10.11646/zootaxa.4838.4.2
publication LSID	lsid:zoobank.org:pub:6778A39E-1625-4D6D-9DD2-5FFB2F02415C
DOI	https://doi.org/10.5281/zenodo.4476099
persistent identifier	https://treatment.plazi.org/id/C25887CC-FFF3-FF86-FF41-493CA9544356
treatment provided by	Plazi
scientific name	Badistemon fulvum
status	sp. nov.

Treatment

Badistemon fulvum View in CoL sp. nov.

( Figs. 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 , 10 A View FIGURE 10 )

Material examined. Holotype: male (cw 48.7 mm, cl 39.5 mm, ch 22.8 mm, fw 11.9 mm), from Bungkucha stream, Bungpa Khunou village, Kamjong District, Manipur, north-east India (24°48´45.93″N; 94°28´23.41″E), altitude 997 m, 22 nd July 2018, coll. Thingbaijiam Monica ( ZSI-C7543 /2).

Paratype: 1 female (cw 31.4 mm, cl 22.8 mm, ch 13.8 mm, fw 9.5 mm), collection data same as above (ZSI-C7544/2).

Comparative material: Potamon turgidulum Alcock, 1909 , lectotype (designated herein): male (28.7 × 23.5 mm); paralectotypes 6 males (cw 24.2–26.3 mm × cl 21.5–22.4 mm) and 1 female (cw 30.2 mm × cl 24 mm), Burma, coll. W. Theobald ( ZSI-C 6952 /3). Potamon (Potamon) pealianum ( Wood-Mason, 1871) , 1 male, holotype (cw 41.6 mm, cl 35.2 mm, ch 18.8 mm, fw 10.4 mm), Sivasagar , Assam ; coll. S. E. Peal ( ZSI-C6958 /3); 2 females (cw 38.2–45.8 mm, cl 33.1–39.4 mm, ch 8.9–15.7 mm), Sivasagar , Assam ; coll. S. E. Peal ( ZSI-C6413 /3). 1 male (cw 47.1 mm, cl 38.4 mm, ch 14.7 mm, fw 11.5 mm), Kakhyen hills, Myanmar, 20 february, 1875 ; coll. J. Anderson ( ZSI-C6915 /3). 1 female (cw 43.6 mm, cl 32.7 mm, ch 16.2 mm), Bokpui village , Lunglei District, Mizoram, India; 19 October, 2103 ; coll. S. Mitra ( ZSI-C6117 /2) .

Diagnosis. Carapace subquadrate, distinctly broader than long, longitudinally convex, dorsal surface glabrous; anterolateral margin longer than posterolateral margin, epigastric cristae well developed, rugose, separated by post orbital cristae by distinct groove, postorbital cristae sharp, confluent with epibranchial tooth ( Fig. 2A View FIGURE 2 ); cornea relatively large ( Fig. 2B View FIGURE 2 ); male pleon broadly triangular, pleonal somite 6 trapezoidal in shape ( Fig. 2C View FIGURE 2 ), exopod of third maxilliped with flagellum, longer than ca. 0.5 times of merus width; G1 terminal segment relatively long, outwardly bent, subcylindrical with low dorsal flap, tip pointed, groove for G2 terminal; G2 long, almost straight, terminal segment distinctly longer than ca. 0.5 times length of basal segment ( Fig. 4 View FIGURE 4 A–E, 5A–C).

Description. Holotype male, carapace broader than long (cw/cl=1.2), longitudinally convex, high (ch/cl=0.6); dorsal surface glabrous, anterolateral margin convex, serrated, converging posteriorly, longer than posterolateral margin ( Fig. 2A View FIGURE 2 ); posterolateral margin gently converging towards posterior border, with short, oblique striae ( Fig. 2A View FIGURE 2 ); front relatively broad, width ca. 0.29 times maximum carapace width, distinctly deflexed ventrally, frontal margin slightly bilobed ( Fig. 2B View FIGURE 2 );

Epigastric cristae well developed, rugose, separated by postorbital cristae by distinct groove; postorbital cristae sharp, confluent with epibranchial tooth; external orbital angle well developed, outer margin distinctly convex, ca. 2 times longer inner margin; epibranchial tooth small, sharp, separated from external orbital angle by a distinct cleft; branchial region with some low granules, frontal region with bilobed eminence immediately behind and parallel of frontal margin, clearly divided by gastric groove; orbital region narrow, smooth, concave; regions behind epigastric and postorbital cristae smooth; gastric and branchial region inflated; cervical groove ‘S’- shaped, shallow, superficial, mesogastric groove long, bifurcated posteriorly, H- shaped groove prominent, cardiac groove deep ( Fig. 2A View FIGURE 2 ); pterygostomial region smooth, frontal median triangle incomplete with dorsal margin only, posterior margin of epistome with triangular median tooth, outer margin sloping downwards laterally; orbital margin sub-triangular, eyes with large cornea, antennae short reaching up to base of eye stalk, antennules long, antennular fossae quadrangular.

Mandibular palp 3 segmented, terminal segment simple, first and second maxilliped has long flagellum on exopod, ischium of third maxilliped subrectangular, almost twice as long as broad, median sulcus prominent, merus as long as broad, almost pentagonal ( Fig. 2B View FIGURE 2 ); exopod long, reaching distal third of merus length, gradually narrower from base to proximal part, flagellum well developed, reaching more than half of merus width.

Chelipeds smooth, glabrous, unequal, right cheliped stouter than left, all margins of merus distinctly serrated, proximal inner margin of merus with sharp tooth, carpus rugose, sunken antero-medially, carpus with a long stout inner distal tooth followed by short basal tooth; pollex of major cheliped with 2 large triangular tooth on its cutting edge, dactylus almost smooth, except basal part with 3 small sharp teeth; palm larger than dactylus, inner and outer surface inflated, 4 sharp serration on dorsal surface of palm, inner and lateral margins of merus serrated, distal part of inner border of merus with slender strong tooth; ambulatory legs long, slender, p3 longest, ca. 1.5 of carapace width, p3 and p4 longer than cheliped, upper margin of merus of p2 to p5 with sub-distal spine, p3 and p4 propodus is longer than ca. 2.5 of width, dactylus distinctly longer than propodus, gently curved ( Fig. 2A View FIGURE 2 ).

Thoracic sternites smooth, glabrous, pitted, suture between thoracic sternite s1/s2 indistinct, suture between thoracic sternites s2/s3 distinct, deep broad groove, not reaching to lateral margin, suture between thoracic sternite s3/s4 visible as small notch on lateral margins, followed by indistinct shallow depression ( Fig. 2C View FIGURE 2 ); suture s7/s8 shallow, interrupted by longitudinal median groove between s7 and s8, lacking transverse ridge; Pleonal locking mechanism with prominent tubercle, sharply pointed towards ventral side, on lower part of s5; sternopleonal cavity deep, long, reaching up to imaginary line joining median part of cheliped coxae.

Pleon triangular, pleonal somite 3 widest, somite 6 trapezoidal, proximal width nearly twice than median length, distinctly longer than preceding somites, shorter than telson; telson broadly triangular, proximal width broader than long, lateral margin concave, apex rounded ( Fig. 2C View FIGURE 2 ).

G1 terminal segment slender, relatively long, ca. 0.4 times combined length of flexible joint and subterminal segments, almost cylindrical, tip triangular, pointed, bent outwards, tip not reaching pleonal locking tubercle; low dorsal flap on outer middle part of terminal segment; subterminal segment stout, basal 1/3 distinctly broad, outer margin straight, remaining 2/3 of subterminal segment gradually narrowing, distal end neck-like, bent outwards, groove for G2 terminal; G2 slender, almost straight, terminal segment more than half of subterminal segment ( Figs. 4 View FIGURE 4 A–E, 5A–C).

Female pleon narrowly ovate in outline, all sternites are not fully covered by the pleon ( Fig. 3C View FIGURE 3 ). The pleonal somite 1 is short, pleonal somites 2-5 are progressively longer, and the pleonal somite 6 is the longest, shorter than the telson, with convex lateral margins ( Fig. 3C View FIGURE 3 ). The telson is broadly triangular, much broader than long, with strongly convex lateral margins ( Fig. 3C View FIGURE 3 ); suture between s3/s4 are not discernible ( Fig. 3C View FIGURE 3 ), the vulvae broader than long, large, oblong ovate, directed towards ventro-medial directions, located on the thoracic sternite s6, with the distal edge touching the suture s5/s6, lower half covered by sternal cover ( Fig. 3D View FIGURE 3 ).

Variation. The female paratype (ZSI-C7544/2) is not ovigerous and shares most of the non-sexual characters with the holotype male, except some characters: carapace grooves and regions are relatively more prominent, chelipeds subequal ( Fig. 3A View FIGURE 3 ) (vs. carapace grooves and regions relatively less distinct, chelipeds unequal in male holotype ( Figs. 2A View FIGURE 2 , 10A View FIGURE 10 ); epistomal median tooth blunt ( Fig. 3B View FIGURE 3 ) (vs. epistomal median tooth sharply pointed in male ( Fig. 2A View FIGURE 2 ).

Live colouration. In the male holotype, the carapace is chestnut brown, chelipeds outer parts orange yellow, ventral parts ivory white; frontal margin, epigastric cristae, post orbital cristae and orbital margins are golden yellow ( Fig. 10 A View FIGURE 10 ); carapace of the female paratype dark brown, chelipeds pale brown, propodus orange-yellow, fingers ashy grey, tip of fingers yellow, third maxilliped ischium with conspicuous brown and white longitudinal stripes.

Etymology. The new species is named after its golden yellow carapace margins, frontal margin, orbital margin and epistome, the name is derived from Latin ‘Fulvus’ means-‘golden yellow’; gender neuter.

Type locality. Bungkucha stream (24°48´45.93″N; 94°28´23.41″E), Bungpa Khunou village, Kamjong District, Manipur, India

Remarks. The present new species, collected from Manipur, India, is adjacent to Myanmar and morphologically agrees with Badistemon , as presently defined, i.e. relatively high, squarish-looking carapace, quite broader than long; epigastric and postorbital cristae well developed, third maxilliped exopod with long flagellum not exceeding merus width, ambulatory legs slender, long; male abdomen narrowly triangular and the G1 slender, terminal segment with low dorsal flap ( Fig. 4 View FIGURE 4 A–D).

Badistemon fulvum n. sp. is distinguished from B. turgidulum ( Alcock, 1909) by the following morphological characters: suture between thoracic sternites s2/s3 distinct, deep broad groove, not reaching up to lateral margins ( Fig. 2C View FIGURE 2 ) (vs. suture between thoracic sternites s2/s3 narrow, groove shallow reaching up to lateral margins in B. turgidulum ; cf. Yeo & Ng 2007: fig. 4 c; Fig. 6B View FIGURE 6 ); suture between thoracic sternites s3/s4 not discernible in new species ( Fig. 2 C View FIGURE 2 ) (vs. suture between sternite s3/s4 distinct, represent as oblique shallow groves towards abdominal cavity; Yeo & Ng, 2007: fig. 4 c; Fig. 6C View FIGURE 6 ); telson broadly triangular, proximal width distinctly broader than long in B. fulvum n. sp. ( Fig. 2C View FIGURE 2 ) (vs. telson as long as broad in B. turgidulum ; cf. Alcock, 1910: pl 2, 5 a; Yeo & Ng, 2007 fig. 4c; Fig. 6C View FIGURE 6 ); G1 subterminal segment distal part neck-like, abruptly narrower than basal width; terminal segment subconical, relatively long, ca. 0.4 times than combined length of subterminal segment, tip pointed in B. fulvum n. sp. ( Fig. 4 View FIGURE 4 A–D, 5A–C) (vs. G1 subterminal segment distal width slightly narrower than basal width; terminal segment subcylindrical, relatively short, ca. 0.32 times than combined length of subterminal segment and flexible joint, tip broad and blunt in B. turgidulum ; cf. Yeo & Ng, 2007: fig. 4d, e; Fig. 8A, B View FIGURE 8 ); flexible zone elongated with triangular median lobe in B. fulvum n. sp. ( Figs. 4B, D View FIGURE 4 ; 5A View FIGURE 5 ); flexible zone short with a small, blunt median lobe in B. turgidulum ; cf. Yeo & Ng, 2007: fig.4 d, e; Fig. 8 A View FIGURE 8 ); G2 terminal part straight, terminal part nearly half length of subterminal part in B. fulvum n. sp. ( Fig. 4E View FIGURE 4 , 5C View FIGURE 5 ) (vs. G2 terminal part twisted, terminal part slightly longer than half of subterminal part in B. turgidulum ; Fig. 8C View FIGURE 8 ); In female, the vulvae large, oblong, directed ventro-medially, situated just below the suture between the fifth and sixth sternites, lower half covered by sternal cover in B. fulvum n. sp. ( Fig. 3D View FIGURE 3 ) (vs. in female, vulvae is relative more rounded, directed towards longitudinal median groove, lower 1/3 only covered by sternal cover in B. turgidulum ; Fig. 9A View FIGURE 9 ).

The new species has several morphological similarities with Badistemon pealianus ( Wood-Mason, 1871) comb. nov. as both the species have a high, roughly quadrangular carapace, broad front, relatively long ambulatory legs, third maxilliped ischium broadly rectangular, with longitudinal median sulcus, the exopod with well developed flagellum not more than merus width, male sterno-pleonal cavity barely exceeding imaginary line jonining posterior edge of cheliped base, and G1 terminal segment relatively long, setose with low, short dorsal flap, G2 straight with terminal segment more than half of subterminal segment.

The new species differs from B. pealianus , in the following morphological characters: Telson distinctly broader than long in B. fulvum n. sp. ( Fig. 2 C View FIGURE 2 ) (vs. telson as long as broad in B. pealianus ; Fig. 7 C View FIGURE 7 ); the external orbital tooth outer margin is almost straight to slightly convex in B. fulvum n. sp. ( Fig. 2A View FIGURE 2 ) (vs. external orbital tooth outer margin relatively more convex in B. pealianus ; Fig. 7 A View FIGURE 7 ); epibranchial tooth short, broad based, pointed laterally in B. fulvum n. sp. ( Fig. 2 A View FIGURE 2 ) (vs. epibranchial tooth short, base narrow, frontally pointed; Fig. 7 A View FIGURE 7 ); cervical groove superficial in B. fulvum n. sp. ( Fig. 2A View FIGURE 2 ) (vs. cervical grooves are distinct in B. pealianus ; Alcock, 1910: pl 10. fig. 44; Fig. 7 A View FIGURE 7 ); terminal segment of the G1 tapered toward the tip in the new species ( Fig. 4 View FIGURE 4 A–D, 5 A, B) (vs. G1 terminal segment subcylindrical, tip truncated in B. pealianus ; Fig. 8. D, E View FIGURE 8 ); female vulvae oblong shaped, occupied slightly less than half of the length of sixth sternite in B. fulvum n. sp. ( Fig. 3D View FIGURE 3 ), (vs. vulvae is ovate, relatively large, occupied more than half of the length of sixth sternite in B. pealianus ; Fig. 9B View FIGURE 9 ).

Ecological notes. The crabs were collected from Bungpa Khunou, at Kamjong District, Manipur, northeast India. Bungpa Khunou is a small village in Kamjong subdistrict head quarter, which was previously under Ukhrul District near the Indo-Myanmar border ( Fig.1 View FIGURE 1 ). The crabs are collected from the Bungkucha stream ( Fig. 10B, C View FIGURE 10 ), it ends in the Angkekung river. This stream is seasonal, almost dried up in summer season. The area is in a secondary forest is almost free from anthropogenic disturbance, as the local people of this place do not depend entirely on forest resources. According to the local people, during the rainy season the crabs come up to the foothills, from the river. Crabs make their nest holes in soft soils under the small stones beside the stream.

Geographical distribution. B. fulvum n. sp. is so far only recorded from its type locality at Bungpa Khunou village , Kamjong District, Manipur, India .