Vanni ashini Bahir & Yeo, 2007

Z, Sameer Kumar Pati, 2025, Taxonomic revision of the freshwater crab genera Travancoriana Bott, 1969, and Vanni Bahir & Yeo, 2007 (Crustacea: Decapoda: Gecarcinucidae), with descriptions of eight new genera and two new species from the Western Ghats, southern India, Zootaxa 5634 (1), pp. 1-77 : 43-48

Vanni ashini Bahir & Yeo, 2007

[Discoverer forest crab]

( Figs. 20, 21)

Vanni ashini Bahir & Yeo, 2007: 343 , figs. 39, 40.

Vanni ashini – Rajesh et al. 2017: 146, fig. 27.—Pati 2020: 162 (list).— Pati & Pradhan 2020: 555836 (list).

Type material examined. Holotype: male ( CW 24.1 mm, CL 18.5 mm) ( ZRC 2003.0232 ), India, Kerala State, Thiruvananthapuram District, Ponmudi , 8.76872° N, 77.11047° E, elev. 975 m a.s.l., collector and collection date unknown.

Other material examined. India – Kerala State: female ( CW 16.9 mm, CL 13.4 mm, CH 7.7 mm, FW 5.6 mm) ( ZSI-WGRC IR/INV/9158) , Thiruvananthapuram District , Bonacaud, Pandipath, 8.68071° N, 77.16733° E, elev. 547 m a.s.l., coll. K. Rajmohana, 15 December 2015 . – Tamil Nadu State: male ( CW 16.5 mm, CL 12.9 mm, CH 7.3 mm, FW 5.4 mm) , female ( CW 15.3 mm, CL 12.0 mm, CH 6.8 mm, FW 5.1 mm) ( ZSI-WRC C.2322) , Kanyakumari District , Kalakad Mundanthurai Tiger Reserve , way to Muthukulivayal II Bend, 8.476° N, 77.383° E, elev. 994 m a.s.l., coll. Varadaraju, 16 February 2020 ; female ( CW 23.0 mm, CL 16.7 mm, CH 10.3 mm, FW 6.6 mm) ( ZSI-WRC C.2323) , Tirunelveli District , Kalakad Mundanthurai Tiger Reserve , Kalakad Range , Sengaltheri, Tiger Cave, 8.523° N, 77.447° E, elev. 1170 m a.s.l., coll. R. Babu et al., 15 March 2022 ; male ( CW 16.4 mm, CL 12.3 mm, CH 6.9 mm, FW 5.1 mm) , 3 females ( CW 21.0– 27.4 mm, CL 15.2–19.9 mm, CH 9.0– 11.8 mm, FW 6.1–7.9 mm) ( ZSI-WRC C.2166) , Tirunelveli District , Kalakad Mundanthurai Tiger Reserve, Kalakad Range , Shengaltheri , Karumandi Amman Kovil, Manimuthar River, 8.530° N, 77.446° E, elev. 983 m a.s.l., coll. R. Babu et al., 14 August 2019 ; 2 males ( CW 19.4–23.6 mm, CL 14.3–17.0 mm, CH 8.3–9.7 mm, FW 5.7–6.9 mm) , 5 females ( CW 22.7–26.6 mm, CL 16.7–18.9 mm, CH 9.7–11.1 mm, FW 6.6–7.5 mm) ( ZSI-WRC C.2324) , Tirunelveli District , Kalakad Mundanthurai Tiger Reserve , Kalakad Range , Sengalteri, Kulirati, 8.531° N, 77.456° E, elev. 962 m a.s.l., coll. R. Babu et al., 16 March 2022 ; male ( CW 14.3 mm, CL 11.2 mm, CH 6.5 mm, FW 4.8 mm) ( ZSI-WRC C.2167) , Tirunelveli District , Kalakad Mundanthurai Tiger Reserve , Ambasamudram Range, Marapalam, 8.544° N, 77.375° E, elev. 1169 m a.s.l., coll. R. Babu et al., 21 August 2019 .

Diagnosis. Medium sized crabs (maximum CW 27.4 mm). Carapace relatively broad (CW/CL = ca. 1.3–1.4), relatively low ( CH /CW = ca. 0.4–0.5) ( Fig. 20A–C, E); external orbital angle triangular, with short outer margin, ca. 2 times length of inner margin ( Fig. 20A, B, E); epibranchial tooth low, discernible ( Fig. 20A, B, E); male sternopleonal cavity reaching to imaginary line joining submedial part of cheliped coxae ( Fig. 20D); male pleonal somite 6 subquadrate, slightly broad, proximal width ca. 1.1 times medial length, longer than telson, with strongly concave lateral margins ( Fig. 20D, G); male telson as long as broad, medial length ca. 1.0 times proximal width ( Fig. 20D, G); G1 relatively stouter ( Figs. 20H, I, 21A, B); G1 ultimate article relatively stouter, gently curved outwards at ca. 10° from longitudinal axis of G1, relatively shorter, ca. 0.2 times length of penultimate article ( Figs. 20H, I, 21A, B); G1 penultimate article with distal portion relatively less narrow than basal portion, outer margin gently sinuous ( Figs. 20H, I, 21A, B); G2 longer than G1, ca. 1.2 times G1 length, ultimate article long, ca. 0.4 times length of penultimate article ( Figs. 20J, 21C); vulvae subovate, relatively large, occupying ca. 0.6 times length of s6, located relatively close to s5/s6 ( Fig. 20K).

Remarks. Vanni ashini was reported by Pati et al. (2014) at a lower elevation ( 118 m a.s.l.) of the central Western Ghats, north of the Palghat Gap, in the Palakkad district of Kerala, which is an erroneous record as evident from their figures (Pati et al. 2014: pl. 2 figs. 7–9, pl. 4 figs. 3–5). Its occurrence there is highly unlikely as the species lives at the relatively higher elevations of the southern Western Ghats (see ecological notes and geographic distribution below).

Vanni ashini can be distinguished from the other species of the same genus by the low but distinct epibranchial tooth ( Fig. 20A, B, E) (versus epibranchial tooth indiscernible; Figs. 14A, 16A, 18A, B, E); the longer male pleonal somite 6 as compared to telson length ( Fig. 20D, G) (versus male pleonal somite 6 as long as telson; Figs. 14C, E, 16C, H, 18D, G); the male telson being equally long as broad, the medial length ca. 1.0 time the proximal width ( Fig. 20D, G) (versus male telson longer than broad, the medial length ca. 1.1–1.3 time the proximal width; Figs. 14C, E, 16C, H, 18D, G); and the relatively stouter G1 ultimate article ( Figs. 20H, I, 21A, B) (versus G1 ultimate article relatively slenderer; Figs. 15A, B, 17A, B, 18H, I, 19A, B).

Ecological notes. Vanni ashini inhabits shady and dry stream margins underneath stones in moist soil ( Bahir & Yeo 2007). The recent specimens were collected from drying to shallow and slow-flowing streams at relatively higher elevations ( 547–1170 m a.s.l.) of the southern Western Ghats.

Geographical distribution. Vanni ashini is endemic to the southernWestern Ghats of Kerala (Thiruvananthapuram district) and Tamil Nadu (Kanyakumari and Tirunelveli districts) in southern India ( Bahir & Yeo 2007; Rajesh et al. 2017; present study) ( Fig. 1B).

Key to the species of Vanni Bahir & Yeo, 2007

1. Epibranchial tooth low but discernible ( Fig. 20A, B, E); male pleonal somite 6 longer than telson ( Fig. 20D, G); male telson as long as broad, medial length ca. 1.0 × proximal width ( Fig. 20D, G); G1 ultimate article relatively stouter ( Figs. 20H, I, 21A, B)......................................................................... Vanni ashini Bahir & Yeo, 2007 [ Kerala (Thiruvananthapuram district) and Tamil Nadu (Kanyakumari and Tirunelveli districts); southern Western Ghats only]

– Epibranchial tooth indiscernible ( Figs. 14A, 16A, 18A, B, E); male pleonal somite 6 as long as telson ( Figs. 14C, E, 16C, H, 18D, G); male telson longer than broad, medial length ca. 1.1–1.3 × proximal width ( Figs. 14C, E, 16C, H, 18D, G); G1 ultimate article relatively slenderer ( Figs. 15A, B, 17A, B, 18H, I, 19A, B).............................................. 2

2. Male pleonal somite 6 relatively narrower, elongated, proximal width ca. 1.1 × medial length ( Fig. 14C, E); male telson relatively more narrow, medial length ca. 1.3 × proximal width ( Fig. 14C, E); G1 ultimate article relatively shorter, ca. 0.2 × length of penultimate article ( Fig. 15A); G1 penultimate article with distal portion conspicuously narrow than basal portion, outer margin basally straight ( Fig. 15A, B); vulvae located clearly away from s5/s6 ( Fig. 14F).............................................................................................. Vanni travancorica ( Henderson, 1913) [ Kerala (Kollam and Thiruvananthapuram districts); southern Western Ghats only]

– Male pleonal somite 6 relatively broader, shorter, proximal width ca. 1.2 × medial length ( Figs. 16C, H, 18D, G); male telson relatively less narrow, medial length ca. 1.1 × proximal width ( Figs. 16C, H, 18D, G); G1 ultimate article relatively longer, ca. 0.3 × length of penultimate article ( Figs. 17A, 18H, 19A); G1 penultimate article with distal portion relatively less narrow than basal portion, outer margin basally concave ( Figs. 17A, B, 18H, I, 19A, B); vulvae located relatively close to s5/s6 ( Figs. 16J, 18K)............................................................................................... 3

3. Male pleonal somite 6 with gently concave lateral margins ( Fig. 18D, G); G1 relatively stouter, with relatively stouter ultimate and penultimate articles ( Figs. 18H, I, 19A, B)..................................... Vanni deepta Bahir & Yeo, 2007 [ Kerala (Idukki and Pathanamthitta districts); southern Western Ghats only]

– Male pleonal somite 6 with strongly concave lateral margins ( Fig. 16C, H); G1 relatively slenderer, with relatively slenderer ultimate and penultimate articles ( Fig. 17A, B)............................................ Vanni gracilis sp. nov. [ Kerala (Ernakulam district); southern Western Ghats only]

Genus Santanusus gen. nov.

( Figs. 22–24)

Type species. Paratelphusa ( Liotelphusa) malabarica Henderson, 1912 , by present designation; gender of genus masculine.

Diagnosis. Medium sized crabs (maximum CW 21.6 mm). Carapace relatively broad (CW/CL = ca. 1.3–1.4), relatively low ( CH /CW = ca. 0.4–0.5), with moderately convex lateral margins; frontal medial triangle incomplete, lateral margins indiscernible; postorbital cristae weakly developed posterolaterally, not reaching lateral margins of carapace; external orbital angle triangular, with short outer margin, ca. 2.5 times length of inner margin; epibranchial tooth low, located at same level of postorbital cristae; epistome posterior margin with low, broadly triangular medial tooth and gently sinuous lateral lobes ( Figs. 22A–C, E–G, 23A). Maxilliped 3 with well-developed flagellum on exopod. Chelipeds relatively slender in adult males ( Figs. 22A, E, 23A). Ambulatory legs relatively stout, shorter, setose ( Figs. 22A, E, 23A). Male s2/s3 and s3/s4 indiscernible ( Fig. 22D, H). Male sternopleonal cavity relatively long, reaching to imaginary line joining bases of maxilliped 3 ( Fig. 22D, H). Male pleon relatively narrow, with strongly concave lateral margins; pleonal somite 6 subquadrate, relatively narrow, proximal width ca. 0.9 times medial length ( Fig. 22H). G1 relatively slender; ultimate article conical, relatively slender, relatively short, ca. 0.25 times length of penultimate article; penultimate article moderately stout ( Fig. 24A, B). G2 as long as G1, ca. 1.0 times G1 length; ultimate article relatively short, ca. 0.3 times length of penultimate article ( Fig. 24C). Vulvae relatively widely located from each other (VD/SW = ca. 0.2) ( Fig. 23C).

Etymology. The genus is named in honour of Santanu Mitra of the Crustacea Section of the Zoological Survey of India, Kolkata, for his contributions to the taxonomy of Indian freshwater crabs, in an arbitrary combination with the ending of Thelphusa Latreille, 1819 . The gender of this genus is masculine.

Remarks. Santanusus gen. nov. is differentiated from the morphologically most closely related Vanni s. str. (see Remarks for Vanni ) and herein designated Paratelphusa ( Liotelphusa) malabarica described by Henderson (1912) as the type species. This new genus thus contains only one species, i.e., S. malabaricus ( Henderson, 1912) comb. nov.

Santanusus gen.nov. is distinct from other freshwater crab genera of southern India in the following morphological features: the relatively low carapace ( CH /CW = ca. 0.4–0.5) ( Fig. 22C, G); the weakly developed postorbital cristae, posterolaterally not reaching the carapace margin ( Figs. 22A, B, E, F, 23A); the triangular external orbital angle, with outer margin short, ca. 2.5 times the inner margin length ( Figs. 22A, B, E, F, 23A); the low epibranchial tooth ( Figs. 22A, B, E, F, 23A); the low, broadly triangular medial tooth of the epistome posterior margin ( Fig. 22C, G); the well-developed flagellum on the maxilliped 3 exopod; the relatively stout and shorter ambulatory legs ( Figs. 22A, E, 23A); the indiscernible male s2/s3 and s3/s4 ( Fig. 22D, H); the relatively long male sternopleonal cavity, reaching to the imaginary line joining the bases of the maxilliped 3 ( Fig. 22D, H); the relatively slender G1, with the conical and short ultimate article, ca. 0.25 times the length of the penultimate article ( Fig. 24A, B); the equally long G2 and G1 ( Fig. 24); the relatively shorter ultimate article of the G2, ca. 0.3 times the length of the penultimate article ( Fig. 24C); and the relatively widely located vulvae (VD/SW = ca. 0.2) ( Fig. 23C).

Geographical distribution. Santanusus gen. nov. is currently known from the central and southern Western Ghats of Kerala ( Kozhikode, Palakkad, and Thrissur districts) and Tamil Nadu (Coimbatore district) of southern India ( Henderson 1912; Roux 1931; Bott 1970a, 1970b; Bahir & Yeo 2007; Klaus et al. 2014; Pati et al. 2014, 2019b; Rajesh et al. 2017; present study) ( Fig. 1B).