Pilarta vaman, Raj & Kumar & Ng, 2025

Raj, Smrithy, Kumar, Appukuttannair Biju & Ng, Peter K. L., 2025, Description of a new species of Pilarta Bahir & Yeo, 2007 (Crustacea: Brachyura: Gecarcinucidae) from the Southern Western Ghats, Kerala, India, Zootaxa 5642 (5), pp. 476-484 : 478-483

publication ID	https://doi.org/10.11646/zootaxa.5642.5.4
publication LSID	lsid:zoobank.org:pub:69A56561-4227-423A-8D0C-4A535BB9B4C9
DOI	https://doi.org/10.5281/zenodo.15818194
persistent identifier	https://treatment.plazi.org/id/EC1DD158-FFA7-8531-FF6A-FA49FB89FC61
treatment provided by	Plazi
scientific name	Pilarta vaman
status	sp. nov.

Treatment

Pilarta vaman sp. nov.

( Figures 2 View FIGURE 2 , 3 View FIGURE 3 , 4E–L View FIGURE 4 )

Material examined. Holotype: male (8.6 × 6.8 mm) (DABFUK/AR-BR-2025-5), Gavi , Pathanamthitta district, Kerala, India, 09º23’20.4504”N 77º09’14.8392”E, 1050 m asl, coll. S. Raj, 17 September 2017 GoogleMaps . Paratype: 1 female (9.1 × 7.6 mm) (DABFUK/AR-BR-2025-6), same data as holotype GoogleMaps .

Comparative material. Pilarta anuka Bahir & Yeo, 2007 : holotype male (14.5 × 10.7 mm) ( ZRC 2003.0238 View Materials ), Ponmudi GoogleMaps , Kerala, India, 08º46’07.4”N 77º06’37.7”E, 975 m asl, [coll. M. Bahir, 2000s].

Diagnosis. Carapace not deep, relatively narrow, quadrate, dorsal surface convex in frontal view; postorbital and epigastric cristae undiscernible ( Fig. 2A, B, D View FIGURE 2 ); frontal region punctate ( Fig. 2D View FIGURE 2 ); dorsal surface weakly punctate; lateral regions of carapace rugose ( Fig. 2A, B View FIGURE 2 ); epistomal median lobe without acute median tooth ( Fig. 2D View FIGURE 2 ); epibranchial tooth minute, blunt, cleft visible ( Fig. 2A, B View FIGURE 2 ); cervical groove and H shaped groove not visible ( Fig. 2A, B View FIGURE 2 ). Third maxilliped exopod without flagellum ( Fig. 2C View FIGURE 2 ). Sutures between male thoracic sternites 2 and 3 visible as low rounded ridge ( Fig. 2E View FIGURE 2 , 3D View FIGURE 3 ). Male pleon T-shaped, pleonal somite 6 trapezoidal, broader than long, lateral margins gently concave ( Fig. 3C View FIGURE 3 ). Male chela and fingers relatively short; inner angle of the carpus of cheliped low, subtruncate ( Figs. 2A View FIGURE 2 , 3A View FIGURE 3 ). Dactyli, propodi, carpi of ambulatory legs covered with dense setae; P2–P5 relatively short ( Fig. 3E View FIGURE 3 ). G1 relatively longer, stout, just reaching to level of tubercle of press-button of pleonal locking mechanism; terminal and subterminal article clearly demarcated, terminal article ca. 0.3 times length of subterminal article, tip slightly curved outwards; subterminal article gradually tapering distally, distal third relatively broad, outer margin gently sinuous to almost straight ( Fig. 4E, F, H–K View FIGURE 4 ); G2 slightly longer than G1 ( Fig. 4G, L View FIGURE 4 ).

Description of male holotype. Carapace more or less quadrate, 1.26 times wider than long; high in frontal view, not deep, dorsal surface convex in frontal view ( Fig. 2A, B, D View FIGURE 2 ); dorsal surface of carapace smooth but weakly punctate; frontal region longitudinally broader, punctate, frontal median triangle small ( Fig. 2A, B, D View FIGURE 2 ); lateral parts of anterolateral, branchial and posterolateral regions with distinct striae ( Fig. 2A, B View FIGURE 2 ); mesogastric, urogastric, cardiac, intestinal region smooth; orbital region punctate, suborbital region smooth, glabrous; pterygostomial region punctate, glabrous separated from suborbital region by low ridge; sub-branchial region gently rugose ( Fig. 2A, B, D, E View FIGURE 2 ). Epigastric cristae and postorbital cristae indistinct; cervical grooves extremely shallow to almost undiscernible; H-shaped groove very shallow ( Fig. 2A, B, D View FIGURE 2 ). Frontal margin long, almost straight, joining supraorbital margin at slight angle ( Fig. 2D View FIGURE 2 ). External orbital tooth broadly triangular; outer margin much longer than inner margin, gently convex; inner margins concave, joining supraorbital margin; epibranchial tooth minute, blunt, almost completely fused with rest of anterolateral margin ( Fig. 2B, D View FIGURE 2 ). Anterolateral margin gently convex, with low, just visible submedian epibranchial tooth, demarcated by small notch; posterolateral margin concave medially, converging towards medially gently concave posterior carapace margin ( Fig. 2A, B View FIGURE 2 ). Orbits subovate; eye filling up most of orbital space, peduncle short, stout; cornea large, pigmented ( Fig. 2A, B, D View FIGURE 2 ). Supraorbital margin almost straight, entire; suborbital margin concave, complete ( Fig. 2D View FIGURE 2 ). Antennae distinctly short, not reaching cornea of eyes. Posterior margin of epistome with distinct median lobe ( Fig. 2D View FIGURE 2 ). Mandibular palp with 2 articles; terminal article distinctly bilobed.

Third maxillipeds covering most of buccal cavity when closed; ischium subrectangular, surface punctate, with distinct sulcus; merus sub-rectangular, punctate, anteroexternal angle convex; exopod relatively stouter, reaching proximal third of merus; exopod lacking flagellum ( Fig. 2C View FIGURE 2 ).

Outer surface of carpus distinctly rugose, with numerous short stiff setae; inner angle with low subtruncate lobe ( Fig. 2A View FIGURE 2 ). Outer surface of chela punctate, fingers of chela short, stout, gently curved, shorter than palm, cutting edge of finger with large blunt teeth ( Fig. 3A View FIGURE 3 ).

Ambulatory legs short, stout, second pair longest, last pair shortest ( Fig. 2A View FIGURE 2 ). Surfaces of coxa and basisischium with scattered short, stiff setae; surface of merus with scattered short setae, denser on dorsal distal margin, ventral surface with numerous short setae; surfaces of carpus, propodus and dactylus with dense fine, short setae ( Fig. 3E View FIGURE 3 ).

Thoracic sternum broader transversely, surface punctate. Sternites 1, 2 completely fused to form broadly triangular plate; separated from sternite 3 by a low rounded ridge ( Fig. 2E View FIGURE 2 , 3D View FIGURE 3 , 4A View FIGURE 4 ); sternites 3, 4 completely fused with no prominent sutures. Sutures between sternites 4/5, 5/6, 6/7 medially interrupted; sutures between sternites 7/8 complete ( Fig. 2E View FIGURE 2 , 3D View FIGURE 3 ). Male pleonal-locking tubercle low, round, positioned on submedian part of sternite 5 ( Fig. 3B View FIGURE 3 ).

Pleon T-shaped, all somites (including telson) free, telson as long as broad, apex rounded, surface gently punctate to almost smooth, lateral margins gently concave; pleonal somite 6 trapezoidal, broader than long, lateral margins gently concave; pleonal somites 3–5 much wider than long, gradually decreasing in width; pleonal somites 1 and 2 subrectangular, conspicuously wide, reaching to bases of coxae of fourth ambulatory legs ( Figs. 2E View FIGURE 2 , 3B, C View FIGURE 3 ).

G1 relatively long, stout, just reaching to level of tubercle of press-button of pleonal locking mechanism; terminal, and subterminal articles clearly demarcated by distinct membranous suture; subterminal article relatively broader basally, gradually tapering distally, distal third relatively broad, outer margin gently sinuous to almost straight, inner margin gently convex; terminal article elongate, gradually tapering to acute tip that curves slightly outwards, ca. 0.3 times length of subterminal article ( Fig. 4E–F, H–K View FIGURE 4 ). G2 slightly longer than G1; basal article long, distal article slender, almost half length of basal article ( Fig. 4G, L View FIGURE 4 ).

Female. Adult paratype female specimen (9.1 × 7.6 mm) (DABFUK/AR-BR-2025-6) resembles holotype in most non-sexual characters, except having relatively smaller and more slender chelae. Pleon is ovate, with all somites and telson free, covering most of thoracic sternum, except lateral edges ( Fig. 3F View FIGURE 3 ). Vulvae on sternite 6 large, obliquely ovate and positioned adjacent to sternite 5, touching suture between sternites 5 and 6, membranous opening without any sternal vulvar cover ( Fig. 3G View FIGURE 3 ).

Colour. Unknown.

Etymology. The species name is named after ‘Vaman’, one of the avtars of Vishnu in Hindu mythology. Vaman is known for his small stature but power, and the name alludes to the small size of the present species. The name is used as a noun in apposition.

Remarks. The carapace of Pilarta vaman sp. nov. is more quadrate, being proportionately less wide ( Fig. 2A, B View FIGURE 2 ) (versus more rectangular in shape, proportionately wider in P. anuka ; Bahir & Yeo 2007: fig. 26A); the regions behind the frontal and orbital margins are gently convex and punctate but otherwise almost smooth ( Fig. 2A, B View FIGURE 2 ) (versus these regions gently depressed and strongly rugose in P. anuka ; Bahir & Yeo 2007: figs. 25A, 26A); the cervical groove is extremely shallow and almost undiscernible ( Fig. 2A, B View FIGURE 2 ) (versus relatively deep and distinct in P. anuka ; Bahir & Yeo 2007: figs. 25A, 26A); the epibranchial tooth is low, almost completely fused with rest of the anterolateral margin ( Fig. 2A, B View FIGURE 2 ) (versus low but visible in P. anuka ; Bahir & Yeo, 2007: fig. 26A); the postorbital cristae are not discernible ( Fig. 2A, B View FIGURE 2 ) (versus postorbital cristae discernible and low but rugose in P. anuka ; Bahir & Yeo 2007: fig. 26A, B); the chela and fingers are relatively short ( Fig. 3A View FIGURE 3 ) (versus chela and fingers distinctly longer in P. anuka ; Bahir & Yeo 2007: fig. 26A, B); the inner angle of the carpus of the cheliped has a low, subtruncate lobe ( Fig. 2A View FIGURE 2 ) (versus the inner angle armed with a prominent sharp tooth with sub-basal tubercles in P. anuka ; Bahir & Yeo 2007: fig. 26A); the P2–P5 merus is proportionately shorter (P5 merus length to width ratio 2.7) ( Figs. 2A, E View FIGURE 2 , 3E View FIGURE 3 ) (versus merus relatively longer in P. anuka , with P5 merus length to width ratio 3.2; Bahir & Yeo 2007: figs. 25E, 26A); and the overall proportions of the G1, with the terminal article slightly longer (ca. 0.3 times length of subterminal article), the distal third of the subterminal article is distinctly broader with the outer margin almost straight to gently sinuous ( Fig. 4E, F, H, I View FIGURE 4 ) (versus G1 terminal article relatively shorter, being ca. 0.2 times length of subterminal article, with the distal third of the subterminal article more tapering and there is concavity on the proximal outer margin of the subterminal article which is distinctly convex in P. anuka ; Fig. 3B, C View FIGURE 3 ; Bahir & Yeo 2007: fig. 25F, G).

Pilarta vaman sp. nov. can be distinguished from P. aroma by the same carapace and chela characters as P. anuka above (cf. Pati et al. 2017: fig. 7a, b, d). In addition, it can be distinguished by its low subtruncate inner angle of the carpus of cheliped ( Fig. 2A View FIGURE 2 ) (versus with low tooth in P. aroma ; Pati et al. 2017: fig. 7e); and the proximal part of the G1 subterminal article is less wide ( Fig. 4E, F, H, I View FIGURE 4 ) (versus proximal part of G1 subterminal article very broad in P. aroma ; Pati et al. 2017: fig. 8a–c). Pilarta punctatissima is similar to P. vaman sp. nov. in the subtruncate and low angle of the carpus of the cheliped and possession of relatively longer P5 (merus length to width ratios 3.8 versus 2.7), but P. vaman sp. nov. can be distinguished in having the carapace and surfaces of the chela weakly punctate ( Figs. 2 View FIGURE 2 , 3A View FIGURE 3 ) (versus strongly punctate in P. punctatissima ; Pati et al. 2017: fig. 9); the male pleonal somite 6 has the lateral margins gently concave ( Fig. 3C View FIGURE 3 ) (versus margins distinctly concave in P. punctatissima ; Pati et al. 2017: fig. 9h); and the overall G1 is more elongate ( Fig. 4E, F, H–K View FIGURE 4 ) (versus G1 is relatively shorter and stouter in P. punctatissima ; Pati et al. 2017: fig. 10a–c).

The type locality of the P. vaman sp. nov., Gavi, is some 75 km north of Ponmudi, which is the type locality of P. anuka . The type locality of P. aroma (Pongalappara, Agasthyamala, Thiruvananthapuram district) is relatively near that of P. anuka , being less than 20 km southeast of Ponmudi. Pilarta punctatissima is found much further north in Ovumkal, in the Thattekkad Bird Sanctuary (Ernakulam district), a site 160 km north of Ponmudi where P. anuka , occurs; with P. vaman sp. nov. occurring in a different mountain range in between these two locations at Gavi.

Ecology. The crabs of the new species were collected from a small mountain stream near grassland and under leaf litter in Gavi , Pathanamthitta , Kerala, India. No other crab species were found near this site. The crabs appear to be rare, as only two individuals were found. The type locality is a well-known tourist destination and falls within a forest protected area. The crabs face significant anthropogenic threats, such as habitat destruction and pollution, despite the protected status of their habitat .

Distribution. The species is known only from Gavi (09º23’20.4504”N 77º09’14.8392”E), a tourist village in the southern Western Ghats, Pathanamthitta district, Kerala state, India ( Fig. 1 View FIGURE 1 ).