Patithelphusa yercaudensis, Mitra & Rath & Jung & Kim & Kundu, 2025

Patithelphusa yercaudensis sp. nov.

Figs 2 View Figure 2 , 4 View Figure 4

Etymology.

This species is named after its type locality, Yercaud, a town and hill station in Salem District in Tamil Nadu, India. Located in the Shevaroy Hills in the Eastern Ghats, it is situated at an altitude of 1515 m. Used as a noun in apposition. Suggested common name: Yercaud crab.

Type specimens.

Holotype: • 1 male (cw 29.22 mm, cl 20.83 mm, ch 12.41 mm, fw 8.36 mm). Locality: Manjakuttai , Shevaroy Hills, Yercaud, District. Salem, Tamil Nadu, India, 11°49'37.6"N, 78°13'59.3"E; elevation 1504 m; date of collection, 27. 02. 2024; collected by S. Mitra; ZSIC Reg no. CR 396 GoogleMaps . Paratype: • 1 female (cw 21.20 mm, cl 15.25 mm, ch 8.82 mm, fw 5.82 mm); collection data same as above; ZSIC Reg. no. CR 397 GoogleMaps .

Colourations.

Dark brown to chocolate colour in live condition. The cheliped and ventral colouration is light brown mixed with light yellow. The female is a little darker than the male.

Distribution.

The species is known only from the type locality, Yercaud (Fig. 1 View Figure 1 ) of the District Salem, Tamil Nadu, India.

Diagnosis.

See genus Diagnosis.

Description.

Carapace distinctly broader than long (cw / cl = 1.4), deep (ch / cl = 0.6), dorsal surface gently convex in frontal view; epigastric cristae low, rugose, slightly anterior to postorbital cristae, postorbital cristae sharp extended up to epibranchial tooth; external orbital angle widely triangular, blunt, outer margin serrated, 4.5 times of inner margin; supraorbital margin sinuate, granulated (Fig. 2 A View Figure 2 ), no notch between infraorbital margin and external orbital tooth (Fig. 2 B View Figure 2 ); epibranchial tooth short, distinct notch between epibranchial tooth and outer margin of external orbital tooth; anterolateral margin distinctly convex, cristate, shorter than posterolateral margins, anterolateral region distinctly convex with some oblique striae, posterolateral margin gently concave.

Cervical groove well demarcated along its course, broad and shallow anteriorly, relatively deep and narrow posteriorly, not reaching to the postorbital cristae; mesogastric groove shallow, I-shaped; H-shaped groove distinct (Fig. 2 A View Figure 2 ); sub-hepatic region rugose with some short striae, suborbital and pterygostomial region smooth. Front relatively narrow (fw / cw = 0.3), orbit bluntly triangular, eyes occupy most of the orbital space, eye stalk massive, cornea large, frontal median triangle complete, very short; epistomal median lobe with a distinct triangular tooth, tip bilobed; antennae short, just reaching to the base of eyestalk; antennular fossae horizontally broad (Fig. 2 B View Figure 2 ).

Third maxilliped ischium almost quadrangular, 1.6 times longer than broad, longitudinal median groove shallow, merus pentagonal, mesial margin straight; exopods longer than ischium, reaching third of merus, with long flagellum wider than merus (Fig. 2 D View Figure 2 ). Suture between S 1 / S 2 not visible, suture between S 2 / S 3 as shallow broad groove not reaching to lateral margins of sternum; suture between S 3 / S 4 shallow broad not interrupted by any ridge, reaching to lateral edge of sternum (Fig. 2 C, F View Figure 2 ). Sternopleonal cavity reaching median part of the cheliped coxae, male pleon T-shaped, somite six squarish, proximal width slightly longer than median length, lateral margin gently concave; telson as long as broad, distinctly shorter than somite six, free end almost truncated to rounded (Fig. 2 E View Figure 2 ).

Cheliped sub-equal, left cheliped slightly larger than right, major cheliped longer than P 3, hands of major cheliped stout, cutting edge of fixed finger with large submedian teeth, along with 2–3 subteeth; cutting edge of movable finger with several small and 3–4 large triangular teeth, tips of both fingers pointed and curved; (Fig. 2 G View Figure 2 ); ambulatory legs stout, merus of P 3 shorter than carapace length.

G 1 subterminal segment relatively slender, basally broad, terminal segment cone shaped, elongated, 0.4 times of subterminal segment, inner margin straight, outer margin convex in middle, with some long setae; tip triangular, not sharp (Fig. 3 A, B View Figure 3 ). The G 2 c. 1.2 times longer than G 1, subterminal segment long, basally broad, terminal segment slightly shorter than half of the subterminal segment (Fig. 3 C View Figure 3 ).

Variation.

Paratype female is morphologically most similar to holotype male, except for the genital characters. Carapace gently convex, postorbital cristae prominent, cervical groove shallow broad, distinct along its course (Fig. 4 A View Figure 4 ); female paratype, however, slightly differs in some morphological characters, median tooth of epistomal median lobe rounded, tip truncated (Fig. 4 B View Figure 4 ) (vs. epistomal median lobe with triangular tooth, tip bilobed in holotype male, Fig. 2 B View Figure 2 ); carapace less convex (Fig. 4 A View Figure 4 ) (vs. carapace more convex in holotype male, Fig. 2 A View Figure 2 ). Female specimen is not fully mature, hence female pleon not fully covering the sternum (Fig. 4 C View Figure 4 ). Female gonopore small, horizontally oval, occupying approximately 1 / 5 of the length of S 6, positioned close to S 5 / S 6 (Fig. 4 D View Figure 4 ).

Remarks.

The newly described species is currently the sole representative of the proposed monotypic genus Patithelphusa . This new species, Patithelphusa yercaudensis sp. nov., has some distinct morphological features; i. e., broad and shallow cervical groove, triangular bilobed median teeth on the epistomial median lobe, a blunt external orbital tooth with a relatively long outer margin and a distinct G 1 terminal segment with a triangular tip (Figs 2 A – F View Figure 2 ; 3 A, B View Figure 3 ). In this study, the female paratype was observed to be smaller than the male holotype, raising the possibility of whether the differences reflect sexual dimorphism or ontogenetic variation. However, given the limited sample size, further investigation is recommended to confirm these morphological differences of the newly proposed species. Overall, the discovery of this new genus and species within Gecarcinucidae represents a significant contribution to the scientific understanding of freshwater crabs in India and globally. This novel species is meticulously described morphologically, with comparisons drawn to its closest relatives within the family Gecarcinucidae . With this addition, the total count of gecarcinucid crabs in India now stands at 112 species under 31 genera.