Aradhya placida Pati & Bajantri & Hegde 2023, sp. nov.
Creators: name: Pati, Sameer Kumar
name: Bajantri, Parashuram Prabhu
name: Hegde, Gopalkrishna Dattatraya
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Gecarcinucidae
Aradhya
Aradhya placida

description: Aradhya placida sp. nov.
[Peaceful Crab]
(Figs. 2–6, 7A–D)
Type material. HOLOTYPE: adult male (CW 25.12 mm, CL 19.85 mm, CH 16.20 mm, FW 5.76 mm), Bare, Uttara Kannada district, Karnataka state, India (14.814°N, 74.473°E), altitude 629 m a.s.l., 26 June 2022, coll. G.D. Hegde (ZSI-WRC C.2292).
PARATYPES: adult male (CW 23.09 mm, CL 18.23 mm, CH 15.14 mm, FW 5.53 mm), adult female (CW 26.69 mm, CL 20.87 mm, CH 18.08 mm, FW 6.02 mm), same collection data as for holotype (ZSI-WRC C.2293); adult male (CW 28.53 mm, CL 21.82 mm, CH 18.83 mm, FW 6.37 mm), adult female (CW 27.03 mm, CL 20.76 mm, CH 18.50 mm, FW 6.41 mm), same collection data as for holotype, 11 July 2022 (ZSI-WRC C.2294); adult male (CW 23.63 mm, CL 19.34 mm, CH 15.67 mm, FW 5.72 mm), adult female (CW 23.51 mm, CL 19.03 mm, CH 16.25 mm, FW 5.69 mm), same collection data as for holotype, 11 July 2022, coll. G.D. Hegde (ZSI-WGRC IR.INV.22823).
Additional material. 2 subadult males, 4 adult / subadult females, same collection data as for holotype (ZSI-WRC C.2295).
Diagnosis. As for new genus.
Description of male holotype. Carapace transversely ovate, broader than long (CW/CL = 1.3), strongly inflated, deep (CH /CW = 0.6); dorsal surface generally smooth, glabrous, strongly arched; anterolateral surface strongly inflated in frontal view, smooth; posterolateral surface with distinct, oblique striations; anterolateral margins convex, cristate, lacking distinct serrations, shorter than posterolateral margins; posterolateral margins converging posteriorly, gently concave medially, joining gently concave posterior margin; front strongly deflexed, trapezoidal, with anterior margin narrow (FW/CW = 0.25), smooth, cristate, sinuous in frontal view; frontal medial triangle incomplete, with dorsal margin only, lateral margins indiscernible; epigastric cristae poorly developed, only visible as 2 low, slightly rugose, round protuberances; postorbital cristae poorly developed, only visible laterally as low, smooth protuberances; external orbital angle indistinct; epibranchial tooth very low, blunt; postorbital region flat, with strong posterolateral depression; branchial regions strongly inflated; cervical grooves visible as medial, shallow, rugose depressions, not reaching level of postorbital cristae; mesogastric groove shallow, narrow, short, bifurcated posteriorly; H-shaped groove poorly developed; subhepatic region rugose; suborbital region with low granules posteriorly; pterygostomial region with low granules anteriorly; supraorbital margin sinuous, cristate, smooth; suborbital margin concave, cristate with low granules, continuous with supraorbital margin; epistome with distinct gape between anterior margin and front exposing antennular fossae, posterior margin with distinct, triangular medial lobe and strongly sinuous lateral lobes (Figs. 2A–C, 5A, B).
Eyes small as compared to orbits; eyestalk short, moderately stout, concave medially; cornea small, pigmented (Fig. 2B).
Antennules short, folded in transversely broad fossae; antennae with flagellum shorter than eyestalks (Fig. 2B). Mandibular palp with 2 articles; terminal article bilobed, anterior lobe narrow, long, posterior lobe broad, short, nearly half length of anterior lobe (Fig. 5A). First, second maxillipeds each with long flagellum on exopod (Fig. 5A). Third maxillipeds cover most of buccal cavity when closed; ischium subrectangular, longer than broad, with deep, oblique submedial groove; merus subquadrate, slightly broader than long, sunken on inner side, anterolateral margin rounded; exopod slender, distally narrow, reaching beyond anterolateral corner of ischium, lacking flagellum (Fig. 5B).
Chelipeds generally smooth, longer than carapace, unequal, left chela larger, sparsely punctate (Fig. 2A, C). Major chela with merus/basis-ischium joint distinct, structures moveable; merus rugose on outer surface, lacking subterminal spine, ventral margins tuberculated; carpus generally smooth, gently inflated, inner distal major tooth short, broad, blunt, triangular, sub-basal tooth small, low, blunt; palm as long as high, generally smooth; dactylus gently curved, slender, longer than upper margin of palm, generally smooth; fingers with distinct gape when closed, teeth low, blunt (Fig. 2A, C).
Ambulatory legs slender, long, P3 longest, ca. 2.0× CL, longer than minor cheliped; merus/basis-ischium joint (P2–P5) distinct, structures moveable; merus (P2–P5) elongated, equal in length to combined length of carpus and propodus, slightly rugose on outer surface, lacking subdistal spine; carpus (P2–P4) with medial crista on outer surface; propodus (P2–P5) with small, sharp chitinous spines on anterior and posterior margins; dactylus (P2–P5) recurved, longer than propodus, with short, sharp chitinous spines on margins, distal chitinous part very short (Fig. 2A, C).
Thoracic sternites punctate, setose anteriorly, glabrous posteriorly; s1 and s2 separated by cristate margin of s2; s2/s3 cristate, incomplete, not reaching edge of sternum; s3/s4 deep, broad, complete, reaching edge of sternum; s4/s5, s5/s6, s6/s7, s7/s8 shallow, narrow, medially interrupted; s7 with longitudinal medial groove; s8 completely covered by pleon, broad medially, with longitudinal medial groove (Figs. 2C, 5C). Pleonal locking mechanism with low tubercles on submedial part of s5 (Fig. 5C). Sternopleonal cavity deep, narrow, short, reaching anteriorly to level of mid-length of cheliped coxae (Figs. 2C, 5C).
Pleon narrow, triangular, with concave lateral margins; pleonal somites 1–6 progressively longer; pleonal somite 1 rectangular, shortest, narrower than pleonal somite 2; pleonal somite 2 trapezoidal, narrower than pleonal somite 3; pleonal somite 3 trapezoidal, broadest among pleonal somites, with strongly convex lateral margins; pleonal somite 4 trapezoidal, with gently concave lateral margins; pleonal somite 5 trapezoidal, with concave lateral margins; pleonal somite 6 trapezoidal, slightly broader than long (proximal width ca. 1.3× medial length), longest among pleonal somites, shorter than telson, with gently concave lateral margins (Figs. 2C, 5D). Telson narrow, elongated (medial length ca. 1.4× proximal width), with gently concave lateral margins, apex broad, rounded (Figs. 2C, 5D).
G1 moderately stout, long, tip reaching pleonal locking structure in situ; flexible zone small; ultimate article stout, conical, short, ca. 0.3× length of penultimate article, gently curved outwards at angle of ca. 15° from longitudinal axis, tip broad, tubular, dorsal flap absent; penultimate article stout, broad at proximal half, abruptly narrow at distal half, outer margin strongly convex, shelf-like at basal half, inner margin characteristically convex distally; groove for G2 marginal (Figs. 5E, 6B–E). G2 distinctly shorter than G1, ca. 0.6× length of G1; ultimate article very short, ca. 0.2× length of penultimate article, straight, narrow, with acute tip; penultimate article much stouter at proximal third, appearing subtriangular (Figs. 5F, 6F).
Colour in life. Crabs have a dark brown dorsal surface of the carapace (Fig. 7A, B, D). Their chelipeds, ambulatory legs and ventral surface of the carapace are paler (Fig. 7A–D).
Etymology. The species epithet is from the Latin for calm or peaceful, which alludes to the behaviour of these crabs. The species name is treated here as a Latin adjective in the nominative singular.
The proposed common name of the new species is “Peaceful Crab” in English and “Shantiyuta Edi” in Kannada.
Paratypes. The paratype males of Aradhya placida sp. nov. possess most of the character states as those present in the holotype except for the following differences. One of the male paratypes (ZSI-WGRC IR.INV.22823) has a proportionally narrower carapace, CW/CL = 1.2 (Fig. 3C) (vs. CW/CL = 1.3 in the holotype and the remaining male paratypes; Figs. 2A, 3A, E). The cervical grooves of the smaller male paratypes (ZSI-WRC C.2293; ZSI-WGRC IR.INV.22823) are visible as smooth depressions (Fig. 3C, E) as compared to the rugose depressions of the cervical grooves of the holotype and the largest paratype male (Figs. 2A, 3A). While the flagellum on the TME is absent in the holotype (Fig. 5B), all the male paratypes possess a short flagellum on the said structure, which can reach up to half the width of the merus (Fig. 3G). The flagellum may be also vestigial or entirely missing in one of the TMEs of the male paratypes (Fig. 3G). The length of the ambulatory legs varied considerably in the largest male paratype (ZSI-WRC C.2294), in which the P3 length is about 2.9 times CL (Fig. 3A, B) (vs. P3 length of about 2.0 times CL in the holotype and up to 2.4 times CL in the smaller male paratypes; Figs. 2A, C, 3C–F). The lateral margins of the pleonal somite 4 are relatively more concave in the male paratypes (Fig. 3B, D) than those of the holotype (Figs. 2C, 5D, 6A). The telson in the smallest male paratype (ZSI-WRC C.2293) is slightly shorter (medial length ca. 1.3 times the proximal width) (Fig. 3F) than the telson in the holotype and larger paratype males (medial length ca. 1.4 times the proximal width) (Figs. 2C, 3B, D, 5D, 6A).
All three female paratypes share most of the non-sexual character states as those described in the holotype male. They differ only in the following features. The smallest female paratype (ZSI-WGRC IR.INV.22823) possesses a proportionally narrower carapace, CW/CL = 1.2 (Fig. 4C). The posterolateral depression on the postorbital region is shallow in the female paratypes (Fig. 4B, C) against the deep posterolateral depression on the postorbital region of the holotype (Fig. 2A). All the female paratypes have the cervical grooves being smooth and narrow (Fig. 4A–C) (vs. cervical grooves rugose and relatively broader in the holotype; Fig. 2A). The flagellum on the TME is missing, vestigial, or short in the female paratypes (Fig. 4D). The chelipeds of the female paratypes are subequal or slightly unequal (Fig. 4A, C) as compared to the noticeably unequal chelipeds of the holotype and paratype males (Figs. 2A, C, 3A–F). The ambulatory legs of the female paratypes are not so long (P3 length ca. 2.3 times CL) reflecting sexual dimorphism (Fig. 4A–C).
The pleon and telson of the female paratypes form an ovate outline and cover the thoracic sternum except for s1–s3 and lateral edges when closed (Fig. 4E). The pleonal somite 1 is the shortest; pleonal somites 2–5 are progressively longer; and pleonal somite 6 is the longest, much broader than long, subequal in length to the telson, with almost straight to convex lateral margins (Fig. 4E). The female telson is subtriangular, broader than long, with almost straight lateral margins, and the apex is broad and straight (Fig. 4E).
The pleopod 2 of the female paratypes has an endopod being slender, longer than the exopod, with long setae on the article joints and margins; the exopod of the pleopod 2 is slender but relatively broader than the endopod, shorter than the endopod, with long setae over the entire structure (Fig. 4F). The pleopods 3–5 of the female paratypes have an endopod being slender, longer than the exopod, with long setae on the article joints and margins; the exopod of each of the pleopods 3–5 is conspicuously stouter than the endopod, shorter than the endopod, with long setae on the margins only (Fig. 4F).
The vulvae of the female paratypes are located close to each other (VD/SW = ca. 0.1) on s6; each vulva opens inwards, subovate, large, occupying ca. 0.6 times the length of s6, touching s5/s6, covered by the soft membranous operculum, the outer margin with a straight, gently projecting sternal vulvar cover, and the inner margin with a strongly concave, raised rim (Fig. 4G).
Ecological notes. Aradhya placida sp. nov. was found in the evergreen forest of the Central Western Ghats. Crabs of this new species were collected from the earthen burrows mixed with gravel (ca. 30–60 cm depth) close to the base of large trees and boulders (Fig. 7C–E) (https://youtu.be/3A4jgXlvMMU). Their burrows are at least 60 cm apart from each other. These crabs are probably adapted to semi-terrestrial life as their burrows are clearly away from water sources. The nearest stream is approximately 30–60 m away from those burrows. About 19 individuals were seen within an area of a radius of 20 m, most of which were found within the burrows; and the remaining crabs were at a short distance from the burrows. These observations were made between 14.30 to 21.00 hrs., which indicate the crepuscular or nocturnal habit of the species. Crabs of Aradhya placida sp. nov. are mostly active during the monsoon (June-September) and emerge out of their burrows when there is light rain. It is noteworthy to report the behaviour of these crabs as they are non-aggressive and quite calm or peaceful, unlike other Indian gecarcinucid crabs.
Geographical distribution. Aradhya placida sp. nov. is currently known only from the type locality (Bare, Uttara Kannada district, Karnataka state), which is located in the Central Western Ghats of India (Fig. 1).
description: Published as part of Pati, Sameer Kumar, Bajantri, Parashuram Prabhu & Hegde, Gopalkrishna Dattatraya, 2023, A new genus and new species of freshwater crab (Decapoda: Brachyura: Gecarcinucidae) from the Central Western Ghats of India, pp. 161-175 in Zootaxa 5285 (1) on pages 170-174, DOI: 10.11646/zootaxa.5285.1.7, http://zenodo.org/record/7935889