Arcithelphusa tumpikkai, Pati & Sujila & Devi, 2019

Pati, S. K., Sujila, P. S. & Devi, A. R. Sudha, 2019, Description of a new species of freshwater crab of the genus Arcithelphusa Pati & Sudha Devi, 2015 (Decapoda: Brachyura: Gecarcinucidae) from the Western Ghats, Kerala, India, Zootaxa 4674 (2), pp. 203-214 : 207-212

publication ID	https://doi.org/ 10.11646/zootaxa.4674.2.2
publication LSID	lsid:zoobank.org:pub:B5BA6E39-C9F3-486E-863F-5496DD879CAF
persistent identifier	https://treatment.plazi.org/id/C55F87B1-E03A-755D-FF3F-F8F5FDF4CBAB
treatment provided by	Plazi
scientific name	Arcithelphusa tumpikkai
status	sp. nov.

Treatment

Arcithelphusa tumpikkai View in CoL sp. nov.

( Figs. 2 View FIGURE 2 A–C, 3A–L, 4A–F, 5A)

Type material. Holotype: adult male (19.40 mm cw, 13.93 mm cl, 12.25 mm ch, 4.63 mm fw), Makkimala , Wayanad district, Kerala, India (11.869°N, 75.948°E; altitude 792 m), 6 September 2017, coll. P.S. Sujila ( ZSI-WRC C.1816). GoogleMaps

Paratypes: male (19.09 mm cw, 14.02 mm cl, 12.21 mm ch, 4.87 mm fw) and female (20.18 mm cw, 14.18 mm cl, 12.23 mm ch, 4.75 mm fw), same collection data as holotype ( ZSI-WRC C.1817); male (18.58 mm cw, 13.85 mm cl, 11.80 mm ch, 4.72 mm fw) and female (17.95 mm cw, 13.17 mm cl, 10.81 mm ch, 4.46 mm fw), Varayal , Wayanad district, Kerala, India (11.838°N, 75.901°E; altitude 729 m), 16 September 2018, coll. P.S. Sujila ( ZSI- WRC C.1818) GoogleMaps .

Other material. 2 males (19.31–19.80 mm cw, 14.18–14.39 mm cl, 11.13–11.26 mm ch, 4.92–5.08 mm fw) and female (18.88 mm cw, 13.37 mm cl, 11.99 mm ch, 4.61 mm fw), same collection data as holotype ( ZSI-WRC C.1819) GoogleMaps ; 3 males (18.44–21.02 mm cw, 14.02–15.79 mm cl, 10.97–13.02 mm ch, 4.86–4.89 mm fw), same locality data as holotype, 13 September 2017, coll. P.S. Sujila ( ZSI-WRC C.1820) GoogleMaps ; 2 males (18.04–19.78 mm cw, 13.18– 14.31 mm cl, 11.02–11.94 mm ch, 4.58–5.04 mm fw), Puthiyidam , Wayanad district, Kerala, India (11.859°N, 75.958°E; altitude 860 m), 13 September 2017, coll. P.S. Sujila et al. ( ZSI-WRC C.1821) GoogleMaps ; 3 males (11.81–15.45 mm cw, 8.99–11.65 mm cl, 6.74–9.21 mm ch, 3.52–3.84 mm fw) and 2 females (15.58–17.45 mm cw, 11.96–12.83 mm cl, 9.58–10.33 mm ch, 3.99–4.71 mm fw), same collection data as preceding paratypes ( ZSI-WRC C.1822) GoogleMaps ; male (20.63 mm cw, 15.44 mm cl, 12.27 mm ch, 5.39 mm fw) and female (23.35 mm cw, 16.69 mm cl, 14.61 mm ch, 5.72 mm fw), Kappikalam , near Thalappuzha , Wayanad district , Kerala, India (11.844°N, 75.940°E; altitude 753 m), 30 September 2018, coll. P.S. Sujila ( ZSI-WRC C.1823) GoogleMaps ; female (20.23 mm cw, 14.84 mm cl, 13.55 mm ch, 5.03 mm fw), Kambamala, Wayanad district, Kerala, India (11.869°N, 75.942°E; altitude 816 m), 26 October 2018, coll. P.S. Sujila ( ZSI-WRC C.1824) GoogleMaps .

Comparative material. A. cochleariformis : holotype male (30.82 mm cw, 24.93 mm cl, 22.82 mm ch, 7.65 mm fw), Ondayangadi , 5 km north east of Mananthavady, Wayanad district, Kerala, India (11.823°N, 76.023°E; altitude 767 m), 25 June 2011, coll. M.K. Smija ( ZSI-WRC C.1188); 3 paratype males (26.86–32.23 mm cw, 21.43–25.21 mm cl, 19.22–23.23 mm ch, 6.86–7.59 mm fw) and GoogleMaps paratype female (26.85 mm cw, 21.15 mm cl, 19.54 mm ch, 6.86 mm fw), same collection data as holotype, coll. M.K. Smija ( ZSI-WRC C.1189); 5 paratype males (24.22–29.03 mm cw, 19.33–22.26 mm cl, 16.69–19.50 mm ch, 5.62–6.87 mm fw) and GoogleMaps paratype female (32.06 mm cw, 24.64 mm cl, 22.63 mm ch, 7.09 mm fw), Ondayangadi , 5 km north east of Mananthavady, Wayanad district, Kerala, India (11.825°N, 76.030°E; altitude 760 m), 16 November 2013, coll. Ammini ( ZSI-WRC C.1190) GoogleMaps .

Diagnosis. Carapace small in adults (<24 mm cw), transversely ovate, relatively broad (cw/cl = 1.3–1.4), relatively low (ch/cw = 0.6); posterior margin of carapace gently sinuous; cervical grooves shallow, with short course; H-shaped groove barely visible ( Figs. 2A, B View FIGURE 2 , 3A View FIGURE 3 , 4A, B, D, E View FIGURE 4 ). Third maxilliped exopod reaching nearly half length of merus, with short flagellum, reaching half width of merus ( Fig. 3B View FIGURE 3 ). Male pleonal somite 6 as long as telson ( Figs. 2C View FIGURE 2 , 3D View FIGURE 3 , 4C View FIGURE 4 ). Female pleon narrowly ovate; pleonal somite 6 much broader than long, as long as telson ( Fig. 4F View FIGURE 4 ). G1 relatively slender, with sharply bent terminal segment; terminal segment relatively long, ca. 0.4× length of subterminal segment, medially curved outwards at angle of 90° along longitudinal axis, relatively slender proximally, tapering distally, tip truncated, upcurved, resembling uplifted trunk of elephant, dorsal flap distinct but low, broad; subterminal segment relatively slender, outer margin with distinct hump at basal half, inner margin sinuous ( Fig. 3 View FIGURE 3 E–G, J). G2 short, ca. 0.6–0.7× length of G1 length; distal segment very short, ca. 0.2× length of basal segment ( Fig. 3H, K View FIGURE 3 ). Vulvae orbicular, large, occupying nearly half length of thoracic sternite 6, situated on submedial part of thoracic sternite 6 adjacent to margin with thoracic sternite 5 ( Fig. 3L View FIGURE 3 ).

Description of male holotype. Carapace transversely ovate, broader than long (cw/cl = 1.4), very deep (ch/cw = 0.6); dorsal surface arched, smooth except for antero- and postero-lateral surfaces; anterolateral surface inflated in frontal view; anterolateral margins short, convex, each with 4 or 5 short, cristate lines, curving into epibranchial region; posterolateral margins long, with oblique striae, converging posteriorly, joining gently sinuous posterior carapace margin; front strongly deflexed, almost rectangular, longitudinally broad, surface almost flat; frontal margin almost straight, narrow (fw/cw = 0.25); epigastric cristae only visible as 2 very low, broad, oval protuberances; postorbital cristae indistinct; external orbital angle indistinct; epibranchial tooth indistinct; postorbital region gently concave; branchial regions highly inflated; cervical grooves shallow, with short course; mesogastric groove shallow, narrow, long, bifurcated posteriorly; H-shaped groove barely visible; subhepatic region rugose; suborbital region rugose; suborbital margin concave, lined with very low, rounded granules; pterygostomial region rugose anteriorly; frontal median triangle incomplete, lateral margins indiscernible; epistome posterior margin with triangular median lobe and sinuous lateral lobes ( Figs. 2 View FIGURE 2 A–C, 3A).

Eyes small, filling up most of orbital space; eye stalk short, stout; cornea moderately large, pigmented. Antennae very short, reaching up to proximal quarter length of eye stalk; antennules long, folded in narrow fossae ( Fig. 2B View FIGURE 2 ).

Mandibular palp 2 segmented; terminal segment bilobed; anterior lobe narrow, long; posterior lobe broad, short, nearly half of anterior lobe. First, second maxillipeds each with long flagellum on exopod. Third maxillipeds cover most of buccal cavity when closed; ischium subrectangular, longer than broad, surface uneven, pitted, with deep, oblique submedial groove; merus subquadrate, slightly broader than long; exopod slender, longer than ischium, reaching nearly half length of merus, with short flagellum, reaching half width of merus ( Figs. 2B, C View FIGURE 2 , 3B View FIGURE 3 ).

Chelipeds almost smooth, asymmetrical, right chela larger ( Fig. 2 View FIGURE 2 A–C). Major cheliped with multiple blunt teeth of different size on each finger, distinct gape when fingers closed; dactylus gently curved, longer than upper margin of palm, smooth; palm as long as high, inner and outer surfaces smooth; carpus slightly rugose on outer surface, inner distal major tooth short, stout, blunt, sub-basal granule distinct, low; merus rugose on outer surface ( Fig. 2 View FIGURE 2 A–C).

Ambulatory legs slender, long; p3 longest, nearly twice length of carapace; p5 shortest; merus (p2–p5) slender, ca. 3 times long as broad, slightly rugose externally, lacking chitinous spines on margins; p3 propodus ca. 2.5 times long as broad, with few short, sharp, chitinous spines along posterior margin; dactylus (p2–p5) longer than propodus, with short, sharp, chitinous spines on both anterior and posterior margins ( Fig. 2 View FIGURE 2 A–C).

Thoracic sternites smooth, scattered with short setae throughout; suture between thoracic sternites s2/s3 visible as shallow, broad groove, not reaching edge of sternum; suture between thoracic sternites s3/s4 deep, broad, reaching edge of sternum; suture between thoracic sternites s4/s5, s5/s6, s6/s7, s7/s8 shallow, medially interrupted ( Figs. 2C View FIGURE 2 , 3C, I View FIGURE 3 ). Pleonal locking mechanism with low, anteriorly directed tubercles on each antero-submedial part of sternite 5 ( Fig. 3I View FIGURE 3 ).

Sternopleonal cavity deep, long, reaching imaginary line joining medial part of cheliped coxae ( Fig. 2C View FIGURE 2 ). Pleon narrowly triangular, lateral margins concave; pleonal somites 1–6 trapezoidal, progressive longer; pleonal somite 1 with convex lateral margins; pleonal somite 2 with distally divergent lateral margins; pleonal somite 3 broadest among pleonal somites, with distally convergent lateral margins; pleonal somites 4, 5 distinctly broad, with distally convergent lateral margins; pleonal somite 6 broader than long, as long as telson, with slightly convex lateral margins ( Figs. 2C View FIGURE 2 , 3D View FIGURE 3 ). Telson narrow, almost as long as broad at base, with strongly concave lateral margins; apex rounded ( Figs. 2C View FIGURE 2 , 3D View FIGURE 3 ).

G1 relatively slender, straight except for sharply bent terminal segment, i.e., medially curved outwards at angle of 90° along longitudinal axis, tip not reaching pleonal locking structure; flexible zone large, with small demarcation of joint between terminal and subterminal segments; terminal segment relatively long, ca. 0.4× length of subterminal segment, relatively slender proximally, tapering distally, tip truncated, upcurved, resembling uplifted trunk of elephant, proximal half with distinct but low, broad dorsal flap; subterminal segment relatively slender, outer margin with distinct hump at basal half, inner margin sinuous ( Fig. 3 View FIGURE 3 E–G). G2 short, ca. 0.7× length of G1; distal segment very short, ca. 0.2× length of basal segment ( Fig. 3H View FIGURE 3 ).

Live colour. The dorsal surface of the carapace is purplish brown anteriorly and light brown posteriorly ( Fig. 5A View FIGURE 5 ). The lateral and ventral surfaces are light brown ( Fig. 5A View FIGURE 5 ). Chelipeds and ambulatory legs are brown to purplish brown ( Fig. 5A View FIGURE 5 ).

Etymology. The species name ‘tumpikkai’ is derived from the Malayalam language for elephant trunk, referring to the G1 terminal segment that resembles an uplifted trunk of an elephant, the state animal of Kerala. Used as a noun in apposition.

The new species is popular among the tribal people of Wayanad as ‘Kunjan Njandu’ meaning small crab.

Remarks. The adult male paratypes resemble the holotype in overall carapace morphology and gonopod structure. The following differences, however, are noticed: the carapace is relatively less broad (cw/cl = 1.3) in the smaller male paratype (ZSI-WRC C.1818) ( Fig. 4A View FIGURE 4 ) [vs. relatively more broad (cw/cl = 1.4) in the holotype ( Fig. 2A View FIGURE 2 ) and the larger male paratype]; the suture between the thoracic sternites s2/s3 is relatively deep in the larger male paratype (ZSI-WRC C.1817) [vs. shallow in the holotype and the smaller male paratype ( Figs. 2C View FIGURE 2 , 3C View FIGURE 3 , 4C View FIGURE 4 )]; the G2 is relatively short, ca. 0.6 times the length of the G 1 in the larger male paratype [vs. relatively long, ca. 0.7 times the length of the G 1 in the holotype and the smaller male paratype ( Fig. 3E, H, J, K View FIGURE 3 )]. The adult female paratypes (ZSI-WRC C.1817, 1818) are similar to the holotype in the non-sexual characters except for the comparatively less asymmetrical chelipeds ( Fig. 4 View FIGURE 4 D–F).

Arcithelphusa tumpikkai sp. nov. resembles A. cochleariformis and species of Cylindrotelphusa mainly due to the presence of a relatively deep carapace (ch/cw = 0.5–0.7), a strongly convex dorsal surface, the highly inflated branchial regions, a narrow frontal margin (ca. 0.25 times the carapace width), an incomplete frontal median tri- angle, the prominent and triangular median lobe on the epistome posterior margin, a narrowly triangular male pleon, and a short G2, with a short distal segment (ca. 0.2–0.3 times the length of the basal segment) ( Figs. 2 View FIGURE 2 A–F, 3D, E, H, J, K, O, P, 4A–E; see Bahir & Yeo 2007: figs. 4A, D, 5A–C; Pati et al. 2017: figs. 11a–c, h, 12a, d, 13a–c, h, 14a, d). Both A. tumpikkai sp. nov. and A. cochleariformis can be distinguished from the species of Cylindrotelphusa by a suite of characters, which includes anterolateral margins of the carapace, third maxilliped exopod, chelipeds, and G1 (see Remarks for Arcithelphusa ).

In addition to the above-mentioned similarities, the new species shares the following prominent characters with A. cochleariformis : the epigastric cristae are only visible as two low and broad protuberances ( Figs. 2A, D View FIGURE 2 , 4A, D View FIGURE 4 ); the postorbital cristae, the external orbital angle, and the epibranchial tooth all are indistinct ( Figs. 2A, D View FIGURE 2 , 4A, D View FIGURE 4 ); the suture between the male thoracic sternites s2/s3 is shallow to deep and broad, which never reaches the edge of the sternum ( Figs. 2C, F View FIGURE 2 , 3C View FIGURE 3 , 4C View FIGURE 4 ); the suture between the male thoracic sternites s3/s4 is deep and broad, which reaches the edge of the sternum ( Figs. 2C, F View FIGURE 2 , 3C View FIGURE 3 , 4C View FIGURE 4 ); the male sternopleonal cavity extends up to the imaginary line joining the medial part of the cheliped coxae ( Figs. 2C, F View FIGURE 2 , 4C View FIGURE 4 ); the male pleonal somite 6 is trapezoidal and broader than long ( Figs. 2C, F View FIGURE 2 , 3D View FIGURE 3 , 4C View FIGURE 4 ); the medial portion of the G1 terminal segment is distinctly curved outwards ( Fig. 3E, F, J, O View FIGURE 3 ). Arcithelphusa tumpikkai sp. nov. is nevertheless differentiated from A. cochleariformis by the characters in the carapace, third maxilliped exopod, male pleonal somite 6, and G1 ( Table 1 View TABLE 1 ). Moreover, the size of adult specimens of A. tumpikkai sp. nov. is apparently smaller (cw 17.45–23.35 mm; n = 17) than that of A. cochleariformis (cw 24.22–32.23 mm; n = 11).

Ecological notes. Arcithelphusa tumpikkai sp. nov. occupies a wide range of habitats such as Shola forests, mountainous streams, natural springs, rice fields, and banana/betel nut/cassava plantations. These crabs live in shallow burrows (<15 cm deep) under small and moist boulders (<40 cm diameter) ( Fig. 5B, C View FIGURE 5 ). They are also known to inhabit muddy banks along the water channels of paddy fields and various plantations ( Fig. 5D View FIGURE 5 ). The new species seems to be locally abundant in rather elevated areas of Wayanad district. Arcithelphusa tumpikkai sp. nov. is syntopic with A. cochleariformis and Vela carli (Roux, 1931) at Kambamala, Kappikalam, Puthiyidam, and Varayal, where soft substrates dominate ( Fig. 1 View FIGURE 1 ).

The ecological requirement of A. tumpikkai sp. nov., however, is different from A. cochleariformis . The new species generally prefers to stay near water bodies or moist places ( Fig. 5C, D View FIGURE 5 ) whereas A. cochleariformis is a more terrestrial crab that can be found adjacent to or away from water bodies (see Pati & Sudha Devi 2015a). The difference in the habitat preferences between both the species could be related to the condition of the flagellum on their third maxilliped exopod, which is relatively well-developed in A. tumpikkai sp. nov. and altogether absent in A. cochleariformis . Vela carli is a larger species with a well-developed flagellum on the third maxilliped exopod, and its burrows are deeper and larger than that of the Arcithelphusa species. The burrows of V. carli are usually water filled, which can be seen along rice field embankments, margins of natural springs, and water channels of banana/betel nut/coconut plantations.

Distribution. Arcithelphusa tumpikkai sp. nov. is endemic to the Western Ghats and currently known only from Wayanad district of Kerala, India ( Fig. 1 View FIGURE 1 ).