Karstarma, Poupin & Crestey & Guelte, 2018

Poupin, Joseph, Crestey, Nicole & Guelte, Jean-Paul Le, 2018, Cave-dwelling crabs of the genus Karstarma from lava tubes of the volcano ‘ Piton de la Fournaise’, in Réunion Island, with description of a new species and redescription of Karstarma jacksoni (Balss, 1934) from Christmas Island (Decapoda, Brachyura, Sesarmidae), Zootaxa 4497 (3), pp. 381-397 : 388-390

Karstarma sp.

( Fig.5A–D )

Material examined. 1 female juvenile 8.6 × 9.8 mm (MNHN-IU-2013-7242), lava tube ‘ Brûlé des Citrons Galets’ , Le Tremblet, Saint Philippe, Réunion Island, coll. A. Barrère, Lucie Lavaud, Agnès Lavaud, Justine Sehedic, 19 February 2016.

Additional observation. In situ photographs (no specimens collected) lava tube ‘ Coulée de 2004 ’, lower section, near end of tunnel, Matthieu Balanger, 13 August 2017.

Diagnosis (juvenile aspect). Carapace trapezoidal, 1.1 as wide as long; dorsal surface gently convex with epigastric and urogastric grooves poorly marked. Lateral margins of carapace diverging posteriorly. Anterolateral margin with 2 main teeth including external orbital angle; first tooth (external orbital angle) blunt, directed inwards at an angle of ~ 30°; second tooth with blunt tip separated from former tooth by deep V-shaped notch; third tooth poorly marked separated from second tooth by minute notch.

Front 0.45 times fronto-orbital width (measured between tip of anterolateral teeth), 2.7 wider than high. Supraorbital margin widely U-shaped, eyes with cornea pigmented as wide as ocular peduncle. Cheliped symmetrical, chela 3.3 as long as high, inner and outer surfaces of palm slightly inflated, upper and lower margin rounded, unarmed; cutting edges of fingers slightly gaping when fingers closed, with minute triangular teeth on proximal ¼, unarmed on distal ¾, tip of fingers corneous, hoof-like, incurved, movable finger 1.2 as long as palm.

Ambulatory legs 1–4 long, third leg (P4) longest 3.8 and 3.4 as long as CL and CW, respectively, tufts of setae present between coxae of ambulatory legs 1, 2 (P2, 3) and 2, 3 (P3, 4); outer faces of meri with sparse short transverse striae, upper and lower margins carinated, unarmed, length to width ratio of meri of legs 2, 3 (P3, 4), 4.6, 5.0, respectively; carpi 0.5 meri length, unarmed, outer faces with 2 longitudinal carinae; propodi 0.6 meri length, unarmed, furnished with longitudinal rows of long stiff setae on upper and lower margins; dactyli sub-cylindrical, unarmed, 1.0–1.1 propodi length, gently curved in distal third, with similar longitudinal rows of setae than on propodi, terminating in corneous claws. Female pleon and vulva juvenile.

Live coloration. ( Fig. 5A–D ) carapace purple or orange, chelipeds orange with white on fingers of chelae, ambulatory legs bright orange on meri and carpi, white on propodi and dactyli.

Habitat. Lava tubes of ‘Brûlé des Citrons Galets’ and ‘Coulée de 2004’. This species seems to prefer the rocky parts of the lava tubes (see Fig. 5 C, D ).

Distribution. Réunion Island.

Remarks. This juvenile specimen, probably collected in the same lava tube than Karstarma vulcan sp. nov., was first thought to be a juvenile of that species. After careful examination it appears that it is distinct from K. vulcan sp. nov. by at least three characters: a) carapace trapezoidal (instead of approximately trapezoidal); b) relatively longer legs, leg 3 being 3.8 and 3.4 times CL and CW, respectively (instead of 3.1–3.4 and 2.6–2.8, respectively) with a merus more elongated having a length to width ratio of 5.0 (instead of 3.9–4.6); c) live colour of ambulatory legs, orange on meri and carpi and white on propodi and dactyli (instead of brown or purple). All these characters are shared by three species identified by Wowor & Ng (2009) as a group of very long-legged species nested within Karstarma , and probably with distinct generic affinities: viz. K. ardea Wowor & Ng, 2009 , K. ultrapes ( Ng, Guinot & Iliffe, 1994) , and K. philippinarum Husana, Naruse & Kase, 2010 . The vulvae of females in this group has a typical “large U-shaped posterior projection and a prominent anterior projection, with both projections partially covering the prominent rounded operculum” ( Wowor & Ng 2009: 29, fig. 5B–D), but this was not observed on the female examined from Réunion Island, probably because it is a juvenile. Collection of additional specimens, including adult males and females, is therefore needed before this species can be identified to species level. The presence of ‘very long-legged’ species, however, cannot be confirmed with certainty in the Indian Ocean with the present observations because characters such as the shape of the carapace and proportion of the legs vary in the juveniles as observed for the gecarcinid Discoplax gracilipes Ng & Guinot 2001 (see variation: 325) and the sesarmid Karstarma boholano (P.K.L. Ng. pers. comm.) If the presence of a ‘very long-legged’ species living sympatrically with K. vulcan sp. nov. can be confirmed in the future, the situation will be similar to that observed in the cave ‘Gua Kalepale’, Waigeo Island, where K. ardea , which has ‘very long legs’ and prefers rocky parts, lives sympatrically with K. waigeo Wowor & Ng, 2009 , which has ‘normal’ legs and prefers muddy substrates.

Figures

FIGURE 5. Live colour of Karstarma sp. A, B) female juv. 8.6 × 9.8 mm (MNHN-IU-2013-7242), probably from lava tube ‘Brûlé des Citrons Galets’, photographs A. Barrère, 19 February 2016; C, D) specimen not collected, from lava tube ‘Coulée de 2004’, lower entrance near the shore, photographs Matthieu Balanger, 13 August 2017.