Socotra pseudocardisoma, Cumberlidge & Wranik, 2002

Cumberlidge, Neil & Wranik, Wolfgang, 2002, A new genus and new species of freshwater crab (Potamoidea, Potamidae) from Socotra Island, Yemen, Journal of Natural History 36 (1), pp. 51-64 : 53-60

Socotra pseudocardisoma n. sp.

(®gures 1±6)

Material examined. Holotype: NHML reg. 1999: adult male (cw 77.2, cl 52.4, ch

28.3, fw 14.7 mm). Paratype: UR reg. 1999: adult male (cw 90.5, cl 59.0, ch 33.5, fw 15.5 mm), from Diksam (12ss29¾N, 53ss59¾E), 700 m, coll. W. Wranik, 4 October 1998. Paratype: NMU reg. 1999: adult female (cw 77.2, cl 52.4, ch 28.3, fw 14.7 mm) from Diksam, 700 m, coll. W. Wranik, 5 November 1997. Eleven other specimens of S. pseudocardisoma are held at UR.

Diagnosis. Cephalothorax heart-shaped (cw>cl): highly arched (ch/fw 1.9), very wide (cw/fw 5.3), very long (cl/fw 3.6); front very narrow (fw/cw 0.2). Postfrontal crest low, faint, complete, ends curving forward to meet anterolateral margins at epibranchial teeth; mid-groove between epigastric crests long, ¯at, wide, forked at posterior end. Exorbital tooth small, low, blunt; epibranchial tooth reduced, almost undetectable, forming part of rim of anterolateral margin; anterolateral margin between exorbital, epibranchial teeth extremely short, lacking intermediate tooth; anterolateral margin posterior to epibranchial tooth forming a smooth raised rim. Front sharply deēxed, meeting inferior margins of antennulular fossae so that antennules almost completely enclosed within fossae. Mandibular palp threesegmented, terminal segment single, undivided. Exopod of third maxilliped distinctly widened at midpoint, base, tip narrow (i.e. not long, columnar with parallel sides). Third sternal sulcus (s3/s4) reduced to two short notches at lateral edges of sternum; anterior margin of sterno-abdominal cavity almost reaching s3/s4 junction. Episternal sulci s4/e4 to s7/e7 not visible. Gonopod 1 long, extending anteriorly as far as s4/s5. Terminal article of gonopod 1 relatively long (about one-third as long as subterminal segment), terminal article of gonopod 2 long, ¯agellum-like (almost as long as subterminal segment of gonopod 2).

Description. Following description based on male holotype ( NHML reg. 1999: adult male, cw 77.2 mm). Cephalothorax heart-shape d (cw>cl): highly arched (ch/fw

(a)

(b)

1.9), very wide (cw/fw 5.3), very long (cl/fw 3.6); front very narrow (fw/cw 0.2). Dorsal surface of carapace texture smooth; semicircular, urogastric grooves deep, cervical grooves deep, short; transverse cardiac grooves faint; branchial grooves not visible. Postfrontal crest low, faint, complete, ends curving forward to meet anterolateral margins at epibranchial teeth; mid-groove between epigastric crests long, ¯at, wide, forked at posterior end; mid-groove extending anteriorly for short distance on to frontal region. Exorbital tooth small, low, blunt; epibranchial tooth reduced, almost undetectable, forming part of rim of anterolateral margin; anterolateral margin between exorbital, epibranchial teeth extremely short, lacking intermediate tooth; anterolateral margin posterior to epibranchial tooth forming a smooth raised rim, posterior end curving inward.

Front sharply deēxed, meeting inferior margins of antennulular fossae so that antennules almost completely enclosed within fossae. Lateral parts of epistome forming upper roof of eOEerent channels overlapping large, triangular, horizontal epistomial tooth. Margins of lateral epistome, epistomial tooth smooth, distinct endostomial ridge visible on lateral epistome marking medial boundary of eOEerent channel formed where broadened endopod of ®rst maxilliped meets endostome. Mandibular palp three-segmented terminal segment single, undivided. Third maxillipeds ®lling oral ®eld, medial margins of ischia, meri vertical, meeting along entire length; ischium with deep vertical sulcus; exopod of third maxilliped distinctly widened at midpoint, base, tip narrow; exopod ¯agellum reduced, measuring only half length of exopod. First sternal sulcus (s1/s2) short, distinct; second sulcus (s2/s3) deep, running horizontally across sternum; third sternal sulcus (s3/s4) reduced to two short notches at lateral edges of sternum, in line with basal segment of third maxillipeds; anterior margin of sterno-abdominal cavity almost reaching s3/s4 junction; episternal sulci (s4/e4 to s7/e7) not visible.

Dactylus of right cheliped narrow (one-quarter height of palm), upper margin smooth; dactylus slightly arched, enclosing long narrow interspace; ®nger of propodus slim (one-quarter height of palm). Lower margin of propodus indented. Both ®ngers with series of small pointed teeth, interspersed with several bigger teeth. Propodus of cheliped with conspicuous rounded boss at articulation point with carpus of pereiopod 1; carpus with raised ¯at process at this junction. Medial, lateral inferior margins of merus lined by small distinct teeth; single large pointed distal meral tooth on medial margin; superior margin of merus slightly granular. First carpal tooth of cheliped large, slender, pointed, second carpal tooth small pointed granule, on raised ridge with similar granules. Walking legs (pereiopods 2±5) long, slender; P3 longest, P5 shortest; dactyli of P2±P5 with four distinct rows of short corneous spines; anterior, posterior margins of propodi of P2±P5 smooth.

Male abdomen (a3±a6, plus telson) triangular; telson triangular with almost straight sides directed inward. Gonopod 1 long, reaching sternal groove s4/s5; terminal article relatively long (about one-third as long as subterminal segment); terminal article initially straight, curving sharply outward at halfway point, then curving sharply upward, tapering to broad tip; longitudinal groove visible only on dorsal side; wide dorsal membrane between last two parts; lateral fold of terminal article of gonopod 1 low, equal to medial fold. Gonopod 2 as long as gonopod 1; terminal article of gonopod 2 long, ¯agellum-like (almost as long as subterminal segment of gonopod 2) basal half straight, distal half either straight or folding back on itself, forming a hook-shape.

Size. The adult size range is up to cw 90.5 mm.

Type locality. Diksam, altitude 700 m, limestone plateau 660±740 m.

Distribution. The species is known only from the type locality (®gures 5, 6).

Colour. In living specimens the dorsal surface of the carapace is dark purple with a broad light brown margin (most males) or brown with a broad yellowish margin (females). In some male specimens the dark surface coloration of the carapace continues over to the pterygostomium of the carapace sidewall. The walking legs (pereiopods P2±P5) are mainly yellowish, except for the ends of the merus, carpus and propodus, which have dark patches.

Ecology. The Haghir massif receives Socotra’s highest rainfall totals, and as a consequence the central highlands are frequently shrouded in clouds and heavy mists. Additional sources of water at these higher altitudes include permanent springs and the mist and dew. The Haghir massif forms the most important watershed on the island and this gives rise to numerous watercourses that run to the north and south of these highlands. The upper reaches of the streams running down the northern slopes tend to ¯ow year round, but at the lower elevations these streams become sporadic and ¯ow freely only after rain.

The following ®eld observation s of the new taxon were made. Socotra pseudocard - isoma is a semi-arid zone crab with terrestrial habits whose behavioural pattern is inūenced by seasonal changes. The type locality is in a part of the island where limestone is dominant, and where climatic erosion of the calcareous substratum has produced sinks, underground streams, caverns, hollows and crevices. These temporary aquatic freshwater habitats are located far from conventional freshwater sources (rivers, streams and lakes) and are fed mainly by rainwater. It is possible that there are year-round, more permanent, water deposits deep below the surface, which could also be accessed by these crabs.

Socotra pseudocardisom a lives in crevices, and crabs are not easy to ®nd, because they spend most of the daylight hours concealed from view. Crabs appear only occasionally on the surface, and startled crabs quickly retreat back into the crevice system. These animals can move rapidly on the ground, and can climb agilely and rapidly up and down rock surfaces. During the night, crabs leave their resting-places and wander on the surface in search of food. We are unsure of the natural diet of S. pseudocardisoma in its natural habitat, but specimens kept in captivity ate plant material and dead animal material.

There are distinct seasonal diOEerences in the behaviour patterns of S. pseudocardi - soma. Crabs were observed to be active only in October and November, and it is thought likely that they are active on the surface mainly during the wet season (November to March). It is possible that crabs mostly remain in their underground retreats during the drier times of the year (April to October). People that live on the limestone plateau near to the type locality, and who occasionally use these crabs as food, also report a similar seasonal pattern of wet season activity, and dry season disappearance.

We are able to report only basic information on the reproduction and life cycle of this species. It would appear that the production of eggs and release of hatchling crabs is timed to coincide with the wettest part of the year, when presumably plant and animal populations on Socotra are at their maxima. Five free-living juvenile crabs (cw 26±27 mm) already released from the maternal abdominal brood pouch were caught by one of the authors (W. W.) in summer 1998. Indeed, juvenile crabs are regularly sighted by local people during the late summer and early autumn when the monthly rainfall totals are at their highest. In captivity, mating was observed between a hard-shelled female and a hard-shelled male who remained in the copulatory position and/or a postmating embrace for about one day, before resuming normal behaviour. The sperm was presumably stored in the spermatheca of the female for later use in the fertilization of the eggs when they are eventually laid.