Eumedonus intermedius, Ng, 2000

Ng, Diana G. B. Chia Peter K. L., 2000, A revision of Eumedonus H. Milne Edwards, 1834 and Gonatonotus White, 1847 (Crustacea: Decapoda: Brachyura: Eumedonidae), two genera of crabs symbiotic with sea urchins, Journal of Natural History 34, pp. 15-56 : 29

Eumedonus intermedius n. sp.

(®gures 8, 9)

Material examined. HOLOTYPE: female (12.4Ö 12.7 mm) ( MNHN), ORSTOM number AC45 , Madagascar, northwest coast Mitsio Island , 30 m, trawl, sand, likely on echinoderms, coll. A. Crosnier, February 1960.

Etymology. The name is derived from Latin for`intermediate’, alluding to the proximity of the species to G. granulosus and E. zebra .

Diagnosis. Carapace pentagonal, rostrum long, length 1.2 times width, tip of rostrum not deēxed; surfaces of carapace, chelipeds and ambulatory legs covered with numerous tall and prominent granules; dorsal surface of carapace not pileiferous. Lateral carapac e teeth very sharp, tip usually directed obliquely forwards; base of tooth not as stout and thick. Antero-external angle of merus of maxilliped 3 not auriculiform. Chelipeds granulose; dorsal margin of palm with distinct lamelliform crests; carpus with distinct spine on distal inner angle; median and inner proximal of merus with strong teeth; inner surface of basis-ischium with a tooth. Anterior margins of all ambulatory meri and carpi distinctly cristate; anterior margin of last ambulatory merus appearing serrated; posterior margins of all meri with two distinct parallel crests; dactylus of leg 1 not much longer than those on other legs. G1 and G2 not known.

Remarks. The present specimen was collected with many specimens of G. granulosus from Madagascar. It was distinctive in having highly crested anterior and posterior margins on all the ambulatory meri and carpi (®gure 9E, G). Except for this character, E. intermedius is similar to G. granulosus in many aspects, viz. the long and slender rostrum, tall and prominent granules on all surfaces, and the nonauriculiform antero-external angle of the merus of maxilliped 3.

In some aspects, E. intermedius is also similar to E. zebra , viz. the highly cristate anterior and posterior margins of all ambulatory legs and the pointed and sharp lateral carapace teeth. However, E. intermedius di ers from E. zebra in being highly tuberculated on all surfaces, possessing a non-auriculiform antero-external angle of the merus of maxilliped 3, and having a longer and more slender rostrum.

Thus, it appears that E. intermedius is intermediate between E. zebra and G. granulosu s. Both the latter two species are also found in Madagascar and probably live in similar habitats. Undoubtedly, more specimens are required to better de®ne E. intermedius .

Distribution. Known only from Madagascar.