Eumedonus vicinus Rathbun, 1918

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 : 29-35

Eumedonus vicinus Rathbun, 1918

(®gures 10±12) Eumedonus vicinus Rathbun, 1918: 28 , plate 13: ®gure 2 [type locality southeast of Double Island Point, Queensland, Australia]; Flipse, 1930: 80, 90 [list only]; Sakai, 1938: 349 [list

only] (part); Sakai, 1940: 41 [list only] (part); Sakai, 1956: 25 [appendix list] [list only] (part); SereÁne et al., 1958: 146, 238, ®gure 1D [list only] (part); Wu, 1983: 134 [name in Chinese]; Stevcic et al., 1988: 1310 [list only]

Material examined. Australia: One male (13.5Ö 13.9 mm) ( WAM 110-93 ), o Queensland, 165 m, coll. W. Good , 1964. One female (10.3Ö 11.0 mm) ( WAM 115-93 ), o Queensland, coll. W. Good , 1964. One male, two females ( QM W3323 ), 26ss31¾S, 153ss33 ¾E, 101±137 m,` Nimbus’ trawl, coll. A.J. Bruce , 26 July 1968. Five males, two females (10.6Ö 10.8 mm) ( QM W17007) , o Mission beach, northeast Queensland, 17ss53.7¾S, 146ss51.2 ¾E, 140±142 m, coll . CSIRO, (Commonwealth Scienti ®c and Industrial Research Organisation ) , R. V.`Soela’, 20 January 1986. One male ( AM P10127), between Newcastle and Manning, New South Wales, coll. Moller. One male ( AM P1953 ), o Coogee , New South Wales, 33ss55 ¾S, 151ss22 ¾E, coll. Thetis Expedition.

Diagnosis. Carapace pentagonal, rostrum long, tip of rostrum not deēxed; surfaces of carapace covered with some ¯at granules and fossae. Lateral carapace teeth sharp, tip usually directed laterally; base of teeth more slender. Infraorbital tooth blunt. Maxilliped 3 tuberculated, antero-externa l angle of merus auriculiform. Surface of male thoracic sternum with tubercles and fossae; median part of male thoracic sternite 4 depressed, followed by a median ridge. Male abdominal segment 7 mildly depressed; surface covered with several fossae. Chelipeds mildly granulated with scattered plumose setae; dorsal margin of palm usually with distinct lamelliform crests in females; carpus with distinct spine on distal inner angle; median, inner proximal and outer proximal part of merus with strong teeth, sometimes appearing lamelliform; inner proximal tooth on the merus is eroded and small in males, inner surface of basis-ischium with a tooth. Anterior margins of ambulatory merus and carpus distinctly cristate; posterior margins of merus usually with two very low, parallel crests; dactylus of leg 1 not much longer than those of other legs. G1 slender, sinuous; tip of G1 bent 90ss.

Sexual dimorphism. In addition to the di erence in the degree of lamelliform crests on the palm, the proximal spine on the anterior margin of the cheliped merus is small in males but large in females (®gure 12B, L).

Remarks. This is a relatively poorly known species. After examining a series of specimens from the eastern coast of Australia, we are con®dent that this species is valid.

Sakai (1938: 349) ®rst synonymized E. vicinus under E. zebra without providing any reasons. This decision was followed by SereÁne et al. (1958). However, in the present study, these two species are regarded as valid and distinct from each other. Eumedonus vicinus is easily di erentiated from E. zebra in having a blunt infraorbital spine (®gure 12M) and a smaller inner proximal tooth on the merus of the cheliped (more evident in males) (®gure 12L). Other minor characters are that in E. vicinus , the posterior crests on the ambulatory merus are weak (vs strong) (®gure 12E, K), abdominal segment 7 of the male is less depressed into the abdominal groove, and the lateral carapace tooth is relatively stouter (vs sharp) (®gures 12, 15).

The species recorded as `Eumedonus vicinus ’ by Huang (1989: 345, ®gure 315) from Zhejiang Province in China cannot be determined until his specimens can be re-examined. The ®gure provided was too schematic to be of much use.

Distribution. Only known from Australia.