Eumedonus brevirhynchus, 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 : 24-29

Eumedonus brevirhynchus n. sp.

(®gures 5±7)

Material examined. HOLOTYPE: male (7.8Ö 7.5 mm) ( MNHN), Large Southern Reef (Grand Re Âcif Sud), Station 373, 22ss28¾S, 167ss11 ¾E, 52±57 m, coll. B. Richer de Forges, 21 January 1989.

PARATYPES: New Caledonia: Three males, three females ( ZRC 1997.163 ±168), same data as holotype. One male (11.8Ö 12.7 mm) ( MNHN) , ORSTOM number AC1 , Landsdowne Shoals, Fairway, Coral Sea, Station CP 2, 20ss31.50 ¾S, 161ss06.45 ¾E, 88 m, coll. B. Richer de Forges, Chalcal Expedition , 1984. One female (10.3 Ö 10.6 mm) ( MNHN) , ORSTOM number AC2 , Landsdowne Shoals, Fairway, Coral Sea, Station CP 2, 20ss31.50 ¾S, 161ss06.45¾E, 88 m, coll. B. Richer de Forges, Chalcal Expedition , 1984. One male (9.4Ö 10.3 mm) ( MNHN) , ORSTOM number AC3 , Chester ®eld Islands, Station CP27, 20ss21.29 ¾S, 160ss58.60 ¾E, 74±75 m, coll. B. Richer de Forges, Corail 2 Expedition, 22 July 1988 . Six males, 10 females ( MNHN), ORSTOM number AC4 ±19, Landsdowne Shoals, Fairway, Coral Sea, Station CP2, 20ss31.50 ¾S, 161ss06.45¾E, 88 m, coll. B. Richer de Forges, Chalcal Expedition, 1984. Two males , one female ( MNHN), ORSTOM number AC20 ±22, Landsdowne Shoals, Fairway, Coral Sea, Station D 11, 20ss31.52 ¾S, 161ss06.60 ¾E, 83 m, coll. B. Richer de Forges, Chalcal Expedition, 1984. One female ( MNHN), ORSTOM number AC23 , Landsdowne Shoals, Fairway, Coral Sea, Station D12, 20ss31.33 ¾S, 161ss06.51 ¾E, 80 m, coll. B. Richer de Forges, Chalcal Expedition, 1984. One male , two females ( MNHN), ORSTOM number AC24 ±26, Landsdowne Shoals, Fairway, Coral Sea, Station D3, 21ss14.00 ¾S, 162ss16.40 ¾E, 120±150 m, coll. B. Richer de Forges, Chalcal Expedition, 1984. One male (5.6Ö 6.0 mm) , one female (9.0Ö 9.2 mm) ( MNHN) , ORSTOM number AC27 ±28, Chester ®eld Islands, Station CP24, 20ss27.35 ¾S, 161ss04.70¾E, 74±75 m, coll. B. Richer de Forges, Corail 2 Expedition, 22 July 1988 . Five males, one female ( MNHN), ORSTOM number AC29 ±34, Chester ®eld Islands, Station CP29, 20ss31.35 ¾S, 160ss52.72¾E, 79±84 m, coll. B. Richer de Forges, Corail 2 Expedition, 22 July 1988 . Four males, three females ( MNHN), ORSTOM number AC35 ±41, Chester ®eld Islands, Station CP23, 20ss30.60 ¾S, 161ss03.55 ¾E, 80±83 m, coll. B. Richer de Forges, Corail 2 Expedition, 22 July 1988 . One female ( MNHN), ORSTOM number AC42 , Norfolk, Station DW 81, 22ss38.2 ¾S, 167ss34.8 ¾E, 110 m, coll. B. Richer de Forges, SMIB 5 Expedition, 9 September 1989 . One juvenile male ( MNHN), ORSTOM number AC43 , Station 0149, 19ss07.6¾S, 163ss22.7 ¾E, coll. B. Richer de Forges, MUSORSTOM 4 Expedition, 14 September 1989 . One juvenile female ( MNHN), ORSTOM number AC44 , Large Southern Reef (Grand Re Âcif Sud), 22ss40¾S, 167ss11 ¾E, coll. B. Richer de Forges, 21 January 1989 .

Others. Vanuatu: Two males, two females ( MNHN), ORSTOM number AC92 ±95, Station CP 1133, 15ss38.83 ¾S, 167ss03.06 ¾E, 174±210 m, coll. B. Richer de Forges, MUSORSTOM 8, N/O` Alis’ , 11 October 1994 . Two males, two females ( MNHN), ORSTOM number AC96 ±99, Station CP 1132, 15ss38.43 ¾S, 167ss02.80 ¾E, coll. B. Richer de Forges, MUSORSTOM 8, N/O` Alis’ , 11 October 1994 . Four males, one juvenile, seven females ( MNHN), ORSTOM number AC100 ±111, Station CP 1131, 15ss38.41 ¾S, 167ss03.52¾E, coll. B. Richer de Forges MUSORSTOM 8, N/O` Alis’ , 11 October 1994 . Philippines: One male ( WAM 362 ±73), Zal Island, southwest Pearl Bank, Sulu Archipelago , coll. B. R. Wilson , R. V.` Pele’ , 22 February 1964 .

Etymology. The name is derived from the Latin for`short nose’, alluding to the relatively short rostrum of the species. Used as a noun in apposition.

Diagnosis. Carapace pentagonal, rostrum short, length 0.5±0.7 times width (mean 0.6), tip of rostrum not deēxed; inner supraorbital teeth absent; regions well de®ned; surfaces of carapace, chelipeds and ambulatory legs covered with numerous granules; distal part of rostrum usually hairless. Antero- and posterolateral margins clearly demarcated by distinct angle or sharp tooth; anterolateral margin entire, without teeth or lobes, distinctly shorter than posterolateral margin. Lateral carapace teeth very stout, tip usually directed laterally; base of tooth stout and thick; posterior part of carapace tooth bending gently towards metabranchial region. Antennules folding obliquely, ca 45ss from horizontal; antennular fossae oblique. Antero-external angle of merus of maxilliped 3 distinctly auriculiform. Median part of male thoracic sternite 4 slightly depressed. Male abdominal segment 7 not markedly depressed into the abdominal groove. Chelipeds granulose; dorsal margin of palm usually with distinct lamelliform crests in females; carpus with distinct spine on distal inner angle; inner surface of basis-ischium, median, inner and outer proximal part of merus with a strong tooth, structure sometimes appearing lamelliform; chela short, stout, palm length two times length of ®ngers, palm height ca two to three times height of ®ngers; ®ngers sometimes carinate, pollex not bent downwards. Anterior margins of ambulatory merus and carpus distinctly cristate; posterior margins of merus usually with two distinct parallel crests; dactylus of leg 1 not much longer than those on other legs. G1 long, slender, distal part lined with short spines, tip bent approximately 45ss.

Remarks. Eumedonus brevirhynchus di ers markedly from all congeners in having proportionately the shortest rostrum in the genus. In fact, the short rostrum in E. brevirhynchus is reminiscent of that of Gonatonotus pentagonus . The excellent series of specimens from New Caledonia and Chester®eld Islands demonstrates that the shape and length of the rostrum is constant. The form of the tip of the rostrum also di erentiates E. brevirhynchus from its nearest congener, E. niger , in that the cleft is distinctly deeper. In E. niger , the lateral carapace tooth is very stout, curving backwards and downwards into the metabranchial region, but in E. brevirhynchus , the lateral carapace teeth are less stout and laterally directed. Adult E. brevirhynchus also di er from E. vicinus and E. niger in usually not having long setae at the tip of the rostrum. In smaller specimens of E. brevirhynchus , however, the distal dorsal part of the rostrum is sometimes densely covered with setae. In addition, male abdominal segment 7 of E. brevirhynchus is not as deeply depressed into the abdominal groove as compared to that of E. niger .

In smaller specimens of E. brevirhynchus , the rostrum appears to be even shorter (®gure 7D) and the ambulatory legs are less cristate (®gure 7E). The G1 varies somewhat, with the tip bent at angles of 45ss or 90ss (®gures 6G, 7B). A specimen collected from the Philippines ®ts into the current concept of E. brevirhynchus and is thus referred there.

Distribution. Known only from New Caledonia, Vanuatu, Chester®eld Islands and probably the Philippines.