Gonatonotus nasutus, 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 : 48-52

Gonatonotus nasutus n. sp.

(®gures 22, 23)

Eumedonus granulosus: Sakai, 1932: 42 , 55, plate 2: ®gure 3 [Izu Peninsula, Honshu Island, Japan]; Sakai, 1936: 18, 111, ®gure 52 [list only]; Sakai, 1938: 348, 360 [list only]; Sakai, 1940: 41 [list only]; Sakai, 1956: 25 [appendix list] [list only]; Ooishi, 1970: 91, plate 13: ®gure 7 [Futami Bay, Ogasawara Islands, Japan]; Sakai, 1976: 296 [volume in English], 178 [volume in Japanese], plate 99: ®gure 4 [colour plate] [Izu Peninsula, Honshu island; Ogasawara and Ryukyu islands, Japan]; Takeda and Miyake, 1976: 107 [list only]; Miyake, 1983: 212 [list only] [not G. granulosus ( MacGilchrist, 1905) , new combination]

Material examined. HOLOTYPE: male (11.3 Ö 10.3 mm) ( MNHN), ORSTOM number AC54 , Coral Sea, Chester ®eld Plateau, Bellona, Station CP 14, 21ss13.50 ¾S, 158ss50.20 ¾E, 66 m, coll. B. Richer de Forges , Chalcal Expedition, 1984.

PARATYPE: One female (12.0Ö 11.1 mm) ( MNHN), ORSTOM number AC55 , Coral Sea, Chester ®eld Plateau, Bellona, Station CP 14, 21ss13.50 ¾S, 158ss50.20 ¾E, 66 m, coll. B. Richer de Forges , Chalcal Expedition , 1984.

Others. Australia: One female (deformed rostrum) ( WAM 116-93 ), west of Lancelin Island, Western Australia, Station 4B, 31ss05¾S, 114ss55 ¾E, 113±123 m, beam trawl, bryozoa, coll. CSIRO (Commonwealth Scienti ®c and Industrial Research Organisation), 5 February 1964 . Two females ( WAM 113-93 ), west of Geraldton, Western Australia, Station 40, 28ss14 ¾S, 113ss28 ¾E, 110 m, beam trawl, bryozoa, coll. CSIRO, 4 February 1964 . One female (15.8Ö 13.7 mm) ( QM W18372), Julian Rocks, Byron Bay ,`Mackerel Boulders’, New South Wales, 28ss36.4 ¾S, 153ss37.7 ¾E, 20 m, marine, reef, symbiotic with urchin, Phyllacanthus parvispinus , coll. K. Sewell, 3 February 1993 . New Caledonia: One juvenile male, one juvenile female, one female (15.9 Ö 12.9 mm) ( MNHN), ORSTOM number AC56-58 , Touho, east coast, at low tide, living on sea urchin Phyllacanthus imperialis (Lamarck) , coll. B. Richer de Forges, no other data . Vanuatu: One juvenile female ( ZRC 1997.312 ), Station CP 1132, 15ss38.43 ¾S, 167ss02.80¾E, 161±182 m, coll. B. Richer de Forges, MUSORSTOM 8, N/O` Alis’, 11 October 1994 . One juvenile female ( MNHN), ORSTOM number AC112 , 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 . Philippines: One male ( WAM 26-67 ), southwest Pearl Bank, Sulu Archipelago , 31±124 m, sponges, coll. B. R. Wilson , R. V.`Pele’, 22 February 1964 .

Etymology. The name is derived from the Latin for`nose’, alluding to the very long rostrum of the species.

Diagnosis. Carapace pentagonal, rostrum very long, length 1.1 ±1.3 times width (mean 1.2); central part of ventral surface of rostrum raised; inner supraorbital teeth absent; regions well de®ned; surfaces of carapace, chelipeds and ambulatory legs covered with numerous tall and distinct granules; dorsal surface of carapace not pileiferous. 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 sharp, tip usually directed laterally; base of tooth stout and thick. Anterior part of interantennular septum very depressed. Maxilliped 3 quadrate; ischium rectangular, median oblique sulcus deep; merus squarish, antero-external angle of merus not distinctly auriculiform; exopod just below antero-externa l edge of merus. Abdomen seven-segmented, sutures for all segments visible; segment 7 depressed into the abdominal groove. Chelipeds granulose; dorsal margin of palm with small lamelliform crests; carpus with distinct spine on distal inner angle; proximal inner, outer and median parts of merus with two or three teeth each; chela short, stout, palm length two times length of ®ngers, palm height ca two to three times height of ®ngers. Anterior margins of ambulatory merus, carpus and propodus not cristate, lined with numerous sharp and rounded granules; posterior margin of merus with low, indistinct parallel crests; dactylus of leg 1 not much longer than those of other legs. G1 long, slightly more sinuous, distal part lined with short spines, tip bent approximately 90ss but slightly more inwards.

Sexual dimorphism. High lamelliform crests on dorsal margin of palm in females, low in males.

Remarks. Gonatonotus nasutus is very close to G. granulosus , but di ers in several key aspects, viz. the rostrum is consistently longer and more slender (the ratio of length to width is 1.2 in G. nasutus , 0.9 in G. granulosus ), the central part of ventral surface of the rostrum is raised in G. nasutus (not in G. granulosus ), the anterior part of the interantennular septum is very depressed in G. nasutus (not in G. granulosus ), and the tooth on the inner distal angle of the carpus of the cheliped is generally longer, more slender and more lamelliform (stout and dentiform in G. granulosus ). It appears that G. granulosus is restricted to the western Indian Ocean, whereas G. nasutus occurs in the waters of northern Australia and the western Paci®c.

There is some variation within this species. The two distal rostral lobes of some specimens may be fused, with the tip of the rostrum appearing rounded and entire (e.g. female, 15.9Ö 12.9 mm, MNHN, ORSTOM number AC56-58 ) and the ratio of rostral length to rostral width is 1.3. However, in the holotype and paratype, the tip of the rostrum has a distinct cleft, with two distinct, rounded rostral lobes; and the ratio of the rostral length to rostral width is 1.1. The largest female specimen (15.9 Ö 12.9 mm, MNHN, ORSTOM number AC56-58 ) seems to be di erent from the rest. Its male thoracic sternites 3±4 appear to be rather more sunken in, the granules in general appear to be ¯atter and the anterior margins of its ambulatory meri 2±4 have one to three very tall tubercles, which are absent in the smaller specimens. These features could possibly be related to size as they are not present in the smaller specimens. The specimen from the Philippines ( WAM 26-67 ) represent the only specimen examined from there. However, it ®ts into the current de®nition of this species .

The Japanese specimens attributed to E. granulosus by Sakai (1932, 1936 1938, 1940, 1956, 1976), Ooishi (1970), Takeda and Miyake (1976) and Miyake (1983) are probably referable to G. nasutus instead. The ®gures provided of the Japanese specimens by Sakai (1932, 1936, 1976) and Ooishi (1970) suggest that they are closer to G. nasutus than G. granulosus .

Distribution. Western and eastern Australia, New Caledonia, Vanuatu, Philippines and Japan.