Gonatonotus pentagonus White, 1847

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 : 41-48

Gonatonotus pentagonus White, 1847

(®gures 16±19)

Gonatonotus pentagonus White, 1847a: 125 [nomen nudum] [type locality`Eastern Seas, Borneo’]

Gonatonotus pentagonus White, 1847b: 58 [type locality`coast of Borneo’]; White, 1847c: 62 [text identical to White, 1847b]; Adams and White, 1848 ±1849: 33, plate 6: ®gure 7, 7a [colour plate] [Borneo]; Miers, 1879b: 19 [Billiton Island= Belitung island, Java Sea, Indonesia]; Haswell, 1880: 455 [Port Denison, Queensland, Australia]; Haswell, 1882: 38 [Port Denison, Queensland, Australia]; Miers, 1884: 182, 204 [Thursday Island, Torres Strait, Queensland, Australia]; Walker, 1887: 109 [ Singapore] [list only]; Ortmann, 1894: 6, 48 [list only]; Rathbun, 1910: 321 [Kram, Kahdat, Chuen and Kut Island, Gulf of Thailand]; Gordon, 1934: ®gure 32c [holotype re-examined]; Suvatti, 1950: 152 [list only]; SereÁne et al., 1958: 232, 238 [list only]; SereÁne, 1968: 63 [list only]; Stevcic et al., 1988: 1310 [list only]

Gonatonotus sp. Roxas, 1930: 18 [Puerto Galera, Mindoro island, Philippines]

Echinoecus pentagonus: Naiyanetr, 1980: 31 (list only) [not Echinoecus pentagonus (A. Milne Edwards, 1879) ]

Eumedonus pentagonus: Buitendijk, 1950: 71 [Siglap, Singapore]; Johnson, 1962: 288 [ Singapore] [not Eumedon pentagonus A. Milne Edwards, 1879 ]

Material examined. HOLOTYPE: female (10.1Ö 12.0 mm) ( BMNH 1847.21 ), eastern seas, Borneo, coll. Capt. Sir Edw. Belcher.

Others. Indonesia: One male (12.5Ö 15.3 mm) ( BMNH 78.11 ), Java seas, 3ss21¾S,108ss39 ¾E, 22 m, coll. J. G. Je reys, no other data . Singapore: One female ( ZRC 1984.785 8), Sudong Island, dredged, coll. D. S. Johnson, 16 March 1953. One juvenile female ( ZRC 1984.785 7), Pawai Island , shell, gravel substratum, on Cidaris sp. , 9 m, coll. D. S. Johnson, December 1952 . Thailand: One male, one female ( BPBM 1776 ), Koh Chuen Island, 30 fms water, shell bottom, Gulf of Thailand, coll. Th. Mortensen, February 1900. Three males, three females (two ovigerous) ( USNM 39707 ), Koh Kram, 30 fms, Gulf of Thailand , coll. Th. Mortensen, 1 and 21 March 1900. One male, one female (ovigerous) ( USNM 39708 ), between Koh Rin and Cli Rock , north of Koh Kram , 15 fms, Gulf of Thailand , coll. Th. Mortensen, 2 March 1900 . Australia: One female ( QM W18673), Northwest Shelf, Western Australia, Station 01B13BT, 19ss45.7 ¾S, 117ss52.0 ¾E, 54 m, trawled, marine, sublittoral, coll. CSIRO (Commonwealth Scienti®c and Industrial Research Organisation), R. V.`Soela’, 20 February 1983. One male ( QM W18678), Northwest Shelf, Western Australia, Station 04B14BT, 19ss43.7¾S, 117ss54.4 ¾E, trawled, marine, sublittoral, coll. CSIRO, R. V.`Soela’, 2 September 1983. One male, one female ( QM W18685), Northwest Shelf, Western Australia, Station 04B17BT, 52 m, trawled, marine, sublittoral, coll. CSIRO, R. V.`Soela’, 4 September 1983. One male ( QM W18669), Northwest Shelf, Western Australia, 19ss57.9 ¾S, 117ss49.3 ¾E, Station 03D07BT, 40 m, trawled, marine, sublittoral, coll. CSIRO, R. V.`Soela’, 26 June 1983. One female ( QM W18677), Northwest Shelf, Western Australia, 19ss56.8¾S, 117ss53.4 ¾E, Station 02B02BT, trawled, marine, sublittoral, coll. CSIRO, R. V.` Soela’ , 22 February 1983. One male ( BMNH 82.7 ), Thursday Island , Torres Strait , coll. D. Coppinger, H.M.S.` Alert’ . One male ( BMNH 81.31 ), Thursday Island , Torres Strait , coll. June 81. Two females ( BMNH 62.35 ), northeast Australia , no other data. Three females ( BMNH 1948.4 .29.7±9), Cocos Keeling Islands , coll. Gibson Hill, no other data .

Description. Carapace pentagonal, rostrum short, slightly beyond orbits; inner supraorbital teeth absent; regions well de®ned; surfaces of carapace, chelipeds and ambulatory legs covered with numerous ¯attened granules; dorsal surface of carapac e 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 stout, tip usually directed laterally; base of tooth stout and thick. Antennules folding obliquely, ca 45ss from horizontal; antennular fossae oblique. Antenna free, does not ®ll orbital hiatus, reaching into orbit; antennal basal segment rectangular. Eyes well developed, ®lling orbit; cornea distinct, pigmented; infraorbital teeth small but distinct, subhepatic teeth absent. Anterior surface of epistome not very low; posterior margin appears entire because of two fused truncate median lobes. Pterygostomial, subhepatic, suborbital regions granulated. Maxilliped 3 quadrate; ischium rectangular, median oblique sulcus deep; merus squarish, antero-external angle of merus not distinctly auriculiform; exopod just below antero-external edge of merus. Sutures between male thoracic sternites 1 and 2 indistinct, 2 and 3 distinct, shallow; between 3 and 4 interrupted; surface of male thoracic sternite 1 smooth, of sternite 2±3 granulated; lateral clefts small. Abdomen seven-segmented, sutures for all segments visible; segment 7 not very depressed into abdominal groove. Chelipeds granulose; dorsal margin of palm does not have distinct lamelliform crests; carpus with distinct spine on distal inner angle; proximal median part of merus with a strong tooth; no tooth at inner proximal margin but replaced by a row of tall tubercles appearing serrated; 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, carpus and propodus not cristate, lined with numerous sharp and rounded granules; posterior margin of merus does not have parallel crests; dactylus of leg 1 not much longer than those of other legs. G1 long, slender, distal part lined with short spines, tip bent approximately 90ss. G2 relatively short, distal segment short.

Sexual dimorphism. None.

Remarks. Specimens reported by Miers (1879b, 1884), Haswell (1880, 1882), Rathbun (1910) and Roxas (1930) seem to ®t the current understanding of this species. Naiyanetr (1980) incorrectly reported a specimen from Thailand as `Echinoecus pentagonus (White, 1847) ’. This is possibly due in part to the confusion in Eumedonus s. l. His record is now re-determined as G. pentagonus . Buitendijk (1950) referred to a female specimen, in her possession as `Eumedonus pentagonus ’, from Singapore, but her specimen cannot be traced, it is not in the ZRC or RMNH. Still, from her description, there can be little doubt that her specimens ®t well into the current concept of G. pentagonus .

The two ZRC female specimens from Singapore had been incorrectly reported as `Eumedonus pentagonus ’ by Johnson (1962) (not Eumedon pentagonus A. Milne Edwards, 1879 ). The smaller female ( ZRC 1984.785 7) is still rather young, with the abdomen triangular and not covering most of the sternum, and the pleopods are poorly developed. The other female ( ZRC 1984.785 8) is ovigerous but none of the eggs are well developed. Both specimens agree very well with G. pentagonus s. str. The specimens from Indonesia and Australia agree in almost all respects with the holotype female and specimens from Singapore.

Distribution. On both Sunda and Sahul Shelves.

Gonatonotu s granulosu s ( MacGilchrist, 1905) n. comb. (®gures 20, 21)

Eumedonus granulosus MacGilchrist, 1905: 253 [type locality Persian Gulf]; Alcock, Annandale and MacGilchrist, 1907: plate 77, ®gure 2, 2a [Persian Gulf]; Rathbun, 1911: 194, 259 [Amirante Islands, Indian Ocean]; Flipse, 1930: 80, 90 [list only]; Ward, 1942: 53, 78 [ Mauritius]; Stephensen, 1946: 114, 204 [list only]; Barnard, 1954: 96, ®gure 1 [Delagoa Bay= LourencËo Marques Bay, Mozambique, East Africa]; Barnard, 1955: 3, 18 [Delagoa Bay= LourencËo Marques Bay, Mozambique, East Africa]; Barnard, 1958: 4 [ Mozambique Island, Mozambique, East Africa]; SereÁne et al., 1958: 146 [in key], 237, ®gure 1G, 1H [list only] (part); Guinot, 1964: 7, 9, 14, ®gure 4 [Dahlak Archipelago, Red Sea]; Michel, 1964: 7 [ Mauritius]; Guinot, 1966: 299 [list only]; SereÁne, 1968: 63 [list only] (part); Kensley, 1969: 151, 155, 178, ®gure 1 [ Mozambique, East Africa]; SereÁne, 1977: 49 [ Seychelles]; Kensley, 1981: 41 [list only]; Wu, 1983: 134 [name in Chinese]; Stevcic et al., 1988: 1310 [list only] (part)

Eumedonus zebra: Lenz, 1905: 344 [Kokotoni, Zanzibar] [not Eumedonus zebra Alcock, 1895 ]

Material examined. Zanzibar: One female ( BMNH 1953.5.28. 4), beach at Kivengwa , presented by J. D. Robertson (Prace Memorial Museum), no other data . Madagascar: Seven males (11.6Ö 11.1 mm, 7.5Ö 7.2 mm, 9.5 Ö 9.2 mm), ten females ( MNHN), ORSTOM number AC113 ±129, northwest coast, Mitsio Island, 30 m, trawl, sand substratum, probably on echinoderms, coll. A. Crosnier, February 1960 . Seychelles: One male, one female ( RMNH D42519), west of Poivre Atoll , Station Sey. 778, 5ss46¾S, 53ss11¾E, 57 m, Agassiz trawl, soft bottom, from echinoids, coll. NIOP-E,`Tyro’ Seychelles Expedition 1992/9, 1 January 1993 . Amirante Islands : One male, one female (damaged) ( USNM 41452 ), western Indian Ocean, Station E11, 46 ± 146 m, coll. H.M.S.`Sealark’, 11 October 1905 .

Diagnosis. Carapace pentagonal, rostrum long, length 0.8±1.1 times width (mean value 0.9); central part of ventral surface of rostrum not 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 not depressed. Maxilliped 3 quadrate; ischium rectangular, median oblique sulcus deep; merus squarish, antero-external angle of merus not distinctly auriculiform; exopod just below antero-external 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; ®ngers sometimes carinate, pollex not bent downwards. 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. The current series of specimens examined agrees well with the description of MacGilchrist (1905). Specimens ( USNM 41452) reported by Rathbun (1911) were examined; they were badly damaged but still clearly identi®able as G. granulosus . From the various descriptions and illustrations by Alcock et al. (1907), Ward (1942), Barnard (1954, 1955, 1958), Guinot (1964), Michel (1964), Kensley (1969) and SereÁne (1977), their specimens also ®t into the current de®nition of this species. We agree with Monod (1938: 111) that the specimen reported by Lenz (1905) as `Eumedonus zebra ’ is in fact G. granulosus .

This species shares close a nities with G. nasutus n. sp. (di erences discussed under G. nasutus ).

Some variation is observed in the current series of specimens. The rostral tips of some specimens may appear to be almost fused (®gure 21M, N), instead of bilobed as observed in most specimens (®gure 21A).

This species has an overlapping distribution with E. zebra in the Indian Ocean. But the di erences between the two species are distinct, viz. the antero-external angle of the merus is not distinctly auriculiform in G. granulosus (distinctly so in E. zebra ), the anterior margins of all ambulatory meri are not cristate and lamelliform in G. granulosus (distinctly so in E. zebra ), and G. granulosus is far more granulose (much smoother in E. zebra ).

Distribution. Only known from the Indian Ocean.