Gonatonotus 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 : 40

Gonatonotus White, 1847

Gonatonotus White, 1847a: 125 [nomen nudum]

Gonatonotus White, 1847b: 57 ; White, 1847c: 62 [text identical to White, 1847b]; Adams and White, 1848 ±1849: 32; Neumann, 1878: 17; Miers, 1879a: 670; Flipse, 1930: 19; Gordon, 1934: 65, 66; SereÁne et al., 1958: 137, 139 [in key], 231, 238; Stevcic et al., 1988: 1310, 1317

Eumedonus: Monod, 1938: 112 (part); Buitendijk, 1950: 71 (part); Balss, 1957: 1631 (part) [not Eumedonus H. Milne Edwards, 1834 ]

T ype species. Gonatonotus pentagonus White, 1847 , by monotypy. Gender of genus masculine.

Etymology. The name was derived from the Greek `gonatos ’ for knee or joint and `notos ’ for back, probably alluding to the angled lateral carapace margins of the type species. Gender masculine.

Diagnosis. Carapace distinctly pentagonal in shape, rostrum long or short; inner supraorbital teeth absent; regions not well de®ned; surfaces of carapace, chelipeds and ambulatory legs covered with numerous small sharp to rounded granules; dorsal surface of carapace usually not pileiferous. Antero-and posterolateral margins clearly demarcated by distinct angle or sharp tooth; anterolateral margin entire, without teeth or lobes, shorter than posterolateral margin. Antennules folding obliquely, ca 45ss from horizontal. Antennal segment 2 short, length to width ratio 1.2±1.6. Chelipeds granulose; dorsal margin of palm sometimes with large granules but never cristate in either sex; carpus with distinct spine on inner angle; anterior surfaces of basis-ischium and proximal part of merus with a low tooth or short, blunt spine each, neither structure appearing lamelliform; chela short, stout, palm length two times length of ®ngers, palm height ca two to three times height of ®ngers; ®ngers deeply grooved, appear carinate, pollex not bent downwards. Ambulatory legs, dorsal margins of merus, carpus and propodus not cristate, lined with numerous sharp and rounded granules; posterior margin of merus may have low or faint parallel crests; dactylus of leg 1 not much longer than those of other legs. G1 long, slender.

Remarks. Balss (1922), when reporting a specimen from the Ogasawara Islands (which is actually Echinoecus pentagonus (A. Milne Edwards, 1879; unpublished data), stated`Die Form (of Eumedonus s.l.) hat eine groûe Ahnlichkeit mit Gonatonotus pentagonus Ad. u. White; ob nicht beide identisch sind?’ without providing any reasons. Gordon (1934: 65) referred to Balss (1922) when she suspected that the di erence between Eumedonus and Gonatonotus was merely in the length of the rostrum. Monod (1938) was the ®rst to formally synonymize Gonatonotus and Echinoecus under Eumedonus , albeit with doubt. Nonetheless, this established a very broad concept for Eumedonus and was followed by Buitendijk (1950). As mentioned for Eumedonus, SereÁne et al. (1958) had retained Gonatonotus White, 1847 , as provisionally distinct from Eumedonus H. Milne Edwards, 1834 .

The di erences between Gonatonotus and Eumedonus have already been discussed under the latter genus. The rede®ned concept of the genus Gonatonotus includes three species, one of which is described as new. The three species are: G. pentagonus White, 1847 , G. granulosus ( MacGilchrist, 1905) , n. comb. and G. nasutus n. sp.