A revision of Eumedonus H. Milne Edwards, 1834 and Gonatonotus White, 1847 (Crustacea: Decapoda: Brachyura: Eumedonidae), two genera of crabs symbiotic with sea urchins

The eumedonid genera Eumedonus H. Milne Edwards, 1834 and Gonatonotus White, 1847, are revised. Members of both genera are obligate symbionts with sea urchins. Eumedonus is separated from Gonatonotus mainly by the presence or absence of crests on the merus of the ambulatory legs. Eumedonus, as here defined, contains five species, viz. E. niger H. Milne Edwards, 1834 (type species), E. vicinus Rathbun, 1918, E. zebra Alcock, 1895, E. brevirhynchus n. sp., and E. intermedius n. sp. Gonatonotus, as here re-diagnosed, includes three species, viz. G. pentagonus White, 1847 (type species), G. granulosus (MacGilchrist, 1905), n. comb. and G. nasutus n. sp.