Revision of the fish parasitic branchial cymothoid genus Agarna Schioedte & Meinert, 1884 (Crustacea: Isopoda: Cymothoidae), with description of Gibbothoa gen. nov.

The genus Agarna Schioedte & Meinert, 1884, is reviewed and rediagnosed. The female, male and transitional stages of Agarna cumulus (Haller, 1880), the senior synonym of the type species, are redescribed based on the newly designated lectotype and additional material collected from the Caribbean parasitising doctorfish, Acanthurus chirurgus (Bloch, 1787), blue tang surgeonfish Acanthurus coeruleus Bloch & Schneider, 1801, and barber surgeonfish Acanthurus bahianus Castelnau, 1855. The types and non-type specimens of Agarna malayi Tiwari, 1952, were re-examined and found to differ from the generic characters of Agarna . We thus propose Gibbothoa gen. nov. distinguished by the following combination of characters: an asymmetrical and hunched body, with one side of the body more or less straight and the other side strongly recurved; an irregular pereonite 1 anterior margin, anterolateral margin conspicuously incised, produced into narrow projections; pereonites all asymmetrically distorted; the pleon wider than pereonite 7; coxae more or less equal on both sides; pereonites 2–7 abruptly increasing in width toward one side, but laterally not expanded from the pereopod basis; the pleotelson broadly rounded and symmetrical; the antenna thicker than the antennula; a maxilliped without an oostegite lobe; and the pleopod 5 endopod with fleshy lobes. Agarna pustulosa (Pillai, 1954) is placed into synonymy with Gibbothoa malayi (Tiwari, 1952) comb. nov., based on morphological and molecular examination of fresh specimens collected from the type host. The taxonomic status of Agarna bengalensis Kumari et al., 1990, is also assessed, and the species is regarded as a species inquirendum .