Glyptothoa sagara gen. and sp. nov. is described from the host fish Glyptophidium macropus Alcock, 1894 (Ophidiidae), at depths 300 to 650 metres from the southwest coast of India. The mitochondrial cytochrome c oxidase subunit I (COI) gene of the species was sequenced and compared with other closely related branchial cymothoid genera. Both morphological and molecular data corroborate the inclusion of this parasitic isopod as a new genus, and we describe Glyptothoa sagara gen. and sp. nov. The following combinations of characters characterise the genus: cephalon immersed in pereonite 1; dorsum vaulted; all coxae visible in dorsal view; coxae shorter than or as long as pereonites; pereonites 4–7 slightly decrease in width towards one side, slightly asymmetrical, lateral margins slightly constricted, in hunched side; relatively wide pleon, with large lateral gaps between pleonites; antennula narrowly separated by rostrum, slender, shorter than antenna; antenna with 13 articles, buccal cone obscuring antennal bases; brood pouch arising from coxae 1–4, 6; oostegite 1 bilobed; pleopods rami all simple, without proximomedial lamellar lobe, without folds or thickened ridges. The adult life stages, such as females (ovigerous and non-ovigerous), males and transitional stage of the new species are described. The species is currently known only from the type locality and the type host. The ecological remarks of the newly described taxon are also provided. The following species are transferred from Elthusa Schioedte and Meinert, 1884: Glyptothoa myripristae (Bruce, 1990) comb. nov., Glyptothoa propinqua (Richardson, 1904) comb. nov. and Glyptothoa caudata (Schioedte and Meinert, 1884) comb. nov.
Marine fish parasite, Branchial cavity, Cytochrome c oxidase subunit I, Cymothoidae, New genus, Indian Ocean, Phylogeny
