Morphological description and molecular characterisation of a new species of Leach, 1818 (Crustacea: Isopoda: Cymothoidae) from India.

A fish parasitic isopod recently reported from India as Bleeker, 1857, was re-examined and morphologically compared to five closely related species: Leach, 1818, Williams and Bunkley-Williams, 1986, Bleeker, 1857, Welicky and Smit, 2019 and Bariche and Trilles, 2006. This species was sequenced and compared to other known species based on mitochondrial cytochrome oxidase subunit I (COI) gene fragments Both morphological and molecular data corroborate that the species parasitising the clupeid fish (Valenciennes, 1847) from India should be recognised as a new species, and we describe n. sp. based on the holotype and paratype females. The key characters of n. sp. include the body being less than 4.0 times as long as wide; antennula article 3 anterodistal margin expanded, 1.2-1.4 times as wide as long; pleonite 1 concealed by pereonite 7 and lateral margin posteriorly produced; pereopods 1-4 with three nodules on dactylus; endopod of pleopods 3-5 with a proximomedial lobe and folding; and pleotelson ovate, with lateral margins converging smoothly to a caudomedial point.