Taxonomy of myid bivalves from fragmented brackish-water habitats in India, with a description of a new genus Indosphenia (Myida, Myoidea, Myidae)

A group of small bivalves inhabiting Indian brackish-water estuaries and lagoons (known locally as backwaters), variously assigned to Corbula, Cuspidaria, and Sphenia, are reviewed and, based on shell characters, shown to be congeneric. Molecular (COI) and morphological data indicate that this group belongs to the family Myidae. Furthermore, the combined data suggest that these Indian myids are a sister taxon of the genus Sphenia. The Indian material studied herein exhibits a functional morphology typical of infaunal bivalves, whereas typical Sphenia are nestling and epibyssate. A new genus, Indosphenia, is thus erected for the Indian group and includes five species, one of which is named in this study. Indosphenia kayalum Oliver, Hallan & Jayachandran, gen. et sp. n. is described from the Cochin Backwater on the western coast of India. Cuneocorbula cochinensis (Preston, 1916) is transferred to Indosphenia. Additionally, the west coast taxa I. abbreviata (Preston, 1907), I. abbreviata chilkaensis (Preston, 1911) and I. sowerbyi (EA Smith, 1893) are recognised herein. Corbula alcocki Preston, 1907, Corbula gracilis Preston, 1907, Corbula calcaria Preston, 1907 and Corbula pfefferi Preston, 1907 are placed in synonymy with I. abbreviata, and Cuspidaria annandalei Preston, 1915 is synonymised with I. abbreviata chilkaensis.