Systematics of Corbulidae supported by anatomical and conchological studies remains confused and controversial because of the considerable phenotypic plasticity of their shells. Ultrastructural spermatozoan study and molecular analyses have been performed to contribute valuable information, which could be used in taxonomy. Electron microscopy was used to analyse sperm cells from specimens of Caryocorbula (Gardner, 1926) exhibiting shell differences. The spermatozoon was of the aquasperm type, showing short acrosome, barrel-shaped nucleus, midpiece composed of four spherical mitochondria and simple flagellum. In addition, about 860 base pairs of mitochondrial large ribosomal subunit (16S rRNA) were sequenced from each individual. The consistent similarity shared by spermatozoa and DNA sequences from all studied specimens indicated that they belonged to one coherent unit, Caryocorbula caribaea (d’Orbigny, 1853), despite the extraordinary plasticity exhibited by their shells.