Molecular and morphological evidence revealed the existence of two cryptic species of Costasiella Pruvot-Fol, 1951 in the Bahamas. A review of the literature indicates that one of these species is the western Atlantic widespread species Costasiella ocellifera (Simroth, 1895), whereas the other species is undescribed. The new species is externally similar to Costasiella ocellifera but can be distinguished by the absence of a penial stylet and the radular morphology. Phylogenetic and species delimitation analyses confirm that the new species is genetically distinct from C. ocellifera. The new species has only been found in the Bahamas, but there are possible records from Cuba and Jamaica.