Molecular Phylogeny and Morphological Distinctions of Two Popular Bivalves, Ctenoides scaber and Ctenoides mitis

One of the most well-known species in the bivalve family Limidae (d’Orbigny, 1846) is the brightly colored Ctenoides scaber (Born, 1778), commonly known as the rough file clam or flame scallop. Distinguishing this bivalve from its close relative, C. mitis (Lamarck, 1807), can be difficult using only morphological features and has led to much taxonomic confusion throughout the literature. In this study, morphological characters were compared to a molecular phylogeny constructed using three genes (COI, 28S, and H3) in order to differentiate C. scaber and C. mitis. The phylogeny recovered two well-supported clades that differ significantly in shell rib numbers, but not tentacle colors. The two species were then placed in a larger phylogenetic context of the Limidae family, which revealed the need for further systematic revision across genera. As these bivalves are popular in aquaria, cannot be tank-raised, and have been overcollected in the past, proper species identification is important for assessing sustainable collection practices.