Cryptic yet colorful: anatomy and relationships of a new genus of Cerithiidae (Caenogastropoda, Cerithioidea) from coral reef drop‐offs

Abstract

AbstractCerithium koperbergi is a rare gastropod of the family Cerithiidae from the tropical Indo‐West Pacific. The species has a small, unusual shell and often inhabits deeper water, fore‐reef habitats that are atypical for the genus. Anatomical investigations reveal that it possesses a combination of features heretofore considered diagnostic of two main cerithiid subfamilies: Cerithiinae and Bittiinae. While the shell is bittiine, the animal lacks mesopodial pedal glands and possesses a seminal receptacle (vs. a spermatophore bursa) in the lateral lamina of the oviduct, which are considered to be cerithiine features. Re‐evaluation of the anatomy of Bittium reticulatum, the type species of Bittium, indicates the defining anatomical difference in oviduct anatomy between the two subfamilies does not stand up to closer scrutiny. Partial mitochondrial cytochrome c oxidase I (COI) sequences support the interpretation that C. koperbergi is a species complex around the western Pacific rim comprising three divergent mitochondrial lineages. Bayesian analysis of partial mitochondrial COI and 16S rRNA sequences confirm the placement of the C. koperbergi complex within a monophyletic Bittiinae, despite the apparent absence of a unifying anatomical feature. Species in the C. koperbergi complex are here united in Pictorium nov. gen. and two species are described as new. It is hypothesized that features of the midgut may be diagnostic of the Bittiinae, but more comparative data are needed.