EVOLUTION OF LABRAL SPINES IN ACANTHAIS, NEW GENUS, AND OTHER RAPANINE MURICID GASTROPODS

The new genus Acanthais is proposed for Acanthina brevidentata (Wood, 1828), a rapanine muricid gastropod common on tropical eastern Pacific rocky shores. It is distinguished by the presence of a labral spine, a central fold on the columella, and other characters of the shell and radula. Acanthais is one of at least five members of the Rapaninae in which a labral spine has evolved independently. This feature is an ex aggeration of an enlarged ventrally projecting crenation at the base o f the outer lip. Such crenations are widespread in the Rapaninae. Biog eographically, Acanthais is one of at least eight endemic tropical eas tern Pacific genera of gastropods with an origin during or after the P liocene.