An Evaluation of the Taxa Muricopsis and Risomurex (Gastropoda: Muricidae), with One New Species of Risomurex

Abstract

Risomurex is considered to be a subgenus of Muricopsis, being distinguished from the latter by lacking true varices, having instead only rounded axial ridges. All species are in the Atlantic Ocean with the majority found in the tropical western Atlantic; three are from West Africa; one is from temperate South America . One fossil species, presumed to be the ancestral form, occurs in the Burdigalian of France and Florida. The habitat of all is extremely shallow water, under rocks or coral boulders, the deepest known occurrence is no more than 30 m (for roseus) but most are intertidal. All are small; the largest (necocheanus and gilbertharrisi) are under 25 mm in height and most are about 15 mm. In all, there are 11 species recognized: two fossil forms; one Pliocene-Recent form; the remaining all Recent, of which one is a new species, M. (R.) withrowi , described from northern South America.