Abstract

The relationship between shell form and mode of life in gastropods is important to the interpretation of fossils, but has been little explored owing, in part, to the great diversity of gastropod shells. Infaunal gastropods that actively bury in sand must conform to the demands of moving efficiently and noiselessly through a dense granular medium, but which shell characters reflect these demands and how infaunal gastropods differ from surface-dwelling (epifaunal) species remain incompletely answered questions. Here, I survey infaunal and epifaunal Indo-West Pacific members of four families (Cerithiidae, Mitridae, Costellariidae and Conidae) and consider more broadly the distribution of shell traits that confer streamlining and other potential benefits to infaunal species. Sand-burying cerithiids, mitrids and costellariids (but not conids) have on average slenderer shells than their epifaunal counterparts. The only shell features unique to sand-burying gastropods are terraced axial ribs, spiral cords or sutures, in each of which the trailing edge is steeper than the leading edge in the direction of movement; but not all infaunal gastropods have such features. An angular profile, wide umbilicus, high-relief shell sculpture and limpet-like shell is exclusive to surface-dwelling species. Specializations to the infaunal habit are more common and better expressed in the Indo-West Pacific than in tropical America.

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