Three Drills and One Cantharus
Some of the shells you’ll find on the beaches of Sanibel and Captiva are relatively similar. Take, for instances, three local species of drills and one drill-look-alike. The image shows photos of the shells and egg capsules of, in clockwise direction from bottom left, the Gulf Oyster Drill (Vokesinotus perrugatus), the Mauve-mouth Drill (Calotrophon ostrearum), the Sharp-ribbed Drill (Eupleura sulcidentata), all members of the family Muricidae, and the non-drilling Ribbed Cantharus (Hesperisternia multangula), a member of the Pisaniidae.
To get their meals, individuals of the three first species drill into the shells of other mollusks, and Ribbed Cantharus feeds on barnacles, apparently without resorting to drilling. The egg capsules in these and other species serve to protect the eggs and embryos from predators and the environment until they are ready to hatch. Each of these four species is treated individually in our SW Florida Shells Guide.