Slug-like naticid snail from northern Chile

Dear Brian,
This certainly qualifies as a sea slug imposter. I am pretty sure this is a snail of the Family Naticidae. They feed on other molluscs, both snails and bivalves, by drilling a hole through their shells. This is probably a species of Sinum, although you would need to consult an expert on the local fauna or an expert on naticids to be sure. In the upper right photo the head is at the bottom of the picture, and there is a 'headshield' with a posterior flap almost covering the somewhat flattened shell. In many ways it mimics a species of the sand-burrowing philinid cephalaspideans such as Philine aperta. The egg ribbon in your photo alongside is a typical egg ribbon of one subgroup of the naticids and is often called a sand collar, because in many species, sand grains are incorporated into the plastic-like ribbon in which the eggs are embedded.

Best wishes,
Bill Rudman