>I've seen many shells that have been eaten by an octopus that has bored
>holes in the shells, especially Cypraea.  Almost all holes in cowries are
>done by octopus.  I never heard of Marginellas boring holes, thats something
>new to me.

Octopus borings are quite distinctive. Acutely colical, with
scalloped edges and often radular scrapemarks on the surrounding
shell surface; the actual perforation is very small.

>Moon snails make a concave boring.  (Oyster) drills make a tubular hole.

A generalization which may not be accurate... if some muricids make
tapered holes. And any naticid boring would have to be mainly
cylindrical if it penetrated an extremely thick shell.