This image shows just a small sampling of the diversity found in gastropod shell designs. Malacology is the study of molluscs, and across the globe there are a number of both professional and amateur malacologists that enjoy studying and collecting mollusc shells. Unfortunately, however, the popularity of many of the more beautiful forms has lead to the demise of several species that are hunted and killed exclusively for their valuable shells, which is rather like killing an elephant for its ivory tusks! uttlefishes are very similar to squids in their anatomy and swimming capabilities. The principal difference between the two groups is the fact that cuttlefishes have a small, curved shell covered by the mantle (the cuttlebone often seen in bird cages) whereas squids have only a vestigial skeleton consisting of a curved plastic-like support called a pen.