According to medieval bestiaries, the aspidochelone is a supersize whale ,sea turtle,or sea monster with spines on the ridge of its back. No matter what form it is, it is always huge, and usually first mistaken for an island as it carries what appears to be beaches on the upper part of its body.
Believing it to be an island, sailors beach their ship alongside the beast, disembark, and plant stakes to tie up the ships. The men usually start to cook a meal after this work, and make fires on the sand as if on land. But when the monster feels the heat of these fires, it immediately submerges into the water, pulling men and ships into the sea with it.