A large spotted cowrie whose shell stays glossy because the mantle covers it.
The largest cowrie a diver meets in this region, with a heavy, humped, glossy shell to about 15 cm, cream to white and covered in irregular dark brown to black spots, the base and the long toothed aperture plain white. Active animals are not white and spotted, because the mantle is extended: two lobes rise from the aperture on either side and meet along the top of the shell, dark grey-brown to nearly black and covered in short branched papillae, so a feeding cowrie reads at first glance as a soft dark lump moving over the rock. The mantle both secretes the outer shell layer and keeps it from being fouled or eroded, which is why cowrie shells are polished in a way that shells left exposed are not. There is nothing else of this size and pattern in the area, and the identification is straightforward once the shell is seen.
Chiefly nocturnal. By day it sits back in a crevice or under a ledge, and on muck sites it is more often on the rocky and coral edges than out on open sediment. It grazes algae, and also takes sponges, soft corals and detritus, so the diet is broader than a pure algal grazer’s. Eggs are laid as a cluster of capsules in a sheltered spot and the female sits over the mass until they hatch, which is one of the few times the animal is found in the open by day. The species has been collected heavily for the shell trade for a long time; polished tiger cowries in a market came from animals taken alive, and the shell is not something the snail sheds.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.