Nudibranchs and sea slugs are mollusks, but there are so many different ones that I've given them their own section. They are among the most distinctively shaped and brightly colored animals you will encounter in diving, although most of them are no bigger than a few inches long.
Giant Clam
Scientific name: Tridacna gigas
Giant clams, such as the one pictured, can reach a size of more than a meter in length and weigh more 200 kilograms. They can also live 100 years or more. What's really amazing is that these guys start life as tiny plankton.
Flamingo Tongue
Scientific name: Cyphoma gibbosum
These close relatives of the cowrie are still common around the Caribbean, but they've suffered badly from people collecting them, not realizing that the distinctive patchwork pattern is part of the mantle. Once the snail dies, all you're left with is a plain white shell.
Horned Helmet
Scientific name: Cassis cornuta
This rather large shelled mollusk is the only non-cowrie sea snail I've seen, so far.