We think of molluscs as animals with shells, like clams and oysters. The nautilus is also a mollusc. It has a shell and hovers in the water, controlling buoyancy by varying the amount of gas in its shell. It has two eyes and many tentacles (twenty). Many of the shelled molluscs have the ability to extend their bodies (mantles) from inside their shell and wrap them entirely around the outside surface. From this ability, it is possible to see how other molluscs like cuttlefish, squid and octopuses evolved to make that condition permanent. Each of these groups has progressively smaller remnants of the old shells inside their bodies. They traded the protection of an external shell for greater mobility and better ability to grasp prey using long tentacles. Cuttlefish and squid have ten tentacles, while octopuses have eight tentacles. Those tentacles are often equipped with suckers or hooks to hold prey tightly. All three of these types of cephalopods have chromatophores in their skin which allow them to change color quickly, while octopuses can also change the texture of their skin. Of 824 species of cephalopods, there are about 6 nautiluses, 200 cuttlefish, 300 squids, and 300 octopuses.