Octopuses and people. There are about 100 species of octopuses. The best-known species inhabit rocky, sandy, or muddy bottoms in shallow parts of oceans throughout the world. Other octopuses live in deep waters. Octopuses vary greatly in size.
Octopuses belong to a group of animals called mollusks.
This group also includes clams, oysters, and snails. Like squids and cuttlefish, octopuses are mollusks that have no outside shell. The body of an octopus is soft and boneless. A fleshy, muscular covering, called the mantle, surrounds the main part of the body, forming a cavity that encloses the gills. An octopus breathes by drawing water into the mantle cavity.