Invertebrate: molluscs

Molluscs are a large group of invertebrate animals. Molluscs have soft bodies, and their bodies are not divided into rings like the segmented worms called annelids . Molluscs don't have legs, though some have flexible tentacles for sensing their environment or grabbing things. Most mollusc species grow a hard shell for protection, but their shell grows in only one or two pieces. It doesn't have joints like the exoskeletons of insects and crustaceans .

There are three main groups of molluscs. 

1)Snails ( Gastropoda (gas′trə pod′), ) are the most diverse group, there are tens of thousands of species. Nearly all snails grow a spiral shell that is all one piece. A few snail groups have stopped growing shells; they're called slugs . 

   

2) Bivalvia  (/ˈbaɪˌvælv/ )  , the clams, oysters, and mussels . These are molluscs with two shells that they can close up tight for protection.

     

 3)Cephalopoda (sef′ə lə pod′) , the squids and octopuses. They only live in salt water. They have no shells, but are larger, smarter, and faster than their relatives in the other groups. Squids and octopuses are all predators; they eat fish, crustaceans, and other mollusks.