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LET'S EXPLORE The animal kingdom

A to Z of marine invertebrates

Barnacles, types of crustaceanBarnacles, types of crustaceanThe oceans are home to a wide range of invertebrate animals. Unlike fish, mammals or reptiles, for example, these animals do not have backbones. They include crustaceans, such as crabs, lobsters and shrimps, which have hard outer parts for protection, and molluscs, which have soft bodies, often protected by shells. Crustaceans and molluscs are sometimes grouped together and called “shellfish”.

Clams with their siphons extendedClams with their siphons extended


Bivalves are kinds of mollusc. They have flat bodies contained inside a shell that has two hinged parts. Clams, cockles, oysters, scallops and mussels are all bivalves. To protect themselves from predators, some bivalves bury themselves in the sand or mud. Others, including scallops, swim away from danger, while oysters and mussels remain permanently attached to rocks. To ensure they stay moist when they are out of the water at low tide, they keep their shells tightly shut.

Among the marine invertebrates is one of the largest animals on Earth: the colossal squid, which may grow up to 14 metres (46 feet) long.

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