There are more than 42,000 species of crustaceans worldwide, almost all of which are marine. They are found in every marine habitat from the upper parts of the seashore to the deepest regions of every ocean.

There are four main classes of crustacean:

sea monsters
The largest crustacean found in British waters is the common lobster Homarus gammarus. The largest individual on record was a 6.57kg monster caught off Pembrokeshire in 1967.

• barnacles and copepods (Maxillopoda)
• ostracods (ostracoda)
• mantis shrimps (Malacostraca)
• crabs and lobsters, amphipods, isopods, shrimps and prawns (Eumalacostraca)

crustacean facts:

• The crustacean body is typically divided into the head, thorax and abdomen, together with an additional tail.
• All crustaceans have two pairs of antennae on or around the head.
• Crustaceans possess a chitinous exoskeleton which forms a rigid and sometimes heavy outer body shell. They have to moult in order to grow.
• The many different crustaceans have many different feeding methods. Crabs, lobsters and many other crustaceans are scavengers, feeding on a range of materials they may find on the seafloor. Barnacles feed by trapping food in their tentacle-like legs, while other crustaceans are active hunters, ambushers, and even parasites.
• Although there are advantages to having a rigid exoskeleton. one of the disadvantages is that crustaceans do not have rotational joints like we do. This can be seen in the way crabs walk - they have to move sideways!
• For quick get-aways (albeit in a backwards direction), shrimps and lobsters have an escape response using their tails: one violent jerk of the abdomen propels the animal backwards at an amazing speed and out of harm’s way.