What Characteristics Do All Crustaceans Share?

Invertebrates

• Crustaceans are a subphylum of the enormous arthropod phylum. They're invertebrates and cold blooded. They have open circulatory systems, which means a fluid called hemolymph gives oxygen and nutrients directly to the organs. The fluid is pumped by the heart, located in the abdomen. The brain is a knot of ganglia, or bunches of nerve endings, near the antenna. There are more ganglia beneath the gut -- this is why, some people believe, that even splitting a lobster's head in two doesn't kill it right away.

Evolution

• Some scientists believe that crustacea evolved during the Middle Cambrian age, from 513 to 499 million years ago.

Body plan

• The body plan of a crustacean is head, thorax and abdomen, much like an insect. One characteristic that separates crustaceans from insects is their limbs branch in two. The segments of the body are protected by an exoskeleton which has to be molted or shed in order for the animal to grow. Each body segment can have a pair of appendages. Legs of whatever number are found on the thorax and the abdomen while the head has two pair of antennae and mouthparts. The head and thorax might be fused, as in most species of crab and water flea, and covered by a carapace. The shell can be divided into the tergum, the abdomen section, the pleuron, part of the tergum that's a plate which overhangs a limb and the sternum, the underpart of the abdomen. Again, these segments may be fused.

Eating

• A crustacean's digestive system is a straight tube with a structure like a gizzard that grinds the animal's food. Digestive glands absorb the food.

Reproduction

• Though crustaceans might have different styles of mating -- or not, as some are parthenogenic -- all of them lay eggs. Some of them are simply released into the water, some carry their eggs either attached to their hindlegs or in brood pouches, or attach them to rocks or plants. Crustaceans emerge from their eggs as pre-larva or pre-zoea. All go through stages of development before they reach adulthood, though the stages vary in number. The larvae of the west coast rock lobster molts at least 11 times before it's mature. Another characteristic that separates crustaceans from insects is the nauplius stage of their larvae. Nauplius means that at one stage the larvae use their antenna to swim. The larvae also develop a single eye at this stage. Many crustacean larvae don't look anything like the adults.