:: crayfish ::

Crayfish, also called crawfish or crawdad, are closely related to the lobster. More than half of the more than 500 species occur in North America, particularly Kentucky (Mammoth Cave) and Louisiana in the Mississippi basin. Crayfish also live in Europe, New Zealand, East Asia and throughout the world, including the Tristan da Cunha Islands. Nearly all live in freshwater, although a few survive in salt water. Crayfish are characterised by a joined head and thorax, or midsection, and a segmented body, which is sandy yellow, green, or dark brown in colour. The head has a sharp snout, and the eyes are on movable stalks. Crayfish are usually about 7.5 cm (3 inches) long.

In the open circulatory system blood flows from the heart through the arteries and returns into open sinuses. The digestive system has a stomach for grinding food and a gland for chemical processing. The antennal gland is the main excretory organ.