Crayfish exhibit the major arthropod characteristics: segmentation, with expansion of key segments into body regions (cephalothorax and abdomen); a chitinous_exoskeleton; and jointed appendages.
Crayfish have two pairs of antennae; whereas all other arthropods have either one pair or none at all. Their cephalothorax consists of a sensory and feeding region called the head (cephalic_region), and the chest (thoracic_region), which provides attachment space for the major motility appendages. The hard outer covering of these regions is called the carapace (exoskeleton). A subsection of the cephalic region is the rostrum, a beak-like process that extends between the eyes.
The paired appendages of the cephalothorax include (1) antennae (sensory), (2) mouth appendages (mandibles for chewing and maxillae for food handling), (3) maxillipeds (accessory food handling and sensory structures), and (4) periopods (walking legs). The first periopeds are the chelipeds, which are enlarged and chelate (pincher-like). These chelipeds are used for defense as well as capturing food. The telson and uropods act as a "tail" to allow the crayfish to propel itself backward.
Crayfish have compound_eyes, which consist of anywhere from 25 to over 14,000 individual receptors (ommatidia). They also have simple eyes (ocelli), which sense light but not images.
Most crustaceans, including the crayfish, have separate sexes (they are dioecious). The ventral male body displays copulatory_swimmerets and sperm_ducts. The ventral female body has a seminal_receptacle and oviducts, which are covered by discs.
Crayfish prey upon other invertebrates, plant matter, and dead/dying animals. Their stomach is specialized for food grinding, and they have digestive_glands, which secrete digestive_enzymes and absorb nutrients.
Special glands called green_glands are the excretory organs of the crayfish. They act as "blood filters" (like our kidneys), and are located behind the eyes.
Crayfish have an open_circulatory_system with a muscular heart. Their blood circulates through a hemocoel (Note: the animal's true coelomic cavity is reduced, and is associated (in the adult) with only the gonads and excretory organs). Blood returning to the heart enters a sinus and goes to the gills prior to returning to a pericardial_sinus, which surrounds the heart. Gills provide the surface area for exchange of respiratory_gases (oxygen and carbon_dioxide).
These animals have a ventral_nervous_system and numerous sensors. This system allows the animal to flex and extend the muscles of the abdomen so it can move forward. The telson and uropods act as a "tail" that allows the crayfish to propel itself backward. Crayfish have compound_eyes, which consist of anywhere from 25 to over 14,000 individual receptors (ommatidia). They also have simple eyes (ocelli; sense light but not images), chemoreceptors, statocysts (balance), proprioreceptors (sense spatial position and body movement), and tactile (touch) setae.