Crab's structure and Function?

Question

What does crabs has for its structure and function? list 5 please

Answer 1

General Characteristics of CRUSTACEANS (from http://www.coolschool.ca/lor/BI11/unit13... )

Crustaceans are a class of arthropods that is mainly marine, and includes such members as crabs, crayfish, shrimp and lobster. The crustaceans all have three body parts, head, thorax, and abdomen. However, the head and thorax are often fused to form the cephalothorax. The head has five pairs of appendages, two pairs of which are antennae, and three are mouthparts. Therefore, these appendages are specialized for sensory and feeding. The thorax also has five pairs of appendages, all of which are legs. The first pair however, are claws and used for eating and defense, where as the others are walking legs. The abdomen is equipped with swimmerettes, which are small paddle-like structures that assist in movement and reproduction, and for those crustaceans that have a tail; the uropod and telson are used to quickly swim backward.

(EXO)SKELETON - All crustaceans have bilaterally symmetrical bodies covered with a chitinous exoskeleton, which may be thick and calcareous (as in the crayfish) or delicate and transparent (as in water fleas). Since it does not grow, the exoskeleton must be periodically molted when the animal undergoes metamorphosis (typically from free-swimming larva to adult) or simply outgrows its shell.

INTERNAL ORGANS

RESPIRATORY AND CIRCULATORY SYSTEMS - Gills are located above the legs for respiration under water, and this is the site where hemocyanin, a blue pigment due to copper content, picks up oxygen molecules to be used by the body. The heart pumps this blood through a blood vessel to an open space surrounding the organs called a hemocoel. Therefore, this is an open circulatory system.

NERVOUS SYSTEM - The nervous system of a crustacean is similar to that of an earthworm. There is a brain, ventral solid nerve chord, and 8-19 lateral nerves. The crustaceans have eyes, and antennae for specialized sensory structures.

REPRODUCTIVE SYSTEM - The gonads are located just below the heart, and Crustaceans are dioeceos, meaning they have separate sexes. Sperm is transferred to the female by specialized swimmerettes, which are the first set. The third set of swimmerettes on the female are where the ovaries are located, and the swimmerettes also function to hold the fertilized eggs.

DIGESTIVE SYSTEM - The digestive system of a crustacean is also a tube-within-a-tube. The digestive system differs from that of the earthworm though. First of all, the green gland near the mouth of the crustacean secretes digestive juices and begins digesting externally. And, the stomach has two regions as opposed to a crop and gizzard. The Gastric mill portion functions as a gizzard, and grinds food with chitinous teeth, while the posterior portion filters out coarse food particles. Also differing, is the site of absorption, this takes place in digestive glands as opposed to the intestine