Subphylum Crustacea

Crustaceans

• Most crustaceans are free-living and aquatic (although there are some parasites and terrestrial species).
• We are going to look at the crayfish as our example of a crustacean. 

The Crayfish

Crayfish

• Covered with a tough exoskeleton
• Divided into three segments: cephalothorax and the abdomen (composed of 6 different segments)
• Beneath the abdomen are a number of paired, small, flipper like appendages called swimmerets (used for swimming and reproduction).
• There are four pairs of walking legs and a pair of prominent chelipeds (or pinchers) attached to the cephalothorax. 

Life Processes

• Movement:
• Muscles
• Legs
• Swimmerets and walking legs
• Nutrition:
• Scavengers: eating virtually any edible material.
• The mouthparts of the crayfish reduce the food to swallowable size.
• Then moves to esophagus then to the anterior part of the stomach where it is ground to fine particles by muscular action and chitinous teeth of the gastric mill.
• The food is sorted in the posterior part of the stomach.
• Food is then moved to the intestines. Undigested food moves through the anus.
• Respiration:
• The crayfish as two sets of feathery gills found in the two lateral gill chambers along the thorax.
• Appendage movement and feathery mouthparts help to keep oxygenated water flowing through the gills. 
• Blood traveling through the thin-walled gills releases carbon dioxide and absorbs oxygen.
• Many can store water in their gill chambers in order to walk on land. The “hold their water” like people “hold their breath.”
• Circulation:
• Open circulatory system.
• Blood collects in the a cavity surrounding the heart. 
• Blood enters the dorsal heart through tiny openings.
• As the heart contracts, valves close to keep the blood from flowing back into the sinus.
• The blood then leaves the heart, bathing the organs with oxygenated blood, to then be collected in the sternal sinus.
• The blood passes again through the gills and the process starts again.
• Excretion:
• Excretion is performed by green glands, which are located near the base of the antennas.
• The green glands filter out waste.
• Fluid wastes are excrete through a pore anterior to the mouth.
• Wastes from the intestines are eliminated through the anus.
• Response:
• Ventral nervous system receives information about the environment from a number of sensory sources.
• Compound eyes
• Antennae
• Antennules, shorter sensory appendages
• Tiny bristles for touch on several appendages
• Statocyst: the organ of balance found at the base of each anteannule
• Reproduction/Regeneration:
• Arthropods cannot reproduce asexually, but as a mode of defense, they can loose an appendage and it will grow back.
• Crayfish mate in the fall.
• The male transfers its sperm to a receptacle in the body of the female using reproductive swimmerets.
• The female stores the sperm until she lays her eggs in the spring. 
• The fertilized eggs are then attached to swimmerets for development. They hatch within 5-6 weeks.
• During the first year, crayfish molt seven times. After that, twice a year for 3-8 years until they die.