• Describe the appearance of various organs found in a crayfish.
• Name the organs that make up systems of the crayfish.
• Gloves, preserved crayfish, dissecting tray, paper towels, scissors, forceps, blunt and sharp probe, scalpel, scissors.
In this lab, you will observe the external structures of a crayfish and dissect it to study its internal structures and systems.
Like all members of the subphylum CRUSTACEA, a crayfish has a fairly hard EXOSKELETON that covers its body. As shown in the diagram on the next page, its body is divided into two main parts, the anterior CEPHALOTHORAXand the more posterior ABDOMEN. The cephalothorax consists of the cephalic (or head) region and the thoracic region. The part of the exoskeleton that covers the cephalothorax dorsally is called the CARAPACE.The abdomen is located behind the cephalothorax and consists of 6 + 1 clearly divided segments. The cephalothorax consists of 13 segments. Each segment of both the cephalothorax and the abdomen contains a pair of appendages. The head (or cephalic) region has five pairs of appendages. The ANTENNULES are organs of balance, hearing, and touch. Long ANTENNAE are organs for touch, taste, and smell. The mandibles, or jaws, crush food by moving from side to side. Two pairs of maxillae hold solid food, tear it, and pass it to the mouth. The second pair of maxillae also helps to draw water over the gills. Of the eight pairs of appendages on the cephalothorax, the first three are maxillipeds, which hold food during eating. The CHELA are the large claws that the crayfish uses for defense and to capture prey. Each of the four remaining segments contains a pair of WALKING LEGS. In the abdomen, the first five segments each have a pair of SWIMMERETS, which create water currents and function in reproduction. The sixth segment contains a modified pair of UROPODS.In the middle of the uropods is a structure called the TELSON, which bears the anus. The uropod and telson together make up the tail fan. The crayfish moves backward by forcing water forward with its tail fan.