If you observe a crescent-shaped slit, you have located a genital pore of a female. Use a magnifying glass to study the inside surface of the base segment of the third pair of walking legs. The base segment is where the leg attaches to the body. Locate the base segment of each pair of walking legs. Now use the walking legs to determine the sex of your specimen. Behind the chelipeds locate the four pairs of walking legs, one pair on each segment.Ĩ. Next observe the largest prominent pair of appendages, the chelipeds, or claws. How are the maxillipeds related to eating? _ħ. On the thoracic portion of the cephalothorax, observe the three pointed maxillipeds. Which appendages in the cephalic region are related to the eating of food? _Ħ. Now locate the two pairs of maxillae, which are the last appendages in the cephalic region. Then observe the mandibles, or true jaws, behind the antennae. Why is it useful to view the specimen on its Dorsal side for this part of your study? _ĥ. Behind them observe the much longer pair of antennae. First locate the antennules in the most anterior segment. Locate the five pairs of appendages on the head region. Notice that each eye is at the end of a stalk.Ĥ. Turn the crayfish with its DORSAL side upward, and locate the rostrum, which is the pointed extension of the carapace at the head of the animal shown in the diagram above. What is the main difference between the cephalothorax and abdomen?ģ. Note the individual segments of the abdomen. On the thoracic region, locate the prominent suture or indentation on the cephalothorax that defines a central area separate from the sides. On the carapace, observe an indentation, the cervical groove, that extends across the midregion and separates the head and thoracic regions. The carapace, a shield of chitin, covers the dorsal surface of the cephalothorax. Use the diagram below to locate the cephalothorax and the abdomen. Place a crayfish on its side in a dissection tray. Put on safety goggles, gloves, and a lab apron.Ģ. Procedure Part 1-External Anatomy of a Crayfishġ. The crayfish moves backward by forcing water forward with its tail fan. The uropod and telson together make up the tail fan. In the middle of the uropods is a structure called the telson, which bears the anus. The sixth segment contains a modified pair of uropods. In the abdomen, the first five segments each have a pair of swimmerets, which create water currents and function in reproduction. Each of the four remaining segments contains a pair of walking legs. The chelipeds are the large claws that the crayfish uses for defense and to capture prey. Of the eight pairs of appendages on the cephalothorax, the first three are maxillipeds, which hold food during eating. The second pair of maxillae also helps to draw water over the gills. Two pairs of maxillae hold solid food, tear it, and pass it to the mouth. The mandibles, or jaws, crush food by moving from side to side. Long antennae are organs for touch, taste, and smell. The antennules are organs of balance, touch, and taste. The head (or cephalic) region has five pairs of appendages. Each segment of both the cephalothorax and the abdomen contains a pair of appendages. The cephalothorax consists of 13 segments. The abdomen is located behind the cephalothorax and consists of six clearly divided segments. The part of the exoskeleton that covers the cephalothorax is called the carapace. The cephalothorax consists of the cephalic (or head) region and the thoracic region. As shown in the diagram on the next page, its body is divided into two main parts, the cephalothorax and the abdomen. Purpose: In this lab, you will observe the external structures of a crayfish and dissect it to study its internal structures and systems.īackground: Like all crustaceans, a crayfish has a fairly hard exoskeleton that covers its body. safety goggles, gloves, magnifying glass, a lab apron, plastic zip lock bag preserved crayfish, pen, dissecting tray, paper towels, scissors, forceps, dissecting needle, and dissecting pins.
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