Segmented worms have been evolved from roundworms and arthropods were given rise from segmented worms with additional modifications in their body structures. The cephalization and the segmentation underwent improvements with the formation of cephalothorax and abdomen.
Since these are two differentiated regions of the arthropod bodies, there are many differences between cephalothorax and abdomen with respect to their form and function. Abdomen is a region of the body in most of the animals but, in order to compare it with the cephalothorax, this article mainly concentrates on the arthropod abdomen. The two words cephalic and thoracic have been put together to mean both head and thorax with the term cephalothorax.
Cephalothorax is simply the region of the arthropod body that comprises the organs and systems of both head and thorax. Chelicerates and crustaceans are the main arthropod groups with the fusion of head and thorax into one unit while the cephalothorax is not present in other groups such as insects.
Cut along the indentations that separate the thoracic portion of the carapace into three regions. Start the cut at the posterior edges of the carapace, and extend it along both sides in the cephalic region. Use forceps to carefully lift away the carapace. Be careful not to pull the carapace away too quickly. Such action would disturb or tear the underlying structures.
Place the specimen on its side, with the head facing left, as shown in the diagram below. Using scissors, start cutting at the base of cut line 1. Cut along the side of the crayfish, as illustrated by cut line 2. Extend the cut line forward toward the rostrum at the top of the head.
Use forceps to carefully lift away the remaining parts of the carapace, exposing the underlying gills and other organs. Use the diagram below to locate and identify the organs of the digestive system.
Locate the maxillae that pass the pieces of food into the mouth. The food travels down the short esophagus into the stomach. Locate the digestive gland , which produces digestive substances and from which the absorption of nutrients occurs.
Undigested material passes into the intestine. Observe that the intestine is attached to the lobed stomach. The undigested material is eliminated from the anus. Use the diagram below to locate and identify the organs of the respiratory system.
Locate the gills , which are featherlike structures found underneath the carapace and attached to the chelipeds and walking legs. A constant flow of blood to the gills releases carbon dioxide and picks up oxygen.
They too will need to be removed so that they do not totally devour the smaller crayfish. How does a crayfish gets pregnant? This sperm packet in which there are millions of live sperms, will remain viable inside the body of the female. Every marbled crayfish is female—and they reproduce by cloning themselves. They were all female, and they all laid hundreds of eggs without mating. These eggs, in turn, hatched into hundreds more females—with each one growing up fully able to reproduce by herself.
Many baby crayfish are eaten because they are so small. The crayfish leaves its mothers protection in weeks after it hatches from the egg. The crayfish will grow and sheds its exoskeleton often. The crayfish will either mate and start the process over again, or it will die.
The eggs hatch in weeks and have the same structure as an adult crawfish. Crawfish reach adult size in months and its life span is years long. Crawfish tails host small appendages, including swimmerets. Male crawfish carry an extra set of these swimmerets, which are enlarged and hardened. Females possess a small hole just behind their swimmerets.
Digestive System: Crayfish are carnivorous scavengers lending to the fact that their digestive systems are relatively simple. As seen in the external anatomy, crayfish of complex mouthparts to aid in the feeding process. Upon entering the mouth, the food travels down the short esophagus into the stomach.
The chelipeds 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. Crayfish and other members of the subphylum Crustacea including crabs, lobsters, shrimp, and amphipods have blue blood.
This is due to the hemocyanin in their blood, a copper based compound which is blue when oxygenated. Human blood contains iron which turns red when oxygenated. The circulatory system of the crayfish is an open system where the blood is contained in vessels for only part of the system. The heart is located in a pericardial sinus located in the upper part of the thorax a sinus is a sac or cavity.
The heart pumps the blood into the arteries. Cephalothorax: The Animal Files.
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