Arthropods Again: The Crustacean

The Crustacean The first type of arthropod that we will study is the crustacean. There are about 25,000 species in this class. They include: Barnacles Shrimp Lobster Crayfish Crab

Crustacean Body Plan Crustaceans have a body plan that consists of: Cephalothorax consisting of: Head, consisting of five segments giving off paired appendages Thoracic Segments – generally modified for food handling or movement Abdomen – usually segmented, but may or may not have appendages.

The Crayfish Our crustacean of choice to study is the crayfish. Like other crustaceans, the crayfish has a head, thorax, and abdomen. Specifically it has: 5 head segments 8 thoracic segments (body segments) 6 abdominal segments

Crayfish Segments In the crayfish, each segment gives rise to a specific appendage which has specific functions. You will need to know and study what these appendages are, and what their functions are.

Head Appendages Head Segment 1: give off antennules shorter pair) that are used as sensory receptors. Head Segment 2: give off antennae (longer pair) that are also used as sensory receptors. Head Segment 3: give off mandibles around the mouth that are used to bite and crush food. Head Segment 4 & 5: give off maxillae that are used to move the food around so that it can be put in the mouth.

Thoracic Appendages Thoracic Segments 6-8: give off maxillipeds which are also used to manipulate food. Thoracic Segment 9: chelipeds (pinchers!!) are used for self-defense, getting, and manipulating food. Thoracic Segments 10-13: walking legs, which are used for locomotion.

Abdominal Appendages Abdominal Segments 14-18: give off swimmerets, which create water currents, enhance air movement to gills, hold eggs in females, and are modified as reproductive structures in males. Abdominal Segment 19: telson (which houses the anus)– used for waste excretion and uropods. Both structures can be used as a paddle to allow for rapid (backwards) locomotion underwater.

Crayfish Internal Structures Do not lose these notes, as this picture will greatly help you with your self-test.

Get to Know the Exoskeleton The dorsal and lateral parts of the cephalothorax are covered with the carapace. The carapace has an anterior extension known as the rostrum. The ventral plates is called the sternum. The abdominal skeletal plates are known as the tergum. All of these structures comprise the exoskeleton and act as protection for internal organs.

Crayfish Muscular System Inside the thoracic and abdominal segments are muscle bundles, nerves, and vessels. The abdominal segments are nearly filled with muscle tissue. This muscle is commonly consumed with crayfish & lobsters. These muscles are used to power the appendages of the abdominal regions; that is, the swimmerets.

Crayfish Digestive System Mouth -> esophagous -> stomach -> digestive gland -> intestine -> anus Their stomach is divided into a cardiac region and a pyloric region. The cardiac chamber has calcified plates that act like teeth to grind up food into digestible bits. The food then moves to the pyloric region and moves on as listed above. Ground up food is digested here in the crayfish.

Crayfish Excretory System The excretory system is made up of green glands. These are consumed by some people when eating the whole lobster. While these glands are capable of some excretion, they cannot handle all of the chemical & water balance needs. The gills play the largest role in regulating body fluids.

Crayfish Circulatory System Crayfish have open circulatory systems. They have vessels, but the vessels empty into sinuses. The blood from the sinuses is then returned to the heart in channels, not vessels. So, though there are vessels, they empty into sinuses – so it is still considered an open system.

Crayfish Respiration Respiration occurs through the gills (found from thoracic segment 2-6). Water is circulated over the gills by movement of a paddle-like gill bailer which moves with the second maxilla.