Arthropods Again: The Crustacean

1. Arthropods Again:The Crustacean HW: Study These Notes & Complete page 16 in RB 2.

2. 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

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

4. The Crayfish • Our crustacean of choice to study is the crayfish. We will complete a lab the week of March 20th. • Like other crustaceans, the crayfish has a head, thorax, and abdomen. • Specifically it has: • 5 head segments • 8 thoracic segments • 6 abdominal segments

5. 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.

6. Head Appendages • Head Segment 1: give off antennules that are used as sensory receptors. • Head Segment 2: give off antennae 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.

7. 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.

8. 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 locomotion underwater.

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

10. 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.

11. Crayfish Muscular System • Inside the thoracic and abdominal segments are muscle bundles, nerves, and vessels. • The abdominal segments are nearly filled with muscle tissue. • These muscles are used to power the appendages of the abdominal regions: swimmerets.

12. 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.

13. Crayfish Excretory System • The excretory system is made up of green glands. • 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.

14. 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.

15. 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.