Arthropods Again:The Crustacean

HW: Study These Notes & Complete page 16 in RB 2.

The CrustaceanThe first type of arthropod that we will study is the crustacean.There are about 25,000 species in this class. They include:BarnaclesShrimpLobsterCrayfishCrab

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.

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 segments8 thoracic segments6 abdominal segments

Crayfish SegmentsIn 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 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.

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 locomotion underwater.

Crayfish Internal StructuresDo 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.These muscles are used to power the

appendages of the abdominal regions: swimmerets.

Crayfish Digestive System

Mouth -> esophagous -> stomach -> digestive gland -> intestine -> anusTheir 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.

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.

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.