Unit 6 Notes #4 –Subphylum crustacea: The Crayfish a crustacea

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Unit 6 Notes #4 –Subphylum CRUSTACEA:

The Crayfish

A) Crustacea:

- Crustaceans are primarily aquatic and range in size from the microscopic to the rather enormous (giant spider crab 5-6 meters across)

- Common characteristics include CaCO3 enforced exoskeletons, two pairs of antennae, and feeding mouthparts called mandibles.


B) External Anatomy:

-They inhabit freshwater streams and lakes.
-The thirteen segments in the head and thorax are fused together to form the “Cephalothorax”
-The rigid dorsal and side portion of the skeleton covering the anterior portion of the body is called the “Carapace”

- The six most posterior segments form the jointed abdomen. Except for the last of these segments, each of these bears a pair of swimmerets. The pair on the first segment is important in determining the sex of the crayfish, this pair is larger and more rigid in the male.
- Each pair of appendages (walking legs) below the Carapace is slightly adapted or specialized to serve a variety of functions.

B) Internal Anatomy:
i) Digestion:

-Crayfish feed on insect larvae, worms, smaller crustaceans, small snails, fish and tadpoles.
-After food is crushed and shredded by their mouth parts, it is passed into the stomach (foregut), which has hard chitinous teeth (gastric mill) that acts to further grind up the food.
-A pair of digestive glands just posterior to the stomach secretes enzymes into the mid-gut. Then digested food passes down the intestine for absorption into the blood.
-Finally, undigested food passes out through the anus. The anus is found just under the Telson. (the flattened terminal paddle used for swimming)

ii) Nervous and Sensory Systems:


- Nervous system is much like that of the annelids (ex. earthworm) with a larger dorsal brain located just above the mouth.

-It connects to a pair of nerve cords (that appears as a single nerve cord) these nerve cords run ventrally along the body to the posterior end.
-The brain is also connected to the eyes, antennae and antennules, to detect various stimuli.
-Each compound eye is supported at the end of a moveable stalk.
-Sensory bristles sensitive to touch are distributed over the body and appendages. Hairs sensitive to taste and smell are located on the antennules, tips of antennae, mouth parts, and the ends of the pincers.
-At the base of the antennules are statocysts, which serve the sense of balance.
-Antennules appear on the second segment of the head. These are organs of balance and hearing.















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