Annelida

General Characteristics: 1. Segmented bodies

2. Bilateral symmetry

3. True body cavity is partitioned by structures called septa.

4. The organs of the digestive, nervous, and circulatory systems penetrate the septa and run the length of the body.

5. One way digestive tract is divided into several well developed organs: pharynx, esophagus, crop, gizzard, and intestine.

The circulatory system is closed.

It contains a dorsal and ventral blood vessel, connected by 5 aortic arches just above the esophagus. The dorsal blood vessel carries blood from the tail to the head, while the ventral one carries the blood back toward the tail.

Cephalization!! The brain is small and is located under the pharynx. A ventral nerve cord extends from the brain and runs the length of the body. In each segment it swells to form a structure called a ganglion.

1. Brain 2. Ventral nerve cord 3. Ganglion

Waste removal Nitrogenous waste is removed from the body by structures called nephridia.

Earthworms are hermaphroditic. Reproduction Earthworms are hermaphroditic. (found in the clitellum which is segments 32-37) .

Locomotion Their muscular system contains both circular and longitudinal muscles. As the circular muscles contract they elongate the body, while the longitudinal muscles shorten it.

Setae, small bristle-like hairs, extend from the body walls and act as anchors as worm moves. There are 4 pair of setae per segment. Therefore the same earthworm with 78 segments has how many Setae?? 312

- No respiratory organs - breathe through moist skin. The Skin - Contain a thin water proof layer called the cuticle. - No respiratory organs - breathe through moist skin.

The Body No skeleton other than the hydrostatic one formed by the fluid filled body cavity.