Phylum Annelida (little Rings) Segmented Worms Phylum Annelida (little Rings)

Characteristics of Phylum Anneldia 1. Bilateral Symmetry 2. Metameric – their bodies are divided into segments, both inside and out; this allows for parts of the worm to be damaged or destroyed without killing the worm 3. Complete nervous, digestive, & circulatory system 4. Triploblastic Coelomates – Triploblasts have an ectoderm, endoderm, and mesoderm. Coelomates have a body cavity within the mesoderm for housing organs. 5. Covered in tiny hairs called chaetae

1. Allows movement w/maximum protection. 2. Each segment contains its own set of excretory organs and muscles, separated from the next segment by a septum. Segmentation

3 Major Classes 1. Class Polychaeta (many hairs) – marine annelids, usually very fancy and beautiful 2. Class Oligochaeta (few hairs) – freshwater, marine, and terrestrial; earthworms 3. Class Hirudinea - Mostly freshwater, some marine, some parasites; leeches

Class Polychaeta Largest of the annelid classes Dioecious Have parapodia, literally meaning “pairs of feet” for swimming and crawling. Have setae – bristles that aid in movement and burrowing Have two to four pairs of eyes, but still see mostly just light and dark. Have a proboscis – modified pharynx used for feeding. What other animals have a proboscis? Have an anus (like roundworms), but their waste has a special name – “castings”. Blood may be either red, green, or colorless depending on the worm. Can regenerate lost parts.

Class Oligochaeta Have a clitellum that secretes mucus during mating, and forms a cocoon for fertilized eggs. Since they are monoecious, they exchange sperm during copulation. Feed primarily on decaying vegetation using their pharynx Have very primitive eyes similar to that of flatworms. These guys are NOT regenerative like other worms.

Class Hirudinea Monoecious Pharynx has evolved into a modified sucker, used for penetrating the outer layers of its prey and feeding on bodily fluids, i.e. blood. Not capable of regeneration!