Annelids (Earthworms) Chapter 25-28

First Animals w/ Segmentation  Worms belong to ancient group  Phylum Annelida  Fossils are 530 million years old  Evolved in the sea  Range in size from >1mm (.04 in) to 3m (10 ft long)  Easily recognized by segments  Series of ring-like structures that contain  Digestive, excretory, circulatory, and locomotor organs

Body Structure  Cerebral Ganglion  Primitive brain in the anterior segment  Connected to a nerve cord that runs on the underside of the body  Septa  Interior body walls that separate the segments

Characteristics of Annelids  1 Coelom  Large fluid filled coelom located within the mesoderm  2 Organ Systems  High degree of specialization  Closed circulatory system  Excretory system contains nephridia  Highly modified gut  3 Bristles  External bristles called setae  Located on each segment for increased crawling traction  Parapodia  Fleshy appendages on fireworms

Earthworms  Member of class  Oligochaeta  Have NO parapodia  Few setae  Lack distinctive head region  No eyes  Have light and touch sensitive organs located at the end of the body