The polychaetes, worms, and leeches

* Annelids are all segmented * Series of repeated ring-like units (segments) * All have a head with a well-developed cerebral ganglion (primitive brain) * Many have eyes with lens and retinas * If an Annelid is cut in pieces, usually only the parts containing the head or tail can regenerate * Segments are divided by partitions called Septa NOAA

* Each segment has a pair of excretory organs (nephridia), a ganglion, structures for locomotion, and many also have a set reproductive structures * Annelids also have a closed- circulatory system (blood vessels) * More advanced digestive system with a: * Crop: stores food prior to: * Gizzard: grinds food particles * Intestine: absorb nutrients

* Nephridia are cilliated tubes open to the outside for removing wastes * Setae are bristles made of chitin on each segment that gives the worm a grip in the dirt Piotr Rotkiewickz

* Phylum Annelida * Class Polychaeta: the Polychaetes * Can swim or crawl and some species even build tubes or burrows of mud, sand, or calcium carbonate Karen Osborn of Scripps Oceanography

* Phylum Annelida * Class Polychaeta Nick Hobgood

* Phylum Annelida * Class Clitellata: Earthworms and Leeches * Only half of known leeches suck blood, the other half eat detritus and small animals