Phylum: Annelida

Dorsal surface

Surface of the worm that faces up, usually darker than the ventral surface

Ventral surface

Surface of the worm that faces down, usually facing the substrate

Saddle/Clitellum

A thickening of the worm body approximately a 1/3 of the way down used to form a cocoon for the eggs, not always present or visible.

Chaeta

Bristles made of chitin on annelid worms (except the leeches).

Segments

Repeating sections of the worm body that are similar internally and separated by a septum. Some segments are specialized and differ to others.

Dorsal blood vessel

Blood vessel that runs longitudinally on the dorsal side of the gut. Visible through the body wall. Blood moves posteriorly.

Cerebral ganglion

A collection of nerve cells that encircles the gut just anterior to the pharynx. Functions as the brain.

Pharynx

A cavity or part of the tube between the mouth and esophagus. In earthworms it's thickened and muscular.

Ventral nerve chords

Paired nerve chords that are attached to the ventral surface of the body wall under the gut.

Pseudohearts

Thickenings of blood vessels that pump blood from the ventral blood vessel to the dorsal blood vessel. There are 5 pairs located in the region of the seminal vesicles.

Crop

Storage section of the gut that holds food before it passes into the gizzard

Gizzard

Muscular part of the gut that often contains grit to help break up good before it passes into the section of the gut where digestion takes place

Seminal vesicles

Sacs that produce, store and release sperm. Often 3 pairs.

Septum

Thin membranous wall that separates segments and holds the body wall and other organs in place

epidermis

Outermost layer of cells of the body wall, usually beneath a cuticle layer

Chloragogenous cells

Yellow in color, cells that envelope the gut and have a similar role as the liver in mammals: detoxify, modify and store substances absorbed from the gut.

parapodium

Paired flap or paddle-like structures on each segment of a polychaete worm. Used for gas exchange and locomotion.