Polygordins

Polygordins, the type-genus of the family Polyyordiidce, and the best-known member of the class of primitive worms known as the Archi-Annelida (q.v.). It is a small marine worm, with the segmentation very feebly marked; they have neither bristles (setas), lateral appendages (parapodia), nor the respiratory processes known as cirri and branchiae. The intestine is straight, and the kidneys (nephridia) also very simple. • The fact that the nerves are retained in the hypodermis is another very primitive character. There are several species which are common in the Mediterranean; when irritated, they break voluntarily into fragments.