Historical reference: Do not rely on this information. It is very old. About this collection
Archichaetopoda, an order of Chaetopoda (or bristle-bearing worms), which contains Saccocirrus, a small worm from the Mediterranean and Black Sea. In the position of the nervous system and the proportions of the two first segments of the body it agrees with the Archiannelida. It differs, however, in the presence of bristles, etc.