Polychaete Worms

Vermes is an obsolete taxon used to group all non-arthropod invertebrates together.  Here the Class Annelides has now been promoted to the Phylum Annelida.  The order Polychaetae errantes is now classified as the Class Polychaeta.  The Annelida are the segmented worms (arguably some memberts have lost segmentation) with the polychaetes being the bristle-worms, both the formal and informal names refer to the many rigid bristles which extend from each segment’s parapodia.  This chart shows adult sand worms (1, 2, 3 & 9) but the group also include burrowing and tube building worms.  Annelids have a closed circulatory system which is highlited in the by the vessels (red), a partitioned through-gut (yellow) and cephalisation (concentration at the anterior end) of sensory organs (6 & 8).