Table 1.

The state of segment specific characters in mid-body segment and the pygidium in P. dumerilii

Character	Body segment	Pygidium
Outer annulus	Present	Present
Appendages	One pair of biramous parapodia with each two cirri and two chaetae bundles	One pair of cirri
Ventral ganglia	Paired ganglia interconnected by a commissure	Absent, but a pygidial commissure is present
Peripheral ganglia	One pair of parapodial ganglia	One pair of presumably cirral ganglia
Muscular elements	Longitudinal muscle bundles, transverse muscles, parapodial muscle complexes	Circular muscles, specific ventral muscle complex
Blood vascular system	Dorsal and ventral longitudinal vessels, lateral and parapodial vessels, gut plexus	Circular blood sinus
Secondary cavity	Paired coelomic sacs delineated by myoepithelial cells formed by schizocoely	Unpaired coelomic cavity delineated by myoepithelial cells, of unclear developmental origin
Free swimming cells in the secondary cavity	Numerous different coelomocytes	Absent
Nephridia	One pair of metanephridia	Absent