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 |