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Table 1 The state of segment specific characters in mid-body segment and the pygidium in P. dumerilii

From: A metameric origin for the annelid pygidium?

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