Family Sipunculidae

1. With a pair of protractor muscles ..................................... Xenosiphon branchiatus (Fischer, 1894)

– Protractor muscles absent ....................................................................................... Sipunculus ........2

2. With 42 or more LMB; digitate processes of the brain present .......................................................... ....................................................................... Sipunculus (Sipunculus) cf. polymyotus Fisher, 1947

– With 41 or less LMB; digitate processes of the brain absent.....................................................3

3. With 34 or less LMB; nephridia partially attached .......................................................................... ............................................................................... Sipunculus (Sipunculus) nudus Linnaeus, 1766

– With 35–41 LMB; nephridia unattached ............................................................................................ ......................................................... Sipunculus (Sipunculus) phalloides phalloides (Pallas, 1774)