5 Fifth hooks with a lateral flange. Hooded hooks from setiger 



10-17. Pygidium with several small pai)illae. [Lives in shells 



of hermit crabs) P. commensalis 



5' Fifth hooks with a twisted sheath or ridge on concave side 

 of apex. Hooded hooks from setiger 7. Pygidium saucer- 

 shaped. [No notosetae on first foot] P. icebsteri 



6 Notosetae present on first foot. Posterior notosetae include 



2-3 short spines slightly stouter than the long capillaries P. caeca 



6' No notosetae on first foot. No specialized posterior notosetae P. socialis 



7 Fifth hooks with a hairy tuft between main and accessory 



tooth. [No eyes. Notosetae present on first foot. No special- 

 ized posterior notosetae] P. hart ntaiiac 



T Fifth hooks without hairs between main and accessory tooth 8 



8 Fifth hooks with two teeth partly encircled by a shelf or flange. 



Posterior notosetae include large hooked spines P. colon ia 



8' Fifth hooks normally bidentate without an encircling flange. 



No specialized posterior notosetae 9 



9 Only four pairs of gills on setigers 7 to 10. Notosetae absent 



from first foot. | Body very small] P. tclrubnnichia 



9' About 14 pairs of gills. No notosetae on first foot. An occipital 

 tentacle on pro.stomium. [Bifid, bristled .setae accompany 

 fifth hooks] P. ligiii 



10 Branchiae entirely absent. Neurosetae of first foot include a 



stout hook-shaped seta. (SpiophaiicK) 11 



10' Branchiae present. No specialized seta on first foot 12 



11 Prostomium with pointed lateral projections. No occipital 



tentacle. Hooded hooks bidentate throughout. [Notopodial 



lobe of setiger 1 well developed] S. boiiibtix 



11 ' Prostomium without lateral projections or occipital tentacle. 

 Anterior hooded hooks minutely tridentate, posterior ones 

 bidentate S. »'/>//((// 



12 Branchiae from setiger 1 13 



12' Branchiae from setiger 2 20 



K' Branchiae present on 20 setigers or more 14 



l.V Branchiae on setiger 1 or 1-3 only 19 



14 Posterior noto.setae include hooded hooks. Branchiae absent 



from posterior .segments. [Prostomium hilobed in front. 



(Scolcculcpidcs)] ^'. rlridis 



14' Posterior notosetae without hooded hooks. Branchiae continue 



to posterior segments 15 



66 



