152 PART II. SYSTEMATIC ACCOUNT 



Key for the determination of orders, families 

 and genera of Pogonophora 



1 (10) Metameric dorsal shields, or more or less metameric glandular portions 



of the integument, are present in the postannular region of the trunk. 

 Transverse rows of cuticular plaques are usually absent from the 

 postannular region. The spermatophores are spindle-shaped. The 

 tentacles are always free. The anterior part of the tube is always flimsy. 



I. Order Athecanephria (p. 154). 



2 (7) Usually 6-10 tentacles; if only 2 tentacles then the anterior part of the 



trunk is without pronounced metamerism. 



I. Family Oligobrachiidae (p. 154). 



3 (6) Less than 10 tentacles. Anterior part of the trunk has no paired metameric 



papillae. 



4 (5) Tentacles 6-9, bearing pinnules. 1. Genus Oligobrachia (p. 154). 



5 (4) Two tentacles; no pinnules. 2. Genus Nereilinum (p. 162). 



6 (3) Twelve tentacles. The anterior part of the trunk bears more or less 



metameric paired papillae, which sometimes carry cuticular plaques. 



3. Genus Birsteinia (p. 169). 



7 (2) Not more than two tentacles. Paired metameric papillae are present. 



II. Family Siboglinidae (p. 174). 



8 (9) One tentacle. 1. Genus Sibogliniim (p. 174). 



9 (8) Two tentacles. 2. Genus Siboglino'ides (p. 325). 



10 (1) The postannular region of the trunk lacks metameric dorsal shields or 



glandular areas, and carries metameric transverse rows of adhesive cuti- 

 cular plaques. The spermatophores are leaf-shaped. The tentacles may 

 be free, or neighbouring ones may adhere at the base. The anterior part 

 of the tube may either be flimsy or end in a hard funnel. 



2. Order Thecanephria (p. 331). 



1 1 (24) Tentacles free. Cuticular plaques in the anterior part of the trunk, if any 



are present at all, lie directly on the papillae. The anterior part of the tube 

 is flimsy, with walls which collapse easily. 



I. Family Polybrachiidae (p. 332). 



12 (21) Tentacles 2-14. The cephalic lobe merges into the protosoma. 



13 (18) The protosoma is divided from the mesosoma by a groove. The anterior 



metameric papillae possess cuticular plaques. 



14 (17) Tentacles 5-13. The keels of the bridle are simple. 



15 (16) The base of the tentacular crown is horseshoe-shaped. The cuticular 



plaques on the anterior papillae are round or oval, with crescentic front 

 edges. There are not more than 30 pairs of metameric papillae. The 

 toothed platelets of the girdles lie in 1-3 rows. The tube may have 

 regular or irregular rings. /. Genus Heptabrachia (p. 332). 



