97 (92) Anterior suctorial tentacle or sucking disc present. . 98 



97 (92) No anterior suctorial tentacle 

 Annotated Systematic List). 



Silenella ovoidea, order Suctorida (see 



98 (97) Cilia restricted to one flattened surface. A short (about 8 cilia) 

 ciliary row at anterolateral margin. Commensal on hydroids, 

 and in branchial cavity of ascidians. Family HYPOCOMIDAE. 



98 (97) Cell ovoid to pyriform in shape. No such short ciliary row, or ciliary 

 rows more extensive. Ectocommensal on gills of bivalve molluscs. Family 

 ANCISTROCOMIDAE (also see couplets 28 and 110). 



99 {8i) Helical torsion reduces aboral surface. Ventral cirri in helical rows. 

 Family SPIROFILIDAE (also see couplet 30). 



99 (84) Aboral surface not so reduced, usually bearing sparse, widely spaced rows of 

 simple (often very short) cilia not used in locomotion 



100 



100 (99) Cirri of midventral axis arranged in a closely set double row — actually a 

 single zigzag series. Family HOLOSTICHIDAE. 



36 



