107 (106) Zone of membranelles in spiraling buccal cavity, paralleled anteriorly 

 by 5 closely set rows of cilia. One to three posterior spines present. 

 Family CAENOMORPHIDAE. 



107 (106) A rectangular group of 9-12 membranelles in small buccal cavity. Seven 

 rows of prebuccal cilia. No posterior spines present 



108 



108 (107) All somatic cilia simple. Family EPALXELLIDAE. 



108 (107) One to two posterior cirri present. Family MYLESTOMATIDAE. 



109 (106) Apical suctorial tentacle or sucking disc present. Ciliary rows 

 straight or spiraled, usually only one-third to two-thirds cell 

 length, terminating near suctorial tentacle. Ectocommensal on 

 gills of bivalve molluscs 



110 



109 (106) No suctorial tentacle or sucking disc. Cilia in 1-3 

 fields, including a ribbon of 4-15 parallel oblique 

 ciliary rows encircling cell like a neck scarf. Cili- 

 ated larvae, order Suctorida. (Families separated 

 by adult morphology, couplets 112-121.) 



39 



