Key: Step 2. 1

1a. Solitary or colonial; body undivided or divided into two or three regions; branchial sac without folds; gonads unpaired, in or below gut loop; common sperm duct, and usually oviduct, accompanying rectum.


Order Enterogona

Step 3. 2

1b. Solitary or colonial; body undivided; branchial sac with or without folds; gonads lateral in mantle wall; no common sperm duct or oviduct accompanying rectum.


Order Pleurogona
Suborder: Stolidobranchia

Step 19. 18