This study compared the sizes of zooids in colonies of the cheilostome bryozoan Cribrilina annulata collected from two differing substrata (stones and algae) in three regions of the White and Barents Seas. Zooids of the colonies growing on stones were larger than those in the colonies growing on the thalli of the red alga Odontalia dentata. Size differences of the zooids in the colonies growing on the same substratum in different regions were minor. Three possible explanations for these dimensional differences of zooids are discussed: (1) larvae of different sizes settle on different substrata; (2) ancestrulae of different sizes survive on different substrata; and (3) substrata influence the ancestrulae's size.
