Sexual Dwarfism in Cribrilina annulata (Cribrilinidae-Bryozoa)

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Abstract
Evidence suggests that Membraniporella corbicula O'Donoghue and O'Donoghue, 1923, described from Vancouver Island, belongs to Cribrilina annulata (Fabricius), a common northern marine cheilostome. The terminology as applied to female individuals in the Cheilostomata is defined here to include three principal types: ovicelled zooids, gonoecia, and gonozooids. The occurrence of dimorphic female zooids in C. annulata is documented, comprising ovicelled zooids as well as accessory dwarf zooids with ovicells (gonozooids). The gonozooids are usually recumbent on the frontal shields of the underlying autozooids and are budded off from frontal dietellae located on the proximal gymnocysts. It is suggested that the term "dietella," formerly restricted to a pore chamber marginally positioned near the base of the zooecial wall, be emended to include frontal and basal chambers as well. The presence of adventitious gonozooids in this species constitutes an important new addition to the range of polymorphism in the Cribrilinidae. No similar instance of dimorphic female individuals occurring simultaneously are recorded for the Cheilostomata. An increase in larval productivity may result from frontal budding of gonozooids.

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