Why bryozoans have avicularia : a review of the evidence. American Museum novitates ; no. 2789

Abstract

"This review summarizes the evidence for alternative functions of avicularia and vibracula. In the present paper I review the history of speculation on the adaptive function of avicularia and evaluate the evidence for the various functions suggested for them: defense, food-gathering, creation of water currents, respiration, cleaning, and nutrient storage. Then I suggest some alternative views and ways in which they might be tested. Early workers believed that their function might be defense of the colony, and since Darwin's time this function has become tied in with a selectionist argument in which increasing polymorphism of colonies, specialization of zooids for feeding, reproduction, and defense leads to increasing success. In only a few cases has the function of avicularia and vibracula been empirically established. The pedunculate Bugula type of avicularia has the ability to capture possible enemies. The vibracula of some lunulitiform colonies are used in locomotion and cleaning. No defensive or other function has been demonstrated for other avicularia and in fact, observations on their morphology, behavior, and position in the colony are incompatible with the hypothesis that they act in defense of the colony"--P. [1].