Group autozooidal behaviour and chimneys in marine bryozoans

Abstract.

Marine bryozoans have a variety of behavioural reactions that are associated with different functions: feeding, cleaning, removal of filtered water, gamete release, avoidance reactions and, probably, sensation. Coordinated activities of polypides are regulated neurophysiologically, physiologically, structurally and, possibly, hormonally. Several group reactions are supposedly non-coordinated. Group autozooidal reactions and different types of colonial behaviour were observed and recorded for 17 bryozoan species and subspecies from the White and Barents Seas. Three local collective reactions (synchronised scanning, repeated particle transfer by circular water currents, and feeding and cleaning of the colony surface by "chains" of inclined lophophores) are described for the first time. The formation of water outlets (chimneys) was observed in four species with encrusting colonies. A new type of chimney was discovered in large colonies of Tegella armifera, in which chimneys are formed by temporary retraction of 10–12 neighbouring polypides. The space thus formed is surrounded by equitentacled lophophores standing vertically. Chimneys associated with elevated areas on the colony surface (monticules) were found in two species. In contrast to all previously published speculations and observations, the monticules were often places of incurrent rather than excurrent flow, and water outlets were formed in depressions between monticules. In Schizomavella lineata, monticules change their function from incurrent to excurrent after polypide degeneration. Conditions for the origin of various types of water outlets are discussed.