The inference of extrazooidal feeding currents in fossil bryozoan colonies

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Abstract
The feeding autozooids in a bryozoan colony may cooperate in differing ways to produce an extrazooidal water-current system organized on a colony-wide or subcolony-wide basis. The presence of an extrazooidal current system may be inferred in fossil stenolaemate bryozoans which exhibit either a differential spacing of open autozooecial apertures or a systematic variation across the zoarial surface in the orientation of autozooecial distal portions. By inference, aggregations of autozooecial apertures represented loci of inhalant extrazooidal flow whereas zoarial protuberances (i.e., monticules) with outwardly leaning autozooecia acted as loci of exhalant extrazooidal flow. Bryozoans having autozooecia opening obliquely into gaps or fenestrules in their zoaria probably drew a unidirectional extrazooidal current of water through the fenestrules. Extrazooidal water currents may function to accelerate colony clearance rate, decrease the chances of recycling filtered water, aid spermatozoan and larval dispersal and clear sediment from the colony surface.