On morphology and reproduction of‘Hippodiplosia’ insculptaandFenestrulina malusii(Bryozoa, Cheilostomata)

Osburn's (1952) Hippodiplosia insculpta and Fenestrulina malusii were studied at Santa Catalina Island, California. In H. insculpta the protruded lophophores form a continuous incurrent area, and the growing edges are the only excurrent areas. The hydrodynamics of this pattern apparently sets a maximum to the size of the colonies. Female zooids can be recognized already at the growing edge; later on they induce their distal neighbour to form an ovicell. While the first oocyte develops the maternal polypide degenerates and a small, non-feeding polypide develops. These non-feeding zooids develop a series of eggs, the nutrients of which must be supplied by the neighbouring zooids. This is made possible through a pattern of zooids in which more than 99 % of the female zooids have four or more male neighbours. Larvae which were prevented from settling for 12 hours or more were not able to settle or the metamorphosis/ancestrula formation was unsuccessful. The ancestrula is composite with three buds which cover the primary zooid except its basal side and orifice. In F. malusii almost all zooids produce eggs and the individual polypides are feeding during several cycles of oocyte development and embryogenesis. When two colonies meet and fuse, a maternal zooid from one colony may induce a zooid from the other colony to form an ovicell. In both species the ovicell consists of an uncalcified ectooecium and a calcified entooecium which are outgrowths from the frontal wall of the zooid distal to the maternal zooid. The development in the ovicell lasts 11–12 days and the next egg enters the ovicell shortly after the liberation of the larva.