The body wall of cheilostome Bryozoa, V. Frontal budding in Schizoporella unicornis floridana

Abstract

Schizoporella unicornis floridana Osburn from Maryland and New Jersey, USA, produces two types of autozoids: (1) “primogenial” zoids, arranged in the brick-like “quincunx” pattern usual among cheilostomes; (2) “adventitious”, or frontally-budded zoids. Adventitious zoids are produced by expansion of the epitheca of primogenial or other adventitious zoids. The old aperture is sealed over and the hypostega becomes the body cavity of a new zoid. Vertical walls of adventitious zoids all contain an intercalary cuticle; basal walls are the frontal walls of zoids beneath. This sometimes results in trepostome-like zoid columns arising from the substrate; zoid columns may bifurcate in a way similar to zoid row-bifurcation in primogenial zoids. Adventitious zoids communicate with zoids at the same depth in the colony through annular septulae; they communicate with younger and older zoids through areolae. Adventitious zoids may sometimes give rise to primogenial subcolonies, which overgrow the colony surface. Frontal budding allows the development of massive nodules, which are of geological importance. These findings indicate that the hypostegal coelom is at least potentially a bud, and that genetic “information” necessary for producing an autozoid may be transferred from one building site to another. This idea has important implications in studying evolution of positions of zoids in a colony.