The erect calcified colonies of the anascan cheilostome bryozoan Melicerita obliqua and members of the ascophoram bryozoan family Cellarinellidae are large and numerous enough to be apparent in underwater photographs taken in shelf environments throughout the Ross Sea. Analysis
of preserved specimens from benthic samples showed that these two abundant groups had contrasting life history patterns. The branching colonies of the cellarinellids occurred in clumps or thickets. Though size and branching pattern differed from species to species, all shared a similar zooid
morphology, characterized by lack of an operculum and associated adaptations. Sexual reproduction appeared to play a small role in their biology partly because zooids in proximal regions became senescent and unable to feed or reproduce. Instead cellarinellids have maximized the ability to
reproduce asexually via fragmentation. Colonies suffered a large amount of partial mortality due to injury by microborers or activities of motile benthos. Broken distal ends of branches were, however, regenerated, while fallen fragments produced new attachment rootlets, and altered their direction
of growth. The blade-shaped colonies of Melicerita were spaced out more evenly over the sea bottom. This species showed a greater amount of sexual reproduction, and a much lower incidence of colony damage or partial mortality, but colonies that fell onto the sediment seemed generally
to die completely. It is suggested that both groups represent very ancient cheilostome stocks with origins in an area common to the Australian-Antarctic remnant of Gondwanaland.
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