A PELAGIC BRYOZOAN FROM ANTARCTICA

Spherical or sub-spherical bryozoan colonies were collected from the s urface waters of a coastal polynya in the southeastern Weddell Sea nea r Halley Station in February 1992. These are the first truly pelagic m arine bryozoan colonies yet recorded. The collection site is at the ed ge of the Brunt ice shelf, which is between 150 and 250m thick in this area, and the depth of water to the seabed is similar or equal to 400 m. The colonies were hollow, composed of a single layer of autozooids , and appeared complete and undamaged. They were between 5.0 and 23.0 mm in diameter, were brownish in colour in life, and pale yellowish br own after preservation. Light and scanning electron microscope investi gations of the colonies indicated that they belonged to the genus Alcy onidium, and they are here compared with A. flabellifome Kirkpatrick, a known antarctic benthic species. Both a pelagic existence and hollow spherical colony form are new attributes for the phylum Bryozoa. Howe ver, because of the plasticity of form of species belonging to the gen us Alcyonidium, there is not enough evidence for the introduction of a new species at this time. The colonies found may represent a previous ly undescribed juvenile stage of a known Alcyonidium species. It is po stulated that these colonies may obtain nutrition from the often abund ant populations of ice algae present in the lower layers of permanent sea-ice.