Peck. L.S., P.J. Hayward and M.E. Spencer-Jones. 1995. A pelagic bryozoan from Antarctica. Marine Biology 123: 757-762.
This paper describes a remarkable Alcyonidium bryozoan that is pelagic and forms spherical colonies. The first bryozoan to exhibit either of these characteristics, it challenges beliefs about the phylum. What is the ecology and morphology of this colony, and how is it related to other Alcyonidium species?
Bryozoans, small marine suspension-feeders, typically form sessile encrusting colonies attached to hard substrates, with very few species being unattached. Alcyonidium species are common in shallow coastal waters, and the benthic, attached Alcyonidium flabelliforme occurs in large palmate colonies near the study site.
Three of the brown pelagic specimens were collected in Antarctica, preserved, and later measured and examined. The hollow spheres ranged in diameter from 5 - 23 mm and consisted of a single sheet of outward-pointing zooids. Their presence in large numbers alongside an ice shelf indicates they likely feed on ice algae in the lower ice layers. These colonies may represent the juvenile stage of A. flabelliforme, as supported by the absence of embryos or gonadal tissue in the three colonies.
This unique pelagic, hollow spherical colony is likely a juvenile form probably of A. flabelliforme, that exploits the presence of algae in the ice and aids in dispersal. Perhaps it will prove to be only the first of previously undescribed pelagic phases in bryozoans.
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