Colonies on the Move

First off, the latest edition of the plant blogging carnival Berry Go Round is up at A Neotropical Savanna, so go take a look.



Secondly, Susannah of Wanderin' Weeta has presented a nice overview of bryozoans. Bryozoans, for those as don't know 'em, are tiny colonial aquatic animals, and are one of the groups of organisms that I personally think are most unfairly overlooked. A great many people will have probably never heard of them, but they are not uncommon, they or the remains of their colonies are easily found attached to rocks, shells, etc. at any beach, and their delicately structured colonies can be exceedingly attractive, as indicated by their sometimes-used common name of "lace animals".

As a follow-on from Susannah's post, I just thought I'd present you with one of the more unusual and eye-catching types of bryozoan. Modern lunulitiform bryozoans belong to three families, Lunulitidae, Selenariidae and Cupuladriidae. Unlike other bryozoans, lunulitiforms colonies are not anchored to their substrate, but lie unattached on the surface of the sediment. While free-living bryozoan colonies sometimes grew quite large during the Palaeozoic, the rise of a well-developed infauna (burrowing animal assemblage) and the resulting bioturbation rather did it in for the large forms, and modern lunulitiforms are small, only about a centimetre and a half across at most. They are disc-shaped and raised in the centre, so they look not unlike a Southeast Asian fieldworker's hat, with the zooids all emerging on the outer surface. As shown in the picture near the top of this post from Aaron O'Dea, lunulitiform colonies are generally highly integrated, with zooids growing in a strict radial pattern.



So highly integrated are these colonies, in fact, that some are able to move as if they were a single organism, as shown in the photo of Selenaria maculata just above by P. L. Cook. The zooids around the edge of the colony develop exceeding long setiform avicularia (to find out what an avicularium is, read Susannah's post) that the colony can use like legs to walk on. Selenaria maculata colonies can reach speeds of about one metre per hour, which may not sound particularly fast until you consider that most bryozoan colonies don't move at all.