Field of Science

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.


  1. Thanks for the link!

    That's a cool wandering colony. The name was in my books, but that's as far as it went.

  2. You're welcome.

    Yeah, I was a little surprised how little mention there was of these guys out there. I mean, in human terms this is the equivalent of everyone on the ground floor of a multi-storey building picking the building up and walking it around. How is that not worth wowing over?

  3. Are there any parasites that specialize in attacking them? Are there any that are themselves parasites (aside from just riding on snail shells)?

  4. I haven't been able to find reference to any bryozoans being parasitic, though, as you note, many are epizoic.

    Nor have I been able to find any references to specific parasites of lunulitiform bryozoans, but there's precious little info about any aspect of lunulitiforms to begin with.

  5. Thank you.

    there's precious little info about any aspect of lunulitiforms

    There's so much basic, descriptive biology still left to be done.

  6. As a physical hydrologist, the world of the microscopic has mystified ... and eluded me. Not that it's ever too late for learning.

  7. Trust me, some of the microscopic is absolutely mind-blowing.


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