Sunday, December 27, 2009

High-density Housing (for Bryozoans)

This beautifully geometric piece of natural architecture is produced by the animal commonly called the sea-mat and scientifically known as a bryozoan (which means 'moss-animal'). This particular species is Membranipora membranacea and I picked it up yesterday, in a rock-pool on the seashore at Seaburn, near Sunderland.

Membranipora forms extensive, fast-growing colonies resembling a lacy mat, that spread over the surface of kelp fronds. It's common on all coasts around Britain and has been introduced into shallow seas in other parts of the world where there is some concern that its rapid rate of growth could suppress the reproduction of some marine algae.

Each calcareous compartment, secreted by the animal inside, contains an individual animal (zooid) that extends a feeding arm called a lophophore, for filtering out plankton.

The zooids retract into a tube within their walled enclosure at the slighest hint of danger but when they're all extended they resemble a garden of transparent flowers, gently waving their arms..

Each walled enclosure has a small tower at the junction with its neighbours' walls and ......

....there are often gaps in the walls, which give the colony a degree of flexibility as the supporting kelp frond bends in the sea currents. The gaps tend to be most conspicuous in older sections of the colony.

There are at least two kinds of zooid - the flower-shaped feeding lophophores and these translucent cylindrical forms.

I'm not sure what their function is but my guess is that they provide additional surface area for oxygen uptake or maybe waste disposal.

You can find out more about bryozoans here or take a look for yourself - these are low-power micrographs (maximum magnification x50) but you can see the living zooids with a hand lens if you put a piece of the colony in a shallow dish of seawater. You can find them all year-round and fine specimens are often attached to kelps that are washed up on beaches after storms.


  1. Utterly fascinating Phil, thank you so much for my continuing education. To think that there is a tiny world where I can't go without your help, wonderful.

  2. Thanks Toffeeapple, it's a real pleasure to be able to dhare it with others.... all the best for 2010..

  3. And have a great time exploring in 2010!! I can't wait to see what all you find for us!

  4. Hi,
    First, thanks for creating such a mesmerizing blog, your images and the accompanying information unlock the magical nature of tiny creatures! I have a question which may be most easily answered through regular e mail, (i can be contacted at, about where I, a nonscientist, can learn more about microorganisms for a children's book I plan to write and illustrate about them, I am finding that it's hard to find any compelling and reader friendly books on the subject with images as detailed and visually delightful as yours. any suggestions or perhaps you know someone else who might have some tips for a curious artist? Thanks!

  5. Hi Daria, Thanks for your kind comments. Most books on the subject tend to be academic ones and mainstream magazine and book publishing tends to ignore any living organisms that don't have fur or feathers. You might find it helpful to visit the excellent Microscopy UK web site at and while you're there take a look at the inspirational images at
    Good luck with your book!


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