Hydroids and Bryozoans: The Weird and Wonderful

, 06 August 2019
Hydroids and Bryozoans: The Weird and Wonderful
© Nikki Hills

By Sarah Ward

Living Seas Officer

This July, Sussex Wildlife Trust was happy to host a specialist marine identification course for our volunteers. Funded by the National Lottery Heritage Fund through our Wild About Seaford project, we were able to arrange for two experts in the field to lead the course: Mary Spencer-Jones of the Natural History Museum and Joanne Porter of Heriot-Watt University. We were also very grateful to have been supported by the Booth Museum of Natural History, who kindly supplied us with specimens from their collection for the group to examine.

But what are hydroids and bryozoans, I hear you ask!

These are two distinct groupings of aquatic animals for which the majority are only found in the marine environment (although there are a few fresh-water species). They are two completely different types of creatures in terms of their classification, however are often easily confused due to having similar asthetics in many specimens – which is why they often get taught together. Hydroids and bryozoans often make up what is known as an ‘animal turf’ on rocks and other hard surfaces below the water – although this is commonly mistaken for being seaweed.

Hydroids are part of the group ‘cnidaria’ which also includes more familiar animals such as jellyfish and anemones – all cnidarians posess some kind of stinging cell. Hydroids tend to be colonial and posess special cells called polyps, which are specialised for particular tasks such as feeding or reproduction.

Bryozoans are a group of their own, and are sometimes more commonly called ‘moss animals’. Most bryozoans are colonial, and consist of a large number of zooids, each living within its own calcified box. Some species grow as ‘crusts’ on seaweeds or hard surfaces, whereas others may be erect or massive, resembling other taxa, like seaweeds or sponges.

The course was a fantastic opportunity to get back to basics and learn how to identify key species and groupings, either by eye or using a microscope. The skills learned by participants will be incredibly useful for identifying species during our Shoresearch and Seasearch surveys. We were also able to provide some identifications on some historical specimens from the Booth collection which did not have a label – some of which were pressings from over 100 years ago!

Many thanks to our tutors and to the enthusiastic group of Shoresearch and Seasearch volunteers who attended! 

 Seaford Community Wildlife Project is Supported by The National Lottery Heritage Fund

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