Star Sea Squirts – what are they?

STAR SEA SQUIRTS or STAR ASCIDIANS: UROCHORDATA, CLASS ASCIDIACEA 

1. Surprisingly, these soft and often jelly-like creatures are related to the Chordata which is a group of animals with a primitive backbone
2. Another name for sea squirts is tunicates
3. These animals do not move around; they are sessile.
4. Most live attached to a firm substrate.
5. They have an outer tunic layer or test and two openings to the outside.
6. These openings are connected to the siphons through which water passes into and out of the body.
7. Small particles of food are filtered out of the water by the internal branchial sac.
8. The individuals in a colony are called zooids and these are more or less fused together.
9. The zooids may only be a few millimetres long and can be embedded in a common test.
10. They may have their own individual oral siphon taking in water but a shared atrial siphon expelling the filtered water and waste products.
11. Mostly, Ascidians live in shallow coastal water stuck onto or encrusting a wide selection of surfaces.
12. A microscope is sometimes needed to identify the different species.

Specific information about the Star Sea Squirt, Botryllus schlosseri (Pallas),  can be found on the Marine Life Information Network site run by the Marine Biological Association UK

More general accounts and pictures of this species can be found in the following books:

Barrett, J. and Yonge C. M. (1958 but reprinted many times) Collins Pocket Guide to the Seas Shore, Collins, ISBN 0 0 219321 3, page 192.

Erwin, D. and Picton, B. (1990) Guide to Inshore Marine Life, Naturalists’ Handbooks 21,  The Marine Conservation Society, Immel Publishing, ISBN 0 907151 345, page 104.

Hayward, P. J. (1988) Animals on seaweed, Naturalists’ Handbooks 9, Richmond Publishing, ISBN 0 85546 265, page 96.

Hayward, P. J.  and Ryland J. S. (1995) Handbook of the Marine Fauna of North-West Europe, Oxford University Press, ISBN 0 19 854055 8 (Pbk), page 709.

Hayward, P., Nelson-Smith, A. and Shields, C. (1996) Sea shore of Britain and Europe, Collins Pocket Guide, , ISBN 0 00 21995, page 304.

[This is a revision of a post first published 10 February 2009]

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