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Runner up - Opal sea squirt
Britain's largest sea squirt.
Adult sea squirts have an unusual circulation system in which blood is pumped in one direction for several seconds and then in the opposite direction for the same length of time. This species has a tough, leathery “tunic” that is milk-white in appearance. It’s the largest British sea squirt growing up to 12cm long – large enough that small anemones can sometimes be found living on it.
Image © Paul Naylor/marinephoto.co.uk