COMMON GREY SEA SLUG

The eggs of Aeolidia papillosa

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Last summer I was surprised to discover the eggs of the Common Grey Sea Slug (Aeolidia papillosa) under a stone at Sandsend. This year on the 2nd of July I scrambled down the cliff at Kettleness for a spot of rockpooling in the beautiful pools there on a baking Summer's day.

Once again, under a stone on the middle shore was an example of one of the characteristically spiral shaped egg masses of this fascinating creature. Normally living in much deeper water, these sea slugs come up the shore every year in July and August to spawn.

This time, under another rock I was lucky enough to find one of these elusive, beautiful sea slugs. It was only partially covered with water in its original position, but once placed on a flat stone in a clear pool it could be seen in all its glory.

Aeolidia papillosa

They feed on sea anemones and can actually use the undischarged stinging cells (nematocysts) of the anemones they've eaten. The stinging cells pass undigested into the tips of the projections, known as cerata, that cover the surface of the sea slug helping to protect it from predators. An effective defence mechanism is vital in a creature whose shell has been lost through evolution

Although known as the Common Grey Sea Slug, the colour of the animals vary according to their local food supply, in this case the red sea anenomes on which it feeds have given it a rosy tinge. They can grow to 120mm in length, although this specimen is much smaller.

Against a £1 coin as a size comparison