Recently whilst diving at one of our local sites we came across an animal we had never seen before. It turned out to be a member of the sea slug family, though significantly larger than most common sea slugs, called the Highland Dancer Pleurobranchus membranaceus see photo below. These beautiful, yet odd looking creatures are found from the Western Mediterranean to the Atlantic coast of Ireland and France as well as the British Isles. An individual is usually about 70mm in length. They swim upside-down using an undulating foot to propel them through the water.
Sea slugs are part of the phylum mollusca, which encompasses animals such as bivalves and squid. The Highland dancer has a hidden in internal shell, different from say a mussel that has an exterior shell. When we saw the Highland Dancers there was an individual every metre or so laying a beautiful ribbon of eggs. The Highland Dancer is well camouflaged, probably the reason we had never noticed the species before. Yet the ribbon of eggs are bright white and each ribbon contains more than one million eggs. It was quite a magical experience watching them lay their ribbon of eggs.