The violet sea snail (Janthina janthina), also known as the Bubble Raft Snail, is a species of sea snail which has a truly strange life cycle. While they are a tropical species which is mainly at home around the equator they have been confirmed to be present around the south west coast of England, in parts of the English Channel and off the coast of Wales and the south of the Republic of Ireland.
This species begins life as a free-swimming larva. Once it reaches its adult form it produces mucus which it agitates with its foot to mix it with air fill it with bubbles. This creates a ‘bubble raft’ which keeps the adult sea snail floating on the surface of the sea, upside down with its shell hanging downwards. This species will spend the rest of its life in this manner, feeding on floating jellyfish. A fully grown violet sea snail is usually around 3 to 4cm across the shell. Mating takes place when the male releases sperm which come into contact with females and fertilise the eggs inside. If at any stage of its life the violet sea snail becomes detached from its bubble raft it will sink to the seabed. Once there it is unable to create another bubble raft since it can only produce the mucus and cannot create bubbles itself. Violet sea snails which find themselves stranded on the seabed are not adapted to life there at all and will soon die. Violet sea snails are so-called simply because the lightweight shell they live in is made up of various shades of purple and the animal inside is itself violet in colour.