The sea swallow (or blue sea slug) is a shell-less mollusc which floats upside down in the open sea utilising ocean currents and the wind to be transported around.
Occassionally they may be washed ashore by onshore winds and are found along with bluebottles and their relatives.
Recently, a Kidd’s Beach resident Karen Jansen reported a specimen found alive on the shore east of the village to museum scientist Kevin Cole.
The specimen was identified as Glaucus atlanticus – interesting to note is it is camouflaged in that the blue side of their body faces upwards, blending in with the blue of the water and the silver/grey side of the sea slugs faces downwards, blending in with the silvery surface of the sea.
Glaucus atlanticus feeds on other pelagic creatures, including the Portuguese man o’war. This sea slug stores stinging nematocysts from the cnidarian within its own tissues as a defense against predation. It would be wise to handle this slug carefully as one may receive a dangerous sting which is very painful.
This sea slug can grow up to 3 cm in length. It has only been recorded from the east and south coasts of South Africa. Below is a photo taken a couple of years back of a sea swallow found at Buffalo Bay, SA by Emil Niksch.