Mary's Naturalist Curiosities
Spring is in the air - and in the sea!
With the arrival of spring we have observed a great deal of mating activity around our local reefs. Male cuttlefish dash about furiously, changing colours as they attempt to ward off competitors. Damselfishes are busy depositing their eggs on any available surface.
It took considerable effort to identify the following fascinating technique of egglaying. The photograph on the left below was taken a few months ago. I have looked through all our invertebrate books and could not find anything that resembled it. Suggestions from biologists who looked at the photo ranged from various worms to sea squirts. However nothing seemed to match until I happened on a photo in a newly published divers' guide to the UAE. The photo on the right was taken a few days ago and confirmed the identification in the book.
The curious little tubules that look as though they are made of cellophane are the egg cases of a murex mollusc. These molluscs are gastropods (Class Gastropoda), commonly known as snails. Most murex have thick, hard shells with many knobbly spines. The animals shown in the photo on the right were in the process of laying their eggs. The picture shows only two shells but there were about 5 or 6, all in a huddle. The eggs were being deposited mostly on the rocks at the base of the reef but one batch ended up on the surface of a neighbouring shell.
Several species of murex were well known thousands of years ago as the source of Royal Purple, the dye used to colour the robes of rulers including Roman emperors. The dye is made by a small gland in the body of the animal. Only two or three drops of the chemical could be obtained from each murex and it was, therefore, extremely expensive.