CONGRESS ON CODIUM

All of the sea slugs in the Sacoglossa order are herbivorous, well nearly all, a very few prey on the eggs of other sea slugs. However, that great majority that feed on plants do so by puncturing the cell walls of algae and sucking out the contents. The sacoglossans are a very diverse group in presentation exhibiting a range of forms from shelled to those with cerata-like appendages on the dorsum and every type of variation in-between but at the same time are highly specialised in method of feeding and diet.

An example to be found on a species of Codium algae is Elysia maoria. If you take the time to slow down and examine those little green velvet-looking patches you may sometimes be rewarded by finding that tiny little sea slug – living thereon feeding, mating and laying spiral egg coils, effectively there for their entire adult lives. (Advice for divers in southern Queensland south to Victoria and New Zealand waters.)

Above – The sacoglossan sea slug Elysia maoria

Curious to relate, these little hermaphrodite sea slugs mate through hypodermic insemination. The body wall of a partner is pierced and sperm is deposited directly into the body cavity eventually making its way to fertilise the eggs.

Above – Spiral spawn of Elysia maoria

David A. Mullins – October 2019