Little egg cowrie snails: masters of disguise
Becky Crew is a Sydney-based science communicator with a love for weird and wonderful animals. From strange behaviours and special adaptations to newly discovered species and the researchers who find them, her topics celebrate how alien yet relatable so many of the creatures that live amongst us can be.
WITH A NAME LIKE ‘little egg cowrie’, and that lovely creamy appearance, you’d be forgiven for thinking these two perfectly formed creatures are some kind of Michelin star dessert.
But you won’t find egg cowries on a dessert plate any time soon – in fact, you’ll have a hard time finding them anywhere, because these little guys are masters of disguise.
Calpurnus verrucosus, also known as the umbilical egg shell, is a species of sea snail found off the coast of Queensland and New South Wales, throughout the Western Pacific Ocean and off the coast of south-east Africa.
They belong to the family Ovulidae, nicknamed ‘false cowries’ because they look just like the beautifully patterned cowry seashells that once served as currency in Africa and China.
However, it’s not the shell that gives egg cowries their distinctive colours and patterns – it’s their retractable mantle, (or flesh) that wraps around the exterior of their plain white shells.
Egg cowries can morph into host colours
Egg cowries don’t pose any danger to humans, but they love to make a meal out of the millions of tiny polyps that come together to form leather coral. And in spite of themselves, these polyps actually help the egg cowries stay hidden from predators while they’re getting their fill.
When egg cowries consume the polyps, their mantles start to mimic their hues and colour patterns until the egg cowries are practically indistinguishable from their hosts. The phenomenon is known as alimentary homochromy, and it’s one of the most effective examples of camouflage seen in marine invertebrates.
Not only can egg cowries adjust the colour of their mantles to perfectly match the organism they’re sitting on and feeding off, some species even have the ability to chnage their external shape and texture too. They have papillae, or little finger-like projections, on their mantles and these can morph and mimic the exact polyp structure of their hosts.