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A violet snail (Janthina janthina). Credit: Dimitrios Poursanidis

Violet snail an ocean wanderer

  • March 06, 2014

The violet snail floats on a homemade raft of bubbles.

Contributor
Becky Crew

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 ITS BRILLIANT purple hue and nifty homemade raft of bubbles, the violet snail (Janthina janthina) is as pretty as it is industrious.

Found all over the world in tropical and temperate oceans, including all round the coast of Australia, the violet snail belongs to the 'Pleuston' group of organisms that live on the surface of the ocean. And it's a pretty important member - while only 3 or 4cm long, it's one of the biggest organisms living in this thin but incredibly expansive habitat.

Here it excretes mucous from a gland in its foot, which binds to a string of air bubbles that are either released from inside its shell or created by the snail agitating the water with its foot.

This mucous-bubble mixture hardens to form a floating raft, which the violet snail attaches itself to for an effortless journey across the open ocean. If the raft ever breaks, the violet snail will sink into the ocean below and die.

Violet snails snack on jellyfish

Violet snails feed off a variety of jellyfish such as by-the-wind-sailors (Velalla velella) and the dreaded bluebottle, or Portuguese Man O' War (Physalia physalis), responsible for up to 10,000 human stings in Australia each summer.

They start out life as males and then gradually become females as they mature. The males don't have a penis, so they just excrete their sperm in a female's direction. The females give birth to live, miniature purple snails that have the capacity to build their own tiny bubble rafts.

These baby snails are protected from day one by a great camouflage strategy known as countershading. It works by having the underside of their shell - which sits on the surface of the ocean when they're floating - be much darker in colour than the top.

Think of penguins when they're swimming with black plumage on their backs and white plumage on their stomachs. Countershading works because predators below think they're looking at the light-coloured sky above, while predators above think they're looking at the deep colour of the sea below.