#CreatureFeature – Chromodoris westraliensis (Western Australian Nudibranch)

Branching Out to Our Nudi Friends!

If you’ve ever dived or snorkeled through reefs off WA’s coast, you may have come across the stunning turquoise, black and rust-coloured Western Australian nudibranch, Chromodoris westraliensis. Whilst you might not think much of them except for their spectacular beauty and cute rabbit ear-like rhinopores, nudibranchs are fascinating animals, vastly different from their similar-looking sea slug cousins.

Their name, meaning ‘naked gills’, refers to the exposure of their breathing organs as a cluster of gills at the back or along the flanks of the animal. Some are vividly coloured or boast elaborate gills, whilst others are cryptic, able to hide away in their reefy habitat using excellent camouflage.

Chromodoris westraliensis- Western Australian Nudibranch (Image: Reef Life Survey)

Incredibly, nudibranchs are masters at chemical conversions and symbiosis. They use chemically-sensitive thin layers of tissue, called rhinopores, to detect chemical signals from their prey, allowing the nudibranchs to navigate towards their food. Many species have chemical defenses, such as stings and toxins, to poison or offend their predators, and can utilize bold warning colouration to indicate that they don’t taste good. Non-toxic species can also ride off this strategy by mimicking the warning colouration. Numerous microscopic algal cells, known as zooxanthellae (also found in corals), have adapted to living inside the nudibranch’s tissues, trading nutrients for the photosynthetic sugars produced by the algae.

Nudibranchs are hermaphrodites, meaning they possess both male and female reproductive organs. However, they don’t fertilise themselves, and instead sexually reproduce by mating head-to-tail. Some species are able to regenerate their penis after it snaps off into their partner! They lay their eggs in a jelly matrix that forms a fettucine-like ribbon, from which the larvae hatch and float on the current until metamorphosing into adults.

In 2000, an unusual nudibranch was spotted by scientist Dr Nerida Wilson whilst diving off Dampier in the State’s North West. This nudibranch, sporting bold orange, blue and white colouring, was found to be a new species. This species preys on Cnidarians – or jellyfish – and absorbs the stinging cells from the prey before redistributing them to the tips of their cerata, the finger-like growths along the length of the animal. Here, the stinging cells provide the nudibranch with its own chemical protection from predators! The nudibranch also performs a warning dance when threatened by waving its cerata.

Moridilla fifo, named after Fly-In Fly-Out workers in WA’s North West (Image: ABC News)

In 2016, a naming competition was held for the species, and Patrick Dwyer from NSW topped it with Moridilla fifo. His reasoning? Like the Fly-In Fly-Out (FIFO) workers of WA’s North West, the nudibranch redeploys its workers – the stinging cells – to where they’re needed most. And to top it off, the blue and orange colouration matches the high-vis cotton drill scheme of the FIFO workers.

This nudibranch sure suits its name!





Title photo: Peter Southwood

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