“Living asteroid” new, super-deep sea star

A “living asteroid” – or sea star – is lurking off the coast of southern Australia, in waters 3,850 metres deep.

It’s the deepest known occurrence of a sea star in the continent’s waters, and also a brand-new species.

The sea star, dubbed Poraniomorpha tartarus, was collected in a 2017 ocean expedition led by the Museums Victoria Research Institute.

But these deep-sea expeditions yield many more specimens than there are experts to identify them – there’s an estimated 250,000 undiscovered species in deep Australian waters.

This is why it’s taken 6 years for the new sea star to be described in Memoirs of Museum Victoria.

These sea-stars are sometimes referred to as asteroids, not because they are from out of this world, but because they are from the class Asteroidea.

“This is the first time this genus has been recorded from not just Australia, but also the Southern Hemisphere,” says Dr Christopher Mah, a researcher at the Smithsonian National Museum of Natural History, US, and self-styled “world’s expert on living asteroids” who was brought to Australia to help with taxonomy and description.

“The family to which Poraniomorpha tartarus belongs is a group that we will eventually get to including in our research of deep-sea sea star species, accounting for its appearance, ecology and genetics, as knowledge becomes available.”

Mah says it was “pretty obvious” that the sea star was a new species once he’d seen it, “mainly because no members of this group of sea stars, the family, Poraniidae, were known from Australia”.

Sea star
Poraniomorpha tartarus. Credit: Museums Victoria

The cold water-loving family has been spotted elsewhere, particularly in the North Atlantic Ocean and while this is the deepest star formally reported in Australian waters, Mah knows they go deeper.

“Deep-sea expeditions around Australia have been VERY active in the last 5-10 years – CSIRO investigating around the South Pacific, the Falkor in various places around Western Australia, such as Ningaloo, et cetera,” he says. These trips have yielded asteroids in deeper areas.

“Experts such as myself must secure relationships, time, and funds to work on these specimens,” says Mah.

“This is one of the aspects of the ‘biodiversity crisis’ is that experts in taxonomy – the science of identification, naming, and recognising species – are increasingly fewer for certain groups.

“Sea stars might be familiar to the public, but there’s surprisingly few specialists who work on them. In part, this is why they brought me down to Australia in the first place.”

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The Ultramarine project – focussing on research and innovation in our marine environments – is supported by Minderoo Foundation.

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