Feather stars are the closest thing we have to walking plants
THESE STRANGE, plant-like creatures hide in plain sight among bright corals and anemones, firmly anchored to the sea floor, as their slender, branching limbs billow like colourful fern fronds.
But things get positively weird when they break free – swimming, floating, or even walking through the ocean like a tiny Triffid that’s yet to realise its apocalyptic agenda.
Just look at this thing:
These are crinoids, members of the echinoderm family that also includes sea stars and sea urchins.
There are 600 or so species of crinoid on Earth, and they’re found all over the globe, in both shallow waters and at depths of up to 9,000 metres.
In Australia, they’re found everywhere from the mysterious eastern abyss that stretches from Launceston to Brisbane, to up in the Great Barrier Reef, and over on the west coast.
While many crinoids develop stalks to attach themselves to the sea floor as juveniles, they often lose these as adults to become free-swimming organisms.
The species that keep their stalks through to adulthood are called sea lilies, because they look like underwater flowers:
(Image Credit: NOAA)
Those that lose their stalks become known as feather stars.
Feather stars can still anchor themselves to rocks and substrate if they need to, using a set of tiny legs called cirri:
(Image Credit: Magnus Deep Below)
Those lovely fringed arms are covered in tiny, mucous-secreting tube feet that can move independently of each other, and this allows the feather stars to catch plankton and other microscopic morsels floating through the water.
But how they actually get this food into their mouths is a whole other story, as Sara Mynott, a marine biologist with University of Exeter in the UK, explains for Nature.
The process begins with the foot furthest away from the mouth being cleaned by the foot directly below it, bundling up the mucus-filled snack before transporting it, foot by foot, along the arm.
“The next foot down wraps around the one above it, and scrapes the food off for a second time,” says Mynott. “This process continues all the way down the arm of the feather star, creating a bolus of food that gradually increases in size.”
The bolus eventually makes it to the mouth, where it’s ingested in a U-shaped gut.
That horseshoe gut is important, because allows the feather star to position its anus right next-door to its mouth, because why complicate things when you can have everything coming and going from roughly the same area of your face?
While feather stars have the ability to move around, they’re very rarely caught doing it, and until recently, it was assumed that they were extremely slow-moving.
According to Tomasz Baumiller, Invertebrate Curator at the University of Michigan’s Museum of Paleontology, scientists used to think feather stars could barely manage to clear half a metre in an hour, but then one was recorded in 2005 clocking speeds of up to 5 cm/second (up to 180 metres per hour).
Here’s what they look like when they’re swimming, and it’s honestly so mesmerising, I think I’m about ready to welcome our Triffid overlords: