World’s Most Beautiful Sponge Dismantles Its Victims Cell by Cell

The harp sponge would make for a pretty lousy household scrubber, except between blinds maybe. Seriously, how do you even clean between blinds? I’m 30 and I have no idea.

If you were a sea creature and you wanted to form a band, you’d have some tough decisions to make. Who should take vocals: dolphins or whales? And what about the drums? Presumably it’d be some sort of cephalopod, what with all those arms, but would it play on giant clams or brain corals? And good luck finding stringed instruments, unless you want to risk anaphylactic shock and strum some jellyfish.

But if you can manage it, plunge to around 10,000 feet deep and you’ll find your strings anchored right to the seafloor. This is the 3-foot-wide harp sponge, and there’s nothing quite like it on the planet. It’s hardly even a sponge as we would recognize it, having left behind the filter-feeding lifestyle and become a carnivore, passively nabbing tiny critters unlucky enough to float through its strings. Think SpongeBob SquarePants, only without the pants and with way more murder.

The remarkable image above is from 2012 when scientists, including marine biologist Henry Reiswig of British Columbia’s University of Victoria, collected two specimens and observed 10 more off the California coast using two remotely operated vehicles from the Monterey Bay Aquarium Research Institute. At such depths, though, collecting good specimens is exceedingly difficult because it can take hours to return to the surface.

“So all kinds of things can happen between the collection and getting a specimen back on deck where we can either look at it or preserve it,” said Reiswig. “So there’s a lot of mystery, a lot of intuition involved in this stuff.”

What scientists know so far about the harp sponge is essentially its morphology. But from that morphology, they can then hypothesize about its biology, determining that it’s an avid carnivore that relies on water currents to push tiny crustaceans into its picket-fence-like upright branches.

The ROV pilots had to shoo away a mysterious white box that had settled on their harp sponge specimen.

If you take a look at the photo at right, you’ll see these branches have tiny hair-like structures called filaments splitting off horizontally. Each of these is positively packed with tiny hooks known as spicules, perhaps 5,000 on each filament, which act essentially like velcro to snare miniscule prey.

And this death will not be a pleasant one. As the catch struggles to free itself, over the course of 10 to 24 hours the cells on the sponge’s branch crawl up onto the critter. There’s no biting, and there are no toxins involved. The prey is simply immobilized and subsumed right into the sponge.

“So it eventually ends up as a little pocket, what we call a prey cyst,” said Reiswig. “And then once the prey dies in there, the cells around it migrate into any little opening—through the mouth, through the nose, through whatever openings there are between the skeleton, and starts to dismantle the cells of the copepod or small crustacean. Insidious!”

This sophistication is highly unusual for sponges, which are among the most primitive multicellular organisms, with no nervous systems or hearts or brains, or any other organs for that matter (and therefore would have made for the ultimate companion in the Wizard of Oz). They simply pump in water, filter out the nutritious bacteria and other particles, and absorb oxygen.

The harp sponge, though, has evolved a more complex carnivorous lifestyle to cope with the depths. Here not only is food incredibly scarce—unless a dead whale falls from the heavens, though that really wouldn’t do the sponge any good, especially if the whale landed on it—but currents are far calmer. That’s a big problem if you depend on them to bring you food, but by growing up to six rows of branches, the harp sponge greatly increases the surface area available to snag prey. It’s a brilliant adaptation to living in an aquatic wasteland.

The Sex Lives of Immobilized Beings

This strategy also solves the problem of sex when you can’t move. Most sponges, including the harp, are hermaphroditic, producing both sperm and eggs, so they’re simultaneously capable of fertilizing and being fertilized themselves. And the harp sponge has figured out a novel way to have sex: by pretending its sperm is prey.

The Monterey Bay Aquarium Research Institute’s remotely operated vehicle Doc Ricketts, one of two used by Reiswig and other scientists to observe the harp sponge. It’s unknown what music the man at lower right was listening to with those headphones. Probably Led Zeppelin, though. Zeppelin is good music for doing a science.

If you’re a carnivorous sponge, “you get to package your sperm into big packets that are about like prey, and then you can send them to somebody who can catch them,” said Reiswig. “There’s no use packaging your sperm if your partner down the road, maybe 100 meters or 1,000 meters away, can’t catch that package.”

Those spheres at the top of each branch in the pictures above are where the sperm is produced and released into the water column, while the smaller bumps about halfway down the animal are where the packages from another sponge have settled and fertilized eggs (it’s important that an individual sponge keeps these bits sufficiently separated, lest it fertilize itself—yeah, that’s a thing). Just like grabbing rare prey at these depths, you need to be damn sure that if there’s scant sperm floating about, you can snag it.

Observing fertilized specimens under a microscope, Reiswig found that once snagged on a hook, the package, also known as a spermatophore, begins to break down, likely due to enzymes released by the package itself. Instead of being digested, the sperm cells are then absorbed directly into the sponge and the waiting egg.

Read more at Wired Science