Sea Star and Worm Swarm Explained


We assume that spineless sea critters like sea stars, worms, and urchins are loafers, idly existing while the real action happens around them. This time-lapse video from the BBC shows us just how wrong we are.

An unlikely army of harmless-looking creatures swarms over the corpse of a leopard seal, and what happens next isn't pretty. A bounty like this comes about once in a decade for these animals, and they'll feast for months.

The BBC does a pretty good job of explaining the basics of what's going on here. But let's learn a little more about the featured creatures' hunting habits. Sea stars, ribbon worms, sea urchins, and their cousins may be spineless, eyeless, and even toothless, but that doesn’t stop them from getting their meal on.

Ninja Stars

For all their beauty, sea stars (the preferred term for starfish, since they're echinoderms, not fish) are pretty ruthless hunters. Instead of eyes, a sea star has an eye spot at the end of each arm, which can sense light and dark. The sea star creeps over the ocean floor, groping for its next victim. Most of the time, these are of the crunchy outside/gooey inside variety: snails, barnacles, clams, and mussels. If a shellfish refuses to cooperate, the sea star will wrap its arms around the bivalve, then use its sticky tube feet to pry the shell open.

Once its prey is near, the sea star will eject its stomach, which oozes over the prey and digests it on the spot. After the prey has been liquefied, the sea star just sucks its stomach back in. Watch this sunflower star nonchalantly sidle up to a juicy-looking (and apparently slow-witted) wolf eel. Just, you know, being friendly.

Worm of Nightmares

Ribbon worms made headlines twice recently, first when a purple specimen spewed its branched proboscis on a man's hand, and again when a shamrock-green beast showed up in Taiwan. It may look silly on land, but in the water, the ribbon worm (phylum Nemertea) is not to be trifled with. They’re enormous, for one thing. The green species, Lineus fuscoviridis, can reach up to 6 feet long. But that’s nothing compared to the rest of its family. Scientists believe that Lineus longissimus may grow to nearly 200 feet. That’s longer than a blue whale, and a whole lot slimier.

Then there’s that proboscis. When a ribbon worm finds something worth eating, it lashes out like a chameleon with its extendable, sticky proboscis. And no morsel is too large; like pythons, ribbon worms can swallow creatures three to four times their own size. For even larger meals, like the seal in the video up top, some species make a hole (or find one), then slither in and eat their prey from the inside out.

Raccoons of the Sea

It’s no surprise that sea urchins turned up at the dead-seal party. They’re notorious trash-eaters, subsisting on algae, dead fish, and other sea garbage. Just as the urchin’s body is bristling with spines, its mouth, located on the underside of its body, bristles with big, sharp teeth. When they’re not gnawing on rotting flesh, urchins use their teeth to scrape algae off of rocks, which can apparently be pretty noisy.

Bonus! Other Unexpected Attackers

They might not have made an appearance in this video, but sea anemones are plenty gross in their own right. These relatives of urchins and sea stars look like beautiful, delicate flowers, but their tentacles are covered with neurotoxins, and they will eat anything they can grab. The giant green anemone pictured below is in the process of devouring an entire baby cormorant:

Image Credit: Lisa Habecker

Even clams, mussels, and oysters are not as defenseless as we long thought. Natural history accounts reaching back to the 19th century tell of birds felled by the very shellfish they intended to eat. After a 1996 storm on the Jersey Shore, huge numbers of surf clams washed up on the beach. Scientists combing the beach found almost 40 birds with their bills or feet snapped tight inside the shells of defiant clams. Some of these birds were able to shake their captors; others fell into the sea and drowned. So let’s not underestimate the little beasts!