I’m usually pretty excited to see starfish on the beach — I’ll gently touch them, get as close as I can, maybe snap some pictures. I generally consider starfish pretty harmless creatures. But not all starfish are created equal, and there’s one that I definitely wouldn’t want to touch: the crown-of-thorns starfish.

Crown-of-thorns starfish live in the Indo-Pacific ocean, and can be found from the coast of east Africa to the Gulf of California. They live on coral reefs, and are particularly common on the Great Barrier Reef. They need to live on coral reefs because that is exactly what these starfish eat: coral. So it wouldn’t be too easy for these guys to live anywhere else.

As their name implies, crown-of-thorns starfish are basically covered in thorns. These large spines are present along the sides of the starfish’s arms, as well as on the central disc of the starfish. The thorns are extremely sharp and are also venomous — causing several hours of pain, nausea, and swelling for any human unlucky enough to touch a crown-of-thorns starfish.

Though this starfish is brightly coloured, crown-of-thorns starfish are usually more muted shades.
Image by jon hanson on flickr., CC BY-SA 2.0, via Wikimedia Commons

Not only are these starfish covered in sharp, toxic spines, but they are also some of the biggest starfish in the world, reaching up to 70 cm in diameter. They don’t follow the usually ‘five armed’ setup of starfish either, instead having up to 21 arms, all of which are covered in deadly spikes. Definitely not a starfish I’d want to tangle with.

Reproduction in crown-of-thorns starfish occurs in the summer, between May and August in the northern hemisphere and November and February in the south. The starfish will scale a high piece of carl or rock, and the starfish then wave their arms and wiggle around as the release sperm or eggs (depending on the sex of the starfish) into the water. It must look pretty silly. Once eggs are fertilized, they hatch into planktonic larvae, which float around eating phytoplankton. As juveniles, crown-of-thorn starfish have only five legs, which then increase as the starfish grows.

Crown-of-thorns starfish racing to munch on some tasty coral.
Image by JSLUCAS75, CC BY-SA 3.0, via Wikimedia Commons

Though they are large and spiky and venomous, crown-of-thorns starfish can’t do a whole lot if they are taken out of water. Once removed from liquid, the starfish’s body ruptures, and the fluid inside leaks out, making the starfish go flat and the spines bend over. If the starfish survives this ordeal, putting it back in the water will restore it to its original shape. So if you want to neutralize one of these guys, just grab it (carefully) and pull it out of the water.

As far as starfish go, I have to say that the crown-of-thorns is one the coolest ones I’ve come across. What’s better than a giant, 21-armed creature with venomous spikes?

Cover image by Rore bzh, CC BY-SA 3.0, via Wikimedia Commons