Weirdos of the Ocean: The Heart Urchin
The sea potato with legs
If you’ve ever been paddling with us and noticed me excitedly poking at something that looks like a hairy rock, there’s a good chance it was one of these: the heart urchin.
Yes, they’re real.Yes, they look like a cross between a fossilised jellybean and a sea hedgehog. And yes-I’ve actually seen one moving. (Video below, because no one believes me otherwise.)
These pudgy little echinoderms live their lives buried in the sand, quietly sifting through sediment and being weird. I do love weird! Lol
So... what is a heart urchin?
Heart urchins belong to the same family as regular spiny sea urchins (the ones you really don’t want to step on) and sand dollars (those flat white discs everyone loves to find). But instead of being flat or spiky, heart urchins are different. They are irregular urchins.
They’re puffy, covered in fine, fuzzy spines are shaped like a valentine’s heart and they burrow through sand like squishy subterranean Roombas.
They have hundreds of tiny tube feet (check that close up photo!) that help them breathe, feed, and very slowly shuffle through their underground lair. You’ll rarely spot one unless the tide or current has disturbed them — which is why we got so excited when we saw one... casually moving along the sand.
We got footage. Obviously.
Heart urchins vs. their famous cousins
Let’s talk family drama. The echinoderm family includes:
Sea Urchins – your typical ocean pincushions. Great for kelp control. Terrible for bare feet.
Sand Dollars – the Insta-famous cousins. Graceful, flat, and symmetrical.
Heart Urchins – the oddballs. Hairy. Lumpy. Quietly doing their own thing beneath the sand.
While a spiny urchin might cling to rocks or reefs and a sand dollar lies elegantly flat, heart urchins are all about the under-sand life. They feed on detritus (dead stuff, basically), use their tube feet to sift food particles, and poop out sand that’s cleaner than what they started with. Thanks, nature.
Sand dollar skeleton Heart urchin skeleton Regular urchin skeleton
Fun facts about heart urchins:
The ones we usually spot are called Echinocardium cordatum, or sea potatoes.
They can live 10cm below the seafloor!
Their skeletons (called tests) wash up on beaches, often bleached white and mistaken for fragile rocks. They are very, very brittle. I have managed to find a few intact ones over the years.
Those fine spines help them move, even if they’re not exactly winning any races.
They’re not slimy — in fact, they feel more like velvet-coated lumps. (Charming.)
Where to find them
The best times to look are low tide or during calm conditions, when the sandy bottom of the creek is most visible. If we’re really lucky, we get to see one walking, which always leads to me getting extremely excited.
The quiet weirdos of the reef
Heart urchins might not be flashy or colourful or fast, but there’s something fascinating about these oddballs. They’re part of the essential clean-up crew under the ocean’s surface, playing a small but important role in the ecosystem. Like the sea cucumber actually. Another Weirdo I wrote about.
Plus, they look like fuzzy potatoes that walk. What more could you ask for really?
Want to meet a few weirdos yourself? Come join us on a Nature Tour — you never know what you’ll spot beneath your kayak.
Read another of the Weirdos of the Ocean blog series here: Weirdos of the Ocean: Southern Sand Sea Star
