TIL: Those Weird Urchin-Like Hairy Shells I Kept Finding This Summer Are Actually Potatoes!

So, this summer I kept finding on the beach those weird shells I had never seen before. Most of them were broken and in bad shape, however I encountered  a couple ones that were in a somewhat good condition. Here's two I have kept as a memento:

Two of the weird shells and other creatures I have discovered in the sea. AA battery for size comparison

Close up photos:

What I found particularly weird about them is that the "fresher" ones appeared to be covered by some weird kind of dense hair. So they had a body that looked somewhat like those urchins have but instead of spines they had hair. Why exactly I kept finding so many of these dead creatures is something I still don't know. I have been going to that same beach where I kept founding them this summer for 15 years now and had never seen one before. But this summer there were hundreds of them washed in the shore... My guess is that an environmental factor or maybe a disease obliterated their populations.

But at least today I finally learned what these things actually are. They are POTATOES! They belong to the cosmopolitan Echinocardium cordatum species (or some other similarly looking species from the same genus), a sea urchin from the family Loveniidae which is commonly known as... the sea potato!

Echinocardium cordatum - Sea Potato (credit)

Sea potato shell (credit)

But why are they called that way? Well, first because with a bit of imagination they look like potatoes. And second, because when alive they stay hidden below the sea floor:

The sea potato buries itself in sand to a depth of ten to fifteen centimetres. It occurs in sediments with a wide range of grain sizes but prefers sediments with a size of 200 to 300 µm and a low mud content.[source]

Their burrowing lifestyle also explains why I have never seen a live one. But next summer I know what to look for if I get hungry:

t makes a respiratory channel leading to the surface and two sanitary channels behind itself, all lined by a mucus secretion. The location of burrows can be recognised by a conical depression on the surface in which detritus collects. This organic debris is used by the buried animal as food and is passed down by means of the long tube feet found in the front of the ambulacrum. [source]

There isn't much else interesting to say about these creatures, I mostly wanted to share this experience with you guys. But if for whatever reason you want to learn more about them here is a link to eol with everything there is to know :)

Now let me close this post with something really cool my beloved @ruth-girl made me with dead animals I collected this summer. Who said death can't be cute?