Hello everybody and welcome to Episode 16 of What’s in that Hole?, a fun series I’m writing for my blog. It’s been nearly two years since the last post in this series – which means I have lots of exciting new material!
In the last episode, I described some holes I found in the desert Coolidge, Arizona. This time, we’re going to look at holes underwater off the coast of Kona, Hawaii – just about as different as you can possibly get!
The Hole
Here’s a pic of the hole:
The hole.
You may be wondering why I’m saying this urchin is a hole. I’m not. The hole is the urchin’s anus. Here’s a quick overview of urchin anatomy: the mouth is on the bottom of the urchin, at the center, and the anus is on the top. Also interesting: urchins have a fivefold symmetry about the center axis, just like most sea stars! It’s just much easier to see the symmetry in a sea star because the arms are pretty hard to miss.
Anyway, the hole here is the urchin’s anus, on top of the urchin. As you can see in the photo, this one has something in it! Here are a few more photos – can you figure out what’s in the urchin’s butt hole?
Side view. The white bits are sand that the urchin has ingested and discarded via it’s anus.
Top view. If you look closely, you can see legs.
What’s in That Hole?
It’s a crab! Specifically, it’s a sea urchin crab, a parasite that lives in (you guessed it) sea urchins’ anuses.
About the size of a quarter, I noticed a sea urchin crab just about every time I looked closely at this urchin species while scuba diving in Kona. However, usually all you can see is one claw or the tip of the urchin’s head (like this). This particular sea urchin crab was pretty unusual because it was almost all the way out of the urchin’s anus.
Here’s a closer look at the crab:
Front view of the sea urchin crab.
View from above the crab. You can see quite a few of its legs here.
You can see its legs really clearly here.
So there you go! Today’s answer to What’s in that hole? is… a sea urchin crab!
Hope you enjoyed learning about urchin butt holes as much as I enjoyed telling you about them. See you next time!
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Next episode coming soon!
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