Under the Sea — April 1, 2015 at 5:00 am

A Spiny Coastal Landmine: The Sea Urchins


The starfishes’ spiny cousins, sea urchins are looked at as coastal landmines by majority of beach goers. On misguided step and ouch… And you’ll likely end-up with a few pencil-like souvenirs from your clumsy mistake too. But, aside from their spiky exterior, sea urchins are alluring, fascinating creatures; you’ve just got to watch your step.

Wait, they can move?
Looking down at a sea urchin, one glaring question is likely to arise: “OK, I see no legs, no arms, not even a tail. How are they able to move from one place to another?” Well, for one, your viewing angle’s all too wrong. Like Drake said, “Started from the bottom.” And that’s exactly where you’ll find the motile appendages that urchins use to slowly trudge across the sea floor.

Tube feet, as biologist and like-minded scientist moniker them, are bundled-up in close knit groups all along the animals anterior. Through the use of a simple water vascular system, the animals are able to create hydraulic pressure in each individual foot, creating a forward movement with each release of pressure. Now multiply that by x-amount of feet, and you’ll have an echinoderm capable of cruising along a mostly obstacle-free sea floor. “Slow and steady wins the race,” and when you’re equipped with a spine encased exoskeleton, feel-free to take your time.

What’s for dinner? Everything. Everything’s for dinner.
Sea urchins are filter feeders, consuming both plant and animal matter that litters the sea floor. And they go about their endemic, endless buffets in the most peculiar fashion. Sea urchins poses a calcium-heavy, jaw-like structure known as an Aristotle’s lantern. I know, it’s arguably the chicest anatomical name in the animal kingdom.

While the urchin travels across the sea floor via the hydraulic compressions of their tube feet, they’ll use their Aristotle’s lantern as a rake, so to speak, picking-up edible food particles as they go. However, heart urchins, don’t possess such a feeding adaptation, rather solely relying on cilia (multicellular elongated bodies) that obtain food particles by enveloping them in a mucosal coating and then later pulling them into their digestive cavity.

A Needle In A Haystack? Quite The Opposite.
Aside from the flat urchins (such as the sand dollars that inundate trinket shops) most carry with them a biotic arsenal of sharp, needle-like spines that line nearly their entire body. And, as you could imagine, it’s a well-evolved deterrence mechanism for any would-be predator. Some species, often given the moniker “fire urchins,” have spines that are encased by a poisonous lining.

If you happen to step on one of these spiny creatures, most spines, if removed in a timely manner, will only cause mild discomfort. But fire urchins will leave a burning sensation that may last nearly twenty-four hours.

Like the idiom goes, “don’t step on the cracks. You’ll break your mother’s back.” Well, the same could be said about treading along a reef system. “You may not break your mother’s back, but you’ll be left with a good story to tell.”

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