Echinoderms in the North Atlantic

As part of the series of blogs I have been doing on the recent NOAA expedition, the Northeast U.S. Canyons Expedition 2013, today I want to turn your attention to Echinoderms. To be honest, I hardly expected to see any when I first started watching the live feed from the Okeanos Explorer in early July. But to my surprise, we have seen a handful of different sea stars, sea pens, sea lilies, and sea urchins.

Sea urchins were found on the flat ocean bottom, along with sea pens, while a few sea lilies were solidly grounded along the sides of rocky substrate. As for sea stars, well, that's a whole subject for me.

When I think sea stars I imagine shallow tidal pools or sandy beaches. I hardly expected to find them in the abyssal plains, but I suppose you learn something new everyday, right?

There are so many species of sea star, it's almost hard to believe. The Common sea star has five legs and is... well, common in appearance. But would you believe there are some sea stars that look so plump they appear to have no arms at all? A prime example of this is the Cushion sea star. Here is a frilly specimen with a similar body structure:

Picture courtesy of NOAA Ocean Explorer

Pink and adorable! A couple of other species we saw were plump in a smaller way. A guess at their diameter would probably be around 20 or more centimeters, give or take a little, whereas one sea star spotted couldn't have been more than a few centimeters.

Picture courtesy of NOAA Ocean Explorer

And yet, would you believe there is a species even smaller, though not observed on this expedition. Patiriella parvivipara is the smallest sea star on record, measuring up to one centimeter in diameter. A creature like this is easily missed.

Picture courtesy of NOAA Ocean Explorer

Though commonly known for having only five arms, some species of sea star have been known to have up to 45 arms. We had the enormous privilege of seeing one, just one, with eight arms.

Picture courtesy of NOAA Ocean Explorer

But not every sea star keeps its appendages attached to the substrate. Brisingid sea stars are curious creatures. They hold onto the rock, sometimes upside down, and let their arms curl out in front of them. There is a very good reason for this. They are suspension feeders, which means they sit and glean their prey from the water current.

Many times the canyon walls or deep crevices in the walls were covered in brisingid sea stars, never moving, simply sitting and waiting.


Picture courtesy of NOAA Ocean Explorer

I couldn't write a post on sea stars without mentioning one of their most fascinating aspects!

Everyone has heard about the sea stars ability to regenerate an arm after its having been broken off. And it's not everyday something like this is seen. But we had the chance to see one. It's definitely a peculiar sight to see, and sometimes reminiscent of a horror film. But it is an incredible characteristic. Because of the loss of two arms, this sea star most likely created another. Some people say this is only possible if the broken appendage still had a bit of the central disc. Either way, it gives a whole new meaning to the the idea of cloning.

Every glance we are able to get of the little known world below gives us more and more to consider. And there is still more to discover out there! Be sure to join me next week as I continue this series of posts examining the remarkable life in the deep!

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