Pelagothuria natatrix

Image: NOAA
Pelagothuria natatrix

It's a deep sea, swimming sea cucumber! The REAL deep sea, swimming sea cucumber!

We've seen swimming sea cucumbers before - in fact, they're quite famous by now. However, they've all been what you might call "bottom bouncers". They lounge around on the sea floor, eat everything in sight, and then swim away to find greener (muddier) pastures to descend upon and eat some more.

Image: Freshwater and Marine Image Bank
Top view

THIS one is different. THIS one spends its entire life swimming through the sea and need never touch the bottom. It's the only truly pelagic echinoderm in the world! As far as anyone knows...

The pictures above both show a top view of P. natatrix. You can see what might be called an umbrella, reaching up to 16 cm (6 in) across.

Apparently the oral tentacles can be extended and spread out

At the centre of the umbrella is a mouth, facing upwards and surrounded by a ring of oral tentacles.

Image: Freshwater and Marine Image Bank
Side view

The body meanwhile dangles below as a rather inconspicuous cone.

This species belongs to the Pelagothuriidae family, which it shares only with our old friends in the Enypniastes genus. Have a look at Enypniastes! You'll notice that the big differences to be seen is that P. natatrix has a much bigger umbrella, a much smaller body and its mouth has shifted to face upwards.

There isn't much known about these gelatinous spectres with their vampiric capes. Apparently they live all over the world and have been spotted at depths from 600 to 6,000 metres (2,000 to 19,700 ft), but it can't be easy to learn about a creature that spends all its life in the middle of nowhere. And few creatures are closer to the very centre of nowhere than this one!

I would dearly love to see that umbrella at work. And given that it's a sea cucumber we're talking about, I imagine those oral tentacles opening up to catch marine snow, the succulent dollops of bacteria-infested muck that constantly drift down from higher regions of the sea.

Image: Freshwater and Marine Image Bank

Alas! The internet offers very little for any of us keen to see a nice Pelagothuria on the move. Or a nasty Pelagothuria on the move. Or a Pelagothuria of any kind, moving or not, at all.

Video stills of Pelagothuria. Just about...

It was Christopher Mah from Echinoblog who, with at least as much excited squealing as required, uncovered that first photograph from the vaults. It was labelled "umbrella jellyfish" as if to ensure no-one would ever find it.

That's the gut-wrenching thing about all this. What if there has been a youtube video of Pelagothuria out there this entire time? Maybe it's called "weird jellyfish" or "?" or "MN_0073" and it's been there for years accumulating ones of views.

Will we ever find it?

I'll ready up my best squeal of excitement, just in case.