What are the DEEPEST known echinoderms??

                     

The depth of the ocean has been in the news a lot lately. Here's Virgin Oceanic planning to send someone down to the bottom,  as well as this excellent infographic from the Washington Post about how deep a challenge MH370's recovery might be..  

and of course 2012 was James Cameron's big dive in the Marianas Trench!

Image from NPR

The other day this came up in conversation "Blah, blah... but its not like echinoderms occur in the deep sea? I mean, I've only seen them inshore, they are mostly shallow water aren't they??"  Au contraire mon frere!!
Echinoderms are DEEP. They live in the deepest depths of the ocean..

But how deep are we talking?? Most folks think of "deep" as anything beyond the intertidal.

Many biologists think of "deep-sea" as anything below 200 m, which is where roughly where light stops penetrating. But then you get beyond THAT... then you start entering the REAL deep sea... the ones where biologists start saying stuff like "THAR be where dragons have lease..."

Via Wikipedia! 

To me, this starts at around 1000 m..and these zones include

1. the Bathyal at roughly 700 to 1000 m
2. the Abyssal at about 2000 to 4000 m
3. the HADAL from 6000 to 10000 m

Basically, the true BOTTOM of the ocean is around 6000 to 10,000 meters. ABSOLUTE FARKING cold, dark, BOTTOM of the ocean.! And yes. Cameron's sub got down to 10,000 ish meters at the bottom of the Marianas Trench.  These are places where it is cold and dark. The coldest and the darkest in that there ocean!

Here is a chart from CNN (from the Cameron dive) which gives you a sense of scale about what these zones mean..

Image from CNN here

Echinoderms are among the DEEPEST living of all animals known on the planet. HOW DEEP? Which ones?? Let's find out!

Sources for this survey include Belyaev's "Hadal Bottom Fauna of the World Ocean", the former Online Echinoderm Newsletter World Records page and the Smithsonian NMNH specimen database!

1. Sea Urchins (Echinoidea) I start with one of the most familiar but also unfamiliar of sea urchin groups! There are many deep-sea urchins. Such as the echinothurioids (the tam o shanter urchins). or the bizarre Dermechinus.  Many of these urchins go deep, but still remain one of the "shallowest" of the Echinodermata. Many urchins occur at depths >1000 m but "only" go down to about 7000 meters.  Which urchins live at that 7000 meter threshold??

Pourtalesiidae: The "coke bottle" urchins! I have written about these bizarre deep-sea sea urchins before.  YES, these are sea urchins, albeit highly strange ones.

They have EXTREMELY thin and delicate skeletons, which can be almost paper thin. They live by burrowin through and digesting mud on the deep-sea bottoms. Records for the genus Pourtalesia sp. (usually only fragments are recovered) have been collected from 6,850 meters in the Java Trench.

2. Sea Stars (Asteroidea) Next up is my favorite group! They go deep but are not among the deepest. They go 2000-8000 m. That's not to say that there aren't a bunch of DEEP weird looking critters to look at! Here are the records!

Freyellid brisingidan starfish:  Freyastera sp. and Freyella sp. Brisingids are starfish that use their arms to pick food out of the water (more here). All the members of the Freyellidae occur in the VERY deepest depths. Typically below 1000m, but many occur between 4000-6000 m. But the deepest record for a freyellid was Freyella kurilokamchatica from 6860 meters.
                                      
"Mud Stars" Family Porcellanasteridae. NOW we're talkin. This entire family lives on muddy bottoms deep on the ocean floor, where they swallow massive amounts of mud for food. Similar to the mud star Ctenodiscus (here).  The specimen figured below from the NMNH collections is from 6, 250 METERS below the ocean surface!  Deepest record for this species, Eremicaster vicinus is from 7,614 meters! These live in the deepest abyssal-hadal bottoms around 4000 to 8000 meters.

Finally, Hymenaster, aka deep-sea slime stars. Here's a post about their shallower relatives. And you can always find more on my blog about them. Pic below is from 2000 m.

The deepest record for Hymenaster is for a species from 8,400 meters in the Kurile-Kamchatka trench!  So, Hymenaster (species remains undetermined) currently holds the record for deepest starfish. But who knows what new specimens and video remain to be discovered!

2.  Brittle Stars (Ophiuroidea)As with sea stars, their close relatives, the brittle stars don't seem to be quite as deep as some of the others but are still plenty deep. Plus, there's probably a bias of sampling as many brittle stars are tiny and more difficult to collect via nets and so forth..

The plate below is from this paper by Belyaev, G.M. & N.M. Litvinova, 1972: New genera and species of deep-sea Ophiuroidea. - Byull.mosk.Obshch.1spyt. rir. 77, 3: 5-20. (In Russian)

From Belyev & Litvinova 1972

The plate above conveniently displays three of the deepest occurring brittle star records known.

1. In the upper two boxes is Perlophiura profundissima, which has been collected between 2265 and 8015 meters.
2. Lower, left box is Homalophiura madseni, collected from 6156 to 7,230 meters! 
3. and finally in the lower right hand box is Bathylepta pacifica which occurs between 5740 and 8006 meters! (thanks to Sabine Stohr for tipping me off to the correct species!)

There's easily a dozen species of brittle stars found below 6000 meters! Probably more...

4. Crinoids (Crinoidea) Down to the deepest TWO groups! 

Bathycrinus carpenteri from the SERPENT website

Among the crinoids, stalked crinoids are famous members of the deep-sea fauna. There are fossils of stalked crinoids which date back to the Paleozoic and there's always been sort of an unusual mystique to them.  Members of the family Bathycrinidae are recorded from 8,175 to 9,050 meters in the Kurile Kamchatka Trench! 

Pictures of some of these very deep stalked crinoids ALIVE at 9000 meters were observed in Japan and reported on Deep-sea News awhile back

5. Sea Cucumbers (Holothuroidea)  So, which group takes the deep-sea CAKE for being deepest?? How could it be any other group than the Sea Cucumbers??? 

There's a LOT of diversity of sea cucumbers at the >5000 meter depth range. All of the swimming sea cucumbers live at these depths (click here) 

And of course, our old friends, the SEA PIGS!! (the one shown from 1500 m). Many members of the Elpidiidae, the group to which the sea pigs belong are among the deepest known. Several species occur as deep as 9,500 meters! 


But the winning sea cuke? the DEEPEST ones? Members of the Myriotrochidae, including Myriotrochus.  Records for these sea cucumbers go down to 10,687 meters!!! The NMNH has records of Myriotrochus bruuni from the Philippine Trench at depths of 10150 to 10190 meters! So yeah, if Cameron didn't see any of these when he was down there? That's HIS problem! 

This pic is from a Myriotrochus from the Kara Sea, but you get the idea.

this image from this Russian page 

This Russian Livejournal page actually has a nice photogallery of various cold-water deep-sea sea cucumber groups. Myriotrochids, molpadiids and sea pigs! Check it out..

There's a lot of weird stuff going on and through deep-sea sea cucumbers! Here's some of it.

So, yeah. Sea Cucumbers. Deep. And don't you forget it!