Tuesday, May 28, 2013

New "Tam O Shanter" urchins (aka the Echinothurioids!) from Deep-Sea New Zealand!

Araesoma thetidis
In February of this year, my friends at the New Zealand Institute of Water and Atmosphere (namely Owen Anderson) published a new paper describing not one but SEVEN new species of deep-sea sea urchins! Here in the journal Zootaxa.

The original NIWA press release is here.  These urchins have been getting all sorts of keen press, including here in the N.Z. Herald and here in The Sun.  And of here on New Zealand's Maori news..

and I thought.. EVERYONE needs to know more about these exciting urchins! and so today is a bit of a "refresher" on echinothurioid sea urchins!

I wrote a short summary about these for Deep Sea News several years ago...(here)  and wrote a short bit about the commensal relationships between these urchins and fish here.

The quick summary version is:
  1. Mostly deep-sea urchins found all over the world (many in greater than 1500 m depths-in NZ they range from 100 to 5000 m!), but with some shallow water relatives (aka the Fire urchins, I'll save these for another day)
  2. They often have very sharp and poisonous spines. And yes, the deep-sea ones too...
  3. They "walk" around on the sea bottom with special spines that have hoof like tips
  4. They were described FIRST as fossils and the living animals were found AFTER...
When the animals are alive they look kind of like this:
Deep Sea Urchin - Submarine Ride 2540 Feet
An Atlantic species by Hankplank
On this purple species from the Pacific (Tromikosoma maybe? this isn't one of the new ones described by Anderson), you can see the white hoof-like spine tips that the urchins use to "walk" along the bottom..
Spiny sea urchin
Image by Neptune Canada
Here is a pic showing the oral surface (ie the bottom). The mouth is at center and as you can see it is surrounded by spines with those white "hoof" like tips. These are what the animals use to "walk" along the bottom of the sea floor.
Sea Urchin underbelly
Also by Neptune Canada

Here's the spine close up showing the "walking tip"
Image from the NIWA Benthic Inverts Facebook page
Or sometimes like this Atlantic Phormosoma placenta which has the mysterious floating "bags" (containing spines).
Image from SERPENT project here

But sadly, when they are brought up on the deck of the ship, the water rapidly drains from their very soft body and they are often left as a shadow of their former self....
From the NIWA page on this story
As a result of this "deflated" appearance, they are often called a variety of names: "pancake urchin", "leather urchin", "bag urchin", or "beret urchin." However in Anderson's new paper he feels a new common sobriquet would be most accurate-the Tam O Shanter urchin!!!

For those who are not as keen on Scottish headwear, a "Tam o Shanter" is a cap, sort of like a beret (wikipedia here)  and you can sort of see the resemblance.
Tam O' Shanter
Image by DrHaggis
dsc_0055 (2)
Image by H2omom.2006
Even alive, looking down on one, you can sort of see the resemblance..(note however this is not one of Anderson's new species)
Sea Urchin and Brittle Stars
Image by Neptune Canada!
Owen's paper (here) describes a whopping SEVEN species in two genera. That's pretty significant given that MOST of these urchins were described in the early part of the 20th Century/late 19th.

These were all discovered and described by looking at a variety of different characteristics. Some as straightforward as body color as well as spine shape and location. But some characteristics are more subtle. These are the individual pieces of pedicellariae-little claw like structures that are present on all sea urchins..which were studied using a Scanning Electron Microscope to yield distinct shapes...
Fig. 28 from Anderson 2013
He also reviewed the many echinothurioid urchins in the New Zealand waters, in addition to the seven known species, Anderson described/reviewed a further nine species (7 were new) culminating in a count of some 16 species of these urchins in the region!, including this beauty... Araeosoma thetidis!! (described by Hubert Lyman Clark in 1909)
Figure 28 from Anderson 2013
What other species will be found?  Here's a brand new report about two new sea pens! 

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