Some Colobocentrotus diversity! (aka the Shingle or Helmet Urchins!)

(photo by Emily Miller Kauai)

So, recently I've gotten a bunch of questions about these peculiar sea urchins via email-and so I thought today might be a good time to re-visit them.

I've written the biology and resistance of these neat sea urchins before in one of my earliest posts (go here!)

Long story short:
1. SEA URCHINS with PLATE-LIKE spines!
2. NAME of the most commonly encountered species is Colobocentrotus atratus, called kaupali in Hawaii
3. HOLD ON TO BOTTOMS in shallow but rough seas at the edge of wave-swept rock like this...                                    
4. LIVE IN CENTRAL/SOUTH INDO-PACIFIC From Hawaii, Japan to the Indian Ocean

Don't believe me that these are actually sea urchins??  here's a nice video that shows the underside with tube feet and everything!  Note this species is the Asian C. mertensi.

Here are some NICE close ups of Colobocentrotus atratus  showing the plates (photo by Ken-ichi)

Another excellent close photo up by "Fishandfungi"

and yet another by Alan Cressler

This species often occurs in these clusters.. presumably to conserve moisture..

(photo by KCClarke)

(photo by Emily Miller Kauai)


Here are some from Christmas Island in the Indian Ocean (that's Northwest of Australia)

(above photos by MerMate)

Here's a nice little video about Colobocentrotus from Reunion Island

There is also a SECOND species of helmet urchin!  This one appears to be present primarily in Asia, including Japan, China and Taiwan...

Colobocentrotus mertenseni  also called ジンガサウニ or Jingasauni

(image above from this Japanese photo image site)

This species has more widely distributed plates (which also seem to be a slightly different shape) and dried and preserved animal are this curious green color...

Here..we see one that is partly denuded (i.e., spines removed) showing the urchin beneath...

The specimen above is from Taiwan, image from the Digital Museum of Nature & Culture

How cool is Colobocentrotus?? Well, Mozambique put them on a stamp!!

(image from this awesome "Biology on Stamps" site)

Three of a Kind: What?? They're all the SAME??

An interesting fact!

DID YOU KNOW: That THIS: Colobocentrotus atratus

THIS... Red Pencil Urchin (Heterocentrotus mammillatus)

AND THIS...

ALL actually all members of the SAME Family!! (i.e., the same group)-the ECHINOMETRIDAE.  Here are all their tests (their skeletons for comparison).  Note how these all have that oblong, almost bilateral shape to them.

Colobocentrotus atratus

https://hu.wikipedia.org/wiki/Colobocentrotus_atratus#/media/File:Colobocentrotus_atratus_MHNT_Bali_Test.jpg

Heterocentrotus mammillatus

https://commons.wikimedia.org/wiki/File:Heterocentrotus_mamillatus_test_aboral.JPG

Echinometra mathaei


Its all about the spines! They all vary with habitat! Evolution is a wonderous thing! 

Holding on in a Rough World: Colobocentrotus atratus-the Shingle Urchin!!

Today's we shift gears from starfish and take a look at sea urchins! Today we look at Colobocentrotus atratus (Echinometridae), a commonly encountered resident of the South and Central Pacific rocky intertidal. If you've ever been to Hawaii they can be frequently encountered along the edge of the harsh-wave swept habitats along its beautiful volcanic shores.
They are commonly known as the Shingle or Helmet Urchin and in Hawaiian is known as kaupali which translates to "cliff-clinging"... (thanks to John Hoover's Hawaii's Sea Creatures for this info)
Notice the uniquely flattened shingle-like mosaic of modified plates covering the surface as well as the flange of flattened spines forming a close fringe around the edge.

Colobocentrotus lives in heavy wave-swept environments and its smooth, flattened plates lead one to automatically interpret them to be adaptations for surviving in these kind of environments.

A recent paper by Santos & Flammang (2007) investigates the biomechanics of how these neat beasties hold on.

It turns out..its ALL in the TUBE FEET!



They measured the adhesion of this species against other more "normal" sea urchins (e.g., the spiny Echinometra) and they found that Colobocentrotus always presented the highest measured values.

* Colobocentrotus' attachment force allowed it to resist dislodgment up to water velocities of 17.5 m/s and even up to 27.5 m/s!!! In contrast, more "typical" echinoids, like Echinometra were disodged by water velocities superior to 7.5 m/s.

How fast is 27.5 m/s??

.....basically if this was compared with a strong windy gale..that would be enough to uproot trees and cause minor damage to buildings!!! Holy Carp!! (and according to Patrick, given the density of seawater, wave strength would actually make it WORSE!)

* The shape does not appear to affect the difference in drag and lift but may function to offset the amount of shear force directed onto the animal into normal force..effectively spreading the energy load around more evenly on all tube feet.

Thus, it seems that the ability to inhabit extreme water velocities in Colobocentrotus is tied to its very high number of tube feet and not to its particular morphology (although it does seem to help in other ways).

Adaptive notions for the overall shape suggest several ideas, including:

1. The streamlined morphology might be an adaptation to lessen other hydrodynamic forces such as wave impact.

2. The flattened spines may reduce spine breakage and therefore the energy expense of constant repair, etc.

3. The morphology seems ideal for retaining extra water which can be essential to resist heat and dessication stress at low tide.

This latter idea seems interesting given this pic of Colobocentrotus huddled together....


Tough little wee beasties...so for goodness sakes! leave em' alone when you go out tide pooling!

(Photos courtesy of Flickr and Photobucket!)