What is Going on with cidaroid sea urchins and their WEIRD spines??

Following the last Okeanos Explorer cruise to Puerto Rico, a got a bunch of questions from folks about what the heck was going on with the very odd looking spines of this cidaroid urchin: Cidaris blakei?

Some Etymology: "Cidaris" the genus name for this species (and the other urchins in the group)? is Latin for a headdress or tiara for ancient Persian kings The species name "blakei" is named in honor of the USS Blake, which was the vessel on which the species was collected.

Now, "normally" (which is to say in the majority of other ciadaroid urchins) the spines are pointy or blunt. Surfaces might be more smooth (as in Cidaris cidaris)

or kind of textured like so...

Cidaroid urchins are unusual in that their spines LACK skin on the surface. Remember that ALL echinoderms display their ENDOSKELETONS. What you are seeing (spines, armor, etc.) are NOT a shell or exoskeleton. All the surfaces are covered by skin (an epithelium)

Because of this, cidaroid urchin spines are affected by the environment. So, epizoics and fouling faunas grow on them. Worm tubes, barnacles, etc. 

                           

From one of my prior posts, these Antarctic urchins, called Austrocidaris, which actually can "seed" new areas with the animals that live on its spines.

So, what is Cidaris blakei doing with those wide, fan-like spines? Their unusual shape doesn't necessarily seem to display any obvious function. Defense? Some bizarre hydrodynamic function? perhaps to more effectively encourage growth of epizoics on the spines??

I also came upon this pic of C. blakei, which seems to grow a lot of critters on its spines...

from this echinoderm Scratchpad

MANY other cidaroid urchin species are known for having very unusual spine morphologies which I've shared with folks over the years. Here's a bunch for comparison

Broadly speaking, cidaroids are the only urchins that have these pretty weird spine morphologies. For what reason? Are they related to the growth on the spines?? (increase in surface area?) Defense? Reproduction? 

A curious bunch of animals. "About which, very little is known.."

Another one from the recent Okeanos 2015 Puerto Rico dive, this one was home to two serpent stars (I think.. Asteroporpa annulata)..

This one is called Chondrocidaris gigantea, a species from the Indo-Pacific, which was in the Paris collections...

Another curious species with very heavily serrated spines...

The above species seems to have a fairly heavy growth on their spines..

Another species of Chondrocidaris, C. brevispina, pic by Arthur Anker

Here's the mysterious Tylocidaris (formerly Psychocidaris) with these thickened "cortex" covering the spines... (see more here)

Some Haeckelian art showing odd cidaroid spines..

More strange treasures from the Paris Museum I've shown before.. BOTH of these urchins are different species in the genus Goniocidaris

But again, its unclear what they use the spines for..

Here's a second species with VERY different spine morphology

and there's a bunch of Paleozoic urchins that are worth checking out...

Starting next week: THREE WEEKS OF BLOGGING FROM CAPETOWN, SOUTH AFRICA!!