Wednesday, October 29, 2008

Dermechinus horridus!! Trick or Treat??

(Thanks to Dave Pawson, NMNH and NIWA for this image)
So, because this is Halloween week..I had to bring out something particularly WEIRD and spooky to share with everyone! And what better than sea urchins that look like Pinhead from Hellraiser??
May I introduce what is possibly one of the strangest sea urchins alive:

Dermechinus horridus!!

UPDATED March 2013- New Video!

Dermechinus is a member of the "archetypical" family of sea urchins-the Echinidae, which includes familiar members such as Echinus and the Antarctic Sterechinus, with which it shares a sister taxon relationship (see SICB abstract by N. cox and R. Mooi!)

These "cactus urchins" live in the Southern Hemisphere, in a subantarctic band-Chile, New Zealand, off Australia and so forth. And of course, they live in the deep-sea!!

Factoids Follow!

(Thanks to Dave Pawson, NMNH and NIWA for this image)

1. Dermechinus has a test height that is THREE times its diameter!
You may have noticed how "high" the aspect is for these strange things. Smaller individuals start out more "globe-like" but larger ones become more cucumber-like. Its unclear why the strange body shape is the way it is...

In addition to the strange body size, the Aristotle's lantern (jaw structure) and oral region (the peristome) are particularly small. But its not clear exactly why....

2. They have numerous long, slender and shiny primary spines.

The name itself describes this feature: Echinus for "sea urchin" and Dermos for skin...described by the species horridus as "horrible" (so translates as: horrible skin sea urchin).

Dermechinus' secondary spines (i.e., the smaller more numerous ones closer to the body) are found with great abundance. These structures evoke the same questions...

3. Are they they Suspension-Feeding Sea Urchins???

One interpretation of the strange morphology was made by F. Julian Fell-son of the famous echinoderm biologist, F. B. Fell.
(from Heezen & Hollister, 1971-the Face of the Deep)
F.J. Fell's PhD dissertation argues that Dermechinus is the ONLY suspension feeding sea urchin based on these reasons:
  1. Posture is similar to sea cucumbers feeding.
  2. Long primary spines are perpendicular to the body forming vertical combs.
  3. Numerous small fur-like secondary spines would be "well-suited to the entrapment of fine suspended particles and the high tests would present a large area to the prevailing currents"
  4. The tiny jaw and oral region would be "adequate for a diet consisting mostly of fine particulates transpoted to the mouth by the secondary spines+ciliary currents
I make NOTE that this is an UNTESTED hypothesis. Even Dr. Fell's comments are clear that feeding has not been confirmed...BUT, its just WEIRD enough to be possible.

What do YOU think?

A trick (untested hypothesis) or treat (making it the ONLY filter feeding sea urchin!!)??


Happy Halloween!


Anonymous said...

Suspension feeding would make sense, given the "high-rise" test morphology. The elongated body reminds me of two clades of "high-rise" edrioasteroids, the edrioblastoids and discocystinids. Both clades possessed a similarly long body relative to their flat-bodied ancestors. Has anyone ever tried to raise one of these weirdo urchins in a tank to observe its behavior?

ChrisM said...

In spite of the nice collections available, my understanding is that Dermechinus is still pretty hard to find.

Its possible that eventually someone will get these into a tank (prolly in New Zealand?)..but given that Dermechinus is subAntarctic, I think there are logistic problems that you don't have operating in and around other areas of nearshore deep-sea operations (e.g., Hawaii, Bahamas, etc.)

tshilson said...

The Antarctic region is pretty rich with plankton, so filter feeding makes a certain amount of sense, but I am skeptical since only *ONE* filter-feeding specie has been found.

ChrisM said...

I think most people are inclined to be skeptical that this species is a filter feeder. But that's the fun of some of the weird critters like this....