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a really strange sea urchin

I mean, look at those really weird spines!

Image from Moorea Biocode via ScienceAlert

This unusual creature is Chondrocidaris brevispina, which appears to be much less spiny than the urchins we're probably all more familiar with. Those pinkish pimply bumps towards the creature's right-hand side are the bases of missing spines, which articulate with their bumps via a type of ball joint.

As the name 'brevispina' suggests, the spines are quite short. Those pink swellings on the end of each are apparently sponges, which leads me to wonder what restricts the sponges' downward spread along each spine. Their lower limit seems very well defined. If this was a 'normal' urchin I'd wonder if that was due to the action of the structures known as pedicellariae, which are capable of nipping & crushing (& are sometimes venomous as well) - they'd certainly take care of an overgrowth of sponge!

Alas! Information on C.brevispina seems fairly scanty - a pity as I really would like to know more about those spines. Hopefully someone more learned in this area than I am can help me out :)

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4 Comments

Looks like one of the slate-pencil urchins, from the Cidaroida. Hey, that fits with the name too.
http://www.nhm.ac.uk/research-curation/research/projects/echinoid-directory/taxa/taxon.jsp?id=1857

Have you asked at Echinoblog?

What's that, Echinoblog? More weird Cinaroida spines?
http://echinoblog.blogspot.com/2013/08/strange-urchin-spines-past-and-present.html

No, I haven't, for I did not know about Echinoblog :(

That's a seriously cool urchin. Looks like there are tiny bivalves living in that sponge too.

I agree it's weird the way the sponge doesn't spread all the way down the spines. I've been trying to find out more about Chondrocidaris, specifically whether they do in fact have pedicellariae but you're right, there's very little info on this species out there - the top-ranked page for a Google search of "Chondrocidaris pedicellariae" is this post! Finally found a bad OCR version of a translation of a Danish paper on "The Danish Ingolf-Expedition" which seems to indicate that Chondrocidaris does have pedicellariae. Not sure why they're not apparent in this picture, but maybe the urchin can bend its spines down against its test and the pedicellariae can nibble some of the way up them?

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Recent Comments

  • David: That's a seriously cool urchin. Looks like there are tiny read more
  • Alison Campbell: No, I haven't, for I did not know about Echinoblog read more
  • herr doktor bimler: What's that, Echinoblog? More weird Cinaroida spines? http://echinoblog.blogspot.com/2013/08/strange-urchin-spines-past-and-present.html read more
  • herr doktor bimler: Looks like one of the slate-pencil urchins, from the Cidaroida. read more