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 🙂
herr doktor bimler says:
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?
herr doktor bimler says:
What’s that, Echinoblog? More weird Cinaroida spines?
http://echinoblog.blogspot.com/2013/08/strange-urchin-spines-past-and-present.html
Alison Campbell says:
No, I haven’t, for I did not know about Echinoblog 🙁
David says:
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?