Saturday, June 16, 2012

Follow up on the Anal Cone! (thanks to the New Scientist)

(Photo by David Fleetham) 
So, a few weeks ago I posted this bit about the enigmatic nature of anal cones in diadematid sea urchins. What do they do?

Remember that Anal Cones are these bizarre floating bulbs that you see atop Astropyga radiata-one kind of fire urchin. This photo by Pauldub shows it nicely...
                 Fire urchin
As does this great video by Rakufuku

Well, earlier this week, the New Scientist posted this great photo and blog taken by marine nature photographer David Fleetham of a sea urchin from off the coat of Maui.

about which the writer, Rowan Hooper sez this

Full Quote:
I CAN'T be the only person who sees this beast - rudely captured as it expels its guts through its mouth - and thinks of a dramatic scene at the end of the  Watchmen graphic novel. In it, a giant alien writhes in its death throes in New York City.(italics are mine)
So, here's the thing. The picture above IS NOT a sea urchin expelling  "guts through its mouth." 
The author may have been might be thinking of sea cucumbers which expel their guts with great gusto! Here's a thing I wrote about that.

So, what is this a picture of??  This is an ANAL CONE at work!  In other words, this is the sac that expels waste from the animal.
This is a structure that is found on the "top" surface of the urchin. Note that the mouth is found on the underside facing "downward" AWAY from its anus and the anal cone.

All those little pellets in the sac? Yup. THAT is sea urchin feces. This is the first good picture I have seen which so clearly shows the scatalogical functions of the anal cone!  WOO!

Yay the things you learn here! 

Echinoblog Present your evidence!

1. The Madreporite is plainly visible.

So you know that offset plate that you see on the top of a starfish? I wrote a whole post about them here.  In sea urchins they are part of what's called the APICAL SYSTEM that is found on the top of the animal.

Photographer Fleetham's excellent photo skills capture this plate quite nicely... (shown below in the black circle)

Here is a nice photo from the British Museum's Echinoid Database of the cleaned test showing the madreporite Darkened in the upper right.

2. That brown tuft at the tip of the structure? Is the same as what's present in other close ups

                    Fire urchin

 Add to the fact that the mouth space would be a lot larger. Image from the British Museum's Echinoid directory

Its also worth noting that photographer Fleetham noted that this was "expelling waste" and not "expelling guts" as noted above. 

So my thanks to the New Scientist and photographer David Fleetham for capturing what is probably a bit of undocumented biology! 

P.S. For comic book Watchmen geeks. As much as echinoderms would love to claim Adrian Veidt's mind blowing monstrosity-it really is more cephalopod/squid like...


John K. Goodman said...

here's a shot of the business end of an urchin I took last year

Rowan said...

You're right - I was thinking about sea cucumbers (which I have enjoyed eating in Japan). Thanks for your correction!

ChrisM said...

John- yes, those are the teeth of the jaw. Called Aristotle's Lantern.

Rowan-You're welcome! thanks for the opportunity to use the pic!

Rowan said...

Chris - I corrected my post and linked to your blog. Cheers!

David Fleetham said...

Thank you for your comments on my photo and the link to my website.
David Fleetham

Unknown said...

Thank you for your posts about the anal cones. I saw this for the first time the other week and I didn't even really know how to begin searching for an answer to what it was. You were the only site that gave me a complete answer with some nice pictures. Thanks!