Crabs & Shrimps that Live in Sea Cucumber Anuses!

Image by Yellowbeetlebug

Image by Jasdivr

One of the things I find fascinating about sea cucumbers is that they're basically a section of intestine, including the mouth and the anus which has evolved to live on its own. We sometimes think of animals by their most prominent features.. jaws in sharks, eyes in insects...

But Sea cucumbers are basically a big living gut! and have developed many unusual ways of living with this body plan..

Image by WhiteBeachDivers

It should not be so unusual that the openings to this "living gut" are especially important. The mouth of course, we see used in feeding but in sea cucumbers, of particular significance seems to be the importance of that second, most prominent opening.. the ANUS!

Awesome image by PacificKlaus

This is of course, where inorganic sediment is defecated after the animal has eaten and removed the organic material that fuels its diet...

But SO many other biological functions in sea cucumbers are now being observed in sea cucumbers..

This account for example about how sea cucumbers can FEED through their ANUS. and of course, the simple fact is that sea cucumbers use the anal opening in order to process water over their internal "gills"...

OPEN

Image by Pacific Klaus

and shut! 

Another fantastic image by Pacific Klaus

And by the way.. Pacific Klaus has assembled an AWESOME photo gallery of echinoderm anuses on Flickr here. 

But of course, sea cucumbers can host several commensal animals. That is, animals which live, in or around the animal as a habitat but which bring neither harm nor advantage to the host sea cucumber..

The most striking example is the "fish-in-sea cucumber-anus" Pearl Fish. Go here to see this. 
or there's video of course...


and just because I can, lets not forget: Anal Teeth!

Image by PacificKlaus

Awhile back I wrote about flatworms living in sea cucumbers and sea urchins..
But another evocative animal living in sea cucumber anuses?  These little crabs!

Image by Yellowbeetlebug

Many of these have been called Lissocarcinus throughout the internet.. but I'm not sure how dependable those names are. They appear to be scavengers taking advantage of any leftover food ..

Is the anal habitation a matter of opportunity? Regular behavior? Species specific?

But clearly, they do seem to make the most out of uh... living in the shadow of greatness...
Sea Cucumber Crab - Where the Sun don't Shine from liquidguru on Vimeo.

Another

Image by Martin "El Grande" Sequerah

Interestingly, there are also photo accounts of these shrimps living around sea cucumber anuses.. perhaps to take advantage of other organic material?

Image by Eric Francis

Here are more shrimp+crab anal assemblages...

Image by Swaflyboy

Incidental occurrence? or preference?

Image by ScubaSchnauzer

This shrimp seems to have found itself completely embedded in sea cucumber anus!

Image by Prillfish

Many questions-what do the crabs and shrimps get out of this? Are they species specific? Is this really a region specific habitat? Or do they just use the whole animal as a house with the anus as a door?