|Image by Ken-Ichi|
This week, Echinoblog brings you:
A sea cucumber that feeds not just using its mouth but ALSO via its butt!!
First, Let's look at some basics...
Jaeckle and Strathmann were studying the Pacific Northwest species Parastichopus californicus-the handsome fellow pictured above (and below)! These occur along the west coast of North America in relatively shallow water...
|Image by Bill Pennell|
|Image by bswift|
As a generaltiy-sea cucumbers can pump quite a bit of water in and out through their anus-with tropical species measured between 40 to 860 milliliters/hour..that translates to about 3.6 to 4 cups of water per hour!
Sea cucumbers are essentially a big fleshy tube with a mouth and a butt that pumps water through itself! Here's the basic anatomy below...
Folllowing the trail of traced algae through the sea cucumber, Jaeckle and Strathmann tracked the isotopes throughout the body and found out where they were most abundant.
Enter The Rete Mirabile! (this sounds like a great episode of Star Trek doesn't it?) Basically after exposing the sea cucumber to tagged algae they found the tags taken in and were present in highest abundance in the Rete Mirabile which connects the respiratory trees with the gut..
This supports the notion that organic food is drawn in from the respiratory trees and eventually transferred to the gut..
|Fig. 3 from Jaeckle & Strathmann|
On top of everything else, histology of the INSIDE of the respiratory trees shows internal tissues that you might expect to find in a gut: such as microvilli (tiny finger like doodahs that serve to absorb or secrete. We have these in our intestine) as well as certain kinds of cells in the stomach lining that are recognized in other animals for digesting food.
Note above that they also found tiny ciliates (protozoans) swimming around inside living commensally. ANOTHER feature common to spaces where food is digested.
|Image by bswift|
But the evidence above suggests but rather something more akin to digestion or UPTAKE of nutrient-like material
In other words: They use their anus as a SECOND MOUTH!
This phenomena is what the authors term "Bipolar Feeding"
To be sure, its not likely that this means of feeding is as substantial as its primary feeding mode (taking organic materials from sediment or from the bottoms via the mouth) but it does appear to be significant. Also, obtaining food in this way may be an important way to supplement its main feeding mode.
Perhaps the sea cucumber version of an apéritif with dinner?
How does this fit into the "Big Picture"??
Another indicator of how echinoderms might be the ecological "canaries in the coal mine" perhaps?
Information like this may seem like an unusual natural history factoid but conceivably things like this can ultimately be VERY important to the big picture...