Careening among the corals

Recently, while Eric was looking at the soft corals, he noticed some interesting animals living among them.  In the photo below, the tentacles of the soft corals are withdrawn, so the polyps look like small orange lumps.  Note the tall, thin, animals standing upright among the corals:

 

The tiny stalked animals are kamptozoans — a unique phylum formerly known as entoprocts, and commonly referred to as "nodding heads."  We think this is Barentsia parva.  It's the first time we've encountered this species. 

It's hard to tell from the microscope photos, but these animals are very small — only ~2 mm high.  (You can see why people don't encounter them very often!)

Here's an individual zooid (below).  Look for the following features:

- The stolon — the "runner" at the bottom from which the rest of the colonial animal arises (in this case, it looks golden and it's covered with debris)

- The calyx — the broad cup-like section at the top, with the feeding tentacles along the rim

- Rods — the long, narrow sections making up the stalk between the calyx and the stolon

- Nodes — the swollen sections at the base of the rod and sometimes in the middle of the rod

 

This illustration of Barentsia parva will also help orient you to their basic anatomy:

 

Modified from Wasson, K.  1997.  Systematic revision of colonial kamptozoans (entoprocts) of the Pacific coast of North America.  Zoological Journal of the Linnean Society 121: 1-63.

I mentioned that kamptozoans are commonly referred to as "nodding heads."  Luckily, Eric captured some of the "nodding" behavior that gives them this name.

In the video below, watch for the distinctive movements of individual zooids as they bend rather abruptly into their neighbors.  

Note that sometimes the feeding tentacles are extended upward; other times, they are withdrawn.  There's a sequence in the video between 29-35 seconds that shows particles moving in the water — the flow is being generated by beating cilia on the feeding tentacles.  If you look very closely, you might even see tiny particles that have been captured moving down the tentacles (from the tip down towards the mouth).  [If you can't see the video below, click on the title of the post above to go to the web page.]

barentsia parva sanford from Jackie Sones on Vimeo.

We hope you enjoyed this introduction to a seldom seen species.

P.S.  To compare Barentsia parva with a different kamptozoan, Barentsia conferta, review the post called "Nodding heads" from 8 July 2012.