Spiky -- Part 2

Apologies for the delay.  A couple of nights ago, I posted a mystery photo and asked if you recognized the type of animal it was:

 

This is a tough one!

But isn't it intriguing?

I can give you a small hint, and tell you that the picture shows the animal viewed from above.

And here's another clue: This is the larval stage of a marine invertebrate.  So it's quite small (microscopic).

What makes it look so "spiky" are very long cilia used for swimming.

As an adult, it's colonial — and the feeding members of the colony extend beautiful, bell-like lophophores to capture food particles from the water (see pictures at the end of this post).

Here's a view of the same animal from the side:

 

Note the triangular shape.  You can see that the lower edge is fringed by cilia, and that there's an apical tuft at the top. 

This is a cyphonautes larva — the swimming stage of some species of bryozoans (the most common example in this area would be Membranipora).

In the image above, perhaps you noticed the long, narrow "bar" in the middle of the cyphonautes larva (it looks like a straw)?  It's one of the ciliated ridges that the larva uses to feed.  

The diagram below illustrates the basic feeding process.  There are different types of cilia on the ridges.  They draw water into an incurrent chamber, sieve particles from that water, move the particles to the mouth, then the water exits through the excurrent chamber:

 

Diagram modified from Strathmann and McEdward.  1986.  Cyphonautes' ciliary sieve breaks a biological rule of inference.  Biol. Bull. 171: 694-700.

Below is a short video clip of a cyphonautes larva swimming — viewed from the side and from above.  After watching the video, be sure to scroll down to see photos of the adults, too.

 

cyphonautes from Jackie Sones on Vimeo.

The larva will swim in the open ocean for several weeks before finding a place to settle down.  You'll recognize adult bryozoan colonies as white, lacy crusts on kelps or other seaweeds.  Here's what they look like under a microscope:

 

The adult bryozoan colony and the cyphonautes larva look so different that it was a long time before the connection was made between the two stages.  It's easy to see why!