Down in the galley

I'm going to follow up last night's post with a little more information about feeding in By-the-wind Sailors (Velella velella).

Remember those beautiful gonozooids?  At the base of the gonozooids, there are reproductive structures that bud off tiny medusae.  But along their sides there are structures that help with subduing prey.  At their tips, they have mouths that open wide to swallow prey.

In the pictures below, look for the shiny patches of nematocyst clusters (stinging cells), and the white tips that indicate the mouth openings.

 

 

While I was scanning the colony, I suddenly realized I was looking at a few gonozooids in the process of eating!

This is a little tricky to see, so I've highlighted in yellow the mouths of the gonozooids that were feeding.  Three of them were feeding on one prey item.  (The prey is clear and shiny.)  The gonozooids on the left and right pretty much stayed in the same position.  But the gonozooid in the middle expanded greatly to cover up a large portion of the prey (see second image — note that the prey is still visible through the transparent body wall of the gonozooid).  Before I saw this, I had no idea that a gonozooid mouth could expand so broadly!

 

 

And here's an extreme closeup of the righthand gonozooid while feeding (marked by the arrow).  I think the prey item was part of crustacean, so I started thinking about this as if the gonozooid was "sucking on a crab leg."  The prey item is on the left.

 

I hadn't really thought too much about exactly how Velella eats.  It was impressive to see the gonozooids in action.

There are only a few papers that have documented feeding in Velella.  In California, Bieri (1961) lists the following prey items: euphausiid (krill) eggs and larvae, copepods, fish eggs, larvaceans, barnacle larvae, hyperiid amphipods, cladocerans, and crab larvae.  

Bon appétit!