One cell at at time

Several days ago, Peter was showing me some algae that he had collected on the tidal flats in Bodega Harbor.  When he picked it up, a small nudibranch-like animal was left behind in the tray.  I was intrigued because it didn't look familiar to me.  

When we looked at the animal under the scope, we realized that it wasn't a nudibranch, but a sacoglossan — a group that is sometimes known as "sap-sucking sea slugs."  From the name, perhaps you can guess that sacoglossans eat algae.

Here's one of the first views we had.  Note the small, black eyes and the large, rolled rhinophores above the eyes:

 

There are many projections called cerata on the back — cylindrical, greenish, with scattered gray flecks and white tips:

 

On the underside, you can see a smooth muscular foot with irregular black splotches (creating a marbled pattern):

 

Meet Aplysiopsis enteromorphae!

While we watched, the most striking thing about this species was its feeding behavior.

Aplysiopsis enteromorphae is known to feed on only a few species of seaweeds.  (This individual was feeding on Chaetomorpha.)  The feeding behavior was described originally by Gonor (1961).  The slug grasps the algal filament with the front of its foot and a pair of oral lobes (see diagram below).  It slices open an algal cell with a single row of teeth on its radula, sucks out the contents, and then repeats this process along the filament.  After the filament passes by the mouth, it's easy to see the now-empty algal cells! 

 

Modified from Gonor, J.J.  1961.  Observations on the biology of Hermaeina smithi, a sacoglossan opisthobranch from the West Coast of North America.  Veliger 4: 85-98.

 This is exactly what we saw:

 

Here's an even closer view.  Look for the solid green algal strand in front of the mouth (at the bottom of the photo), and the nearly-clear algal strand after it leaves the mouth and passes along the foot.  The eaten portion of the strand is a little hard to see because it's almost transparent, but there are a few green cells left:

 

We were curious about whether you could see the slits in the algal cells.  We couldn't with our eyes alone, so we put a strand under a compound microscope (200x magnification), and voilà!  Below, the arrows are pointing to two of the slits:

 

Eric was able to capture a few seconds of feeding behavior on video.  Watch carefully as the slug moves along the single strand of Chaetomorpha — grasping, slitting, and sucking out the contents.

Aplysiopsis enteromorphae from Jackie Sones on Vimeo.