Meet Marsenina!

 

 

A fun view of an often overlooked snail — meet Marsenina rhombica!

With a large mantle that almost completely envelops the shell, this snail can be mistaken for a nudibranch.  But note the tentacles, the lack of rhinophores, the inhalant siphon (a short tube visible between the tentacles), and that you can see some of the shell at the top of the mantle (the part that looks white and shiny).

 

Marsenina has adaptive coloration — they are often associated with compound ascidians (colonial sea squirts), but when they're on the sea squirts, they almost disappear!

 

If you're curious about the shell, here's a scan of one I found years ago (see below).  The shell is very thin and shaped like a small abalone with a flattened spire and a very large body whorl:

 

 

P.S.  Many thanks to Caroline for spotting this snail and for Eric for scanning the shell!

The tunicate with a twist

Eric and I had a funny experience with a little mystery animal this morning.  We were doing a survey in Bodega Harbor when we encountered something unfamiliar.  At first it looked like a small tunicate (sea squirt):

 

But something didn't feel right about it, so we kept wondering about it in the back of our minds.  Here's a view from above:

 

And then we found another one that looked just like it.  Hmmmphh.  Puzzling.  Another small reddish-orange tunicate?

While continuing our survey, I thought to myself, "Well, if it's a tunicate, it should be attached, so if we find another one, I'll push it a little and see what happens."

We did find a third individual, and as soon as I touched the little mystery lump, it just slid away from where it had been.  

Okay, it wasn't attached, so it probably wasn't a tunicate...but then what was it?  We were distracted by something else for several seconds, and when I looked back, the little orange mystery animal was moving!  It had started crawling away.  When we looked closely, we could see a snail-like foot underneath.

Now I was confused.  It looked so much like a tunicate!  Was it possible that a tunicate was growing on top of a snail or a limpet?  But all three of the little mystery animals looked exactly the same...same shape, same color, same patterning, same texture.  (An aside: The interesting angles that are visible from the side and the coloration reminded me of a pomegranate seed, so that's what I started calling them.)

We decided to look at it under water and with a microscope, and here's what we saw:

 

Aha!  Two tentacles, a long foot trailing behind, and a rolled-up siphon (visible between the tentacles).  It had to be a snail...but which species?  

We worked on this for a little while and finally identified it as Hainotis sharonae (formerly Marseniopsis sharonae).  They feed on tunicates, and they have evolved incredibly effective camouflage to look just like them.

Here's another view, this one from below.  The snail is upside down, looking up.  In this position you can see how much it looks like a snail, but return to the first picture of this post and I'm guessing that snail is not the first thing you think of!

 

There's always something new to learn!