Eating peanuts

  

Here's a fun story.  In Monterey County, I came across an Ida's Mitra snail (Atrimitra idae, formerly Mitra idae).  Although we see their shells occasionally in Bodega Bay, I haven't seen a live snail in the field, so I was excited to find one.

I have read that Ida's Mitra specializes on eating an unusual prey item —  peanut worms (sipunculans).  I've always been curious about how that works, since peanut worms often live deep within rock crevices.  

After photographing this individual, I looked up to see a second Ida's Mitra not too far away.  I took a quick photo and noticed something brown that I wasn't sure about.  I was under the impression that Ida's Mitra's body was primarily white, so I wasn't sure what the brown part might be.  Here's the next photo and then a second even closer image from a slightly different angle:

 

 

 

 

Ahh!  This snail was eating a peanut worm!  That brown object is the posterior end of Phascolosoma agassizii, a common peanut worm in rocky shore areas.

I waited a while to see what would happen and took a couple more photos for the record:

 

 

 

 

I didn't see the position of the peanut worm change very much.  Later I read about two possible feeding strategies in this family of snails — (1) the snail could rasp a hole in the peanut worm's skin and then extend its proboscis into the peanut worm to access the inner tissues, or (2) the snail could swallow the peanut worm whole and digest it once it reached the stomach.  I can't say for sure which was happening here, but my instinct was that the snail was swallowing this peanut worm.

Later I found a different individual under water with its siphon fully extended, apparently searching for prey (it's likely they can detect the scent of a peanut worm in the water).  The siphon is the tubular structure above the head:

 

 

And I also encountered a very pretty juvenile snail:

 

 

 

Although I'm a big fan of peanut worms (see below), it was amazing to see this feeding behavior in the field.