Gelatinous thimble

Here's a gelatinous beach find from 29 July 2012.  I didn't get a chance to post it then, but it's from an intriguing animal, so I thought it would be worth doing so now.

 

It was ~4 cm long.  Although it may be somewhat difficult to imagine, it has a thimble-like structure — hollow, and covered with small bumps or tubercles.  You could insert it onto the tip of your finger.  

This photo from March 2011 shows the tubercles:

Here's another view from above (the same individual as in the first photo):

 

Remarkably, this structure belongs to a pelagic snail, a species of pteropod called Corolla spectabilis.  Instead of having a hard, external shell, Corolla has a soft, internal pseudoconch ("false shell") that supports most of its internal organs or viscera.

The diagram below illustrates the position of the pseudoconch in relation to the rest of the animal.  It also shows the broad wingplate, a modified foot used for swimming and the reason for the name pteropod (ptero = wing, pod = foot).

 

Modified from The Light & Smith Manual: Intertidal Invertebrates from Central California to Oregon (2007)

The Light & Smith Manual says that Corolla spectabilis is "relatively common in the California Current.  Reported in the eastern Pacific between 20°N and 45°N.  Pseudoconchs occasionally found washed up on beaches." [Do you know the latitude of Bodega Head?  Answer at bottom of post.]

It's worth searching for images of Corolla spectabilis on the Internet, as it's truly a spectacular snail.  There's a pretty good one on The JelliesZone website.  And a few more shared by Kevin Lee (scroll through the images until you see Corolla spectabilis).

[Bodega Head is at 38°N]