Tropical butterflies -- Part 2

On 28 September, I wrote about a pteropod, or sea butterfly, Hyalocylis striata, found near Bodega Canyon.

On 21 October, we were very excited to receive an e-mail from Carol letting us know that she had found another one in a plankton sample from about 1 km off Bodega Head.

It turns out that Carol's specimen was in very good condition.  And because Hyalocylis is rare in northern California, we took some time to document this individual carefully.  We learned a lot along the way!

 

Note the very broad wings.  And that the tip (lower third) of the shell is smooth, lacking striations.  At first we didn't know what this meant, but Eric eventually found a description that led us to understand that the smooth tip of the shell is a protoconch, or larval shell.  Hyalocylis retains its protoconch for a while, but eventually sheds it and then seals the opening with a membrane!  See illustration below:

 

 Modified from van der Spoel, S. and L. Newman.  1990.  Juveniles of the pteropod Hyalocylis striata (Gastropoda, Pteropoda).  Basteria 54: 203-2010.

Van Der Spoel, S. and L. Newman (1990). Juveniles of the pteropod Hyalocylis striata (Gastropoda, Pteropoda). Basteria, 54: 203-210. - See more at: http://australianmuseum.net.au/Publications-1990#sthash.t8AyVi6z.dpuf

Van Der Spoel, S. and L. Newman (1990). Juveniles of the pteropod Hyalocylis striata (Gastropoda, Pteropoda). Basteria, 54: 203-210. - See more at: http://australianmuseum.net.au/Publications-1990#sthash.t8AyVi6z.dpuf

Van Der Spoel, S. and L. Newman (1990). Juveniles of the pteropod Hyalocylis striata (Gastropoda, Pteropoda). Basteria, 54: 203-210. - See more at: http://australianmuseum.net.au/Publications-1990#sthash.t8AyVi6z.dpuf

Here's another view of this juvenile found in October: 

 

Because we don't get a chance to look at pteropods very often, we also zoomed in for a closer view of the head region and the base of the wings:

 

There's a lot to see, and we were curious about all of it!  We've labeled some of the anatomy in the next picture (below).  Our attention was  drawn especially to the two paired circles in the center of the image.  These are statocysts — sense organs that assist with balance and orientation as the pteropod moves through the water.

 

The story doesn't end here because last night, on 4 November, we received another e-mail, this time from Emily saying that she had discovered some more pteropods in a plankton tow offshore of Bodega Head.

When we went to look at them, we found a tiny Hyalocylis — even smaller than the juvenile from October! (see next image):

 

This small shell lacked striations, and all of the other characteristics looked good for Hyalocylis.

To make it easier to appreciate the size differences among these individuals, we put together a composite picture with all three side-by-side.  An explanation — the first two pteropods didn't survive and are now important specimens at the California Academy of Sciences documenting their occurrence in northern California during the 2014 warm-water event.  From top to bottom, the picture below shows the shell of the September adult (note that it's missing its protoconch), the October juvenile, and the November juvenile.  Approximate shell sizes = 4.75 mm, 0.93 mm, and 0.33 mm.

 

It's potentially significant that juveniles have been documented in the plankton here, as it suggests that Hyalocylis was reproducing in California this year.

Okay, I hope you're still with me.  If so, you won't be disappointed.  You're in for a treat, as the next music video from Spineless Studios has been released!  

Click on the link below for wonderful video footage of Hyalocylis striata.  Note that some of the sequences were slowed down to allow observation and appreciation of the swimming behavior.

Video footage of a juvenile sea butterfly (pteropod), Hyalocylis striata