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Friday, October 19, 2012

Fiona


On 6 October 2012, I was walking the beach and found a small stick covered with pelagic gooseneck barnacles, Lepas anatifera.  Upon closer inspection, I also noticed one of my favorite nudibranchs crawling along the stick.  This is Fiona pinnata, a pelagic nudibranch that spends all of its time associated with floating objects in the open ocean.

Here's a closer view:


And one of the anterior end, where you can see the simple white tentacles (lower) and rhinophores (higher).


Note the numerous cerata (finger-like projections) with brown cores.  When seen up close, each cerata has an unusual membranous sail-like flap along the back edge (next photo).  This feature is important when identifying Fiona.


Fiona is an active carnivore, feeding on other animals that are part of the drifting pelagic community — e.g., hydroids, By-the-wind-sailors (Velella velella), pelagic gooseneck barnacles (Lepas sp.), and Purple Sea Snails (Janthina).

This individual was feeding on small barnacles, two of which are visible at the bottom edge of the first photo.  When Fiona feeds on barnacles, it's predominantly brown, but when it feeds on By-the-wind-sailors, it's apparently blue!

In my experience, it's somewhat unusual to find Fiona in the fall.  Your best chance of finding this fascinating nudibranch is in the spring, when strong winds push lots of floating debris onshore.


P.S.  Here's another interesting connection to Russian history in the northeast Pacific Ocean.  Fiona was first described by Eschscholtz, the same naturalist associated with Russian expeditions to this area for whom the California Poppy (Eschscholzia californica) was named.

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