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Thursday, June 4, 2015

Inhaling bubbles

Here's a close-up mystery photo (below).  Can you guess what type of animal this is?

It might be tricky unless you're familiar with it.

Here's the entire animal:

Meet Navanax inermis.  Although it looks very similar to a nudibranch, Navanax is in a related but different group (Order Cephalaspidea, Family Aglajidae) that includes headshield slugs and bubble snails.

I didn't get a great picture of it, but animals in this group have a well-developed cephalic shield — note the broad head on the left end — that aids in plowing through the sand.  Most have shells, but the shells may be reduced and internal, which makes them hard to see on live animals.  And many have wing-like parapodia that can be folded up over their backs.

Grace spotted Navanax in Bodega Harbor on 4 June 2015.  I'm glad she mentioned that she had found something interesting, because this is an unusual record for this area.  Bodega Harbor is the northern range limit for this species.  In fact, many books still describe the range limit as either Monterey or Bolinas.  But there are local Navanax records from the 1970s (see The Natural Resources of Bodega Harbor by Standing et al., 1975) and Bodega Harbor is also listed as the northern limit in The Light & Smith Manual (2007).

Navanax is known to be a voracious predator.  They eat bubble snails and nudibranchs.

Grace has noticed that one of the bubble snails (Haminoea vesicula) is common in Bodega Harbor right now.  If you haven't seen a bubble snail, here are two quick photos (the second shows the bubble-like shell for which the group is named).

If you want to see something really impressive, watch Jeff's video of Navanax inhaling a bubble snail.

I don't know how many Navanax are in Bodega Harbor right now.  If you see any, I'd love to hear about it!

1 comment:

John W. Wall said...

What a cool animal. I'll have my eyes peeled at low tide in Pt. Reyes tomorrow. I love the video clip too.