Plane to see

I'll show some more photos from The Cedars soon, but we recently encountered a rarely observed marine invertebrate and Eric created a short video clip for the record, so we thought it would be fun to share it with you.

While assisting with a mussel bed survey, Sarah's sharp eyes found a couple of these tiny yellowish gastropods.  They're somewhat similar to sea slugs, but they're in their own group — Order Runcinida (formerly included in the Order Cephalaspidea).  Sometimes you'll see them referred to as Runcinid slugs.

We hadn't seen one before, but that's probably not surprising.  They're only 3-5 mm long, so hard to spot, especially if living among mussels or seaweeds.

Meet MacFarland's Runcina (Runcina macfarlandi)!  In the photo above (and the video below), you can look for a few different characteristics:

- elongate oval shape without many features obvious at first
- yellowish-brown coloration overall
- darker coloration in the center of the body
- head shield flattened in the front, giving it a squared-off appearance (at the right side in the photo above)
- two small black eyes (barely visible on the right side above)
- a fairly long foot, often trailing behind the body
- two rounded, flattened gills at the posterior (back) end

Terry Gosliner (at the California Academy of Sciences) described this species in 1991.  The description was based on observations from only two sites in Oregon and two older records from Pacific Grove.  It sounds like there might be a couple of recent records from southern California, but in general this species has rarely been reported from the West Coast.

You're likely among the first to see a video of MacFarland's Runcina!  Watch for the active foot, two dark eyes (at the left side now), a close-up of the two semicircular gills at the tail end (at about 20 seconds into the video):

 

P.S.  Many thanks to Sarah's spotting and Emily's project for documenting this species locally and to Eric for providing the photo and video clip.

P.P.S.  I was curious about the name "Runcina."  I'm not totally sure, but it might refer to a carpenter's plane?  If so, maybe the first person to describe a species in this genus thought it looked like a hand plane (perhaps due to its squared front end)?  Fascinating to name a sea slug after a tool!