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Thursday, November 20, 2014

Crab trap surprise!

What fun to open my e-mail, to see a request for help with identifying a local animal, and then to see this photo:


This animal came up in Doug Wilgis's crab trap!  He was in Bodega Bay, off the Estero de San Antonio, on November 12th.  The trap had been set at about 25 fathoms (150 feet).  This curious animal was about 4 inches (10 cm) long.  Do you recognize it?

I've mentioned this type of animal on the blog before (a couple of years ago), but I haven't shown this stage because I've never seen it!

This is the solitary stage of a salp (or pelagic tunicate) called Thetys vagina.  Note the two fascinating amber-colored projections they're on the back end.  And I'm sure you can also see the banding in the mid-section.  These are muscle bands that the salp uses for swimming and pumping water for filter-feeding.

A salp spends its entire life in the open ocean.  Its life cycle includes two stagesa solitary stage and an aggregate stage.  [For comparison, on 30 July 2012, I showed a picture of a Thetys from the aggregate stage.]

The solitary stage shown in Doug's picture is asexual and produces chains of aggregates (shown in my July 2012 picture, and see below).  The aggregate stage is sexual and produces the solitary stage.

In late October, I found some small aggregate stage Thetys washed up on the beach, which made me wonder if there were some actively reproducing solitary stage individuals around.  Doug's observation confirms that there are!

Here are the small aggregate stage individuals that I encountered in October (see below).  They don't look like much after being washed up on the sand, but I thought it would be useful to document these smaller individuals.

You can see that the first is ~8 cm (3 inches) long, and the second is only ~4 cm (1.5 inches) long.




I'm very thankful to Doug for sharing his picture.  Not many people get to see these offshore animals, so it's fun to pass along this story to you!

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