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Friday, February 17, 2012

The tiny tunicate, Pycnoclavella

A tiny colonial tunicate, or sea squirt, called Pycnoclavella stanleyi.  Each zooid is only a few millimeters tall and is covered in white confetti-like spots.  They're found in the low intertidal zone on rocky shores.

A few fun things to note: Look for the two siphons (one inhalant, one exhalant). 

The incurrent siphon has oral tentacles to prevent larger particles from entering (see photo below, view looking down at the top of the tunicate).

The "brain" or cerebral ganglion is visible as a golden spot between the two siphons.

Gill slits (or stigmata) can be seen through the outer tunic.  Look closely for the elongate oval "windows" or perforations arranged in rows (two photos below). 

To feed, water is drawn through the inhalant siphon into a sac called the pharynx.  The water is then pushed through the gill slits and exits through the exhalant siphon.  Because the pharynx is lined with mucous on the inside, as the water passes through the gill slits, suspended particles are captured on mucous sheets.  These food-filled mucous sheets are then transferred to the bottom of the pharynx (opposite the siphons) where the intestine begins.

The gill slits are one of the characters that link tunicates to other chordates, including us!

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