Hello Valerie and a happy thanksgiving to you too!
First of all, D. B. Carlisle was a man not a woman- I
heard him give a lecture once.
Second of all, didemnid ascidians are indeed capable
of locomotion as Carlisle stated. They have been
calculated to move at average speeds of 4.7 mm during
a 12 hr period (Birkeland et al. 1981, Bull. Mar. Sci.
31, 170). The mechanism appears to be as you describe.
Billie Swalla writes "therefore, I would only believe
that ascidians were "moving" on their ampullae if I
saw a time-lapse movie on a gridded surface that
clearly showed a change in position for each
individual." Time-lapse photo maps of the movements of
Diplosoma virens are given by Ryland et al.( Zool. J.
Linnean Soc. 1984, 80, 261). This species,which has
green prochlorophyte symbionts living inside its
cloacal cavity, is positively phototactic and
apparently it moves in relation to light in such away
as to maximize photosynthesis. This would presumably
benefit the colony as well as the symbiont if
metabolites can be transferred between them. The
failure of Billie's specimens to move might be
related to the fact that they lack photosynthetic
symbionts.
Mario
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