Dear Pierre,
I have no idea about obligate parasitism.
Ascidians occasionally settle on other organisms, such as crabs.
These cases may be regard as facultative parasitism.
Since ascidians often contain chemicals against predators and/or solar
radiation, these are possibly mutual associations.
Tunicates are usually suspension feeders. If there are parasitic
tunicates, the resources they steal from the host would be space for
settlement or energy to make water current.
If there are any tunicates that directly absorb the nutrients from the
host body, their organizations would be highly transformed. It would
be very difficult for us to recognize that they are tunicates, and we
may need to examine their ontogeny or the presence of cellulosic tissue.
Luigi
--
Prof. Euichi (Luigi) Hirose, Ph D.
Tunicate Laboratory,
Dpt. Chem., Biol. & Mar. Sci.,
Fac. Sci., Univ. Ryukyus.
Okinawa 903-0213, JAPAN
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