Specificity in the Convoluta Roscoffensis/Tetraselmis Symbiosis
Convoluta roscoffensis is an intertidal acoel turbellarian (fflatworm1) that is locally abundant on sandy beaches of the Brittany coast of France and nearby Channel Islands. It is a conspicuous member of the beach fauna, for two reasons: first, the animals are green, due to the presence of algal symbionts of the genus Tetraselmis (=Platymonas, Prasinocladus) in their tissues (Parke & Manton, 19 67); and, secondly, they are gregarious, forming large dark-green patches on the surface of the beach at low tide (Holligan & Gooday, 1975). The details of the life cycle of C. roscoffensis was established by Keeble & Gamble (1907). The adult animals reproduce exclusively sexually and the fertilized eggs are deposited, within a common gelatinous capsule, in the sand. The algal symbionts are not transmitted directly into the eggs and the association is reestablished at each generation of C. roscoffensis when recently-hatched juveniles feed on free-living algae in the interstitial water. The symbiosis appears to be obligate for C. roscoffensis; all adult animals are green in the field and, in the laboratory, aposymbiotic juveniles die within a few weeks of hatching.
KeywordsAlgal Cell Mucous Gland Channel Island Algal Symbiont Green Hydra
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