Ultrastructure of the ‘Zooxanthella’Endodinium Chattoniiin Situ

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Abstract
INTRODUCTIONRecent experiments with symbiosis in the flatwormConvoluta roscqffensisGraff (Provasoli, Yamasu & Manton, 1968; Provasoli, Yamasu & Mabuchi, 1969) reveal an important area in the investigation of algal-invertebrate associations, demonstrating the potential of studies based on the principle of cross-infections using various experimental symbionts. The studies which these authors describe are feasible only if detailed taxonomic data are available to facilitate rapid identification of symbiontsin situ. This kind of experimentation is impossible in symbiotic systems involving ‘zooxanthellae’, because of the general failure to provide adequate descriptions of the genera and species included in this ill-defined group. Admittedly, the situation shows signs of improvement. We now know that the ‘zooxanthella’ associated withC. convolutaAbildgaard is a diatom belonging to the genusLicmophora(Ax & Apelt, 1965; Apelt, 1969), the morphological criteria for the identification ofSymbiodinium microadriaticumFreudenthal have been redefined (Taylor, 1969 a) and a revised taxonomic description of this species is now available (Kevin, Hall, McLaughlin & Zahl, 1969). Nevertheless, we are still a long way from achieving a representative collection of well known experimental symbionts for use in comparative studies. It therefore seems worthwhile (not merely an exercise in micro-taxonomy and micro-horticulture) to continue to collect, identify and describe the range of genera and species that may be hidden among the ‘zooxanthellae’. The present paper is one in a series (see Taylor, 1969a,b,c) intended to explore the potential variety of these organisms.