Ultrastructure of the ‘Zooxanthella’<i>Endodinium Chattonii</i>in Situ

Abstract

INTRODUCTION Recent experiments with symbiosis in the flatworm Convoluta roscqffensis Graff (Provasoli, Yamasu &amp; Manton, 1968; Provasoli, Yamasu &amp; 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 symbionts in 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 with C. convoluta Abildgaard is a diatom belonging to the genus Licmophora (Ax &amp; Apelt, 1965; Apelt, 1969), the morphological criteria for the identification of Symbiodinium microadriaticum Freudenthal have been redefined (Taylor, 1969 a) and a revised taxonomic description of this species is now available (Kevin, Hall, McLaughlin &amp; 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, 1969 a , b , c ) intended to explore the potential variety of these organisms.