SYMBIONTS OF THE TROPICAL DINOPHYSIALES (DINOPHYCEAE)

The pigmented phaeosomes noted by earlier observers have been confirmed as cyanobacteria, following examination in the electron microscope. Representatives of the genera Ornithocercus, Histioneis and Citharistes have been investigated and shown to possess at least two and possibly three distinct forms of symbiotic cyanobacteria. The structure of these organisms and their position within the host organism have been examined, and the nature of the relationship discussed. In the genus Amphisolenia a further, distinct species of cyanobacterium was observed as an internal symbiont of A. globifera. In A. thrinax and A. bidentata two other symbiotic organisms were seen, one an entire eucaryotic cell and the other a bacterium. The significance of these various associations is considered.