Electron Microscopy on the Symbiosis between Blue-Green Algae and an Opisthobranch, Placobranchus

In 1941 the senior author reported an association between unicellular algae and Placobranchus ocellatus from a reef flat in the Palau Islands.2'He found many specimens of a different species, Placobranchus ianthobapsus,5' at a lagoon in front of the Marine Laboratory of the University of Hawaii on Coconut Island in 1960. Ecological observationswere made in the lagoon and histological preparations for light and electron microscopy were made with preserved specimens.Unfortunately, however, the results of the electron microscopic treatments were not satisfactory.He had another chance to visit there again in April, 1964 and brought back some living specimens to Okayama for electron microscopy.This is a summary of studies on the problem; details will be given elsewhere.Placobranchus ianthobapsus GOULD is usually found on a shallow bottom.It is completely covered with a thin layer of fine sand and there is no sign of the animal except for two small holes which are the anterior inhalent and the posterior exhalent of sea water to the