Studies on the Genus M esodinium I: Ultrastructure and Description of M esodinium chamaeleon n. sp., a Benthic Marine Species with Green or Red Chloroplasts

We provide here the description of a new marine species that harbors green or red chloroplasts. In contrast to certain other species of the genus, M esodinium chamaeleon n. sp. can be maintained in culture for short periods only. It captures and ingests flagellates including cryptomonads. The prey is ingested very rapidly into a food vacuole without the cryptomonad flagella being shed and the trichocysts being discharged. The individual food vacuoles subsequently serve as photosynthetic units, each containing the cryptomonad chloroplast, a nucleus, and some mitochondria. The ingested cells are eventually digested. This type of symbiosis differs from other plastid‐bearing M esodinium spp. in retaining ingested cryptomonad cells almost intact. The food strategy of the new species appears to be intermediate between heterotrophic species, such as M esodinium pulex and M esodinium pupula , and species with red cryptomonad endosymbionts, such as M esodinium rubrum .