ULTRASTRUCTURE OF VEGETATIVE STAGES IN LABYRINTHOMYXA MARINA (=DERMOCYSTIDIUM MARINUM) A COMMERCIALLY SIGNIFICANT OYSTER PATHOGEN

The microstructure of the protist Labyrinthomyxa marina as found in a host organism, Crassostrea virginica, is described. Most of the organelles were similar to those of many eucaryotic protists; however, a few unusual structural features were observed. Viruslike particles (460-530 Å diameter) were found in the nucleus and cytoplasm of the Virginia, but not the Florida, pathogens. Cell-wall formation appeared to occur, in part, by formation of material in vesicles derived from the endoplasmic reticulum. The vesicles appeared to fuse with the plasmalemma and release material into the cell wall. Funguslike lomasomes were found between the cell wall and plasmalemma. Vacuoplast formation occurred by synthesis of droplets of electrondense material through the membranes of large vacuoles followed by coalescence to form one or two large vacuoplasts. Mitochondria were involved in the formation of vesicles which contained electron-dense material and which were delimited by two membranes. Since L. marina has previously been allied with the Labyrinthulia (Protozoa) and the Saprolegniales (Phycomycetes), comparisons are made with the ultra-structure of representatives from both groups. Affinities with the fungi seem to be the closest on the strength of lomasome formation and the repeated formation of cell walls in all vegetative stages. © 1969.