THE MORPHOLOGY OF GONYOSTOMUM SEMEN FROM WOODS HOLE, MASSACHUSETTS

Abstract

1. The chloromonad, Gonyostomum Semen (Ehrenb.) Diesing, was collected in a sphagnum swamp at Woods Hole, Massachusetts, during July, 1934. The organism has been seen so rarely since it was first described that certain morphological features of the vegetative cells have been imperfectly known, and cell division and encystment have not previously been recorded.2. The vegetative cells are flattened dorsoventrally and vary in shape in ventral view from lanceolate to circular. The anterior end is two-lobed, and a short caudus terminates the posterior end. No cell wall is present: the cells are somewhat metabolic and under certain conditions become amœbid. The extreme size measurements of a hundred cells were 36-92 µ x23-69 µ On the ventral surface, a shallow longitudinal groove runs from anterior to posterior regions. Two flagella are present, one projected forward, and one trailing close to the cell body in the ventral groove. A broadly conical cavity lies in the anterior cytoplasm and opens to the outside by a small aperture between the anterior lobes. A large contractile vacuole is seen near this cavity, and several smaller ones may be present. The nucleus is ovoid or subspherical and usually located centrally in the cell. Its structure has not yet been clearly shown. The chromatophores are small, ovoid, and arranged peripherally in the cytoplasm. Oil is the product of metabolism, and under obviously unfavorable conditions it is formed in large quantities. Many hyaline rod-like bodies are arranged radially in a peripheral layer in the cytoplasm. These bodies absorb large amounts of stains from very dilute solutions. Under pressure, or upon addition of chemicals, these bodies shoot out of the cell and usually elongate into threads of slime. They act like the trichocysts in Paramœcium and force the worker to exercise extreme care in fixing, preserving, and culturing the organisms.3. Division of vegetative cells is longitudinal; it occurs, as a rule, only among the smaller cells of the population. Nuclear division and cytoplasmic constriction are described.4. Encystment of cells was observed in old cultures. Division of encysted cells was not observed.