PERIDINIUM GREGARIUM,A NEW SPECIES OF DINOFLAGELLATE1,2

A dinoflagellate has been found in tidepools on the coast of the Palos Verdes Peninsula in southern California. It is described as a new species, Peridinium gregarium. In the tidepool habitat, great numbers of the organism form cloud-like masses held together by a mucous matrix. The gregarious cloud formation seems to be shared by only one other species of dinoflagellate, Peridinium sociale (Henneguy ex Labbé) Biecheler, 1935.     

OBSERVATIONS ON THE TIDEPOOL ECOLOGY AND BEHAVIOR OF PERIDINIUM GREGARIUM1,2

Dense populations of a new species of dinoflagellate, Peridinium gregarium, have been found in a limited number of small rock tidepools on the coast of southern California. The organism is present throughout the year, but during periods of low temperatures and heavy tides it remains on the bottom of the pools in small aggregations. At other seasons P. gregarium leaves the aggregations during the morning hours and collects around the upper surface of small rocks in masses held together by a mucous matrix. Oxygen bubbles accumulated in the matrix eventually float the mass to the surface of the tidepool. During the afternoon or evening, the individuals return to the bottom aggregations leaving the matrix behind. Field and laboratory studies have attempted to define the nature of this organism's tidepool habitat and factors involved in the regulation of its diurnal movements.