A new primitive protozoan devouring centric diatoms in the plankton

A new primitive protozoan Asterocaelum algophilum gen. et sp. nov., is described from the plankton of Loch Leven, Scotland where it was found primarily feeding on the centric diatoms Stephanodiscus rotula (Kütz) Hendey and Cyclotella pseudostelligera Hustedt. Stages in its life cycle consist of a trophic amoeba, a cyst from which the protoplasm emerges as one or several units similar to the amoeboid stage and a resting cyst containing a double walled resting spore. The amoeboid stage produces numerous clear hyaline pseudopodia which are often broad based and taper apically and within which a core of denser material, possibly an axial filament, is sometimes seen. The cyst and resting cyst stages externally bear long tapering empty spines formed by the laying down of a wall and subsequent emptying of the protoplasm from a number of rather stiff radiating processes produced by the amoeboid stage. All external surfaces are surrounded by an envelope of mucilage and the walls laid down by this organism give a positive reaction for cellulose. The similarity of its life cycle to that of the vampyrellids is noted.