Ultrastructure of the Amoeboflagellate Tetramitus rostratus


  • This manuscript in its present form was prepared from a preliminary draft that was in Dr. William Balamuth's files at the time of his death. Some changes were made in the illustrative material used, and the Discussion was updated to include recent relevant studies on amoeboflagellates. We thank Mrs. Mollie Balamuth and Dr. Tom Gong for their assistance in collecting the data and original electronmicrographs on which this report is based. We are grateful to Mrs. Emily Reid (Zoology Department, University of California, Berkeley) for her skilled preparation of the diagram of the Tetramitus flagellate. One of us (FLS) is pleased to acknowledge the generous assistance of Mr. Robert Two-mey in preparing specimens for scanning electron microscopy.

  • Deceased.

To whom correspondence should be addressed.


The life-cycle of the amoeboflagellate Tetramitus rostratus includes amoeboid, cyst, and flagellate stages. The ultrastructure of these three stages is illustrated, with particular emphasis on flagellate morphology. Amoeba morphology is typical of that of limax amoebas. Cysts, forming from trophic amoebas, are enclosed by a wall made up of two layers: ectocyst (ca. 70 nm), and endocyst (200 nm). The wall apparently forms from precursor material present in vesicles in the pre-cyst stage cytoplasm. Flagellate morphology is characterized by a well-defined top-shaped profile, maintained by microtubules under the plasma membrane. The flagellar apparatus or mastigont consists of four flagella, their basal bodies, sheaves of microtubules associated with two of the basal bodies, and several rhizoplasts (periodicity 20 nm). A deep, microtubule-supported, ventral invagination appears to function as a gullet. A small number of mitotic stages observed in amoeboid and flagellate individuals suggests similarity in the division process in both stages: intranuclear mitotic apparatus, nucleolus persisting through mitosis, no centrioles or basal bodies functioning as centrioles, difficulty in resolving chromosomes. The text compares ultrastructures of several amoeboflagellate organisms and evaluates the phylogenetic significance of those features common to different species. On the basis of this study, Tetramitus most closely resembles Naegleria spp.