ULTRASTRUCTURE OF MITOSIS IN DIPLONEMA-AMBULATOR LARSEN AND PATTERSON (EUGLENOZOA)

The fine structural features of mitosis are described in a small biflagellated phagotrophic protist, Diplonema ambulator. Flagella replicate early in mitosis and move to opposite sides of the nucleus where they remain lateral to the spindle poles. An array of microtubules diverge from two foci located on opposite sides of the nucleus adjacent to the nuclear envelope. At metaphase, the chromosomes compact and align to form a distinct ring around the elongating nucleolus. The chromosomal plates then separate and move towards the poles followed by elongation of the nucleus. By telophase, the nucleus and nucleolus assume a dumbbell-shape. Constriction of the nuclear envelope around the chromosomal masses cleaves the nucleolus and produces the daughter nuclei. The nuclear envelope and nucleolus persist through mitosis. A comparison of the ultrastructural features of mitosis in Diplonema with that found in the euglenoids, the group with which they are believed to be most closely related, reveals marked differences.