Cell Structure of Predatory Flagellate Metromonas grandis Larsen et Patterson (Cercozoa)

Abstract

The ultrathin structure of carnivorous flagellate Metromonas grandis Larsen et Patterson has been investigated. The predator captures the whole cell of the prey (bodonids or chrysomonads). Cytostome as a cell pocket has not been found. The cell, besides the flagella and small parts of the folds, is surrounded by a fibrous layer 0.05–0.12 µm in thickness which consists of thick and thin bent shafts. The plasmalemma is beneath this layer. Two unequal flagella come out of a small pocket. The long flagellum bears multiple, very thin mastigonemes (hairs) 0.8–1.0 µm in length; the short flagellum is reduced and is covered by rare mastigonemes. The transversal plate is raised above the cell surface, surrounded by osmiophilic muff. Helix is absent. The root system is simplified and consists of two microtubular bands which originated near the kinetosome of the long flagellum. The kinetosomes lie parallel to each other and are interconnected with at least one fibrous bridge. Cylindrical extrusomes (trichocysts) 1.0–1.4 µm in length and 0.12–0.08 µm in diameter have been found in the cytoplasm. Trichocysts are divided by a diaphragm and contain a wheel-shaped structure with 13 spokes visible in cross sections. Contractile vacuole is absent. The resemblance of Metromonas grandis to M. simplex (Griessmann, 1913) Larsen et Patterson, 1990, Metopion fluens Larsen et Patterson, 1990 cryomonadids, and other predatory flagellates is discussed.