Colpodella vorax:: ultrastructure, predation, life-cycle mitosis, and phylogenetic relationships

The flagellar apparatus of Colpodella vorax comprises two widely separated basal bodies/flagella linked by a pluri-lamellar connector, very short basal bodies and a slightly longer transitional zone. The anterior flagellum arises from a flagellar pit: its basal body is connected to a root of three apically oriented microtubules. Two roots are connected to the basal body of the posterior flagellum: the oblique root composed of a ribbon of 6-7 microtubules is directed towards the anterior flagellar pit and the rostrum, the posterior root of two microtubules is short and directed towards the rear of the cell. The apical complex is composed of a C-ring of interlinked microtubules forming a pseudo-conoid which arises at the apex, as do the associated rhoptries and micronemes. The pellicle is composed of the endoplasmic reticulum beneath the plasma-membrane and of widely separated microtubules arising subapically and present only in the anterior part of the cell. For predation on Bodo and Spumella flagellates, C. vorax attaches itself to the prey by its anterior portion; the pseudo-conoid transforms into a ring of microtubules encircling the attachment zone. The cytoplasm of the prey is aspirated and drawn into a large posterior food vacuole. After feeding the cell encysts and divides, producing four flagellate cells; the mitosis is of the semi-open type similar to that of the apicomplexan Diplauxis hatti. These observations on C vorax contribute to the ultrastructural definition of the genus Colpodella, which also includes C. gonderi and C. edax (= C. angusta). The species Spiromonas perforans differs from Colpodella in its flagellar apparatus, apical complex, the presence of dinoflagellate-type trichocysts and predatory behaviour. Colpodella is also distinct from the genera Perkinsus, Parvilucifera, and Cryptophagus which are bona fide alveolate protists.