[ref. ID; 2013]
Occurs in 2 morphological forms depending upon nature of food supply. The smaller (microstome) form grows when micro-algae and bacteria are the food source; this transforms into the larger (macrostome) form when fed upon ciliates.
Microstome: Shape reniform to ellipsoid, plastic, dorso-ventrally compressed. Uniformly ciliated, cilia in pairs. Indentation on left side marking the entrance to the ventrally situated vestibulum. Morphology and vestibulum of microstomes similar to that of Colpoda except that in Bresslaua when viewed orally the apex of the triangular-shaped vestibular opening is directed posteriorly (in Colpoda in points anteriorly). Contractile vacuole terminal.
Macrostome: Oval in outline with rigid body, dorsally convex, ventrally flattened. Vestibulum greatly enlarged so that it occupies almost two-thirds of body. Viewed dorsally there is a cleft on the left anterior margin which marks the vestibular opening and below it lies the ventral half of the body which juts out anteriorly to the dorsal half. Macronucleus rounded. Division takes place within cysts. Resting cysts with thicker walls also formed. Contractile vacuole on dorsal side in posterior half but not terminal.
Quote; Colin R. Curds "British and other freshwater ciliated protozoa Part I Ciliophora: Kinetofragminophora" Cambridge University Press, 1982 (ref. ID; 2013)