Body usually broadly obovoid to barrel-shaped, appearing to consist of 2 hemispherical portions; pre-equatorial furrow separates wider anterior from narrower and sometimes slightly tapering posterior portion; very fragile. Usually reddish-brown from cryptophycean endosymbionts, sometimes green or colourless. Macronuclei 1-2 in number, 1 micronucleus. Contractile vacuole lacking (?). Around 40 kinety belt rows in area of pre-equatorial furrow composed 1) of basal body patches at anterior ends, from which anteriorly, laterally and posteriorly directed bundles of long, stiff cilia ("cirri") project; and 2) of longitudinal rows of paired basal bodies in posterior portions. Without cytostome; however, 6-8 bifurcated oral processes (perhaps extrusomes) and several basal bodies surround anterior pole in some populations. Movement jumping. Size in vivo 10-70 x 20-37 µm. Very likely sometimes confused with other similar-sized reddish species, which already suggests the variety of shapes and sizes (Kahl, 1930; Lindholm, 1985; Crawford, 1989; Petz et al., 1995a). The systematic position of M. rubra is uncertain: Kahl (1930) synonymized it with Mesodinium pulex (which was followed by, e.g., Revelante and Gilmartin, 1983), whereas Jankowski (1976) established the new but very insufficiently diagnosed genus Myrionecta for it. Mass occurrences of this ciliate cause red tides.
Ref.: Hamburger and Buddenbrock (1911), Kahl (1930), Taylor et al. (1971), Lindholm (1981, 1985), Grain et al. (1982).