[ref. ID; 2014]
Medium to large (100-200 um long) more or less reniform ciliate. Oral aperture oval in outline centrally located in the concavity of the reniform body. The system of membranelles is prominent and occupies about half the body length. The undulating membrane defines the right edge of the peristome and terminates around the oral aperture in a cup. Membranelles M1 and M2 are obliquely situated at the anterior end of the peristome while membranelle M3 lies across the body in the upper half of the peristome almost at right angles to the undulating membrane. Somatic ciliation complete, comprised of mainly short cilia interspersed with long one. Kineties travel symmetrically centered about the oral aperture so that both pre- and post-oral sutures are present. Caudal cilium absent. Contractile vacuole in posterior body half. Macronucleus with an irregular shape, usually divided into two parts with several micronuclei. Most easily confused with Pleuronema which often has caudal cilia but whose somatic cilia are of equal length.
Quote; Colin R. Curds, Michael A. Gates and David McL. Roberts "British and other freshwater ciliated protozoa Part II Ciliophora: Oligohymenophora and Polyhymenophora" Cambridge University Press, 1983 (ref. ID; 2014)
[ref. ID; 7230]
Remarks; The genus Histiobalantium was identified following Kahl (1930-35). Diagnostic features are the large oral aperture, the prominent system of oral membranelles and the dense somatic ciliation, interspersed with longer bristles. While these long cilia are easily distinguished in live specimens, they are hardly visible in fixed cells. Thus, identification of this genus is problematic in studies which are based entirely on fixed water samples. The species found in Lake Constance is rather small (cell length 40-60 um, cell width 35-45 um). We observed a single, oviform macronucleus and three contractile vacuoles. These features do not correspond to any of the described Histiobalantium species (Kahl, 1930-35; Dragesco, 1968; Dragesco and Iftode, 1972; Wilbert, 1986). Thus, this is most likely a new species. With the cryptophyte Rhodomonas as food organism, Histiobalantium showed the following movement pattern: periods of 'resting' were interrupted by sudden jumps, which occurred either spontaneously or as a response to mechanical disturbance. The undulating membrane moved very slowly and we did not observe any water currents generated by the membranelles. Rhodomonas cells which happened to collide with Histiobalantium caused a rapid reaction of the ciliate, by which the prey cells were trapped in the buccal cavity and subsequently ingested. Thus, since Histiobalantium apparently depends on the motility of its prey, it must be classified as a diffusion feeder according to the terminology of Fenchel (1987). (ref. ID; 7230)