Fabre-Domergue (1888: 35, figs 34–50)
Dragesco & Dragesco-Kernéis (1986: 173), Foissner et al. (1995: 235)
Didinium balbianii (Fabre-Domergue) Kahl (1930: 125, fig. 18.24)
In vivo 50–80 (–120) × 30–80 µm. Body ovoid, with a prominent anterior oral cone. Somatic kineties 54–80 (–100), longitudinal, non-ciliferous except for 1 ciliary band at anterior end of kineties. Brosse posterior to ciliary band, composed of 4 or 5 short rows of bristle-like cilia. Circumoral kinety immediately anterior to ciliary band. Extrusomes 5–10 µm long, in oral cone and body. Granular mucocysts present in cortex. Macronucleus horseshoe-shaped to reniform. Contractile vacuole in posterior end. Movement: usually very rapidly to and fro.
Indian sector of the Southern Ocean (Hada, 1970); Weddell Sea (Garrison & Buck, 1989a); occurs also in freshwater and soil, cosmopolitan. Records from Antarctic freshwater lakes (Hada, 1970) and moss (Sudzuki, 1979) probably belong to a different species (Petz & Valbonesi, unpublished data).
This ciliate is apparently highly variable and comprises several rather similar subspecies or species. Didinium balbianii var. nanum Kahl (1930: 126, fig. 18.27) (correct identification: Monodinium balbianii nanum), also reported from the Southern Ocean by, for example, Hada (1970) and Klöser (1990), is only 20–35 µm long and perhaps a separate species. An unidentified Monodinium sp. was found in an Antarctic hypersaline lake close to the sea (Highway Lake, Vestfold Hills), at 68°29’S 78°09’E (Scott, unpublished data).