[ref. ID; 4894 (Helmut Berger and Wilhelm Foissner, 1997)]

Family Oxytrichidae Ehrenberg, 1838
Characterization; Euhypotrichina with flexible or rigid body and usually 18 FVT cirri clustered to six distinct groups. The FVT cirri originate from six longitudinal primordia segregating 1,3,3,3,4,4 cirri. Six or less parental FVT cirri participate in primordia formation. At least one fragmenting dorsal kinety.
Type genus (original designation); Oxytricha Bory de Saint-Vincent in Lamouroux, Bory de Saint-Vincent & Deslongchamps, 1824
Remarks; Jankowski (1979) split the Oxytrichidae into three subfamilies, viz. Oxytrichinae (type Oxytricha), Ancystropodiinae (type Ancystropodium), and Psammomitrinae (type Psammomitra). The Oxytrichinae include all 18 FVT cirri oxytrichids, the Ancystropodiinae are monotypic, and the Psammomitrinae are an artificial assemblage including poorly known genera, some of which have been assigned to other families. Thus, we establish a new subfamily for the oxytrichids of the Stylonychia branch.

Subfamily Oxytrichinae Jankowski, 1979
Characterization; Oxytrichidae with flexible body. Cirrus V/3 participates in primordia formation. Often with distinct cortical granules.
Type genus (original designation); Oxytricha Bory de Saint-Vincent in Lamouroux, Bory de Saint-Vincent & Deslongchamps, 1824
Remarks; This subfamily contains the genera Cyrtohymena, Gonostomum, Notohymena, Onychodromopsis, Oxytricha, Tachysoma, Urosoma, and Urosomoida. Very likely, Parurosoma, Pseudostrombidium, and Australocirrus oscitans also belong to this assemblage, because they have a flexible body. However, this has to be confirmed by morphogenetic studies.

Subfamily Stylonychinae n. subfam.
Characterization; Oxytrichidae with rigid body. Cirrus V/3 not involved in primordia formation.
Type genus; Stylonychia Ehrenberg, 1830
Remarks; The subfamily includes the genera of the Stylonychia branch in our cladograms, viz. Coniculostomum, Histriculus, Steinia, Sterkiella, and Stylonychia. Furthermore, Parastylonychia and Pleurotricha are assigned to this subfamily because they have a rigid body, a rather unique character within the euhypotrichs. The other two autapomorphies shown in the cladogram, the relative length (> / - 40%) of the adoral zone and the lack of cortical granules are rather weak and were thus not used in the characterization. Very likely, Onychodromus, Laurentiella, and Pattersoniella belong to this subfamily, too. Their exact position within the cladogram is, however, beyond the scope of the present paper.