[ref. ID; 7590 (Barry J. Wicklow, 1981)]

Diagnosis of the Families and Subfamilies of the Urostylina

Order HYPOTRICHIDA Stein, 1859
Suborder Urostylina Jankowski, 1979
Diagnosis; Frontal ciliature includes midventral cirri that develop during division morphogenesis from a longitudinal series of oblique streaks; somatic ciliature includes dorsal bristle rows and marginal cirral rows (marginal cirri are replaced in one group by longitudinal ventral cirral rows that differentiate from ventral primordia).

Superfamily Urostyloidea Butschli, 1889
Diagnosis; In addition to midventral cirri, 5 other frontal derivatives may be present: malar, migratory, transverse, accessory transverse, and thigmotactic cirri. All non-midventral, longitudinal cirral rows arise by somatic (within row) development and are considered marginal cirral rows.

Family Urostylidae Butschli, 1889
Diagnosis; Anterior frontal cirri are differentiated from other midventral cirri becoming markedly hypertrophied; the distal end of the adoral zone of paramembranelles extends only to the anterior of the cell.

Subfamily Holostichinae (n. subfam.)
Diagnosis; In addition to midventral and one or more left marginal cirral rows, only one right marginal cirral row is present.
Genus; Holosticha, Bakuella, Uroleptus

Subfamily Urostylinae (n. subfam.)
Diagnosis; In addition to midvental and left marginal cirral rows, several right marginal cirral are present.
Genus; Urostyla

Family Keronopsidae Jankowski, 1979
Diagnosis; All midventral cirri are of equal size (no hypertrophy of anterior frontal cirri has occurred.) Distal paramembranelles extend past the anterior end of the cell to a point along the right lateral cell border.

Subfamily Keronopsinae (n. subfam.)
Diagnosis; Frontal ciliature may comprise malar, migratory, midventral and transverse cirri; a thigmotactic cirral field is absent.
Genus; Keronopsis

Subfamily Thigmokeronopsinae (n. subfam.)
Diagnosis; In addition to malar, migratory, midventral and transverse cirri, a thigmotactic cirral field is present.
Genus; Thigmokeronopsis

Superfamily Pseudourostyloidea (n. superfam.)
Diagnosis; In addition to midventral cirri, malar and transverse cirri also differentiate from frontal streaks. Marginal cirri are absent; all non-midventral, longitudinal cirral rows develop from ventral primordia.

Family Pseudourostylidae Jankowski, 1979
Diagnosis; As above. Includes one genus Pseudourostyla.

Faure-Fremiet, in 1961, proposed 2 suborders within the Hypotrichida: the Stichotrichina and the Sporadotrichina. This division has been accepted in the classification schemes of Jankowki (1967), Puytorac et al. (1974), Corliss (1977), and Levine et al. (1980). Such a division was opposed by Borror (1972) due to the high diversity within, and overlapping ontogenetic patterns between, the two suborders. Faure-Fremiet included families within his 2 hypotrich suborders in 1961; Corliss, in 1979, recognized 11 families: Aspidiscidae, Euplotidae, Gastrocirridae, Holostichidae, Keronidae, Kiitrichidae, Oxytrichidae, Psilotrichidae, Spirofilidae, Strongylidiidae, and Urostylidae. Borror (1979) transferred the genus Holosticha to the family Urostylidae, thereby dropping the name Holostichidae as a junior synonym. Also in 1979, Tuffrau described an additional family, the Kahliellidae. Jankowski (1979) in his revision of the order suggests new names for many previously described taxa, elevates many genera to family status and proposes superfamilial and subordinal changes that he deems acceptable.
Jankowski, in his 1979 revision of the Hypotrichida, suggests 6 new suborders: Urostylina, Holostichina, Oxytrichina, Euplotina, Gastrocirrhina, and Apidiscina. The Urostylina, according to Jankowski, includes the Urostylidae, Keronopsidae, Psilotrichidae, Kiitrichidae, Strongyliidae, Atractidae, Spirofilopside, Hypotrichidiidae, Spiretellidae, and Chaetospiridae. Both the Urostylids and Keronopsids possess midventral ciliature; all of the remaining families within this proposed group do not, thereby rendering the group polyphyletic. In order to maintain a monophyletic classification, these remaining families cannot be assinged to the Urostylina.
Jankowski also proposes the suborder Holostichina, including the families: Holostichidae, Bakuellidae, Pseudourostylidae, and Banyulsellidae. There is no morphogenetic information regarding the family Banyulsellidae (represented by a single genus and species), hence, its systematic position remains uncertain. Bakuella does not differ significantly in structure or mophogenesis from Holosticha, thus its separation at the familial level is unjustified. Borror (1979) demonstrated the morphological and morphogenetic similarities between Holosticha and Urostyla; he therefore dropped the name Holostichidae as a junior synonym. I consider Holosticha and Bakuella as belonging to the subfamily Holostichinae in the family Urostylidae. The erection of the order Holostichina is therefore unwarranted. The morphogenetic pattern of Pseudourostyla differs significantly from that of other Urostylines. It should be separated into its own superfamily: the Pseudourostyloidea.