[ref. ID; 2014]
Elongate body, broadly rounded posterior region. At least 2 and usually several rows of marginal cirri on each side; 2 rows of midventral cirri arranged in a zigzag formation extending into the frontal region. No other cirri in frontal zone except a buccal cirrus. Transverse cirri present. AZM moderate, occupying the anterior body third. Macronuclei are numerous and scattered throughout the body. Only a few species have been described.
The genus was erected by Borror (1972) for Urostyla cristata and 2 similar species because of their morphogenetic pattern involving the midventral cirri which arise from a longitudinal series of short transverse rows of kinetosomes. Borror (1979) transfers the genus to the Urostylidae.
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; 3925]
Two to many rows each of right and left marginal cirri; midventral cirri in typical zigzag series, 2 cirri per original oblique ciliary streak; frontal and midventral cirri not distinct, with anteriormost cirri somewhat hypertrophied; AZM extended posteriorly to the cell's right of frontal cirri; transverse cirri usually present; groups of marginal cirri arising from a common primordium to the right of the rightmost row of each group.
Type genus (by original designation); Pseudourostyla cristata (Jerka-Dziadosz, 1964) Borror, 1972
Pseudourostyla originally was separated from Urostyla primarily on the basis of possession of midventral cirri. Subsequently, Jerka-Dziadosz discovered that U. grandis Ehrenberg, 1830 (type species of Urostyla) also has midventral cirri; thus that supposed distinction is no longer valid. Nevertheless, other structural and morphogenetic differences require separation of Pseudourostyla and Urostyla. Pseudourostyla cristata (Jerka-Dziadosz, 1964) has a pattern of frontal cirri similar to that of Keronopsis, whereas species of Urostyla more closely resemble Holosticha and Uroleptus in conformation of frontal cirri. Also, P. cristata marginal cirri arise from groups of longitudinal streaks in a common field on each side, rather than in streaks associated with each row of cirri as in Urostyla. (ref. ID; 3925)