Opisthostyla Stokes, 1886 (ref. ID; 2014)
Class Oligohymenophora: Subclass Peritricha: Order Peritrichida: Suborder Sessilina (ref. ID; 2014)

[ref. ID; 2014]
Solitary. Inverted bell-like zooid mounted upon a long non-contractile stalk which is usually at least twice the length of the zooid and bent at its point of attachment so it acts like a spring causing the whole animal to be thrown backwards when the zooid contracts. There is a definite lip to the peristome. First described by Stokes (1886). Most easily confused with Rhabdostyla which has a short stalk without a spring-like attachment and with Propyxidium which has an Opercularia-like peristome.
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)

Opisthostyla annulata Stokes, 1886 (ref. ID; 1620) reported year? (ref. ID; 1618)
Measurements; Body about 23 um long. (ref. ID; 1618)
Opisthostyla globularis Stokes, 1889 (ref. ID; 1620) reported year? (ref. ID; 3342)
Measurements; 34 x 17-20 um. (ref. ID; 3342)