[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)