Haplocaulus Precht, 1935 (ref. ID; 1248, 2014)
Class Oligohymenophora: Subclass Peritricha: Order Peritrichida: Suborder Sessilina (ref. ID; 2014)
Family Zoothamniidae (ref. ID; 1248)

[ref. ID; 2014]
Inverted bell-shaped zooid borne upon a stalk which contracts in a zigzag manner. The organism solitary, never colonial and carried on an unbranched stalk, circular in cross-section. The myoneme travels down the inside of the stalk parallel to its walls. Haplocaulus is most easily confused with two other solitary peritrich genera whose stalks contracts spirally, these are Vorticella and Pseudovorticella.
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; 2082]
Warren (1988) recognized two species, H. kahlii (Stiller) and H. epizoicus (Sramek-Husek) (ref. ID; 2082)

See Pseudohaplocaulus.

Haplocaulus rhabdostyloides (Kellicott, 1885) (ref. ID; 2082)
Syn; Vorticella rhabdostyloides Kellicott, 1885 (ref. ID; 2082)
Description; This species was synonymized with Vorticella striata var. octava by Noland and Finley (1931), possibly because Kellicott (1885) did not provide a figure. Thus, Warren (1986) excluded it from his annotated list of nomila species. However, a careful examination of Kellicott's rather detailed description revealed that V. rhabdostyloides is very likely a distinct species with characters, however, perfectly matching those of Haplocaulus. Because Kellicott's paper is difficult to obtain, Foissner et al. (1996) provide his description: "Body nearly globular, cuticular surface smooth, peristome border thickened, narrow, cilia relatively stout, endoplast thick, short and but slightly curved. When contracted the body becomes more nearly globular or even depressed until it is napiform. The pedicle is filiform, length about equaling that of the body: length of body 1/900 to 1/800 of an inch. This vorticellid is plentiful during the winter months attached singly to flatting diatoms in Niagara-water. It appears to prefer Stephanodiscus niagarae, which support, if it may be so called, it tows about by the activity of its cilia. Foissner (1996) have called it Rhabdostyloides, from the fact that the shorter-stalked examples are so reluctant to contract their pedicles; shap blows upon the cover glass do not always induce this movement; it then has much the appearance of a species of Rhabdostyla. The pedicle when contracted is thrown more or less into a zigzag than into a coil, as is usual with members of the genus. The animal is not unlike R. ovum, but is more nearly spherical and very different when contracted with the contractile vesicle more nearly in the centre of the body. The peristome-border and pedicle separate it with sufficient sharpness from the only spherical form which it approaches in size." (ref. ID; 2082)