Tachysoma Stokes, 1887 (ref. ID; 2014)
Class Polyhymenophora: Subclass Spirotricha: Order Hypotrichida: Suborder Sporadotrichina: Family Oxytrichidae (ref. ID; 2014)
Family Oxytrichidae Ehrenberg, 1838: Subfamily Oxytrichinae Jankowski, 1979 (ref. ID; 4894)

Synonym Actinotricha Cohn (ref. ID; 1618)

[ref. ID; 2014]
Elongate, oval, dorso-ventrally flattened quite flexible body with a relatively small AZM (often less than third of body length). 2 rows of marginal cirri not joining posteriorly. Caudal cirri absent. Typical arrangement of front-ventral and transverse cirri with 3 strong anterior cirri. Macronucleus in two parts with 1 or 2 micronuclei. The genus may be distinguished from Oxytricha by its discontinuous marginal cirri and from Opisthotricha by the absence of caudal cirri. Several species have been described. Borror (1972) placed some of these forms in Oxytricha. Jankowski (1979) notes that to include Actinotricha Cohn, 1866 here requires submerging Tachysoma as a junior synonym. Jankowski recommends retaining the name as a subgenus of Oxytricha.
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; 4894]
Improved characterization; Adoral zone of membranelles formed like a question mark. Undulating membranes in Oxytricha pattern. Frontoventral cirri in V-shaped pattern. Postoral ventral cirri in dense cluster underneath buccal vertex. Two pretransverse ventral and five transverse cirri. One right and one left row of marginal cirri. Four to six dorsal kineties. Caudal cirri absent. FVT-cirri originate from primary primordia or separate anlagen. Dorsal morphogenesis in Tachysoma, Oxytricha, or Urosomoida pattern. (ref. ID; 4894)
Remarks; Very likely an artificial assemblage of flexible oxytrichids without caudal cirri. The type species is one of the most common oxytrichids in freshwater (Foissner et al. 1991). Histriculus also lacks caudal cirri, but is broader and much more rigid.
Type species (subsequent designation by Borror 1972); Trichoda pellionella Muller, 1773 (ref. ID; 4894)

Tachysoma parvistyla Stokes, 1887 (ref. ID; 1621) reported year? (ref. ID; 1618)
Description; 10 frontals scattered; in shallow fresh water pools. (ref. ID; 1618)
Measurements; About 63 um long. (ref. ID; 1618)
Tachysoma parvulum Corliss & Snyder, 1986 (ref. ID; 7603 original paper)
Description; Long, narrow, small body, 60 um long x 20 um wide (n = 6), most specimens exhibiting some degree of contraction. Large oral cavity opening ventrally, concave cell outline on left anterior end. Macronucleus long, cylindrical, 32 um x 5 um, separated into two lobes. Single micronucleus, 2 um in diameter, located near the juncture of the two macronuclear lobes. Two rows of dorsal kinetosomes are convergent posteriorly with a set of single files of kinetosomes between. Right dorsal row extends to the anterior tip of the cell, left dorsal row extends anteriorly to just posterior of the concavity on the left side created by the oral cavity. On the ventral surface, two rows of marginal cirri originate in line with the posterior portion of the oral cavity. The left marginal cirri extend directly posteriorly. The right marginal cirri cross the ventral surface to form a narrow corridor between the two marginal cirri rows for the posterior one-third of the cell, although this narrowing may be an artifact of contraction. The two marginal rows do not converge posteriorly, but terminate on either side of the transverse cirri, which are five in number. Eleven frontoventral cirri, arranged as follows: three anterior to the oral caivty, two pair and a single one (# 5) at the level of the posterior portion of the oral cavity, and a longitudinal row of three posterior to the opening of the oral cavity. Ca. 56 oral membranelles extend from the right ventral surface level with the middle of the oral cavity around to the dorsal surface on the right marginal, around the anterior end on the dorsal surface, back over on the ventral surface on the left cell margin, and down into the oral cavity. The oral dikinetid is located along the right margin of the inside of the oral cavity. (ref. ID; 7603)
Remarks; T. parvulum n. sp. appears most closely related to T. rigescens Kahl, 1932, but differs in the number and position of the frontoventral cirri. The new specific name refers to the rather unusually small body size for members of this widely dispersed genus. Diatoms were found in food vacuoles of some specimens. (ref. ID; 7603)
Type locality; Our specimens were commonly found in divserse samples of sea-ice slush and sea-ice pore water from the Weddell Sea, Antarctica. (ref. ID; 7603)
Tachysoma pellionella (O.F. Muller) (ref. ID; 1219, 3698, 5462)
Syn; Oxytricha pellionella O.F. Muller (ref. ID; 1219)
Description; Body outline elongate ellipsoid, flexible; ventrally flattened and equipped with 8 frontal, 5 ventral 5 strong transversal cirri; buccal area with adoral zone of membranelles usual for the family Oxytrichidae; dorsal side convex with 3 rows of long tactile bristles; 2 macronuclei, a single micronucleus; 1 contractile vacuole near the left margin just behind the buccal area. (ref. ID; 1219)
Measurements; Length about 80 um. (ref. ID; 1219)
Tachysoma pellionella (O.F. Muller, 1786) Kahl, 1932 (ref. ID; 4695)
Description; [Paroral formation]: The paroral formation marks the right-hand edge of the oral area and is composed of two parts: paroral formation 1 and paroral formation 2 (PF 1 and PF 2). PF 2 is a single row of 32 kinetosomes (avg.). PF 1 is a rows of 54 kinetosomes (avg.) in zig-zag arrangement, i.e., a haplokinety. There are 2 parallel fibres, one for each part of the paroral formation. These are the subparoral fibres (SPF 1 and SPF 2). There is also a thick fibre extending in anterioposterior direction in the middle zone of the oral area, designated suboral fibre (SOF). A set of subfibres lead out from this fibre. Some of them reach the subparoral fibres and another part extends to the adoral membranelles. These subfibres are called suboral subfibres (SOSF) (Fernandez-Leborans 1983). (ref. ID; 4695)