Spirostomum Ehrenberg, 1833 (ref. ID; 2014)
Class Polyhymenophora: Subclass Spirotricha: Order Heterotrichida: Suborder Heterotrichina (ref. ID; 2014)
Family Spirostomidae Stein (ref. ID; 4813)

[ref. ID; 2014]
Body highly elongate, often worm-like, large (150 um to 4 mm long), cylindrical or flattened. The apical pole either rounded or with a slight beak-like projection towards the left. Terminal pole usually truncated but tapered in some species. Generally non-pigmented but some appear yellow to brown. The well-developed sub-pellicular myonemes lying along the longitudinal axis account for the high degree of contractility and body torsion. The body uniformly ciliated and the number of ciliary rows appears in most species extends to the equator. An undulating membrane absent on this genus. Single terminal contractile vacuole with a long single canal leading anteriorly. The macronucleus may be spherical, elongate or moniliform. The genus is most easily confused with Blepharisma which does not have a collecting canal associated with the contractile vacuole, does not display body contraction and always has an undulating membrane.
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)

Spirostomum ambiguum Ehrenberg (ref. ID; 1618), (O.F. Muller) (ref. ID; 3698) or (Mueller, 1786) Ehrenberg, 1835 (ref. ID; 4488, 4610), (O.F. Muller) Ehrenberg, 1838 (ref. ID; 1308, 1335, 1621, 2245, 3116) reported year? (ref. ID; 1219, 3690, 5462)
Syn; Trichoda ambigua O.F. Muller, 1786 (ref. ID; 4610)
Description; Elongated, cylindrical body, brownish in color; very large, easily distinguished with the unaided eye; highly contractile on account of longitudinal myonemes; uniform ciliation in longitudinal rows; peristome two-thirds of the body length, closely lined with short membranelles; the long macronucleus appears like a string of beads; many micronuclei; a single large contractile vacuole terminally, with 1 long canal close to the dorsal side. (ref. ID; 1219)
Macronucleus composed of many beads; many micronuclei; peristome two-thirds the body length; fresh water. (ref. ID; 1618)
Measurements; Length 1-3 mm. (ref. ID; 1219, 1618)
Spirostomum filum (Ehrenberg) (ref. ID; 1618) or (Ehrenberg) Penard, 1922 (ref. ID; 1308, 1621) reported year? (ref. ID; 3690)
Description; Peristome one-fourth the body length; posterior end drawn out; fresh water. (ref. ID; 1618)
Measurements; 200-300 up to 700 um long. (ref. ID; 1618)
Spirostomum intermedium (Kahl, 1932) (ref. ID; 4610) reported year? (ref. ID; 1308, 1618, 1621, 3690) reported author and year? (ref. ID; 191)
See; Spirostomum minus (ref. ID; 4610, 4813)
Description; Slender; macronucleus chain-form; fresh water. (ref. ID; 1618)
Measurements; 400-600 um long. (ref. ID; 1618)
Spirostomum loxodes Stokes, 1885 (ref. ID; 1308, 1621, 4488) reported year? (ref. ID; 1618)
Description; Peristome about one-third the body length; oblique striation; longer cilia at ends; macronucleus chain-form; fresh water. (ref. ID; 1618)
Measurements; About 300 um long (length:width = 6-7:1) (ref. ID; 1618)
Spirostomum minus Roux, 1901 (ref. ID; 1308, 1621, 1629, 4488, 4610, 4813) reported year? (ref. ID; 1618, 3698) reported author and year? (ref. ID; 3292)
Syn; Spirostomum ambiguum var. minor Roux, 1901 (ref. ID; 1621, 4610, 4813); Spirostomum intermedium Kahl, 1932 (ref. ID; 4610, 4813)
Description; Macronucleus chain-form; in fresh and salt water. (ref. ID; 1618)
Measurements; 500-800 um long. (ref. ID; 1618)
Spirostomum teres Claparede & Lachmann, 1858 (ref. ID; 4488, 4610, 4813) or 1859 (ref. ID; 1308, 1335, 1621, 1629, 2245, 3116) reported year? (ref. ID; 1219, 1618, 3342, 3690, 3698, 3942, 5462) reported author and year? (ref. ID; 191, 4429)
Description; Body shape similar to that of S. ambiguum but comparatively small; color yellowish or slightly brown; peristome about one-third of the body length; macronucleus oval. (ref. ID; 1219)
Macronucleus oval; in fresh water and also reported from salt water. (ref. ID; 1618)
Spirostomum teres is the smallest of the three abundantly occurring species of this genus, typically measuring 300 um in length when relaxed and about one-half that length while contracted. The interphase macronucleus is ellipsoidal, 25 x 45 um in size, and centrally located within the cell. Generally there are four spherical micronuclei, 4 um in diameter, situated with in very pronounced depressions in the macronuclear surface. Observations made on > 100 cells have revealed a few cells with five micronuclei, but never more; and no cells have fewer than three. A cell in the early stages of division is identified by a lengthened mid-region, the appearance of the new contractile vacuole of the presumptive proter, and the forming adoral zone membranelles (AZM) of the presumptive opisthe. Cells in the earliest stage of division identified in this study lacked detectable micronuclear birefringence or macronuclear changes but could be routinely identified the presence of the short, asynchronous cilia composing the developing AZM of the presumptive posterior daughter. This morphogenetic feature can be detected under the dissecting microscope and allows for the selection of cells in which micronuclei have not yet entered mitosis. (ref. ID; 3942)
Measurements; Length 150-400 um. (ref. ID; 1219, 1618)
340-410 um. (ref. ID; 3342)