Plectus cirratus
Bastian, 1865
Photo Gallery- Konza Prairie 
Photo Gallery- Long's Peak, Colorado

Female, length 1/16". breadth 1/435".
External Characters. Body slender, tapering at both extremities, especiall posteriorly.  Head rounded, provided with a circle of four very shor cirri, about 1/15000" long.  Integumental striae 1/20000" apart, transverse.
Pharyngeal cavity slightly dilated at first, then long and narrow, length being about 1/666".  Oesophagus less than 1/4th of total length.  Intestinal cells not well marked, and containing but few fat-particles.  Anus 1/154" from posterior extremity.  Vulva slightly posterior to the middle of body.  Duct of excretory gland opening opposite middle of oesophagus.  Lateral vessels commencing at 1/1250" from anterior extremity.
Male not seen.
Hab. About lower decaying leaves of Myriophyllum verticillatum, pond, Bagshot.
(Description- Bastian, 1865)

L = 1.27; a = 23; b = 27.6; c = 3.4; V =46
L = 1.32; a = 31.4; b = 38.8; c = 3.3

    The females of this species correspond very closely to deMan's description of Plectus cirratus and have been identified by Dr. Cobb and Dr. Steiner as being that species.  However the rare males that occur in the western states differ greatly from the single specimen collected by deMan but the writer feels that too much importance should not be attached to these occasional, aberrant forms.
    Lip region distinctly set off.  Four short, stout setae.  Cutinous framework about the vestibule leading to the pharynx.  Amphids with sensilla pouches located near the base of the pharynx.  Front ovary on the right, the rear on the left side of the body.  Several setae on the tail not shown by deMan but figured by Cobb.
    The tail of the male bears a small acute, elevated ventral organ just on front of the anus and anterior to this is a series of four to six ventral supplements with long tube-like extensions reaching far back into the body, passing between the testes.  These organs are very similar to those being reflexed a distance equal to three times the body width.
    About fifty females and one male in this collection.
(Description- Thorne, 1929)

Measurements (from Andrassy, 1985)
L = 0.9-1.2 mm; a = 25-29; b = 3.7-4.7; c = 9-10; V = 48-51

(Bastian, 1865)    L = 1.58 mm; a = 27; b = 4; c = 9.6
(DeMan, 1884)    L = 1.3 mm; a = 24-30; b = 4-5; c = 8-9
                             L = 0.9 mm; c = 9
(Cobb, 1918)       L = 1.0 mm; a = 15; b = 5; c = 8.3; V = 48
(Andrassy, 1977) L = 1.0-1.1 mm; a = 23-27; b = 4.2-4.4; c = 8.9-9.2; V = 50-51
                             L = 1.0 mm; a = 25; b = 4.5; c = 8.5; spicules = 35/25 um

Description (from Andrassy, 1985)
    Body arcuate ventrally.  Cuticle 2-2.5 um thick on mid-body, finely but distinctly annulated; annulation especially visible on both extremities.  Annules 1.2-1.5 um wide on the middle region of body.  Lateral field 3.5-4 um wide, 1/9 - 1/11 of body diameter, consisting of two alae.  Hypodermal glands present, comparatively large (14-17 um), arranged in two rows on each side of body.
    Head 10-12 um wide, slightly set off, lips low, rounded.  Body at posterior end of oesophagus 2.8-3 times as wide as head.  Cephalic setae located on the third annule, 3-3.5 um long, obliquely directed forward.  Amphids 2.5-3 um wide, 11-15 um behind anterior body end, mostly somewhat posterior to middle of stoma.
    Stoma 21-24 um long, about twice as long as cephalic diameter; protostom 1/3 of stomatal length.  Oesophagus 230-245 um long, corpus and isthmus nearly equal in length, bulbus strong, oval.  Cardial process long.  Excretory opening 126-143 um from the anterior extremity, in 54-61% of the oesophagus length.  Deirids somewhat behind excretory pore.  Rectum as long as anal diameter.
    Vagina 1/3 of corresponding body width, showing four muscle circles.  Each gonad 3-3.8 times as long as body diameter, or 12-14% of body length, respectively.  Egg oval, 46-49 X 24-28 um.  Distance between vulva and anus 3.4-4 times as long as tail.  Tail 96-115 um long, arcuate, gradually narrowing to the tip, 4-5 times longer than the anal body diameter.  Spur (subterminal seta) about two tail tip diameters from the extremity.  Other caudal setae three pairs in number.
    The male of this species seems to be not so extremely rare than in other Plectus species.  It has been described by DeMan (1884), Gagarin (1977) and Andrassy (1977).  All descriptions fit very well.  The spicules are asymmetrical: the left one is longer (35 um) than the right one (25-30 um).  There are no tubular organs, only three weak preanal papillae.  The tail is supplied with 7 pairs of subventral and 6 pairs of subdorsal setae.