Plectus armatus
Butschli, 1873
Photo Gallery- Konza Prairie
Photo Gallery- Long's Peak, Colorado

Measurements (from Mulk & Coomans, 1978)
L = 0.33-0.47 mm; a = 14.6-18.8; b = 3.3-4.1; c = 7.7-10.2; V = ;48-51 stoma = 15-21 um
L = 0.36 mm; a = 16.4; b = 3.6; c = 9.2; T = 50; stoma = 16 um

Description (from Mulk & Coomans, 1978)
    Female: body almost straight to slightly arcuate upon fixation, regularly tapering towards extremities.  Cuticle with distinct annules, more prominent on mid-tail region.  Two longitudinal alae, interrupting the transverse striae on either lateral side of the body, occupy about one-sixth of the body diameter near mid-body.
    Lip region truncate, 2.5-3 times broader than high, continuous with body; lips low, anteriorly rounded.  Four, anteriorly directed, cephalic setae, with flattened base, tapering in distal half to two-thirds; 3-4 um long, i.e. about 0.7-0.9 times the width of lip region; cheilostome obscure.  Prostome about one-third the meso-metastome.  Amphid apertures almost circular, 2.0-2.5 um wide, i.e. one-fifth to one-fourth as wide as body diameter at their level; located just behink the base of the prostome, 7-8 um from anterior extremity.  Excretory pore 60-75 um from anterior extremity, 60-70% of total oesophageal length.  Nerve ring slightly abouve level of excretory pore.  Cervical papillae setiform, situated between longitudinal alae, 5-7 annules posterior to excretory pore.  Endbulb almost circular, very muscular with sclerotized moderately developed, denticulated valves slightly anterior to middle of bulb.  Cardia well developed, one-fourth to one-third body diameter ongl at its level.  Intestine filled with small granules.  Rectum about one anal body diameter long or slightly larger.  Anus in slight depression.
    Vulva slit-like.  Vagina with moderately thick cuticlular lining, extends inwardly about one-fifth to one- fourth the uvlval body-width.  Ovaries reflexed, anterior on right and posterior on left side of intestine.  Tail straight to arcuate, tapering abruptly shortly behing anus; 4-5 anal body-widths long; bearing two pairs of subdorsal and one pair of subventral caudal setae on each side; left subdorsal of last pair more posterior than right subdorsal.  Spinneret 1.0-1.5 um long.
    Male: similar to female.  Testis diorchic, anterior and posterior testes on right and left side of intestine respectively.  Spicules nearly symmetrical, right one slightly more arcuate than left one which is almost straight with slight curvature distally, about 15 um long.  Preanal supplementary accessory organs absent.  Gubernaculum rod-shaped, aobut 0.45 times the lingth of spicules.  Number of setae on tail, as well as throughout the body, greater than in female.  Tail distally more arcuate; about 2.7 anal body-widths long.  Lateral field constricted on right side just above the spicule and dilated with a short seta in between, on left side, above the middle of the tail.