Plectus assimilis
Bütschlii, 1873
Photo Gallery- Konza Prairie
Photo Gallery- Long's Peak, Colorado

Dimensions: 10 Females- L = .72-.84 mm, a = 14-17.2, b = 4-5, c = 10.4-13.4, V = 47-51, Stoma = 20-27u

Body stout, tapering only slightly anteriorly; posteriorly body tapers rapidly to short tail.  Cuticle marked by transverse striae most prominent in cephalic region.  Transverse striae interrupted on each side of body by two longitudinal alae, each wing area occupies approximately one-ninth of body width at vulva.  Lip region truncate-rounded, very low, less than one-fourth  as high as broad.  Six very low, connate lips, not set off from neck.  Lips delineated by beginning of transverse striations.  Four cephalic setae, broad at base, tapering rapidly (4-4.6 microns).  Cephalic setae located one or two annules behind lips.  Stoma length (20-26.6 microns) equal to one and one-half times lip region width.  Stoma wide, prostom length about one-half length of meso-metastom.  Amphids 6.6-10 microns from anterior extremity located at level of prostom.  Amphid diameter (2-2.6 microns) one-fifth of neck width at their level.  Esophagus approximately one-fourth of total body  length. Excretory pore located at 52-60% of esophagus length.  Nerve ring just anterior to excretory pore, cervical papillae setiform, situated between the longitudinal ridges just posterior to excretory pore.  Esophago-intestinal valve length slightly more than one-fourth body width at its level.  Vulva equatorial 47-51% of total body length, vulva lips not protruding.  Vagina extends into body about one-fifth of body diameter at vulva.  Eggs 70 microns x 32-34 microns.  Rectum length 24-28 microns.  Tail short (c = 10.4-13.4) tapering rapidly to very narrow tip.  Tail length three to three and one-half anal body diameters.  Five caudal setae: two subdorsal and three subventral.  Body with stout setae irregularly placed but concentrated in cephalic region.  Cuticularized orifice of caudal glands (spinneret) 2-2.6 microns in length.

Male: Not known.
Type habitat: Moss on tree trunk
Type locality: Germany.

P. assimilis can be separated from P. armatus by the shape of the cephalic setae and the stout setae scattered over the body.  In comparison with other Plectus the shape of the body (Rhabditis-like), the shape of the lip region, and the anteriorly placed amphids are considered diagnostic.
Although scattered setae are a universal occurrence in the genus Plectus, it is their large stout form that is different in Plectus assimilis, and their concentration on the neck region.
(Description- Maggenti, 1961)