Description (from Thorne, 1974)
Body cylindroid, slightly arcuate. Lip region 1/3 width of neck base. Lateral fields 1/4 body width containing large cells obscured by dense granules. Lip region set off by deep constriction with rounded lips. Spear about as wide as adjacent cuticle, 18 um long, the aperture 2/5 its length. Guiding ring double but usually collapsed until appearing single, refractive, about 1/3 head width. Esophagus at first 1/3 then 1/6 as wide as neck, expanding gradually until 1/2 body width. Cardia discoid, then conoid, about 1/2 as long as body width. Intestine packed with dense yellowish granules. Prerectum length 3 times body width. Vulva longitudinal. Ovaries reflexed 1/2 way back to vulva. Uterus serving as a spermatheca and an additional spherical spermatheca at entrance to each oviduct.
Male more arcuate posteriorly with 21-28 supplements extending as far forward as the prerectum. Supplements sometimes closely approximated, or slightly spaced as illustrated. Spicula with strong ventral angle, lateral guiding pieces simple.
Labronema rapax is immediately distinguished by the low, rounded, set off lip region, short, massive spear, spheroid spermatheca, supplement numbers and arrangement and bluntly subdigitate tails.
Habitat: Small numbers from cultivated and virgin soil Milbank, Waubay Preserve and Black Hills, South Dakota; Tagus and Rugby, North Dakota; Downer, Minnesota; Baker, Montana; Hadashville, Manitoba, and Moosomin, Saskatchewan, Canada.