Description (from Thorne, 1974):
Body moderately arcuate.  Lateral field about 1/3 body width.  Lips angular with prominent papillae. Spear about 16 um long with aperture 2/5 its length.  Guiding ring refractive.  Esophagus enlarged near middle by rather abrupt expansion.  Cardia cylindroid, then conoid, 1 1/2 body widths long.  Ovaries reflexed 2/3 their length.  Vagina extending halfway across body.  Vulva longitudinal.  Uterus forming a massive spermatheca packed with sperms.  Female prerectum length about equal to body diameter, often extending back forming a short pouch.  Rectum about equal in length to anal body diameter.  Two pairs of closely approximated pores present.
Males with 11 or 12 pairs of mammiform supplements, the series beginning well in front of spicula.  Spicula massive, about 50 um long.
Eudorylaimus arcus is distinctive because of the wide lateral field, tail form and supplement arrangement.
Habitat: Dry farm soil near Highmore, lawn near Brookings, native sod near Rapid City, South Dakota; and native sod west of Devils Lake, North Dakota.