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Description (from Thorne, 1974)
Female body slightly arcuate, male straighter but
arcuate in region of supplements. Lateral field 1/3 - 1/4 body width
without visible cellular structure. Lip region angular, set off by
deep constriction, 1/3 width of neck base. Spear about 13 um long
with aperture 1/2 its length. Cephalic papillae prominent.
Esophagus enlarged by rather abrupt expansion near middle. Intestinal
cells with scattered, rather coarse brown granules. Prerectum length
about twice body width. Rectum longer than anal body diameter.
Vulva transverse with sclerotized labia. Ovaries reflexed halfway
to vulva. Eggs 45 x 80 um. Sperms present in uterine tracts,
indicating that males are functional. Tail elongate hemispheroid
with thick cuticle and two pairs of pores. Male similar to female
with slightly arcuate tail bearing 9 supplements arranged as illustrated.
Spicula about 50 um long with simple lateral guiding pieces.
Thonus major is immediately distinguished
by its length, set off lip region and 9 supplements.
Habitat: Alfalfa field near Bear Butte, South
Dakota