A new species of the genus Hypochthonius (Acari: Oribatida)

Introduction Three specimens belonging to the genus Hypochthonius were collected from the bottom of hollows on a tree trunk at the Shirakami-sanchi World Heritage Area, and from deposit at the bottom of a hollow between a rock and the root (-50 cm in depth) of a tree at Mt. Hayachine. The genus is one of the interesting groups in the progress of systematics as suggested by Norton (1984). In Japan two species of the genus, H. luteus Oudemans, 1917 and H. rufulus C. L. Koch, 1836 have been recorded to date (Fujikawa et al., 1993). Although it was impossible to study the type specimen of H. rufulus, the present specimens were studied in comparison with the type specimen of H. luteus and European specimens of H. luteus and H. rufulus in Berlese's Collection as well as van der Hammen's, Moritz's, Oudemans', and Tuxen's, in addition to the original and other descriptions by Aoki (1959), Berlese (1896), Grandjean (1933, 1935, 1941 & 1946), Hammen (1952), Hammer (1952), Jacot (1934 & 1936), Michael (1888), Oudemans (1914), Schweizer (1956), Sellnick (1928) and Willmann (1931). The present specimens were considered to represent a new species in this work. Hypochthonius montanus spec. nov. [Japanese name: Miyama-hiwadani] (Figs. 1 & 2) Hypochthonius sp. SH-20 sup *: Fujikawa, Report of soil animals from the Shirakami-sanchi World Heritage Area (in press). Measurements and color (3 exs.): Body length, 757 (793)829 micro m; wide, 429 469)493 micro m. Light yellowish brown. The whole integument with fine granules and large light coloured area being irregular in shape and size; the inside of every spot scabrous bearing convex polygons. Prodorsum: Rostral border senate; serrate fifteen (in each specimen). Prodorsal lateral sides concave at the level of rostral setae (ro) as well as antero-lateral to lamellar setae (le). Large spots present in the vicinity of setae ro and le, at the anterior position of interlamellar setae (in) and bothridia, and at the interlamellar region. Setae ro smooth setiform, extending to anterior rostral margin. Setae le flagelliform, sparsely ciliated, extending near anterior rostral margin. Setae in flagelliform, minutely and sparsely barbed unilaterally, extending for almost mid-distance between anterior rostral margin and the insertions of setae ro. Sensillus with five long and eight short branches (in holotype; the number uncertain in case of paratypes because of broaken portions), appreciably longer than setae in. Two pairs of exobothridial setae smooth and short. Relative distances: (in-in) > (ro-le) NE (le-le) NE (le-in) > (ro-ro). Notogaster: Straight anteriorly, broadest at the middle suture, and posteriorly angular in shape. Many spots with inside reticulation present; spots variable in shape and size. Fourteen pairs of dorsal setae and two pairs of vestigial organs of setae e sub 1 and e sub 2 present. Dorsal setae flagelliform sparsely and minutely barbed unilaterally; varible in length. Relative lengths: h sub 1 =>f sub 1 >h sub 2 >d sub 1 > d sub 2 >f sub 2 > cp NE h sub 3 > c sub 1 > ps sub 1 > c sub 3 > c sub 2 > ps sub 2 NE ps sub 3. Relative distances: (h sub 1-h sub 1) > (c sub 2-c sub 2) NE (d sub 1-d sub 1) > (c sub 1-d sub 1) > (f sub 1-f sub 1) >