Oskoron brevichelis Shear, new species

Oskoron brevichelis Shear, new species

Figs. 1, 142–153

Types. Male holotype from Section 10, Transect 11S, Range 10W, 0.6 mi NW of Elk City, Yaquina River Valley, Lincoln Co., Oregon, collected 20 December 1971 by Ellen M. Benedict; three female paratypes from three separate Oregon localities, viz., Douglas Co., Section 20, Transect 23S, Range 10W, 1 mi. S, 2 mi W of Ash, 1100’asl, collected 11 December 1971 by Ellen M. Benedict; Section 23, Transect 26S, Range 2E, 3 mi S, 9 mi E of Steamboat on OR138, 1600’ asl; Lane Co., Transect 16S, Range 6E, 2 mi N, 7mi W of McKenzie Bridge on US 126, 1800’ asl, collected 28 February 1972 by Ellen M. Benedict. All types deposited in CAS.

Diagnosis. Oskoron brevichelis, the smallest of Oskoron and Taracus species at maturity, can be separated from all others by the short chelicerae, as it is the only species in which the chelicerae are approximately the length of the body in males and shorter than the length of the body in females. The short chelicerae make this species appear smaller than it really is relative to its congeners.

Etymology. The species epithet refers to the short chelicerae.

Description. Male holotype from near Elk City. Total length, 2.25 mm. Carapace tan to light brown, merging at lateral margins into white, membranous cuticle; central region strongly domed; midline sulcus extends from anterior margin to ocularium. Ocularium as wide as long, rounded, with three stout, curved setae on tubercles above each eye; eyes large, black, ringed with black pigment. Metapelitidium sclerotized, appearing coalesced with carapace, with two setae on tubercles each side of sensory cone; sensory cone brown, acute, set in distinct socketlike patch of white cuticle. Abdomen soft, white or pale tan, with scutum parvum but lateral margins of scutum indistinct; scutum set with rows of curved, stout, small black setae raised on low plaques, these rows distinct anteriorly, becoming irregular posterior on scutum (Figs. 148–149). Ventrally, coxae tan, unspotted. Palpal coxae with 3 stout setae on distinct tubercles, leg coxae with strong, black setae not on tubercles. No indication of thoracic sternum. Genital operculum apically rounded, heavily setose, pale tan, unspotted. Abdominal sternites distinct, sclerotized, tan to brown, each with single row of small, black setae.

Chelicerae (Figs. 152, 153) relatively short, black. Basal article 0.94 mm long, 0.23 mm wide (L/W = 4.1); second article 1.24 mm long, 0.25 mm wide (L/W = 5.0). Basal article with prominent mediobasal knob, with only few, small seta-tipped tubercles in basal third, few distal tubercles; second article with more prominent, rounded seta-tipped tubercles ranged in about four irregular rows, tubercles more widely spaced and smaller distally. Fixed and movable fingers with paired, articulating triangular teeth, narrow, acute tips of fingers cross each other at rest.

Palpi (Fig. 143) brown, stout, total length 2.86 mm, trochanter with three low, seta-tipped tubercles, femur with setae on small tubercles, patella distinctly swollen. Lengths of articles as given in Table 24. Legs long, thin; yellowish tan with but one or two dark brown dots on femora; femora of leg 1 slightly darker. Autospasy suture of femora distinct on all legs. Tibiae without false articulations, all metatarsi with false articulations, numbering 3, 7, 4, 7 respectively. Total lengths in mm of legs 1–4: 6.13, 10.76, 6.25, 8.32. Measurements of leg articles given in Table 24.

Penis (Figs. 144, 145) short, relatively narrow, sides of shaft slightly sinuate; glans very distinctly swollen, abruptly tapering to twisted aculeus; aculeus with subtending crown of setae incomplete ventrally; shaft with three setae on each side subequal to crown setae.

Female from near McKenzie Bridge: Appendages proportionally shorter, stouter, except palpi longer and thinner than in males. Total length, 2.7 mm, width 1.07 mm. Carapace light brown; abdomen pale tan, finely mottled purplish brown, with irregular rows of small, black setae set on raised, more heavily sclerotized bumps, bumps glossy, translucent tan, largest either side of midline, sometimes coalesced in midline (Figs. 146, 147).

Cheliceral basal article (Fig. 150) 0.94 mm long, 0.25 mm wide (L/W = 3.8); second article (Fig. 151) 1.26 mm long, 0.34 mm wide (L/W = 3.7). Total length of palpus (Fig. 142), 3.68 mm; patella of palpus not swollen, femoral setae not on tubercles. Total lengths in mm of legs 1–4: 5.38, 8.98, 5.75, 7.82; lengths of articles as given in Table 25. Leg metatarsi with 3, 5, 4, 5 false articulations respectively. Ovipositor typical. Other characters as in male.

Distribution. In addition to the localities given above; all samples WAS: OREGON: Benton Co.: 10 mi N Philomath, from newt stomach, (no date) R. Freiburg, Ƌ (CAS). Clatsop Co., 3 mi SE Olney on OR202, 400’ asl, 27 November 1971, E. M. Benedict, Ƌ. Coos Co., 10 mi E, 1 mi S Allegany, Weyerhouser Millicoma Tree Farm, company road 4110, 20 November 1971, E. M. Benedict, Ƌ. Douglas Co., 11 mi E, 4 mi S Allegany, Weyerhauser Millicoma Tree Farm, company road 6040, 21 November 1971, E. M. Benedict, Ƌ; 3.2 mi NE Scottsburg, 400’ asl, 11 December 1971, E. M. Benedict, ♀. Lane Co., Rd 1602 to White Branch Youth Camp, 3 mi E McKenzie Bridge, 2400’ asl, 16 October 1971, E. M. Benedict, ƋƋ. WASHINGTON: Cowlitz Co., Germany Creek at end of county road, 5.5 mi N Stella, 450’ asl, N46°15.561’, W123°08.067’, 22 November 2003, W. Leonard, C. Richart, ♀. Lewis Co., Forest Service Road 25, 8.5 mi S Randle, Gifford Pinchot National Forest, 1050’ asl, N46°26.456’, W121°59.796’, 6 December 2003, W. Leonard, C. Richart, ♀. Thurston Co., McAllister Springs, 60–123’ asl, N47°02.837’, W122°43.722’, 7 February 2004, W. Leonard, C. Richart, Ƌ.

The two areas of distribution, in southwest Oregon and southwest Washington, are disjunct, but direct side-byside comparison shows the specimens to be virtually identical morphologically. Nevertheless we have not designated the Washington specimens as paratypes in the event that future morphological or molecular study refutes the hypothesis that only one species is present. This species should be searched for in the intervening area, but because of its small size and winter-active habits (all records are from November–February), it may be some time before the distribution is filled in. All specimens were either hand-sifted from forest litter (Washington) or collected in Berlese funnels (Oregon).

Notes. The chelicerae of the male holotype of O. brevichelis have attached to them several minute nematodes. The nematodes are attached very firmly by one end but do not seem to be penetrating the thick cuticle of the chelicerae. A single male from Benton Co., Oregon, was taken from the stomach of a newt.