Oskoron crawfordi Shear, new species
Creators: name: Shear, William A.
name: Warfel, Joseph G.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Opiliones
Sabaconidae
Oskoron
Oskoron crawfordi

description: Oskoron crawfordi Shear, new species
Figs. 154–163
Types. Male holotype, male and two female paratypes from Holder Creek Valley, 47.467°N, 121.954°W, 1375– 1400 ’ asl, King Co., Washington, taken from 12 overwinter pitfall traps (129d), 12 December 1996 to 20 April 1997, collected by James Bergdahl. All types deposited in UWBM.
Diagnosis. Oskoron crawfordi resembles O. brevichelis, but differs from that species in many respects, being larger overall, with much longer, spinier chelicerae in comparison to body length, having much smaller seta-tipped tubercles on the ocularium, having the metapeltidium unsclerotized and with a row of setae (rather than two setae as in brevichelis), having more setae on the abdomen (both dorsal and ventral), and with shorter legs in proportion to body length.
Etymology. The species name honors Rod Crawford, curator at the Burke Memorial Museum, Seattle, Washington, who maintains one of the premier collections of terrestrial arthropods from the Pacific Northwest.
Description. Male holotype. Total length, 3.00 mm. Carapace medium to dark brown to black; anterior, posterior, anteriolateral borders well-defined; central region strongly domed; midline sulcus extends from anterior margin to ocularium; three indistinct dark “hash marks” on either side of ocularium; large slit sense organs anterior to ocularium distinct. Ocularium somewhat longer than wide, rounded, with five small setae on tubercles in single row above each eye; eyes large, black, ringed with black pigment. Metapelitidium not sclerotized, with single row of four setae at posterior margin; sensory cone brown, acute, set in small embayment in posterior edge of carapace. Abdomen soft, white, with scutum parvum, margins of scutum indistinct, irregular, scutum with widely scattered small black setae on low humps (Fig. 160). Ventrally, coxae tan, unspotted. Palpal coxae with stout setae on distinct tubercles, first leg coxae with strong, black setae on tubercles; setae on coxae two, three and four not on tubercles. Leg coxae two and three with very obvious anteriomesal groups of slit sense organs. No indication of thoracic sternum. Genital operculum apically rounded, heavily setose, light brown, unspotted. Abdominal sternites not sclerotized, white, indicated by single rows of small, black setae.
Chelicerae about one third longer (3.92 mm long) than body, dark brown to black. Basal article 1.67 mm long, 0.32 mm wide (L/W = 5.22); second article 2.25 mm long, 0.49 mm wide (L/W = 4.6). Basal article with prominent mediobasal knob, in mesal view with distinct dorsal and ventral rows of 8–10 seta-tipped tubercles; second article with more prominent, rounded seta-tipped tubercles ranged in about five irregular rows, tubercles more widely spaced and smaller distally; seen dorsally, rows of tubercles give angular, carinate appearance to article. Fixed and movable fingers with paired, articulating triangular teeth, narrow, acute tips of fingers cross each other at rest.
Palpi (Figs. 155, 162, 163) light brown, slender, total length 3.86 mm; trochanter with seven low, seta-tipped tubercles, femur basally with setae on small tubercles, more distally, setae not on tubercles. Lengths of articles as given in Table 26. Legs short relative to body length, medium brown, unspotted. Basal false articulation of femora distinct on all legs. Tibiae without false articulations, false articulations of metatarsi 0, 10, 2, 0 respectively. Total lengths in mm of legs 1–4: 6.31, 9.21, 5.97, 7.92. Measurements of leg articles given in Table 26.
Penis (Figs. 156–157) broad, widest at base of shaft, not distally expanded, setose glans abruptly narrows to curved aculeus.
Female paratype. Total length, 4.75 mm. Carapace medium to dark brown, merging at posteriolateral margins into white, membranous cuticle; anterior, posterior, anteriolateral borders well-defined; central region strongly domed; midline sulcus extends from anterior margin to ocularium; three distinct dark “hash marks” on either side of ocularium. Ocularium somewhat longer than wide, rounded, with few small, nearly undetectable setae above each eye; eyes large, black, ringed with black pigment. Metapelitidium not sclerotized, with single row of setae at posterior margin; sensory cone brown, acute, set in small embayment in posterior edge of carapace. Abdomen soft, white, with densely scattered small setae set on low, orange-brown, sclerotized mounds; central sclerotized patches of two or three coalesced in midlines of areas two and three, otherwise patches near midline larger, becoming very much smaller laterally (Figs. 158, 159) Ventrally, coxae tan, unspotted. Palpal coxae with 5–7 stout setae on distinct tubercles, first leg coxae with strong, black setae on tubercles; setae on coxae two, three and four not on tubercles. No indication of thoracic sternum. Genital operculum apically rounded, heavily setose, light brown, unspotted. Abdominal sternites not sclerotized, white, indicated by dense bands of small, black setae.
Chelicerae (Fig. 161) slightly longer than body, black. Basal article 1.98 mm long, 0.40 mm wide (L/W = 4.95); second article 2.86 mm long, 0.59 mm wide (L/W = 4.85). Basal article with prominent mediobasal knob, in mesal view with distinct dorsal and ventral rows of 8–10 seta-tipped tubercles; second article with more prominent, rounded seta-tipped tubercles ranged in about five irregular rows, tubercles more widely spaced and smaller distally; seen dorsally, rows of tubercles give angular, carinate appearance to article. Fixed and movable fingers with paired, articulating triangular teeth, narrow, acute tips of fingers cross each other at rest.
Palpi (Fig.) brown, slender, total length 4.79 mm; trochanter with five low, seta-tipped tubercles, femur basally with setae on small tubercles, more distally, setae not on tubercles. Lengths of articles as given in Table 27. Legs short relative to body length, medium brown, unspotted. Basal false articulation of femora distinct on all legs. Tibiae without false articulations, all metatarsi with false articulations, numbering 3, 7, 4, 6 respectively. Total lengths in mm of legs 1–4: 6.86, 10.81, 6.88, 9.43. Measurements of leg articles given in Table 27.
Distribution. All records UWBM unless otherwise noted. OREGON: Hood River Co.: Perham Creek, 45°40’N, 121°38’W, 28 November 1940, J. and W. Ivie, ƋƋ (AMNH). WASHINGTON: King Co.: Old Stevens Pass road crossing powerline, 47.748N, 121,093°W, 3900’ asl, 26 November 1980, R. E. Nelson, ƋƋ; west of Deep Creek, 6 overwinter pitfalls (154d) 47.468°N, 121.934°W, 1450’ asl, 17 November 1996 – 20 April 1997, J. Bergdahl, Ƌ; Klickitat Co.: Poacher’s Cave, 45.985°N, 121.570°W, 2240’ asl, 12 April 1986, R. Crawford, ♀; Lewis Co.: #4000 Road, SW of Pe El MacDonald Road, 650’ asl, N46°31.45’, W123°11.61’, 3 January 2005, W. P. Leonard, ♀ (WAS); head of Hanaford Valley, 46.754°N, 122.770°W, 240’ asl, 9 November 1998, R. Crawford, ♀; Pierce Co.: Elbe, 46.766°N, 122.189°N, 1300’ asl, 14 September 1975, R. Crawford, ♀; Skamania Co.: McCloskey Creek at Maybee Mines Road, 1500’ asl, 20 November 2003, C. H. Richart, ♀ (WAS); Snohomish Co.: Crystal Creek, 47.831°N, 121.652°W, 300’ asl, 24 October 1986, R. Crawford, ♀♀; Thurston Co.: Centralia Canal, 46.940°N, 122.567°W, 320’ asl, 23 October 2007, R. Crawford, ♀; Olympia, 47.0°N, 122.8°W, 6–10 June 1944, H. Exline, ♀.
Notes. Variation in pigmentation and sclerotization of specimens is probably related to age; a few mature males and females are pale and lightly sclerotized while others are dark and more heavily sclerotized. The former were mostly collected in October–November, while the latter were taken in December–April. The type collection, which came from a series of pitfall traps left out over the winter, contains one light male and one dark one; these may have fallen in at quite different times of the year. The pitfall traps also collected specimens of Taracus pallipes, so the two species are syntopic.
Oskoron crawfordi specimens have very prominent groups of 3–5 large slit sense-organs on the probasal sides of the leg coxae. We have not noticed this feature in any other species of Oskoron or Taracus.
All of the specimens for which ecological data were available were taken from deciduous leaf litter, predominantly maple and alder. Aside from one June record, all were collected from October to April, indicating winter activity. Elevations of collection sites ranged from 240 to 3900’ asl, an unusually large range of altitudes.
The Hood River Co., Oregon, population is somewhat disjunct and should be targeted for genetic work if specimens can be recollected.
description: Published as part of Shear, William A. & Warfel, Joseph G., 2016, The harvestman genus Taracus Simon 1879, and the new genus Oskoron (Opiliones: Ischyropsalidoidea: Taracidae), pp. 1-71 in Zootaxa 4180 (1) on pages 65-68, DOI: 10.11646/zootaxa.4180.1.1, http://zenodo.org/record/164222