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

description: Oskoron spinosus (Banks) 1894.
Figs. 127–141, Map 8
Taracus spinosus Banks 1894, p. 51; 1904, p. 362. Cokendolpher & Lee, 1993, p. 7 (in list). Taracus malkini Goodnight & Goodnight 1945, p. 242. New synonymy.
Type: Oskoron spinosus was described (in Taracus) by Banks from an unspecified locality in California. The holotype, an immature specimen, is held in the collection of the MCZ (examined 1971 and 2012; label confusingly says “Colo 1890”). Despite its immaturity, the holotype of O. spinosus has a distinctive appearance that made it recognizable when mature specimens turned up. The abdomen is densely covered with even-sized, conical tubercles, each of which is tipped by a stout, curved seta, the metipeltidium is marked by a row of eight such setae, and the ocularium has similar prominent tubercles and setae. The species epithet “ spinosus ” is quite apt.
The holotype of Taracus malkini could not be located in the collections of the AMNH. It was described from Manzanita Lake, Lassen National Volcanic Park, Shasta Co., California. From the measurements and description (Goodnight and Goodnight 1945), the type probably was (or is) immature. In describing malkini, the Goodnights made comparisons to (then Taracus) spinosus, but from the context we doubt these comparisions were based on an examination of the type of spinosus, which closely resembles their illustration of malkini. Their uncharacteristically detailed illustration of the malkini holotype, said to be a female but probably immature, shows strong, curved setae over the eyes and scattered, curved setae on the abdomen without any other sclerotization. The metapeltidium is shown as distinct and with a prominent single row of eight setae. These are characters of Oskoron spinosus. The AMNH collection contains a single female specimen of spinosus from Manzanita Lake, collected in 1965, that fits the description well (but is mature), and specimens from surrounding counties likewise are referable to spinosus. Therefore we consider malkini a synonym of spinosus. If the type of malkini eventually cannot be found, the AMNH specimen could be designated a neotype for that species. This action is not taken here for reasons described below.
Diagnosis. Oskoron spinosus, the largest Oskoron species, can be separated from all others by the relatively longer chelicerae, the very strong, curved spines of the ocularium, and the row of 8 or more setae on the metapeltidium. Taracus ubicki is narrowly sympatric with O. spinosus, and juveniles could be confusing; ubicki, however, has much longer chelicerae in comparison to the body (and these are much smoother), lacks the strong seta-tipped tubercles of the ocularium, and while the armature of the abdomen may be superficially similar, the setae of spinosus are larger and curved, those of ubicki smaller and straight. Oskoron spinosus is sympatric and even syntopic in caves with Taracus audisioae n. sp. in Fresno and Tulare Cos., but the latter species is more than twice as large and at all stages has much longer chelicerae in proportion to body length.
Description. Male from Lilburn Cave. Total length, 2.67 mm. Carapace well sclerotized, brown to black; central region strongly domed; indistinct, closed midline sulcus extends from anterior margin to ocularium. Ocularium as wide as long, rounded, with three to five stout, curved setae on prominent tubercles above each eye (Fig. 134), tubercles at least as tall as one-half diameter of eyes; eyes black, ringed with black pigment. Metapelitidium weakly sclerotized, but obviously distinct from carapace, with row of eight small setae on tubercles; sensory cone brown, acute, set in distinct notch in carapace of white cuticle; on each side two setabearing tubercles, the lateralmost smaller. Abdomen soft, white or pale tan, with scutum parvum but lateral margins of scutum indistinct; scutum set with rows of curved, stout, black setae raised on prominent tubercles, these rows relatively distinct anteriorly, becoming more irregular posterior on scutum; tubercles near midline larger (Figs. 132, 133). Ventrally, coxae tan, unspotted. Palpal coxae with five stout setae on distinct tubercles, leg coxae with strong, black setae on prominent 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 relatively short, black. Basal article 2.21 mm long, 0.37 mm wide (L/W = 6.0); second article (Fig. 137) 2.70 mm long, 0.44 mm wide (L/W = 6.1); total length 4.91 mm. Basal article with prominent mediobasal knob, with rows of large seta-tipped tubercles extending nearly to distal end, larger tubercles ventrally; second article with prominent, rounded seta-tipped tubercles ranged in about five to seven irregular rows, tubercles more densely distributed, larger on frontal (dorsal) side. Fixed and movable fingers with paired, articulating triangular teeth, narrow, acute tips of fingers cross each other at rest.
Palpi (Fig. 128, 139–141) dark brown, prominent white ring at base of femur, stout, total length 5.41 mm; trochanter with five prominent, seta-tipped tubercles, femur with setae on small tubercles, patella distinctly swollen, with patch of fine setae on mesoventral surface. Lengths of articles as given in Table 22. Legs yellowish tan. Autospasy suture of femora distinct on all legs. Tibiae without false articulations, all metatarsi with false articulations, numbering 5,9,5,6 respectively. Total lengths in mm of legs 1–4: 9.73, 14.92, 9.97, 13.46. Measurements of leg articles given in Table 22.
Penis (Figs. 129–130) short, 1.52 mm long, 0.16 mm wide (L/W = 9.5), sides of shaft relatively straight, widening distally then abruptly narrowed to aculeus; glans narrow, gradually tapering to curved aculeus; aculeus with subtending crown of setae incomplete ventrally; shaft without setae.
Female from Lilburn Cave: As described for male, except as follows. Appendages mostly shorter, stouter than in males, but chelicerae more slender. Total length, 3.37 mm. Carapace light brown; abdomen pale tan, finely mottled purplish brown, with irregular rows of small, black setae set on raised, sclerotized tubercles, tubercles glossy, translucent tan, largest either side of midline, two or three tubercles near midline may be coalesced in first two to three areas (Fig. 131).
Cheliceral basal article (Fig. 135) 2.35 mm long, 0.33 mm wide (L/W = 7.12); second article (Fig. 136) 2.62 mm long, 0.44 mm wide (L/W = 5.95); total length 4.97 mm. Total length of palpus (Fig. 127), 5.32 mm; patella of palpus not swollen, femoral setae not on tubercles. Total lengths in mm of legs 1–4: 8.43, 13.34, 8.68, 12.14; lengths of leg and palpal articles as given in Table 23. Leg metatarsi with 5, 10, 6, 8 false articulations respectively. Ovipositor typical.
Distribution. All specimens CAS unless otherwise noted. CALIFORNIA: Calaveras Co.: Avery, 8 July 1958, W. J. Gertsch, V. Roth, juvs. (AMNH). Eldorado Co.: Echo Summit, 7382’ asl, 4 mi southwest of Meyers, 9 September 1959, W. J. Gertsch, V. Roth, ƋƋ ♀♀ (AMNH); Fallen Leaf Lake, 9 September 1959, W. J. Gertsch, V. Roth, ♀ (AMNH); 6 mi east of Camp Connell, 10 September 1959, ƋƋ ♀♀ (AMNH). Fresno Co.: Shaver Cave, 1.5 mi S of Dinky Creek Road, 5400’ asl, 15 October 1973, W. Icenogle, ♀. Mariposa Co.: 6 mi South of Mather, 4 September 1958, V. Roth, juv. (AMNH). Mendocino Co.: Mendocino, 1 January 1958, J. R. Helfer, ♀ (AMNH); Navarro River 6 mi south of Albion, 13 September 1961, W. Ivie, W. J. Gertsch, juv. (AMNH). Modoc Co.: 15 mi north of Alturas, 17 June 1954, R. Schuster, Ƌ(AMNH). Plumas Co.: 9.2 mi NE of Buck’s Lake, 4 September 1988, D. Ubick, ♀; south side of Lake Almanor, 5 September 1959, V. Roth, Ƌ (AMNH). Shasta Co: 3 mi eastnortheast of Manzanita Lake, 16 September 1965, W. & J. Ivie, ♀ (AMNH); “Lassen Park “(Lassen Volcanic National Park), 7 September 1936, W. Ivie, R. V. Chamberlin, Ƌ ♀ (AMNH). Sierra Co.: Big Avalanche Cave, 5900’ asl, 28 June 1992, D. Ubick, juv.; 8 miles northeast of Sierra City, Lunch Creek, 7000’ asl, 12–16 August 1996, D. Ubick, Ƌ; 5 miles east of Camptonville, 3000’ asl, 16 August 1996, D Ubick, Ƌ. Siskiyou Co.: 3 mi east of McCloud, 2 September 1953, V. Roth, W. J. Gertsch, many juvs. (AMNH); Panther Mtn. Road, Mt. Shasta, 7000’ asl, 17 September 1961, W. Ivie, W. J. Gertsch, many juvs. (AMNH); O’Neil Creek, 5.4 mi southeast Seaid Valley, 2 July 1976, L. & N. Herman, ♀ (AMNH). Trinity Co: Indian Valley Creek Cave, 1800’ asl, 17 October 1990, D. Ubick, W. Rauscher, ♀; 11 mi east of Douglas City, 11 July 1954, E. Gilbert, juv. (AMNH). Tulare Co.: Sequoia National Park, Stony Creek Camground, 7000’ asl, 6 September 1987, T. Briggs & W. Rausher, juvs.; Lost Grove, 24 July 1966, F. Heppner, K. Hom, P. Lum, juvs.; Kings Canyon National Park, Redwood Canyon, 2.5 mi SE Redwood Saddle, 1700 m asl, 16 August 1984, T. Briggs, V. Lee, D. Ubick, Ƌ; Lilburn Cave, near Pinehurst, 5500’ asl, 10 September 1960, T. Briggs, Ƌ; 4 July 1971, T. Briggs, ƋƋ ♀♀; 17 August 1984, T. Briggs & D. Ubick, Ƌ ♀; 30 July 2003, 15 May 2004, J. Krejca et al., ƋƋ; 4 July 2010, T. Audisio, Ƌ; Cirque Cave, 3 mi S of Mineral King post office, 15 September 1968, T. Briggs, juv. Tuolumne Co.: Aspen Valley, Yosemite National Park, 11 August 1931, W. Ivie, Ƌ(AMNH); 12 mi east of Bunk Meadows, 11 September 1959, W. J. Gertsch, ƋƋ (AMNH); “Yosemite Park (Yosemite National Park)” 18 September 1941, W. Ivie, Ƌ(AMNH); Tamarack Flat, Yosemite National Park, 3 September 1958, V. Roth, Ƌ(AMNH).
The appearance of O. spinosus is distinctive enough that we have based some of the records given above on juvenile specimens, especially from the northern Sierras.
Oskoron spinosus has been collected most abundantly in Kings Canyon and Sequoia National Parks, mostly in caves but also on the surface. Records further north are scattered and many are from immature specimens, due to a lack of collecting at the right season. Banks (1904) reported the species from “Southern California,” a record repeated by Roewer (1914), but the specimens have been lost; we do not know what Banks might have meant by “Southern California,” but the southernmost documented occurrence is in Sequoia National Park.
Notes. Several of the male specimens from Lilburn Cave had clotted secretion adhering to the mesal surfaces of the palpal patellae, suggesting that a secretion is offered to females during mating, as it is in some other Dyspnoi. The specialized setae in the secretory area seem clearly to be derived from the plumose setae found on the tibiae and tarsi, but differ in that the tubules are restricted to the tip and occur all round the seta (Fig. 141).
While O. spinosus has been collected frequently in caves, it shows no adaptations for subterranean life and also occurs abundantly on the surface in regions where caves are not available. As with several other taracine species, it is strongly troglophilic, though the situation is biased by the much greater collection effort that has been devoted to Sierra Nevada caves in comparison to surface habitats. Similarly, the May-to-October collecting dates may reflect the activity of this species, or the habits of collectors. In any case, heavy snow in the Sierra Nevada would probably preclude this species being active on the surface during the winter. Specimens have been taken at recorded elevations from 3000’ to 7000’ asl. Oskoron spinosus is sympatric in Fresno and Tulare Cos. with the much larger Taracus audisioae and both species have been collected in Cirque Cave in Sequoia Kings Canyon National Park. Ortholasma colossus Shear 2010 is an ortholasmatine nemastomatid harvestman that occurs with Oskoron spinosus in Lilburn Cave; like O. spinosus, the ortholasmatine is troglophilic and shows no adaptation to troglobiosis.
The 80-mile gap in the distribution of this species, from Eldorado Co. to Yosemite National Park, is probably due to a lack of collecting in the intervening region rather than representative of the actual distribution. However, if the gap proves to be real and the populations genetically distinct, the name malkini is available for the northern populations. The name spinosus can be assigned arbitrarily to the Sierra populations, since the type locality is unspecified. In view of this remote possibility we have based the description of spinosus on specimens from the southern part of the range, and have not designated a neotype for malkini.
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 58-62, DOI: 10.11646/zootaxa.4180.1.1, http://zenodo.org/record/164222