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

description: Oskoron Shear, new genus
Type species: Taracus spinosus Banks 1894.
Diagnosis. Distinct from Taracus, to which it is closely related, in the enlarged, glandular patellae of the male palps (Figs. 139, 140, 143, 155, 162), the prominent, curved, black setae of the abdomen set on conical tubercles, and the similar enlarged setae of the ocularium (Fig. 134); the small endites of the second coxae are set in unsclerotized recesses in the coxae, rather than entirely free from them, as in Taracus. The first leg coxae bear prominent seta-tipped tubercles, sometimes weak or absent in Taracus. In males, the glans penis is abruptly narrowed into the aculeus (Fig. 130), not evenly tapered as in Taracus. For distinctions from other sabaconid genera, see the Diagnosis section under Taracus.
Description. Body length from 2–5 mm. Carapace black or dark chestnut brown in adults, broadest behind, with midline sulcus extending from between chelicerae to ocularium; in lightly pigmented specimens, two prominent slit sense-organs just anterior and lateral to ocularium; carapace often poorly sclerotized posteriorlaterally, smooth to finely shagreened texture. Ozopores prominent, not concealed, dorsolateral, over first leg coxae. Ocularium relatively high, at least as wide as long; sharply inclined anteriorly, gradually sloping posteriorly; prominent tubercles with large, black, curved setae above each eye. Eyes large, protuberant. Metapeltidium sclerotized or not, may appear free, or partially or wholly coalesced with carapace, with transverse row of prominent setae; sensory cone single, median, flanked by smaller acute tubercles with apical setae, set into unsclerotized embayment in posterior margin of carapace. Abdomen soft, white, densely but irregularly set with distinct sclerotized tubercles, each bearing single, black, curved seta, tubercles sometimes larger near midline, sometimes coalesced in midline to form small segmental sclerites (partial scutum laminatum), or with true scutum laminatum; males often with scutum parvum, but lateral boundaries of scutum irregular, tubercles remain prominent within scutum.
Labral sclerite large, pentagonal, with three prominent projections. Labium small, setose. Thoracic sternum absent in males, present in females as small sclerite, broader than long, two small setae immediately posterior. Endites free from second coxae but immediately appressed to coxae, not directed ventrally. Genital operculum with sclerotized distal rim. Abdominal sternites not sclerotized, with small setae scattered or sparsely arranged in rows.
Chelicerae black, robust, elongate, ranging from two-thirds to as much as 1.5 times body length; basal articles with mediobasal opposed tubercles, set throughout length with seta-bearing tubercles of various sizes, usually largest near basoventral section of articles, smaller distally. Second articles generally more robust, longer; setatipped tubercles of these may be at least partially in regular rows, very numerous. Fixed and movable fingers turned sharply mesad at approximate 125° angle to long axis of second article; fingers with diaphanous cleaning comb.
Palpi short, stout; coxae, trochanters with few to several ventral seta-tipped tubercles, much stronger on coxae; femora and patellae with moderately dense coat of ordinary setae; palpal patellae swollen in males, mesoventral surface glandular, with closely set very fine setae; tibiae and tarsi densely set with glandular hairs, spigots of glands open on one side of hairs only. Tibiae lack glabrous area opposite tarsi. Tarsi short, not strongly reflexed, without claw.
Legs in order of length: 2,4,3,1 or 2,4,1,3 or 2, 4, 1 = 3. Coxae of first legs with strong black setae set on tubercles. Femora with autospasy suture near base; may be obscure or absent. Tibiae without false articulations, metatarsi with many obvious false articulations, tarsi multiarticulate, bearing single untoothed claw, vestiture of fine setae, appressed trichomes (Fig.)
Ovipositor typical of ischyropsalidoids, short, unsegmented, without special apical sensilla, distally divided into two setose lobes. Penis relatively long, straight, distally tapered or expanded, muscles extending length of shaft; glans distinct, swollen, sclerotized, evidently not movable, abruptly narrowed into short aculeus, witout macrosetae, set with small, short setae around base of aculeus, sometimes with short rows of lateral setae subtending glans.
Distribution. Coast Ranges and Cascades from south end of Puget Sound to southern Oregon; Cascade Mountains and Sierra Nevada from Sierra (Shasta?) to Tulare counties, California.
Included species: Oskoron spinosus (Banks 1894), O. crawfordi n. sp. and O. brevichelis n. sp.
Etymology. Simon established something of a series in naming the genera Sabacon and Taracus after Egyptian kings (though the rationale remains unknown; see Gruber 2003). Dunlop et al. (2012) followed suit by naming a Baltic amber fossil ischyropsalidoid Piankhi steineri, Piankhi “the Nubian” being the father of Taracus. We continue the tradition by naming this genus for Oskoron, King of Egypt (reigned 760-740 bce). While both Sabacon (Shabako, or Shabaka) and Taracus (Taharqa, or Tarhqua) were of the 25th Dynasty, Nubian kings who ruled from Kush, Oskoron belonged to the preceding 23rd Dynasty, which hailed from Libya. The genus name is to be treated as masculine in gender.
Notes. The key character for the genus is the sexually dimorphic pedipalp patella, not seen in Taracus, and the abruptly narrowed (as opposed to evenly tapering) aculeus of the penis. In some male specimens the secretion from the patella is still present as a coagulated mass, held by the very fine setae of the mesoventral surface. Somewhat secondary to the diagnosis are the rather heavy, recurved black setae on tubercles over the ocularium, and on the abdomen. The abdominal tubercles are acute and very prominent in O. spinosus but less so in brevichelis and crawfordi, and in crawfordi the row of setae marking the metapeltidium is reduced to just four or six. In fact there appears to be a south to north cline in the reduction of this unusual armature, which is very distinctive in spinosus (California), less prominent in brevichelis (Oregon), and still less so in crawfordi (Washington). While Taracus species males are usually no smaller than 4 mm long, the largest Oskoron males are about 2.5 mm long, and most are much smaller. Finally, the different form of the endites of the second coxae distinguishes the two genera.
Oskoron spinosus seems to be a montane species of the Sierra Nevada and its ecology is postulated to be similar to that of Taracus audisioae. Indeed, the two species are broadly sympatric--and even syntopic in Sierra Nevada caves. Oskoron brevichelis and O. crawfordi, on the other hand, fit the winter-active pattern; crawfordi has been collected in numbers in pitfall traps left out all winter in King Co., Washington, in company with Taracus pallipes.
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 56-58, DOI: 10.11646/zootaxa.4180.1.1, http://zenodo.org/record/164222