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

description: Taracus marchingtoni Shear, new species
Figs. 53–67, Map 4
Types. Male holotype and two male paratypes from Lava River Cave, N43°53.728’, W121°22.102’, Deschutes Co., Oregon, collected March 2008 by N. Marchington; two female paratypes from Lee’s Cave, Deschutes Co., Oregon, collected 30 August 2008 by N. Marchington; four female paratypes from Walk-the-Crevice Cave, Lake Co., Oregon, collected 30 August 2008 by N. Marchington. One of the male paratypes was dissected and mounted for SEM examination. All specimens and the SEM stubs (WS 26-1 through WS 26-8) deposited in California Academy of Sciences, San Francisco.
Diagnosis. Taracus marchingtoni is geographically distant (Map 4) from the similarly troglomorphic T. fluvipileus n. sp., and the latter has even longer legs, but shorter chelicerae. Males of T. marchingtoni have no abdominal sclerotization, while those of T. fluvipileus have small central sclerites on the first two abdominal areas. Taracus silvestrii occurs in a limestone cave relatively closer, but lacks the troglobiotic adaptations of marchingtoni, and has very much shorter chelicerae.
Etymology. The species epithet honors cave explorer Neil Marchington, whose collecting in Oregon and California has yielded a striking array of new taxa.
Description. Male from Lava River Cave. Total length, 6.0 mm. Carapace dark chestnut brown to black, 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, higher behind, with few small setae; eyes strongly reduced, unpigmented, present only as small, oblong, white spots. Metapelitidium unsclerotized, with row of small setae; sensory cone brown, acute (Fig.), not set in embayment in posterior margin of carapace. Abomen soft, white, unsclerotized, set with irregular rows of small, black setae; central two setae in each area larger, on small but unsclerotized mounds (Figs. 62, 63). Ventrally, coxae white to tan, irregularly mottled dark brown. Palpal coxae with stout setae on distinct tubercles, leg coxae with strong, black setae not on tubercles. Four setae mark presumed position of unsclerotized thoracic sternum. Genital operculum apically rounded, heavily setose, pale tan with large, dark brown spots. Venter of abdomen with setae in irregular rows, marking positions of unsclerotized and insdistinct abdominal sternites.
Chelicerae (Figs. 66, 67) 16.30 mm long, slender, black. Basal article 7.4 mm long, 0.42 mm wide (L/W = 17.6); second article 8.9 mm long, 0.45 mm wide (L/W = 18.9). Basal article with more prominent, acute setatipped tubercles in basal third, attenuating distally to single row of slightly smaller tubercles, dorsally almost smooth; second article with relatively low, rounded seta-tipped tubercles ranged in about five irregular rows, tubercles more widely spaced distally. Fixed and movable fingers with paired, articulating triangular teeth, narrow, acute tips of fingers cross each other at rest.
Palpi (Figs. 53–55) dark brown, very thin, total length 16.95 mm, typical for genus; trochanter with few low, scattered seta-tipped tubercles. Lengths of articles as given in Table 9. Legs long, thin; yellowish tan with widely scattered dark brown dots, mostly on femora; femora of leg 1 slightly darker. Basal false articulation of femur indistinct on legs 1, 3. Tibiae without false articulations, all metatarsi with numerous false articulations, number proportional to article length. Total lengths in mm of legs 1–4: 20.98, 32.17, 22.73, 26.67. Measurements of leg articles given in Table 9.
Penis (Figs. 59, 60) relatively short and broad, 2.81 mm long, 0.36 mm wide, L/W = 7.8, sides of shaft straight, tapering abruptly to spirally twisted, short aculeus; glans not set off by suture but swollen, well-sclerotized; aculeus subtended by sparse crown of blunt, flattened setae continuous on ventral side but interrupted in midline on dorsal side; shaft with several smaller, lateral setae on either side below glans, but few scattered setae proximally.
Female from Lee’s Cave: Females (Figs. 58, 61) differ from males largely in appendages that are proportionally shorter and stouter except for the longer palpus. Total length, 6.3 mm. Cheliceral (Figs. 64, 65) basal article 6.5 mm long, 0.52 mm wide (L/W = 12.5); second article 6.72 mm long, 0.60 mm wide (L/W = 11.2). Total length of palpus, 17.04 mm. Metatarsal false articulations obvious only in metatarsi 2. Total lengths in mm of legs 1–4: 17.97, 26.66, 17.61. 22.47; lengths of leg and palpal articles as given in Table 10. Ovipositor typical. Other characters as in male.
Distribution. In addition to the localities listed above: OREGON: Deschutes Co.: Arnold Ice Cave, 15 mi southeast of Bend, 2011, N. Marchington, Ƌ (WAS); Paulina Crack, 10 mi south of Bend, August 2012, N. Marchington, Ƌ (WAS); Lavacicle Cave, 30 mi southeast of Bend, 2 July 1982, J. R. Holsinger, L. M. Ferguson, L. Nieland, ƋƋ ♀♀ (CAS).
Marchington (pers. comm. 2012) has observed what is very probably T. marchingtoni in other lava tubes in Deschutes and Lake Cos. Interestingly, a single male (AMNH) had been collected in 1965 in Lava River Cave by Jean and Wilton Ivie, but evidently went unrecognized as a new species. Given the propensity of lava tube troglobionts to disperse through the porous lava (Crawford 1993; Wynne & Shear 2016), T. marchingtoni probably will be found in many other localities in the Newberry lava fields.
Notes. A few of the paratypes were paler than others, perhaps slightly teneral, and in these females 4 to 6 diagonal dark markings (“hash marks”) are present on either side of the carapace beside and behind the ocularium. The male from Paulina Crack has very lightly sclerotized patches central on abdominal areas two and three.
I am indebted to Neil Marchington for the following information on the distribution and habits of T. marchingtoni. In addition to the localities for which specimens are available, T. marchingtoni has been observed in widely scattered lava tubes in central Oregon, largely centered around Paulina Peak, a shield volcano dominating the Newberry National Volcanic Monument. The type locality, Lava River Cave, is located within the Monument. Lava River Cave is a massive lava tube about 5400’ in length, with passages 23–30’ wide and 30–40’ high. It is a tourist attraction visited by tens of thousands each year, despite which it is used as a hibernaculum by a modest population of bats. Surface vegetation is characteristic of the elevation, with ponderosa and lodgepole pines and a manzanita understory.
Exact locations and descriptions are not given here for Lee’s and Walk-the-Crevice Caves, due to their archeological and geological sensitivity. It is hoped that the presence of this unique harvestman species may contribute to the conservation of these and other lava tubes in which it occurs.
All the caves in which T. marchingtoni has been collected or observed are damp, have some level of seasonal bat use, and are at elevations ranging from 4100 to 6100 feet. The harvestmen have been observed to be active at temperatures as low as 38° F, and as high as 55° F. Observations by Marchington suggest that the harvestmen are sit-and-wait predators that ambush their prey, often from an elevated position on the walls just above the cave floor. The prey items observed were all millipedes of the genus Plumatyla Shear 1971, also a troglobiont, which itself feeds on organic debris, especially moldy animal feces. These millipedes are very abundant in the lava tubes, and they may represent a new species. Taracus marchingtoni individuals use their large chelicerae to sieze, overcome, and maneuver the millipedes, which they often drag away from the point of capture to devour. Plumatyla is a genus of the millipede order Chordeumatida, all members of which have lost the chemical defenses otherwise characteristic of the class Diplopoda. Their only defense appears to be the long dorsal setae on which drops of a sticky secretion may appear (Shear & Krejca 2010 Shear 2015).
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 36-40, DOI: 10.11646/zootaxa.4180.1.1, http://zenodo.org/record/164222