Taracus fluvipileus Shear

Shear, William A. & Warfel, Joseph G., 2016, The harvestman genus Taracus Simon 1879, and the new genus Oskoron (Opiliones: Ischyropsalidoidea: Taracidae), Zootaxa 4180 (1), pp. 1-71: 40-42

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Taracus fluvipileus Shear

new species

Taracus fluvipileus Shear   , new species

Figs. 68–76 View FIGURES 68 – 76 , Map 4

Types. Male holotype, male and female paratypes from Subway Cave, 0.5 mi NE of Old Station, Lassen National Forest , Siskyou Co., California, collected 26 July 1971 by R. Lem and T. Briggs ( CAS).  

Diagnosis. This species could only be confused with T. marchingtoni   n. sp., because of its range in northern California, extremely long and thin legs, palpi and chelicerae, and reduced eyes. However, marchingtoni   has longer chelicerae than fluvipileus   , while fluvipileus   has longer legs and palpi (compare Table 9 with Table 11) especially in comparison to its smaller body length. Taracus fluvipileus   males have two small anterior abdominal sclerites (these are not seen in most marchingtoni   males) and the penis is shorter and wider. While both species are found in lava tubes, the localities are far apart (Map 4).

Etymology. The species epithet is a Latinization of “Hat Creek,” in recognition of the fact that all known localities for this species are in the Hat Creek Lava Flow.

Description. Male from Subway Cave. Total length, 4.7 mm. Carapace medium to dark chestnut brown, lightly sclerotized in general, more so laterally; central region strongly domed; midline sulcus closed, reaching anterior margin of ocularium. Ocularium relatively low, as wide as long, rounded, higher behind, with few small setae; unpigmented eyes reduced to about one-half diameter of those of epigean species. Metapelitidium lightly sclerotized, with short row of small setae; sensory cone white, darker distally, very long, acute, inclined forward. Abdomen soft, white, unsclerotized, set with few scattered, small, black setae on small sclerotized plaques, very lightly sclerotized midline patches on first two areas ( Figs. 72, 73 View FIGURES 68 – 76 ). Ventrally, coxae white. Palpal and first leg coxae white to tan, with stout setae on distinct tubercles on palpal coxae only, second to fourth leg coxae pale tan, with strong, black setae not on tubercles. Five or six setae in two groups on lightly sclerotized patches mark presumed position of thoracic sternum. Second coxal endites long, narrow, separate from coxae. Genital operculum apically rounded, heavily setose, pale tan with large, dark brown spots. Venter of abdomen with setae in irregular rows on lightly sclerotized transverse bands marking positions indistinct abdominal sternites.

Chelicerae ( Fig. 76 View FIGURES 68 – 76 ) 13.00 mm long, slender, black. Basal article 5.76 mm long, 0.35 mm wide (L/W = 16.5); second article 7.24 mm long, 0.59 mm wide (L/W = 12.3). Basal article with prominent, acute seta-tipped tubercles extending three-quarters of length, dorsal tubercles much smaller; second article noticeably wider distally, with relatively low, rounded seta-tipped tubercles ranged in about five irregular rows, tubercles more widely spaced distally. Fixed and movable fingers long, with paired, articulating triangular teeth, narrow, acute tips of fingers cross each other at rest.

Palpi ( Fig. 69 View FIGURES 68 – 76 ) dark brown, total length 17.98 mm, typical for genus; trochanter with prominent scattered setatipped tubercles. Lengths of articles as given in Table 11. Legs long, thin; first leg brown, becoming lighter distally, other legs yellowish tan without markings.. Autospasy sutures of femora distinct on all legs. Tibiae without false articulations, metatarsi of leg 2 with about 15–17 false articulations. Total lengths in mm of legs 1–4: 23.43, 37.32, 24.45, 31.50. Measurements of leg articles given in Table 11.

Penis ( Figs. 70–71 View FIGURES 68 – 76 ) 2.44 mm long, 0.46 mm wide (L/W = 5.3), sides of shaft straight, tapering moderately to slightly twisted, short aculeus with small flap-like basal process; glans set off by indistinct suture; aculeus subtended by crown of few small, acute setae; shaft with numerous shorter, scattered setae on either side below glans.

Female from Subway Cave: As for the male holotype, except as follows. Total length, 5.75 mm. Cheliceral ( Figs. 74–75 View FIGURES 68 – 76 ) basal article 6.50 mm long, 0.35 mm wide (L/W = 18.6); second article 8.25 mm long, 0.60 mm wide (L/W = 13.75). Total length of palpus ( Fig. 68 View FIGURES 68 – 76 ), 16.98 mm. Abdomen entirely without sclerotization, very few scattered setae. Metatarsus 2 with up to 26 indistinct false articulations; false articulations absent from other legs. Total lengths in mm of legs 1–4: 22.46, 37.67, 23.33, 29.12; lengths of leg and palpal articles as given in Table 12. Ovipositor typical.

Distribution. All specimens INHS unless otherwise indicated. CALIFORNIA: Siskiyou Co.: Lassen National Forest, Hat Creek Lava Flow, Subway Cave, 26 July 1971, H. Lem & T. Briggs, ƋƋ ♀♀ ( CAS); 3 November 2012, G. O. Groening, ♀♀ ( CAS); Cave 4, 27 August 2015, T. Rickman et al..; Cave 5, 27 August 2015, T. Rickman et al.; Cave 6, 27 August 2015, T. Rickman et al.; Cave 26, 30 July 2015, T. Rickman et al.; Cave 28, 7 June 2015, T. Rickman et al.; Cave 51, 3 September 2015, T. Rickman et al.; Christmas Tree North Cave, 20 August 2015, T. Rickman et al.; Christmas Tree South Cave, 20 August 2015, T. Rickman et al, ƋƋ ♀♀.

Notes. Subway Cave is located just northwest of the village of Old Station, in the Hat Creek Lava Flow, at 40°41’ 06.25N, 121°25’08.33”W. Elevation is 4366’ asl. The lava tube is about one-third of a mile in length, stretching between two roof collapses of what was once a much longer tube. Many people visit Subway Cave each year. According to the Lassen National Forest website (http://www.fs.usda.gov/recarea/lassen/recarea/?recid=11435), the tube formed about 20,000 years ago. The temperature in the totally dark area is a constant 46°F. The surrounding environment (viewed on Google Earth and internet images) is lightly forested pineland, with a sparse understory of sagebrush and other drought-tolerant shrubs, and little groundcover. This habitat does not appear to be favorable for Taracus   species to survive on the surface, and with its troglomorphic adaptations, T. fluvipileus   must almost certainly be limited to lava tubes, or to the joints, vesicles and interflow sediment layers with which lava flows are permeated ( Crawford 1993). All other localities listed are from lava tubes in the Hat Creek Lava Flow, but their exact localities are not given here.

G. O. Graening (pers. comm. 2013) has collected specimens of Plumatyla   millipedes in Subway Cave, and as with T. marchingtoni   , these may be the chief prey of T. fluvipileus   .

The recent discovery of a new family of primitive haplogyne spiders in caves and deep leaf litter in the Klamath-Siskiyou region ( Griswold et al. 2012) draws attention to how little is known about the arthropod fauna there. Taracus fluvipileus   is another component of this fauna.

TABLE 11. Lengths in mm of palpal and leg articles of male Taracus fluvipileus.


TABLE 12. Lengths in mm of palpal and leg articles of female Taracus fluvipileus.

    Patella Tibia    

California Academy of Sciences


Illinois Natural History Survey