Taracus silvestrii Roewer 1929

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: 27-30

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Taracus silvestrii Roewer 1929


Taracus silvestrii Roewer 1929  

Figs. 3 View FIGURES 1 – 3 , 32–36 View FIGURES 32 – 36 , Map 4

Taracus silvestrii Roewer 1929:10   . Cokendolpher & Lee 1993:6 (list). Schönhofer 2013:21 (list).

Type. Juvenile holotype from “Westliches Nordamerika: Oregon Cave [now Oregon Caves National Monument, Josephine Co., Oregon]”, conserved in the Senckenberg Museum, Frankfurt am Main, Germany (RII/1745/15; examined 2012). The type was collected in 1928 by the Italian entomologist Filippo Silvestri, hence the name. The drawings and description in Roewer (1929) would lead one to believe that the type is mature, but it is at best a midterm instar juvenile, as are the other two specimens mentioned in the original account, but not given status as paratypes   . However, topotypical specimens from Oregon Caves support the hypothesis that T. silvestrii   is a distinct species.  

Diagnosis. Taracus silvestrii   is quite similar in body size and general appearance to T. pallipes   , which is probably nearly sympatric, but comparison of the two side-by-side immediately allows separation. While the two species are close in body length and bulk, T. silvestrii   has significantly longer legs, chelicerae and palpi, and the abdomen has fewer setae and less sclerotization. Taracus silvestrii   is distinct from T. marchingtoni   , n. sp., in having a larger body yet shorter legs, chelicerae and palpi, and in having much larger, darkly pigmented eyes. Unlike most other Taracus   species in the region, the anterior sulcus of the carapace is not open but fused, and present only as a deep groove which does not reach the anterior margin of the ocularium.

Description. Female from Oregon Caves National Monument, Oregon: Total length, 7.26 mm. Carapace dark brown to black, with three or four darker “hash marks” faintly discernable on either side of ocularium, all carapace edges well-defined, anterior and posterior margined; strongly domed, without setae; midline sulcus fused (closed) and extending as deep groove partway to ocularium. Preocularial slit sense organs prominent. Ocularium somewhat longer than wide, higher anteriorly, tapering posteriorly to posterior border of carapace, four prominent setae above each eye; eyes large, black, ringed with black pigment. Metapelitidium unsclerotized but marked by single row of eight small setae, two of which are at base of sensory cone; sensory cone small, gray-brown, base white, apparently membranous (Fig.), arising from embayment in carapace. Abdomen white, with few setae arising from small sclerotized plaques, plaques not distinctly raised, in indefinite transverse rows; midline plaques fused as small midline sclerites on first two or three abdominal segments ( Figs. 32, 33 View FIGURES 32 – 36 ). Unsclerotized sides of abdomen with very few similar setae. Ventrally, leg coxae white, unspotted. Palpal coxae brown, with numerous stout setae on distinct tubercles, leg coxae with strong, black setae, not on tubercles. No indication of thoracic sternum. Genital operculum apically rounded, heavily setose, white shaded darker distally, unspotted. Abdominal sternites not sclerotized, defined by dense bands of black setae.

Chelicerae ( Figs. 34, 35 View FIGURES 32 – 36 ) 12.38 mm long, black. Basal article 5.75 mm long, 0.63 mm wide (L/W = 9.12); second article 6.63 mm long, 0.88 mm wide (L/W = 7.53). Basal article with prominent mediobasal knob, with few long, seta-tipped tubercles, diminishing in size and number distally; second article with more numerous, but more rounded, smaller seta-tipped tubercles ranged in several irregular rows, tubercles densely spaced over anterior face of article to base of fixed finger. Fixed and movable fingers with paired, articulating triangular teeth, narrow, acute tips of fingers cross each other at rest.

Palpi ( Fig. 36 View FIGURES 32 – 36 ) light brown, total length 14.54 mm, slender; trochanter darker brown (as coxa) with five or more prominent seta-tipped tubercles, additional smaller ones, femur with regularly spaced slender setae, not set on tubercles. Patella not swollen. Tibia, tarsus slightly darker than femur, patella; with dense glandular hairs. Lengths of articles as given in Table 5. Legs long, thin; white, unspotted, with numerous black setae. Autospasy sutures of femora indistinct on some legs, especially third legs. Tibiae without false articulations, metatarsal false articulations (4?), 20, 0, 0 respectively (false articulations, if present on first leg, poorly indicated). Total lengths in mm of legs 1–4: 17.36, 26.26, 16.88, 21.70. Measurements of leg articles given in Table 5.

MAP 3. Puget Sound region , northwestern Washington. Filled circles, localities for ‘crassichelis’ form of Taracus pallipes Banks.    

MAP 4. Southwestern Oregon and northwestern California. Filled circles, localities for Taracus marchingtoni   , n. sp.; filled square, type locality of T. silvestrii Roewer   ; filled triangle   , type locality of T. fluvipileus   , n. sp.

Distribution. All specimens available to us were collected at various places in Oregon Cave, Oregon Caves National Monument, Josephine Co., Oregon, 42.098°N, 123.407°W. The species occurs in both twilight and dark zones of the cave. Collections made in May 2011 and September 2012 by park staff consist of eight females and two juvenile specimens. Additional females and juveniles collected earlier from the same locality by Rod Crawford are in the Burke Memorial Museum, and others are in the CAS and AMNH collections. The Burke Museum had a male, but it was not returned after having been loaned and is presently lost (R. Crawford, pers. comm. 2012). Unfortunately additional males have not been collected at this time.

Notes. Though T. silvestrii   has so far been found only in Oregon Cave itself, observers report that Taracus   specimens have been seen in the forests surrounding the cave (John Roth, Axel Schönhofer, pers. comm. 2012). It seems likely that these individuals would be examples of T. silvestrii   . The species has no obvious morphological adaptations for cave life but is evidently strongly troglophilic. It is possible that T. silvestrii   arose as an isolated population of T. pallipes   or a common ancestor of both species, the longer appendages of the former species resulting from modest adaptation to the cave environment.

Given the location and elevation of Oregon Caves National Monument, and the similarity of this species to T. pallipes   , we would expect it to be winter-active, but all the mature specimens were taken in May or September. However, only females were found. It may be possible that females live longer than males and that the cool, humid conditions in the cave promote their survival. The presence of central areas of sclerotization anterior on the abdomens of females suggests (by analogy with other species) that males probably show scutum parvum. Perhaps males mature in winter and die after reproducing, while females live on, especially if they find their way into the cave. All speculation, as we know little or nothing of the life histories of any Taracus   species.

TABLE 5. Lengths in mm of palpal and leg articles of female Taracus silvestrii.

    Patella Tibia    

California Academy of Sciences


American Museum of Natural History














Taracus silvestrii Roewer 1929

Shear, William A. & Warfel, Joseph G. 2016

Taracus silvestrii

Schonhofer 2013: 21
Cokendolpher 1993: 6
Roewer 1929: 10