Tenuiphantes zibus

Tenuiphantes zibus (Zorch, 1937)

Fig. 5–7.

Lepthyphantes ziba Zorsch 1937

Lepthyphantes zibus Roewer 1942

Tenuiphantes zibus Saaristo and Tanasevitch 1996

Type. Male and one male paratype. Lake Sutherland, Washington, USA. 11 Aug 1927, coll: C. R. Crosby. In AMNH. Examined.

Specimens measured. USA: Alaska: 1 female 1 male, Prince of Wales Island, Hatchery Ck. 2, 55.89356°N 132.9437°W 134 m elv., 10–31 July 2010 coll: J. Stockbridge, C. Bickford, 2nd growth, pitfall 4, UAM: Ento:227060; 1 female, Prince of Wales Island, Hatchery Ck. 2, 55.89356°N 132.9437°W 134 m elv., 2–29 June 2010 coll: J. Stockbridge, C. Bickford, 2nd growth, pitfall 1, UAM: Ento:227040; 2 Female, Prince of Wales Island, Hatchery Ck. 2, 55.89356°N 132.9437°W 134 m elv., 2–29 June 2010 coll: J. Stockbridge, C. Bickford, 2nd growth, pitfall 2, UAM: Ento:227041; 1 male, Prince of Wales Island, Luck Lk. 3 Rd., 55.95347°N 132.7708°W 117 m elv., 8–30 July 2010 coll: J. Stockbridge, C. Bickford, old growth, pitfall 3, UAM: Ento:227896; 1 male, Prince of Wales Island, Luck Pt., 55.98256°N 132.77943°W 129 m elv., 2 June–27 June 2010 coll: J. Stockbridge, C. Bickford, 2nd growth, pitfall 2, UAM: Ento:226921; 1 female, Prince of Wales Island, Staney Ck. 1B, 55.872°N 133.06523°W 77 m elv., 30 May-12 June 2010 coll: J. Stockbridge, C. Bickford, clear cut, Pitfall #2; Washington: San Juan County: 1 male, Orcas Island, Mt. Constitution Bog #2, 48.677°N 122.834°W 670 m elv., 23 July 1993 - 18 March 1994, coll: J. Bergdahl, pitfall, DMNS ZA.14797; 1 male, San Juan Island, Streams S of Cady Mtn., 48.535°N 123.099°W 25 m elv., 8 September–7 October 1991, coll: J. Bergdahl, pitfall, DMNS ZA.12819.

Diagnosis. Male T. zibus can be distinguished from all other Tenuiphantes species by a paracymbium lacking denticles and a lamella characteristica with a rounded oblique ventral fork and a dorsal fork originating at the base of the curve and projecting away from the lamella characteristica (Fig. 6). The dorsal fork may curve behind the rest of the lamella characteristica towards the bulb and may not be visible from a ventral or pro-lateral angle. Females can be distinguished by an inverted “Y” shaped scape (Fig. 7) and a posterior plate with narrow, lateral lobes curving along the lateral side of the scape. For additional characters see T. zelatus diagnosis above.

Description. Male (n = 5). Total length = 1.43–1.45 mm; carapace length = 0.79–0.83 mm; carapace width = 0.65–0.73 mm; carapace L:W ratio 0.87. TmI = 0.22, TmIV absent. Chaetotaxy: FI, 0-1-0-0; FII-IV, 0-0-0-0; Pt I-IV, 1-0-0-0; TiI, 2-1-1-0; TiII, 1-1-1-0; TiIII-IV, 2-0-1-0; MtI-IV, 1-0-0-0. Carapace uniformly yellow. ALE, PME, PLE similarly sized, AME about 3/4 size of other eyes, 1/2 eye width apart. Lateral eyes adjacent, PME separated from lateral eyes by 1/2 eye width, PME 3/4 eye width apart. Clypeus two ALE width. Sternum yellow. Abdomen light grey, suffused with white along the median and lateral edges, 2–5 dark chevrons, often faint. Sides dark with a few white patches. Venter light grey to yellow. Legs yellow and unmarked. Three cheliceral promarginal teeth and one retromarginal denticle. Paracymbium base with several stout hairs, no teeth along the inner flange. The distal ridge with an oblong indentation along the proximal edge, narrower than wide, distal section a narrow elongated semispatulate shape, often twisted (Fig. 5). Embolus narrow at the point of attachment to the suprategulm with a single spine along the base of the ridge, expanding to a denticle-covered bisected spatulate shape with a thumb. Embolus proper spear-shaped. Lamella characteristica directed distally then curving at a right angle laterally, with the ventral fork widening into a right triangle shape, widest at the tip. A dorsal fork originates along the proximal edge at the point where the lamella characteristica curves laterally (Fig. 6) and projects away from the lamella characteristica. The extension is almost as long as the main part of the lamella characteristica and curves slightly towards the broader tip but may curve inward towards the bulb making it difficult to view.

Female (n = 5). Total length = 1.79–1.87 mm; carapace length = 0.77–0.85 mm; carapace width = 0.71–0.73 mm; carapace L:W ratio 0.9. TmI = 0.21, TmIV absent. Chaetotaxy: FI, 0-1-0-0; FII-IV, 0-0-0-0; Pt I-IV, 1-0-0-0; TiI, 2-1-1-0; TiII, 1-1-1-0; TiIII-IV, 2-0-1-0; MtI-IV, 1-0-0-0. Coloration same as male, although generally lighter in color and chevrons on abdomen less visible. Scape “Y” shaped, narrowing and curving under itself before terminating in a narrow projection which extends posteriorly (Fig. 7). Posterior median plate wider than scape, deep indentation along ventral edge. Lateral lobes of the posterior plate along the sides of the scape, directed medially.

Variation. In one male specimen the spur of the lamella characteristica was found to be directed towards the paracymium, the opposite of its normal orientation. This specimen also had two large spines at the base of the palp. In females the extent of scape that is narrowed before the posterior expansion is a variable character. Females with a short stem may be confused with T. zelatus but can be separated by the distinct lateral lobes of the posterior plate. Females with a long stem may be confused with T. tenuis but can be separated by the arms, or posterior expansion of the scape, being directed posteriorly, whereas in T. tenuis they curve anteriorly (compare Fig. 7 to figure 16 in van Helsdingen et al. (1977)). As mentioned under T. zelatus, measured specimens all came from coastal Alaska and do appear to be smaller and darker than those collected elsewhere. Zorch (1937) gave a total length measurement for the male as 2.1 mm.

DNA barcoding. One specimen (UAM:Ento:113769) was DNA barcoded by Slowik and Blagoev (2012) and falls into BIN BOLD:AAL6435 with 17 other specimens, which is 9.98% distant from its nearest neighbor.

Distribution. The species can be found throughout forested coastal regions of the Pacific Northwest from Oregon to Alaska. In Washington, by far the best surveyed area in the region, it has not been found east of of the Cascades (Rod Crawford pers. comm.). This species does not appear to have a forest habitat preference and has been collected in old growth forests, second growth forests as well as clear cuts from sea level to tree line. Adults have been collected from the end of May through July, with the highest proportion being collected in the end of June.

Discussion. In southeastern Alaska T. zelatus and T. zibus are very common forest floor inhabiting spiders, often building small sheet webs in the layers of moss and low shrubbery. Specimens collected in Washington were also collected from a similar habitat. Populations of T. zelatus extend much further east into very different habitats in Alberta and Colorado (Don Buckle pers. comm. Bennett et al. 2017, DMNS specimen za.4818).

For identification, the shape of the lamella characteristica and the scape are the primary useful characters. Except for the presence or absences of denticles the three Tenuiphantes species found in the Pacific Northwest share similar paracymbium shapes, with the distal thumb and indentation along the proximal edge showing much intraspecies variation. There is also much intraspecies variation in size and coloration. Tenuiphantes zibus and T. tenuis tend to be larger, lighter species, often with a light abdomen venter, but specimens of T. zelatus have been collected of similar size and color to T. zibus specimens.

There remains debate over the recognition of many of the ex- Lepthyphantes genera designated by Saaristo, Tanasevitch, Marusik and others (for example Saaristo and Tanasevitch 1996, Tanasevitch 1992, and Eskov and Marusik 1994 in which 17 new genera are designated for previous Lepthyphantes species). Because the defining character of Tenuiphantes has to do with an embolus character it is not known whether the genus is evolutionarily supported or a taxonomic convenience at this time. There are many other ex- Lepthyphantes genera which seem to share similar female morphology. Likely because of this, the recognition of the genus has not been universally accepted (for example see Thaler et al. 1994, Ubick et al. 2005 and Paquin et al. 2010 which retain T. zelatus and T. zibus in the genus Lepthyphantes). I have chosen to acknowledge the genus as there do appear to be synapomorphic characters among the species, and proper morphological identification will have to precede any molecular work that may clarify the relationships in the genus.