Cybaeus amicus Chamberlin & Ivie 1932,

Bennett, Robb, Copley, Claudia & Copley, Darren, 2019, Cybaeus (Araneae: Cybaeidae): the adenes species group of the Californian clade, Zootaxa 4711 (2), pp. 245-274: 251-253

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Cybaeus amicus Chamberlin & Ivie 1932


Cybaeus amicus Chamberlin & Ivie 1932 

Figs 12–16, 56, 69

Cybaeus amicus Chamberlin & Ivie 1932:24  , fig. 58. Roewer 1954:89. Bonnet 1956:1300. Roth & Brown 1986:3. World Spider Catalog 2019.

Type material. Holotype ♀. U.S.A.: California: Santa Cruz County, Brookdale [midway between Ben Lomond and Boulder Creek, Highway 9], March 1913, R. V. Chamberlin ( AMNH), examined. 

Other material examined. U.S.A.: California: Alameda  . 1♀, Niles Canyon , 21.iii.1941, W.M. Pearce ( AMNH)  ; Monterey   . 4 ♀, Aromas , 8.xii.1974, D. Ubick ( DU)  ; San Mateo. 1♂, Alpine Road, 0.5 mi. SE of Pesca- dero Road , 18.xi.1988, D. Ubick ( DU)  ; 2♂ 1♀, 2 air mi. S of La Honda , 18.xi.1988, D. Ubick ( DU)  ; 2♀, Portola [Valley?], 30.x.1921, J.C. Chamberlin ( AMNH)  ; 1♀, San Gregorio Beach , 1920/1921, J.C. Chamberlin ( AMNH)  ; 1♀, Woodside , winter 1957/1958, Washburn ( AMNH)  ; 1♂, S of Woodside , 17.ix.1964, J. & W. Ivie ( AMNH)  ; Santa Clara. 1♂, Alum Rock Park , 8.x.1979, D. Ubick ( DU)  ; 2♀, Highway 17, 2 mi. N of Holy City, 6.xii.1966, V. D. Roth & Ferguson ( AMNH)  ; 1♀, Los Gatos , 18.iii.1984, D. Ubick ( DU)  ; 2♀, Stanford University environs, x.1920, no collector data ( AMNH)  ; Santa Cruz. 1♀, Ben Lomond , 2000’, iv.1934, L.W. Saylor ( AMNH)  ; 2♀, Brookdale , iii.1913, R. V. Chamberlin ( AMNH)  , 1♀, Felton , iii.1913, no collector data ( AMNH)  .

Diagnosis. The banded femora of male and female C. amicus  may often be sufficient to separate them from specimens of other adenes  group species except for C. auburn  and C. torosus  .

In addition, the male of C. amicus  is diagnosed by the number and arrangement of peg setae on the patellar apophysis and the morphology of the proximal end of the tegular apophysis. Forty to 50 peg setae are distributed over the entire dorsal surface of the patellar apophysis (Fig. 13). The proximal arm of the tegular apophysis has a single tip and its ventral and retrolateral surfaces are concave (Figs 12, 56). No other known male of the adenes  group has this combination of features.

The female of C. amicus  may be difficult to differentiate from some of the females of other species of the adenes  group. Its strongly concave atrium ( Figs 15–16View FIGURES 15–17) distinguishes it from females with weakly concave atria: C. auburn  ( Figs 21–22View FIGURES 21–24) and some C. reducens  ( Figs 38–39View FIGURES 38–43). From specimens of C. reducens  with moderately concave atria, females of C. amicus  can be distinguished by the length-to-width ratio of the atrium and the general form of the vulva: length> width and vulva “normal” in C. amicus  ( Figs 15–17View FIGURES 15–17) versus length <width and vulva appearing reduced or compressed in C. reducens  ( Figs 41, 43View FIGURES 38–43). From females of the other adenes  group species with strongly concave atria, females of C. amicus  can be distinguished by the atrium being inverted U-shaped and widest posteriorly ( Figs 15–16View FIGURES 15–17) versus inverted vase-shaped and widest posteriorly in C. schusteri  ( Fig. 53View FIGURES 50–53), inverted lyriform and widest anteriorly in C. adenes  ( Figs 4-7View FIGURES 4–8, 9–11View FIGURES 9–11) and C. grizzlyi  ( Figs 28, 30View FIGURES 28–30), or inverted U-shaped but parallelsided in C. pearcei  ( Fig. 33View FIGURES 33–34); by the lateral ends of the atrium being unmodified ( Figs 15–16View FIGURES 15–17) versus strongly curved antero-medially in C. sanbruno  ( Figs 47–48View FIGURES 47–49); and by the copulatory ducts being of relatively narrow diameter and lightly sclerotized throughout their length ( Figs 16–17View FIGURES 15–17) versus very broad and lightly sclerotized anteriorly and narrow and heavily sclerotized posteriorly in females of C. torosus  ( Fig. 55View FIGURES 54–55).

Description. Femora lightly to strongly banded.

Male: (n=5). Very small retrolateral ridge anteriorly on tibia dorsal to carinate retrolateral tibial apophysis (Fig. 14).

(n=5). CL 2.4–2.9 (2.6), CW 1.75–2.03 (1.89), SL 1.17–1.35 (1.28), SW 1.16–1.33 (1.24).

Female: (n=20). Atrium ( Figs 9–11View FIGURES 9–11) with anterior margin smoothly curved, length (from epigastric groove to anterior margin) 1.2–1.6 times width (between lateral margins). Vulva ( Figs 10–11View FIGURES 9–11) similar to C. adenes  .

(n=20). CL 2.38–3.3 (2.8±0.3), CW 1.55–2.33 (1.91±0.20), SL 1.18–1.50 (1.31±0.09), SW 1.09–1.43 (1.24±0.09). Holotype CL 2.5, CW 1.76, SL 1.22, SW 1.15.

Distribution and natural history. West central California from southern San Francisco Bay area south to northern Monterey County ( Fig. 69View FIGURE 69). Males have been collected from mid–September to mid–November. Oak and redwood forests support populations of this species.


Departamento de Geologia, Universidad de Chile


Royal British Columbia Museum - Herbarium


American Museum of Natural History


Duke University Vertebrate Collection














Cybaeus amicus Chamberlin & Ivie 1932

Bennett, Robb, Copley, Claudia & Copley, Darren 2019

Cybaeus amicus

Chamberlin & Ivie 1932: 24