Genus Promyrmekiaphila Schenkel 1950

Promyrmekiaphila Schenkel 1950: 29 (type species by monotypy Promyrmekiaphila gertschi Schenkel).

Diagnosis: Males can be separated from those of other euctenizine genera by a patch of thin spines on the ventral and retrolateral ventral aspect of tibia of leg I (e.g., Figs 26, 31). Promyrmekiaphila females are easily distinguished from other closely related taxa (e.g., Aptostichus) by an extensive patch of cuspules that is distributed across the entire endite surface (Figs 10, 14). A second diagnostic feature is a distinctive abdominal coloration pattern (Fig. 1) that consists of wide, dark uniform bands (i.e., little to no mottling) in a chevron pattern.

Description: Moderate-sized trapdoor spiders, carapace 5.60–7.84 long by 4.76–6.88 wide, glabrous or very lightly hirsute (Fig. 8), fringe of stout black bristles (ɗ’s, Fig. 13). Carapace coloration ranges from dark yellowish brown to strong brown (Figs 1, 8, 13). Abdominal coloration uniform dark reddish-brown dorsally (ɗ’s) or some species with wide dusky stripes on dorsum (Ψ’s, Fig. 1), ventrum and spinnerets pale yellow. Carapace sclerotization uniform (Fig. 8). Foveal groove generally deep and procurved (Fig. 8). Eyes slightly elevated (Fig. 9). AME, PME subequal in diameter; AER slightly procurved, PER slightly recurved (Fig. 8). Pars cephalica moderately elevated (not steep, Fig. 9).

Sternum as in most euctenizines, wider posteriorly and tapering anteriorly with widest point at coxae III (Figs 10, 12). Posterior pair of sigilla usually much larger, nearly contiguous. Palpal endites longer than wide, large patch of many cuspules (ca. 100) distributed evenly across endite surface (Figs 10, 14). Labium wider than long or subquadrate, with no to few cuspules (Fig. 10). Prolateral margin of chelicerae with 7 or more teeth (Fig. 15), retrolateral margin with single row/patch of small denticles. Rastellum not a distinct mound, armed with row of 8–10 prominent short spines (Fig. 15). Articles of legs I, II slender relative to those of III, IV, all lacking pseudosegmentation; thin ventral spines only (Fig. 11). Tarsi III, IV straight. Moderately dense scopulae on tarsi and metatarsi I–II in both sexes (Fig. 11, 26, 27, 31, 32, 34, 35, 39, 40), tarsi of legs III–IV (ɗ’s), and metatarsi of legs III–IV in P. clathrata (ɗ’s). Tarsi I with single row of filiform trichobothria, usually arranged in zig-zag pattern. Trichobothria bases elevated distally, with small ridges (Fig. 16), tarsal organ a low dome with faint concentric ridges (Fig. 17). Rudimentary preening comb at tarsus–metatarsus joint of metatarsus on leg IV (Ψ’s). Palpal claw with single row of few teeth, basal-most tooth elongate, unbranched (Fig. 18). STC leg I with single inner row of multiple teeth (ɗ, Ψ), basal-most tooth (Ψ’s) slightly longer, unbranched (Fig. 19); STC leg IV (Ψ’s) few teeth (ca. 2, Fig. 20).

Apical article of PLS digitiform, short; all three segments with articulated spigots (Fig. 21). Three morphologically distinguishable spigot types (Figs 22, 23): large conical bases (Fig. 22); small conical base (Fig. 22), spherical base (Fig. 23). Terminal segment with 2–3 enlarged spigots at tip. PMS single segment, with spigots (Fig. 24), short, with rounded apex.

Spermathecae relatively simple, a single pair of unbranched (Fig. 29, 30, 33) or branched bulbs (Fig. 37, 38, 41) with moderately sclerotized base. Distinctive male mating clasper (modified tibia and metatarsus of leg I, e.g., Fig. 31); metatarsus relatively straight with slight proximal ventral excavation. Cymbium of male pedipalp lacks spines (Fig. 28, 36), short pyriform palpal bulb simple, embolus relatively straight, lacks serrations (Fig. 25).

Distribution: Central-western and northwestern California.

Remarks: Unlike its more diverse relative Aptostichus, widely distributed throughout southern and central California, Promyrmekiaphila has a relatively restricted distribution (Figs 4–6). Distributed west of the Central Valley, the genus extends to south of the San Francisco Bay area into Santa Cruz County and north into Mendocino County. A single disjunct species is found at the northwestern apex of the Central Valley, in Tehama and Shasta Counties. Members of the genus are unknown from the agriculturally dominated Central Valley, and no spiders have yet been found east of it. Niche-based distribution models created using Maxent (Phillips, Anderson, & Schapire, 2006) for each of the two species (Figs 5, 6, see Stockman & Bond 2007) indicate that each are found under very different environmental conditions. Promyrmekiaphila clathrata populations are most abundant in rich, dark soils of the mesic mixed oak and redwood forests common along the Pacific Coast near the San Francisco Bay Area (Fig. 4). The probability of occurrence tends to decrease towards the east, likely corresponding to a general increase in aridity (Stockman & Bond 2007) in that direction (Fig. 6). A few, rare populations have been found in very dry, hard soils near the western edge of the Central Valley. These populations are typically located in more mesic microhabitat zones associated with some degree of vegetation coverage. Promyrmekiaphila winnemem populations are greatly separated geographically from P. clathrata populations by large expanses of unsuitable habitat (Fig. 5).

Natural History: Throughout its range, all known Promyrmekiaphila individuals build subterranean burrows, easily located on steep road cuts and creek banks. However, burrows can also be found under leaf litter, moss, bare soil, and tall grass. The sometimes-convoluted burrows tend to extend back and downward from the bank face to depths over 30 cm. The entire length of the burrow typically has a moderate lining of opaque white silk. The burrow entrance is covered with a wafer-like trapdoor, constructed of silk, soil and other detritus, rendering the burrow highly cryptic (Figs 2, 3). Although rare, smaller side chambers have been observed, some extending upward to the soil surface and others perpendicular to the main chamber and blind. Unlike in burrows of Myrmekiaphila Atkinson 1886, its Euctenizine kin, internal trapdoors have not been observed.