Aptostichus Simon, 1891

Bond, Jason E., 2012, Phylogenetic treatment and taxonomic revision of the trapdoor spider genus Aptostichus Simon (Araneae, Mygalomorphae, Euctenizidae), ZooKeys 252, pp. 1-209 : 19-26

Genus Aptostichus Simon, 1891 Figs 31-68Map 1

Aptostichus Simon, 1891: 317 (type species by monotypy Aptostichus atomarius female lectotype from CA, San Bernardino; specimen AR4263 in MNHP, examined).-E. Simon 1892: 108.-E. Simon 1903: 901.-P. Smith 1908: 220 –221– Bond & Opell 2002.

Actinoxia Simon, 1891: 318 (type species by monotypy Actinoxia versicolor Simon juvenile holotype in MNHP, examined).-E. Simon 1892: 109. P. Smith 1908: 214 (Smith considered Actinoxia to be a junior synonym of Entychides Simon).-R. Chamberlin 1937: 9.-Synonymized by Bond & Opell 2002: 518.

Nemesoides Chamberlin, 1919: 1-2 ( Nemesoides hespera Chamberlin female holotype in MCZ, examined).-Synonymized by Bond & Opell 2002: 518.

Diagnosis.

Males of this genus can be recognized by the presence of three or more spines on the distal most surface of the palpal cymbium (Figs 49, 56, 68) and a number of large, very thick spines on the distal-prolateral aspect of tibia I (Figs 48, 55). Tibia I spines are more offset proximally in the Simus and Sierra group species (Fig. 55). Entychides males have similar spination, however their spines are borne on a low apophysis whereas those of Aptostichus are not ( Bond and Opell 2002). Aptostichus females have cuspules on both the labium and palpal endites; labial cuspules are generally few and/or restricted to the inner margins of the endites (Figs 38, 39). This condition is similar to that for Apomastus , however Apomastus species appear to lack labial cuspules and the distinctive Aptostichus abdominal coloration, which consists of a mottled chevron pattern (Fig. 51).

General description.

Small to medium sized trapdoor spiders. Cephalothorax longer than wide, sloping posteriorly, moderate pubescence in most species (Figs 31, 54). Carapace sclerotization equal across its length. Thoracic groove intermediate to wide, procurved or straight (Fig. 33) and deep. In some males the thoracic groove is transverse or recurved (Fig. 51). Carapace of males fringed in stout black setae (Fig. 53). Eyes on a low tubercle (Fig. 35). AME and PME subequal diameter, except in a few species, particularly in some Simus group species where the PME diameter is noticeably less than that of AME. PME row slightly procurved or straight, AME row slightly recurved (Fig. 34). Caput moderately high (Fig. 31). Carapace of ethanol preserved specimens appears orangish-yellow. The coloration of living spiders tends to be a darker brown, however there is considerable variation in the intensity of coloration. Male coloration in most specimens is dark reddish-brown. Female and male abdominal coloration very distinctive consisting of light brown or gray background with a dark mottled chevron like pattern (Fig. 51). This pattern is less distinctive in Aptostichus simus , closely related species and is reduced in most desert-adapted species.

Sternum wider posteriorly, sometimes wider than in other euctenizids, tapering anteriorly (Figs 32, 52). Posterior sigilla large and positioned mid-posteriorly in most species (Fig. 32), in some species contiguous (e.g., Aptostichus hesperus ). Anterior margin of sigilla has a rounded margin. Palpal endites longer than wide often with only a few cuspules, which are restricted to the posterior margin, except in Aptostichus simus that has many cuspules arranged in a characteristic pattern (Figs 38-39). Labium wider than long, with a few, to a moderate number of cuspules (Fig. 32). Chelicerae dark brown. Rastellum consists of numerous spines not borne on a distinctive mound (Fig. 57). Fangs long and slender. Cheliceral furrow promargin with row of very large teeth. Retromarginal row consists of a patch of denticles.

Apical PLS article short, digitiform (Fig. 64). Spinnerets mostly with pumpkiniform spigots with several articulated spigots interspersed on apical and median articles of PLS and the PMS (Fig. 65). Two to three large, articulated spigots on apical most aspect of the PLS. PMS article robust. See Bond and Opell (2002) for more detailed descriptions of these spigot types.

Anterior leg articles slender relative to posterior. Tarsi short and robust (Fig. 36). Female scopulae long, dense, asymmetrical, extending full length of tarsus, no further than the metatarsus (Figs 36, 44, 60). Scopulae extend no further than the tarsus of the pedipalp. Posterior legs lack distinct scopulae. Pedipalp claw with a few (Fig. 40) to many teeth (Fig. 58). Male tarsi I and II with short sparse scopulae that are restricted to the ventral surface. In some species male tarsi are slightly bent, elongate and pseudosegmented (e.g., Aptostichus simus ). Basal palpal tooth and STC I–IV basal tooth elongate and positioned on the median keel but not bifid (Figs 41, 59, 61). STC IV with 5 or more teeth (Fig. 61). Female anterior legs with very few ventral spines (Fig. 36). Prolateral surface of female patella III covered in numerous thick spines. Distal ventral aspect of tarsus IV with short, sparse spine patch. Preening combs on distal most retrolateral surface of metatarsus IV (Figs 37, 45, 62). Tarsal trichobothria arranged in a zigzag pattern with typical base (Fig. 43); low tarsal organ with central pit (Figs 42, 63). Spermathecae with an elongate base that forms a secondary spermathecal bulb in some species (Figs 46, 47, 66, 67).

Male mating clasper morphology is distinctive. Articles of leg I bear a number of large, thickened spines positioned retrolaterally on the distal aspect of the tibia (Fig. 55), except members of the Sierra and Simus species groups whose tibial spines are more concentrated proximally (Fig. 55). In most species, metatarsus I with proximal ventral to prolateral excavation bordered distally by a low mound (Fig. 55). Tibia I with 3-5 elongate spines distributed retrolaterally except in some species which have denser spine patches. Palpal cymbium with four or more dorsal spines (Figs 49, 56, 68). Palpal bulb normal (Fig. 68), embolus of some Simus group species with serrations (Fig. 50). Palpal femur short with a dorsal row of thin spines, tibia short and robust in some species (e.g., Aptostichus simus ) there is a distinctive prolateral spine patch on the palpal tibia.

Distribution.

Distributed primarily throughout the California Floristic Province with the greatest number of species known from Southern California; a few species are recorded from Nevada and Arizona (Table 1, Map 1).

Key to species groups and to males

Note. Like many mygalomorph taxa, species identification is a non-trivial task. These spiders generally lack distinctive somatic differences that render development of a key to females virtually impossible and a key to males difficult at best. Although, I have attempted to provide a key to male specimens, I would caution that it is far from perfect and thus suggest that the key be used in conjunction with careful examination of specimens, the species description, knowledge of from where the specimen was collected (many species are narrowly endemic), and molecular characters (if available). Generally speaking no single characteristic should be taken as definitive evidence of a species’ determination. Because species placed in the Atomarius Sibling Species Complex have been delineated on the basis of a combination of biogeographic, general somatic, ecological, and molecular characteristics, the provided key to these taxa relies heavily on data taken from the geographic location and habitat from which the specimen was collected.

The Atomarius species group

Included species.

Aptostichus atomarius Simon, 1891

Aptostichus stephencolberti Bond, 2008

Aptostichus angelinajolieae Bond, 2008

Aptostichus stanfordianus Smith, 1908

Aptostichus miwok Bond, 2008

Aptostichus dantrippi Bond sp. n.

Aptostichus pennjillettei Bond sp. n.

Aptostichus asmodaeus Bond sp. n.

Aptostichus nateevansi Bond sp. n.

Aptostichus chiricahua Bond sp. n.

Aptostichus icenoglei Bond sp. n.

Aptostichus cabrillo Bond sp. n.

Aptostichus isabella Bond sp. n.

Aptostichus muiri Bond sp. n.

Aptostichus barackobamai Bond sp. n.

The Atomarius Sibling Species Complex

The Atomarius Sibling Species Complex ( Bond and Stockman 2008) comprises six closely related sibling species: Aptostichus atomarius , Aptostichus stephencolberti , Aptostichus angelinajolieae , Aptostichus stanfordianus , Aptostichus miwok Bond, and Aptostichus dantrippi sp. n. With the exception of a number of coastal dune and desert-adapted lineages these species are relatively morphologically homogenous (see analysis of morphological variation in Bond and Stockman 2008) and are difficult to distinguish; modifications to the male leg I tibia and metatarsus are indistinguishable among species. However, all species in this complex have non-overlapping ranges and thus can be ascribed to species on the basis of collecting locality and habitat; examination of diagnostic molecular markers should be employed to definitively confirm any determinations made solely on the basis of geography. Molecular studies to date further indicate Aptostichus atomarius , as defined below, may actually comprise 2-3 species; sampling at the time was insufficient to formulate these additional hypotheses with rigor.