Phylogenetic treatment and taxonomic revision of the trapdoor spider genus Aptostichus Simon (Araneae, Mygalomorphae, Euctenizidae)

Abstract This systematic study documents the taxonomy, diversity, and distribution of 40 species of the predominately Californian trapdoor spider genus Aptostichus Simon, 1891. Thirty-three of these species are newly described: Aptostichus dantrippi, Aptostichus cabrillo, Aptostichus pennjillettei, Aptostichus asmodaeus, Aptostichus nateevansi, Aptostichus chiricahua, Aptostichus icenoglei, Aptostichus isabella, Aptostichus muiri, Aptostichus barackobamai, Aptostichus sinnombre, Aptostichus hedinorum, Aptostichus aguacaliente, Aptostichus chemehuevi, Aptostichus sarlacc, Aptostichus derhamgiulianii, Aptostichus anzaborrego, Aptostichus serrano, Aptostichus mikeradtkei, Aptostichus edwardabbeyi, Aptostichus killerdana, Aptostichus cahuilla, Aptostichus satleri, Aptostichus elisabethae, Aptostichus fornax, Aptostichus lucerne, Aptostichus fisheri, Aptostichus bonoi, Aptostichus cajalco, Aptostichus sierra, Aptostichus huntington, Aptostichus dorothealangeae, and Aptostichus chavezi. Most of these species are restricted to the California Floristic Province, a known biodiversity hotspot. Of the 40 recognized species, over half are considered to be imperiled or vulnerable and two have likely gone extinct over the past half-century; the conservation status of only 11 species is considered to be secure. Using 73 quantitative and qualitative morphological characters I propose a preliminary phylogeny for the genus that recognizes four major lineages: the Atomarius, Simus, Hesperus, and Sierra species groups. Additionally, the phylogenetic analysis indicates that adaptations favoring the invasion of the arid desert habitats of southern California have evolved multiple times across the group. The existence of both desert and non - desert species in three of the four species groups makes this genus an ideal candidate for the study of the evolutionary ecology of desert arthropods. A set of molecular characters based on the contiguous mitochondrial DNA genes 16S-tRNA valine-12S is used in an independent analysis to assist in placement of specimens into species. The taxonomy section explicitly identifies the concept employed in species delimitation. Niche based distribution models are constructed to predict the ranges of species for which an adequate number of sampling sites were known.


Introduction
The mygalomorph family Euctenizidae is a geographically widespread group of fossorial spiders most of whom capture prey at the entrance of a burrow covered by a silken -soil trapdoor. Raven (1985) originally established this group as a subfamily of the Cyrtaucheniidae, however a number of phylogenetic treatments of the infraorder Mygalomorphae (Bond and Opell 2002, and Bond et al. 2012b) indicated that the family was a classical dumping ground, comprising a number of genera and species that were difficult to place. A recent phylogenetic treatment by Bond et al. (2012b) concluded that Raven's subfamily Euctenizinae, a group that included all of the North American cyrtaucheniids, was a monophyletic taxon that is closely related to idiopids and should be elevated to the family rank. This group comprises the eastern North American genus Myrmekiaphila Atkinson, 1886 (recently revised by Bond and Platnick 2007, also see Bailey et al. 2010 andBond et al. 2012a), and the southwestern genera Neoapachella, Bond & Opell 2002, Eucteniza Ausserer, 1875, Promyrmekiaphila Schenkel, 1950 (recently revised by Stockman and Bond 2008, but also see Stockman and Bond 2007), Entychides Simon, 1888, Apomastus Bond & Opell, 2002, and Aptostichus Simon, 1891. Although the basal euctenizid lineages are probably relatively old  most of the genera are depauperate with respect to morphological and species diversity. Many consist of very few species and two, Neopachella and Promyrmekiaphila, are either monotypic (Bond and Opell 2002) or comprise only two morphological species . That said, morphological assessments likely underestimate the evolutionary diversity contained within these groups (Bailey et al. 2010, Bond et al. 2001, Starrett and Hedin 2006, Stockman and Bond 2007. In terms of diversity the trapdoor spider genus Aptostichus, the subject of this revision, is an anomaly with respect to high species diversity relative to the other euctenizid genera and many other mygalomorph groups. It comprises > 40 species restricted primarily to the state of California, with additional, species, in the states of Nevada and Arizona (one and two respectively). Among southwestern mygalomorph genera (save theraphosids, tarantulas), this diversity is rivaled only by the antrodiaetid genus Aliatypus Smith, 1908 that contains a third as many species. Aptostichus species range widely in size (carapace length 3 -7.5 mm), coloration, and habitat type. These features, and others (described below) make the genus very interesting from an evolutionary and ecological perspective. Although relatively restricted geographically its species are found in disparate habitats (Figs 1-6), ranging from Mediterranean climates to the arid Mojave and Colorado deserts. Their apparent ecological specialization coupled with high species diversity makes these spiders ideal for investigations of the evolution of characters associated with desert adaptations. The "trapdoor spider desert adaptation paradigm" has been addressed by others (Main 1978, Coyle andIcenogle 1994) but never in an explicit phylogenetic context. Additionally, the distribution of this genus across the unique taxonomically and geologically diverse Californian Floristic Province (Myers et al. 2000), a region recognized as a biodiversity hotspot, provides an important and well-studied system in which to consider questions about the geography of speciation and adaptation and makes this group of high conservation interest.
Although Aptostichus may be noteworthy from an evolutionary and conservation perspective, its taxonomy has been largely neglected. Since the original description of the genus by Simon (1891) only three species of Aptostichus were subsequently described during the 20 th Century (Smith 1908;Chamberlin 1917Chamberlin , 1919. Largely through the efforts of Mr. Wendell Icenogle and Dr. Willis Gertsch during the late 1960's through the 1970's, many Aptostichus specimens were collected and the high diversity in this group began to come to light. It is apparent from letters and preliminary taxonomic worksheets created during the 1970's that Gertsch had intended to revise the genus, a project that never reached fruition. More recently, molecular studies focusing on a speciation pattern and process within the Aptostichus atomarius species complex, a wide- spread, morphologically homogenous species distributed broadly throughout southern and western California , have resulted in the description of an additional three species (A. stephencolberti, A. miwok, and A. angelinajolieae). These results were consistent with earlier molecular studies of the coastal dune endemic species A. simus (Bond et al. 2001) that likewise seemed to indicate species crypsis.
The covert behavior and simple morphology of many mygalomorph groups (Coyle 1971), particularly when compared to many other more "advanced" araneomorph spider groups, is probably why Aptostichus has been overlooked by other spider workers. Like many mygalomorph groups, it is perhaps even more difficult to study because females of many species lack obvious distinguishing morphological features altogether (humorously characterized as "hopeless" by Gertsch in lit.). Additionally, many species can be collected only during certain times of the year and collecting typically requires that the burrows be excavated, an activity that is often very time-consuming. Because Aptostichus species construct flimsy, thin wafer trapdoors (Figs 7-10) that often have plant debri attached rendering them cryptic, these doors cannot easily be detected by simply searching a substrate for a thin door outline. Therefore, one must sometimes use a "scraping" technique to find burrows by removing the first few centimeters of topsoil, thereby exposing the silk lined burrow. This technique however, is not very effective in sandy desert habitats. The only way to find desert Aptostichus females appears to be after winter rains when the spiders extend, or clean out their burrows, leaving a small mound of sand at the burrow entrance. In contrast, males are much easier to distinguish than females and have been widely collected in standard pitfall traps. This sex-specific disparity is reflected herein in that some female dryad.3b95n)]. Characters for the phylogenetic analysis were scored from the type specimens, with the exception of the quantitative characters, which were scored on the basis of multiple specimens. Outgroup taxa were scored using the euctenizid specimens listed in Bond and Opell (2002) and in Bond and Hedin (2006) as exemplars. Quantitative values were taken from each of these exemplar taxa.
Mating clasper and palpal line drawings were made for some specimens (when needed to further clarify spination patterns) with the aid of a dissecting scope Figures 11-16. Diagrammatic representation of quantitative measurements of morphological features and leg articles. 11, 12 carapace, labium, sternum length and width 13 lengths of leg I femur, tibia, metatarsus, tarsus, metatarsal proximal/ventral excavated region, number of tibia distal retrolateral spines 14 lengths of leg IV femur and tarsus 15 male palpal tibia length and width 16 male copulatory bulb length. equipped with a camera lucida. Line drawings were scanned as digital images and converted to vector drawing objects in Adobe Illustrator (Adobe Systems Inc.). Digital images of specimens were made using a Visionary Digital Imaging System (Visionary Digital TM , Richmond, VA) where images were recorded at multiple focal planes and then assembled into a single focused image using the computer program Helicon Focus (Helicon Soft, Ltd., Ukraine). The female genital region was removed from the abdominal wall and tissues dissolved using trypsin; spermathecae were examined and photographed in the manner described above. Habitus illustrations were constructed from whole body images that were bisected, copied, and reflected in Adobe Photoshop (Adobe Systems, Inc.) to produce a roughly symmetrical image; the actual raw image on which the habitus illustration is based has been deposited in Morphbank and its record number noted in the figure legend (value in square [ ] brackets). For scanning electron microscopy, specimens were air-dried and sputter-coated with gold prior to viewing on an FEI Quanta 200 scanning electron microscope.

Evaluation of quantitative morphological characters for diagnosis and phylogenetic analyses
Quantitative morphological features that were determined to have discrete, nonoverlapping ranges for individual subsets of species were scored as phylogenetic characters and were used as features for morphological diagnosis of species. The criterion that employs only non-overlapping features limits the number of quantitative features and character states available to our analysis; these non-overlapping characters were chosen from a much larger suite of morphological measurements, many of which lacked discrete non-overlapping ranges (but may have differed statistically). Coyle (e.g., 1994Coyle (e.g., , 1995 has frequently used an analysis of variance method to delineate states of quantitative characters for mygalomorph phylogenetic analyses. Mean values that statistically differ are scored as discrete states, regardless of potentially overlapping ranges. This approach is not uncommon and a number of other authors have likewise proposed methods for scoring overlapping quantitative characters (e.g., Chappill 1989, Goldman 1988, Thiele 1993, Wiens 2001, Goloboff et al. 2006. The use of these quantitative data has received some "conceptual" scrutiny, both negative (Farris 1990) and positive (e.g., Goloboff et al. 2006; see Garcia-Cruz and Sosa 2006 for detailed assessment of various approaches). However, the utility of overlapping quantitative character states has not been adequately tested (but see Hendrixson and Bond 2009). For this reason and others, I am hesitant to use these data as such in this present study. However, acknowledge that the approach I have employed here is not without certain problems. For example, in the case of species represented by only a few specimens, additional collecting could add specimens whose features expand the range of some characters and possibly negate, or change the scoring of said characters.  (Fig. 277). 54. Sperm duct directly below bulb embolus junction: straight = 0; looped = 1. 55. Tip of embolus: normal, gradual taper = 0; tapers sharply into a very thin terminus = 1 (Fig. 335). 56. Male pedipalp distal prolateral tibial spine: absent = 0; present = 1 (Fig. 271). 57. Palpal bulb (Fig. 25): short (Bl/Cl < 17) = 0; long (Bl/Cl > 17) = 1. 58. Prolateral cymbial lobe: normal = 0; extended = 1. 60. Retrolateral, distal most aspect of cymbium forms a distinct process: no (normal) = 0; yes = 1 (Fig. 278). 61. Retrolateral cymbium spine row: absent = 0; present = 1 (Figs 246, 248). 62. Retrolateral distal tibial spines: absent = 0 (Fig. 165); present = 1 (Fig. 55). 63. Retrolateral distal tibial spines: absent = 0; short = 1 (Fig. 194); long = 2 (Fig. 123). 64. Retrolateral distal spines: absent = 0; arranged distally = 1 (Figs 73-75); offset behind distal margin = 2 (Fig. 167).

Morphological and molecular character matrix construction and phylogenetic analyses
Phylogenetic analyses of Aptostichus relationships were conducted using molecular and morphological data sets employing parsimony, Bayesian, and likelihood optimality criteria. Molecular data sets analyzed include data drawn from previous smaller studies (Bond et al. 2001, Bailey et al. 2010) and from newly collected data. Handling of tissues, DNA preparation, and sequencing followed procedures outlined in Bond and Stockman (2008). Legs were removed from specimens and preserved in RNAlater (Qiagen, Valencia, CA) and stored at −80C; whole specimens were preserved for morphological studies in 80% ethanol. Genomic DNA was extracted using the Qiagen DNeasy Tissue Kit. Standard PCR protocols were used to amplify an approximately 1500-base pair region of the mitochondrial genome spanning the region coding for the 12S rRNA, val-tRNA, and 16S rRNA genes. Amplification products were produced using the primers LR-J-12887 CCGCTCTGAACTCAGAT-CACGT and SR-N-14612spid AAGACAAGGATTAGATACCCT. After agarose gel verification and purification using ExoSAP-IT (USB, Cleveland, Ohio), products were sequenced on an ABI 3130 automated sequencer (Applied Biosystems, Foster City, CA) directly using the PCR primers and an additional internal sequencing primer (LR-J-13XXXa GGCAAATGATTATGCTACC). Sequence data were edited using the computer program Sequencher (Genecodes, Madison, WI) and then aligned using the software package Muscle (Edgar 2004) with default opening and gap extension penalties; minor adjustments to the alignment were made manually using the computer program Mesquite (Maddison and Maddison 2010). Molecular analyses primarily focused on identification of specimens, particularly juveniles, to species by phylogenetic association; that is, evidence of common ancestry with specimens identified by other means (e.g., morphological or cohesion species criteria). Given the paucity of species for which molecular data were available (less than half ), it would be unwise to infer intra-generic relationships among species from these analyses.
Phylogenetic analyses of the molecular data comprised Bayesian and likelihood analyses. For Bayesian analyses the appropriate model of DNA substitution for each of the mtDNA data partitions was chosen using the computer program Kakusan 3 (Tanabe 2007) by Bayesian Information Criterion (BIC). MrBayes ver. 3.1.2 (Ronquist and Huelsenbeck 2003, Huelsenbeck andRonquist 2001) was used to implement a Bayesian inference of phylogeny using the substitutions models indicated by BIC. Analyses comprised four concurrent Markov Chain Monte Carlo (MCMC) chains run for 40,000,000 generations with trees saved every 1,000 generations. The two independent runs were considered to have converged when the standard deviation of split frequencies value was < 0.01. Topologies were discarded as burn-in following visual inspection in the program Tracer (Rambaut and Drummond 2007); clade posterior probabilities were computed from the remaining trees. The reported likelihood score and post burn-in tree topology was computed using the sump and sumt command with the option contype=allcompat, respectively. Likelihood analyses were conducted using the computer program RAxML ver. 7.2.8 (Stamatakis 2006). Parameters employed in the analysis included 1000 random addition sequence replicates with the general time reversible model and gamma model of site heterogeneity (-m = GTRGAMMA, -# = 1000). Branch support values were computed via 1000 non-parametric bootstrap replicates. Bootstrap bipartitions were drawn onto the best tree topology obtained in the previous analysis.
Phylogenetic analyses of the morphological data set were performed using PAUP* version 4.0b10 (Swofford 2002). All binary characters were treated as reversible, multistate characters and were treated as unordered, and all characters were initially weighted equally. Heuristic searches were performed using random stepwise addition (1000 replicates) of taxa followed by TBR (tree bisection-reconnection) branch swapping held to one million rearrangements per replicate. Branches with a maximum length of zero were collapsed. The preferred tree topology (presented herein) is based on the search conducted in PAUP* using the "Goloboff Fit Criterion" (Goloboff 1993a(Goloboff , b, c, 1995 with the search parameters described above. Solutions using an array of concavity function constants (k= 3-12) were explored.

Locality data, georeferencing, generation of niche-based distribution models, and conservation status
Latitude and longitude for all collecting localities were recorded in the field using a Garmin® Global Positioning System receiver (Garmin International Ltd., Olathe, KS) using WGS84 map datum. For previously collected specimens (e.g., loaned museum specimens) locality data were georeferenced by hand by finding the approximate locality on United States Geological Survey topographic maps (NAD83 map datum) or Google Earth (WGS84 datum). All georeferenced and field recorded locality data (latitude, longitude, elevation) were crosschecked by hand in Google Earth prior to generating distribution map illustrations and database entry. Distribution maps were constructed using ArcGIS using NAD83 map datum. Because many older collecting labels lack sufficient locality information, many georeferenced values are imprecise and should be used with caution. Data for labels that document only county and/or town information were georeferenced to the approximate geographic center of the locality given. Precision for each georeferenced point is annotated as a superscript in each material examined section of the species' taxonomy using the confidence value scheme employed by Murphey et al. (2004): 1 = exact coordinates given; 2 = amended exact coordinates (i.e., exact coordinates given but were emended on validation); 3 = public land survey system (or herein geographic place name); 4 = within 1km radius; 5 = within 5km radius; 6 = within 10km radius; 7 = to county or > 10km; 8 = to state; 9 = to project region. Latitude and longitude are recorded to the 4 th decimal place as an indication of the precision in the point assigned by us (i.e., where I have assigned the locality place-holder for the specimen in question), not precision in the recording of the value or to specify the exact point of collection. Actual precision of the record is to be inferred from the numbering system described above. Detailed locality and associated GIS data as supplemental data files in spreadsheet and KML file format can be downloaded online from the Dryad Data Repository at doi: 10.5061/dryad.3b95n.
As an approach to facilitating species discovery and determination, niche-based distribution models (DM's) were constructed for species for which sufficient locality data were available (> 5 points). Niche-based DM's provide estimates for the probability of finding a species at a location on the landscape given the set of correlate ecological and climatic parameters used to construct the model. Locality coordinates for each specimen were imported into ArcMap (ESRI, Redlands, CA) and converted into shape files. Following the procedure outlined in Bond and Stockman (2008), DM's were constructed using environmental layers thought to "likely influence the suitability of the environment" (Phillips et al. 2006) based on our previous analyses of A. atomarius species complex distributions (see Stockman and Bond 2007, for further justification of layer choice). Seven climatic layers were obtained from the WORLDCLIM data set (Hijmans et al. 2005): annual precipitation, precipitation seasonality, annual maximum temperature, annual minimum temperature, tempera-ture seasonality, and mean precipitation during the driest and wettest quarters. A seventh layer, elevation, was constructed from a mosaic of Digital Elevation Models (DEMs) derived from the National Elevation Dataset (USGS). DEMs were converted to Raster format in ArcMap and resampled from 30-m resolution to 1-km resolution using bilinear interpolation. All seven layers were clipped to the same extent, cell size, and projection. Niche-based (DMs) were created using the computer program Maxent (Phillips et al. 2006). Maxent employs a maximum likelihood method that estimates a species' distribution that has maximum entropy subject to the constraint that the environmental variables for the predicted distribution must match the empirical average (Elith et al. 2006;Phillips et al., 2006). Parameters for all Maxent analyses used the default values: convergence threshold = 10−5, maximum iterations = 500, regularization multiplier = 1, and auto features selected. Additional larger values of the regularization multiplier were used to ensure that models were not overfitting the data.
A hypothesized conservation status of all species has been included with each description. I have used the NatureServe ranking scheme-secure, apparently secure, vulnerable, imperiled, critically imperiled, and extinct-to describe perceived status. The designations provided are not based on any formal calculations (see Faber-Langendoen et al. 2009 for explicit criteria) and thus should not be viewed as formal status declarations. Many Aptostichus species are rare in collections and very difficult to collect, consequently parameters like rarity and abundance are impossible to accurately assess at this time. As such, I have based conservation status designations on extent of distribution and apparent threats to habitat (e.g., is the species known only from a highly impacted area?); a brief rationale is provided with each determination. These designations are likely to be very conservative and may belie the imperiled nature of some species. Future studies will seek to formally evaluate conservation status.

Species delimitation and conceptualization
Although often not discussed, any taxonomic revision contains an implicit concept of a species. The general convention within spider taxonomy is a "diagnosable" species concept (Nelson andPlatnick 1981, Nixon andWheeler 1990) wherein populations are delineated as species as a consequence of sharing a set of qualitative, fixed differences. For the vast majority of spider species described these differences are essentially morphological, usually features related to differences in genitalia (male pedipalps, female spermathecae). Alternatively, one could simply think of this as a "morphological" species construct-if populations differ in a set of morphological characters they are delimited as separate species.
As discussed in number of papers related to species delineation in mygalomorph taxa, morphological stasis seems to be more the rule rather than the exception. That is, the prevailing hypothesis is that extreme geographic structuring due to limited dispersal capability may lead to speciation in the absence of morphological or apparent ecological divergence (Bond et al. 2001). As such a number of studies (e.g., Stockman and Bond 2007, Bailey et al. 2010 advocate that an integrative approach to mygalomorph spider species delimitation must be employed if an accurate representation of evolutionary diversity is to be achieved. Ideally an integrative approach to species delimitation would use data from many sources (e.g., genetic, ecological, and traditional morphological) taken together to formulate species hypotheses. Such an approach serves to more thoroughly document evolutionary diversity whereas an approach that focuses on a single character system (e.g., genitalic features) may overlook species diversity but is easier to implement and is pragmatic both in terms of species documentation and discovery, and subsequent identification by non-specialists. Reflected in the amount of data available for any given set of specimens/populations, the species reported herein generally represent one of three construct classes-morphological, or traditionally delineated species, phylogenetic species, or "cohesion species". Traditional morphologically delineated species are defined as those populations that represent qualitative differences in phenotype that differ in a discrete manner from other populations groups. Cohesion species follow Templeton's (1989) concept wherein a species is defined as lineages that are genetically or demographically interchangeable. Cohesion species are those for which genetic and or ecological data has been considered in concert with the distribution of species (see Bond and Stockman 2008) and morphological characteristics. Each species' account notes the species concept that has been applied. In a number of instances additional phylogenetic information, based on molecular analyses was available and considered as corroborative support for the species hypothesis being put forth. As such I have applied a phylogenetic species concept wherein individuals (populations) share common ancestry in a molecular phylogenetic analysis and thus are mutually exclusive and diagnosably distinct (Cracraft 1989). Operationally, I simply employ the phylogenetic information from this single gene analysis as corrabotive support for hypothesized morphological species when they are recovered as a clade on the gene tree; that is, these data are not necessarily used exclusively to delineate species.

Data resources
The data underpinning the analysis reported in this paper (see below) were deposited on 19 November 2012 in the Dryad Data Repository at doi: 10.5061/dryad.3b95n and at GBIF, the Global Biodiversity Information Facility, http://ipt.pensoft.net/ipt/ resource.do?r=aptostichus_locality_data. Images associated with species descriptions have been deposited in Morphbank (http://www.morphbank.net); Morphbank image record numbers are noted in brackets by each figure in the figure legend.

Summary of taxodiversity
At present the genus Aptostichus comprises 40 species, 33 of which are newly recognized herein. Table 1 summarizes species, type localities, and material available for each species described; >2000 specimens in total were examined. Of these 33 new species, 12 are known only from male specimens; of these, three are described on the basis of a single specimen. Such a sex-based disparity and lack of material for rare taxa has been noted in taxonomic revisions of other mygalomorph groups (e.g., the migid genus Moggridgea O. P. Cambridge, 1875;Griswold 1987) and is not uncommon in systematic works in general (Huber 2003, Lim et al. 2011. As already discussed the number of species will likely increase dramatically as more is learned about this group of spiders; molecular studies to date suggest that "morphological" species, particularly those that are widely distributed, likely disguise a great deal of evolutionary and ecological diversity. Moreover, some underestimation may in part be due to the lack of males collected for populations of unplaced female specimens. The genus Aptostichus has diversified within an extensive area that spans the California Floristic Province. Species are found in virtually every habitat type (see discussion of ecological evolution below) including extreme arid desert environments, mesic montane and coastal habitats, to high elevation alpine habitats of the Sierra Nevada Mountains. Without question the genus represents a classical adaptive radiation where lineages have diversified and apparently adapted to inhabit a set of disparate environments, climates, and habitat types. Ecological factors that may influence Aptostichus diversity and distributions include climatic suitability during dispersal, prey type and availability, water and temperature, and soil type (to name a few). Given their close ties to the substrate, as fossorial organisms, parameters associated with burrow architecture and design (depth, thickness of silk lining, trap door design, etc.), it is not surprising that many of these features vary from species to species.
Understanding of Aptostichus ecology and behavior is severely limited at this time. To date approximately 15 of the 40 species have been collected only from pitfall traps thus female burrows have never been observed. Of these about half are known from only a few specimens and thus are quite rare in collections. Moreover, some species like A. derhamgiulianii and A. sierra have not been collected since they were first discovered over 40 years ago and at least two species are now presumed extinct (A. killerdana, A. lucerne). Alternatively, recent collecting efforts have uncovered a number of new morphologically distinct species (e.g., A. satleri, A. isabella, A. cajalco). Given how narrowly endemic many species are there is likely to be considerable diversity that both awaits discovery but is also threatened due to development and habitat destruction throughout the California Floristic Province biodiversity hotspot. Table 1. Summary of Aptostichus species diversity. Columns summarize nominal species and conservation status (see footnote); three-letter identifier; US state and county of type locality; latitude and longitude of type locality; characterization of (sex of specimens) and amount of material available for examination. Figure 28 summarizes the maximum likelihood and Bayesian inference analyses of the mtDNA data set. The data set comprises 337 individual specimens representing 15 of the 40 species documented herein, sequenced for the mitochondrial region spanning the 16S-tRNA-valine-12S genes; of these 206 were newly generated sequences (GenBank Accession numbers: JX103235-JX103440). The matrix is an aligned 1618 base pairs; Kakusan chose the GTRGAMMA model for each of the three partitions. The -ln likelihood value for the best tree from the RAxML analysis is -59821.7255. The Bayesian analysis was run for 40,000,000 generations with half of the trees discarded as burnin. The harmonic and arithmetic means of the postburnin tree topology likelihoods were -60532.81 and -60373.61, respectively. The summary tree (Fig. 28) supports the basal placement of A. simus, the monophyly of the Atomarius Sibling Species Complex, and general placement of other species into species groups delineated on the basis of the morphological analysis (see below). However, as discussed earlier these data were used principally to place undetermined individuals into species rather than formulate hypotheses of deeper relationships across the tree; that is, many of the internal nodes are not strongly supported. Using the results from this analysis in combination with specimens, particularly males that could be identified to species, many female and juvenile A. atomarius, A. stanfordianus, A. angelinajolieae, A. icenoglei, and A. barackobamai specimens were determined. This analysis indicates that A. stanfordianus likely comprises more than one species (previously noted by Bond and Stockman 2008) and that specimens collected from Madera County may be an undescribed species related the A. simus (A. sp. Madera, Fig. 28). However, mature males and females are not currently available and thus the status of these specimens remains unanswered.

Aptostichus phylogeny
The morphological matrix comprised 72 characters scored for all 40 Aptostichus species. Figures 17-27 summarize the quantitative character scorings for all taxa but A. satleri, A. isabella, and A. sinnombre. Table 2 summarizes the results for the parsimony analysis based on characters equally weighted (EW) and the implied weighting analyses (IW) using a range of concavity function constants (k=3-12). The EW analysis resulted in > 440,000 trees comprising 238 steps whereas the implied weights analyses resulted in considerably fewer trees with tree lengths ranging from 238-241 steps.
The preferred tree topology is based on the analysis using IW with a concavity function constant of k=7 (Fig. 29). The EW and IW analyses were moderately incongruent with respect to the tree topologies. The EW analysis failed to recover an Aptostichus clade that was monophyletic with respect to Apomastus. A strict consensus of the >440,000 resulted in a largely unresolved tree (towards the tips) that recovered the Sierra, Simus, and Hesperus clades, or species groups (Fig. 29); the Atomarius clade was paraphyletic with respect to the Hesperus clade. Implied weighting analyses that employed concavity function constants k=3-5 resulted in trees that recovered a monophyletic Aptostichus, Sierra, Simus, and Hesperus clades but like the EW analysis the Atomarius clade was paraphyletic. Tree topology stabilized for IW analyses where k=6-12 recovering a pattern similar to that illustrated in Figure 29 where all four major species groups are monophyletic. These clades are largely delineated on the basis of shared male mating clasper and pedipalp differences (illustrated for each species group in Fig. 29).
Both molecular and morphological data matrices and associated trees (all trees recovered and consensus), formatted as Nexus and Phylip files can be downloaded from the Dryad Data Repository at doi: 10.5061/dryad.3b95n.
Figures 17-20. Box plots for quantitative measurements used in phylogenetic analysis and species diagnosis; ratios are given in values multiplied by 100 (y-axis); characters states are indicated above and below horizontal line bisecting graph; species abbreviations (x-axis) defined in Table 1. 17 sternum length to width 18 labium length to width 19 leg IV tarsus length to femur length 20 leg I tibia length to femur length. Table 3 summarizes the unambiguous character state support for each of the major nodes in the preferred tree topology (Fig. 29). I summarize below the support for only the major nodes in the analysis and formally diagnose the four nominal Aptostichus species groups. At this time it would be premature to overemphasize resolution among all of the terminal relationships within Aptostichus because of the incomplete nature of the data set due to missing taxa and few female representatives of some species.

Character support of major clades and Aptostichus species groups
Four characters (given parenthetically following the description of the state) provide unambiguous support for the monophyly of Aptostichus: a mottled, striped abdominal Figures 21-24. Box plots for quantitative measurements used in phylogenetic analysis and species diagnosis; ratios are given in values multiplied by 100 (y-axis); characters states are indicated above and below horizontal line bisecting graph; species abbreviations (x-axis) defined in Table 1. 21 leg I metatarsus length to femur length 22 leg I tarsus length to femur length 23 male palpal tibia width to length 24 palpal tibia length to carapace length. color pattern (19), distal 1/2 of the male metatarsus I lighter in color (31), extended prolateral cymbial lobe (58), and a cymbium with spines (59). Two characters support the monophyly of the clade that comprises the Sierra and Simus species groups: a short male palpal tibia (42), and an embolus with a single distinct bend (51). Six synapomorphies support the node that unites the Hesperus and Atomarius species groups: a anteverted male metatarsus I (48), a long palpal bulb (57), the presence of a male retrolateral distal tibial spine (62), long male retrolateral distal tibial spines (63), a triangular male mating apophysis (64), and uniform, non-overlapping male retrolateral distal tibial spines (65).
Sierra Species Group. Four species comprise the Sierra species group, which is supported by two synapomorphies: long sternum (8) and a long male metatarsus I (33).

Figures 25-27.
Box plot and counts for quantitative and meristic measurements used in phylogenetic analysis and species diagnosis; ratio given in values multiplied by 100 (y-axis); characters states are indicated above and below horizontal line bisecting graph; species abbreviations (x-axis) defined in Table  1. 25 male copulatory bulb length to carapace length 26 number of male, leg I tibia retrolateral spines 27 number of male, leg I tibia prolateral spines.
Hesperus Species Group. Thirteen species comprise this diverse species group. The key distinguishing feature of this group is the presence of an offset retrolateral rastellar spine (character 11). Additionally, four other characters support the monophyly of this species group: lighter carapace and abdominal coloration (18, 20) and a long and sinuous spermathecal stalk (72, 74).
Atomarius Species Group. Fifteen species comprise the Atomarius species group, the monophyly of which is supported weakly by three synapomorphies: heavy carapace pubescence (2), dense female tarsal scopulae (38) and a distinct secondary spermathecal bulb (71).

Desert adaptation in Aptostichus
Aptostichus is an ideal group for evaluating changes in spider morphology and behaviors associated with invasions of arid, desert and other habitat types (e.g., coastal dunes). Figure 30 maps habitat type on the preferred tree topology (Fig. 29) using parsimony; alternative optimization criteria were not possible due to the polytomies in the preferred tree. The current phylogeny requires at least three independent derivations of strictly desert habitation for 15 species occurring in three of the four species groups. Additional independent derivations of arid habitat are required if chaparral is classified similarly to desert habitats (i.e., all arid habitats are grouped together).    Main (1978) suggested eight adaptations that may allow trapdoor spiders to survive in very arid habitats: 1) larger body size, 2) deeper burrows, 3) increasing foraging area achieved by burrow rim modifications, 4) differential timing of breeding and dispersal, 5) the tendency of brooding females to plug their burrows, presumably for water retention, 6) aestivation of young in sealed burrows, 7) mature non-brooding females that do not plug burrows and are therefore able to feed sporadically, and 8) increased longevity of females. Concentrated efforts to obtain female specimens and additional natural history data will be required to address these questions more thoroughly for this group. Moreover, a complete molecular phylogeny for the genus will likely go further to resolve relationships among the species and will help to abrogate any confounding issues that morphological characters and attendant homoplasy associated with habitat may have.  Bond & Opell, 2002 Note. Defined as a euctenizid subfamily comprising the genera Myrmekiaphila, Apomastus, and Aptostichus in Bond et al. (2012b), the new designation, despite considerable phylogenetic support was dismissed as a nomen nudum in an online catalog (Platnick 2012) due to the absence of a formal diagnosis. To correct this oversight, I formally diagnose below the newsubfamily Apomastinae and again provide a list of included genera. As was originally intended, authorship is to be attributed to Bond and Hedin. Diagnosis. Apomastinae, a lineage defined in extensive phylogenetic analyses that include multiple lines of evidence that comprises genes and morphology Bond et al. 2012b) can be morphologically distinguished from all other euctenizids by having a patch of endite cuspules that is restricted to the proximal inner margin ( Fig. 38; rather than being uniformly distributed across the endite face, see Stockman and Bond 2008, fig. 10) and by having two distinct posterior median spinneret spigot types (as opposed to a single type, Stockman and Bond 2008, fig. 24 (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 reddishbrown. 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 A. simus, closely related species and is reduced in most desert-adapted species.

Taxonomy
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 A. simus that has many cuspules arranged in a characteristic pattern . 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., A. 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 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., A. 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. 1 Mid -ventral apophysis of metatarsus I triangular (Fig. 69), knob-like ( Fig.  128), or absent (Fig. 333)  Tibia I spines arranged along the distal most retrolateral aspect of the article, and/or with prolateral spines arranged in one or two rows along the prolateral surface of tibia I (Fig. 69)  Tibia I spines slightly behind (proximal) the distal most retrolateral aspect of the article, prolateral spines arranged in a single row along the medial prolateral surface of tibia I. Numerous distal tibia I spines (TSrd) offset slightly proximal from the distal margin (Fig. 175)  Rastellum with a single spine offset retrolaterally (Fig. 189)  Sternum as wide as it is long, appears round and raised (Fig. 256)  Lightly colored carapace and abdomen, abdominal striping reduced comprising a set of light distinct bands, found in western Nevada (Fig. 120) ....A. pennjillettei -Carapace and abdomen usually darkly pigmented, abdomen with distinct heavy, mottled pattern of stripes (e.g., Fig. 106 Diagnosis. Like all Atomarius Sibling Species Complex males, A. atomarius can be diagnosed by virtue of having a sharp triangular metatarsal mating apophysis and four or more TSrd spines arranged linearly without overlapping . Male pedi-palp morphology relatively homogenous, comprising a slender palpal tibia that lacks a retrolateral spine patch (Fig. 74) and a simple unserrated bulb (Fig. 75). Females can be distinguished by having a secondary spermathecal bulb that extends below the horizontal plane of the lateral spermathecal base . Specimens in life have a mottled abdominal coloration pattern and tend to have carapace and legs with an orange tint (Figs 79-81) whereas other sympatric species (e.g., A. icenoglei) have darker leg and carapace coloration. Aptostichus atomarius females also tend to have a narrower sternum than A. icenoglei, however, this difference is very subtle and not quantifiable. Generally, individuals of this species are difficult to distinguish from other Atomarius Sibling Species Complex members on the basis of morphological features alone but can be diagnosed on the basis of a set of unique mtDNA site substitutions (see Bond and Stockman 2008). The distribution of A. atomarius is restricted to Southern California and does not overlap with other closely related sibling species (Map 2).
Distribution and natural history. Aptostichus atomarius is widely distributed throughout southern California and has been collected in San Diego, Orange, Riverside, San Bernardino, Inyo, Los Angeles, Ventura, and San Luis Obispo counties (Map 2). Populations to the south are found throughout the Peninsular Ranges including the San Ysidro and Jamul Mountains, bounded to the east by the Laguna Mountain range. Moving northward in the Peninsular Ranges populations are abundant in the San Jacinto and Santa Ana Mountains. Like species described for the closely related genus Apomastus Bond and Opell 2002, A. atomarius was probably once more extensively distributed across the Los Angeles Basin but is now restricted to the steep ravines of the surrounding San Gabriel and Santa Monica Mountains and the Palos Verdes Hills along the coast. Populations to the north are distributed throughout the northeast extent of the Transverse Ranges bounded by the San Bernardino Mountains but extending northward along the coast in the Santa Ynez Mountains into the southernmost extent of the Coastal Ranges. A couple of morphologically similar specimens, collected from Tulare County in the southern extent of the Sierra Nevada Mountain range, are considered herein to be A. atomarius but will likely be removed to a separate species at a later date. From a geographical perspective it would seem reasonable to include these specimens in the A. dantrippi hypothesis, however, A. dantrippi individuals are distinctive morphologically and are considered a separate cohesion species at this time. Future molecular studies will likely resolve the placement of these outlier populations but until such data are available they are retained here as A. atomarius on the basis of their morphological affinity with all other specimens. Finally, a number of additional allopatric populations are found out on the Channel Islands and have likely been separated for a considerable amount of time but are likewise retained herein as A. atomarius until additional character systems can be employed to resolve their placement (or allocation to a new species).
The DM produced for this species (Map 3) shows the areas with the highest probability of predicted occurrence to be in the Peninsular and southernmost extent of the Transverse Ranges (around the Los Angeles Basin). Many of the populations in the desert to the east and the Coastal and Sierra Nevada Ranges to the north fall in areas predicted to have a very low probability of occurrence in the model, likely reflecting the fact that this species delineation comprises > 1 species.
In the Peninsular, Transverse, and Coastal Ranges, A. atomarius is restricted primarily to the California Coastal Range Open Woodland-Shrub-Coniferous and California Coastal Chaparral Forest and Shrub ecoregions. Vegetation types comprise mainly mixed chaparral, chamise-redshank chaparral, and coastal scrub. Male dispersal times are widely varied across specimens examined as part of this study. However, the majority of males were collected during the late fall to winter months of October through to March. Occasionally specimens have been collected during the summer months of June and August but these represent very rare occurrences. Females construct burrows that are typical for members of the genus.
Conservation status. Aptostichus atomarius is widespread, abundant, and appears to thrive in moderately developed suburban areas throughout Southern California and thus is likely secure.
Species concept applied. Morphological. Aptostichus atomarius presents a number of problems with respect to species delineation and diagnosis and thus is delineated herein as a single morphologically distinguishable species with the expectation that it will be further divided at some point in the future on the basis of other criteria.
Remarks. The type locality of A. atomarius as "San Bernardino" coupled with the relatively similar morphology of A. atomarius and A. icenoglei females contributes some uncertainty to the identity of the species attributed to this name. That is, without a more specific locality or the ability to recover DNA for molecular studies from the type specimen, the A. atomarius type could potentially be either. However, as discussed in the diagnosis the sternum of A. icenoglei is subtlety narrower than that of A. atomarius. Based on my morphological and molecular surveys of many specimens of both species I feel confident that A. atomarius, as described by Simon, is correctly attributed to the specimens I have identified as such. Second, as mentioned above, the molecular data indicate that the A. atomarius specimens listed in the material examined section above likely comprise a number of additional species. However, the data and sampling currently on hand are, in my opinion, insufficient to further split this complex into species lineages. Future studies of the entire Atomarius species complex will address these issues. GenBank accessions. 16S-tRNAval-12S: EU569930-EU569939, EU570008-EU570021, EU570028-EU570031, JX103357-JX103366; 18S (partial)-ITS1-5.8S-ITS2: EU569888-EU569892.

Aptostichus stephencolberti
Distribution and natural history. Aptostichus stephencolberti is distributed throughout the coastal dune habitats of San Francisco, San Mateo, Santa Cruz, and Monterey Counties with a single population recorded from San Luis Obispo County (Map 4). Individuals are found in relatively deep burrows on the steep faces of sand dunes and at the base of coastal vegetation. Burrows comprise a thick silk lining and are covered by a very cryptic trapdoor constructed of silk and sand. Dune habitats disturbed by high concentrations of the invasive Carpobrotus edulis (ice plant) tend to lack A. stephencolberti individuals entirely. The DM for this species (Map 5) follows closely with the known distribution to include the southernmost-recorded locality for the species. Wandering males (2) have been collected in August and September; two males have been collected from burrows in January.
Conservation status. Aptostichus stephencolberti is generally abundant at localities along the California coast (Map 4). However, the species is particularly vulnerable to invasive plant species (e.g., ice plant, Carpobrotus edulis) and is highly structured  genetically across its distribution thus many populations contain unique alleles . Moreover, divergent populations at the southernmost extent of the distribution comprise very few individuals (specimens are rare, despite extensive searching). Consequently, I would consider this species to be apparently secure or vulnerable, contingent upon future delimitation of divergent lineages as nominal taxa.
Species concept applied. Cohesion. Aptostichus stephencolberti is considered to be ecological non-interchangeable from other closely related lineages-it is restricted to coastal dune habitat and has psammophilic features (e.g., lighter coloration). the east by the Salinas River Valley (SRV). The ecoregion is characterized as California Coastal Chaparral Forest and Shrub. As discussed in Bond and Stockman (2008) the DM (Map 7) predicts the areas with the highest probability of occurrence in the regions east of the SRV, with the valley likely serving as a barrier to dispersal. The few male specimens known were collected during the late fall through winter months (October-December, February), with one specimen collected in July that molted to the final adult stage a month later in August. Female specimens are frequently found on shaded, damp steep banks and road cuts throughout the region. Burrows are generally shallow comprising a white silken lined retreat, covered by a thin silk-soil trapdoor. Conservation status. The conservation status of A. angelinajolieae is likely classified as secure because it is widespread, abundant, and appears to thrive in moderately developed residential areas.

Aptostichus angelinajolieae
Species concept applied. Cohesion. Aptostichus angelinajolieae is considered a cohesion species on the basis of it exclusivity as a lineage in DNA studies and lack of genetic exchangeability (gene flow) with other Atomarius Sibling Species Complex lineages as a consequence of the SRV barrier to gene flow.
Distribution and natural history. Aptostichus miwok is distributed throughout the geographically disjunct coastal dune habitats of Del Norte, Humboldt, Mendocino, Sonoma, Marin, and San Francisco counties of central and northern California (Map 8). A single inland specimen (Humboldt) is placed with this species on the basis of the molecular data. The DM for A. miwok (Map 9) corresponds closely to the known occurrences with the largest areas of high probability of occurrence in the more northern extent of the species' distribution. The model indicates that inland localities may be suitable despite the paucity of known inland populations. The habitat requirements and general burrow structure is very similar to that described for A. stephencol- berti. All populations are located in the coastal dune habitat. Males have been collected in the months of September, November, January, March, and April.
Conservation status. Aptostichus miwok is abundant and widespread across its distribution and thus is likely classified as secure.
Species concept applied. Cohesion. Aptostichus miwok is considered to be ecological non-interchangeable from other closely related lineages-it is restricted to coastal dune habitat and has psammophilic features (e.g., lighter coloration).
Remarks. The recognition of A. miwok by Bond and Stockman (2008) as a species renders one of the A. stanfordianus lineages paraphyletic (Fig. 28). While this is somewhat problematic, I have chosen to uphold this decision because of the adaptive diversity contained within the nominal A. miwok lineage and apparent lack of both genetic and ecological interchangeability between this lineage and A. stanfordianus. Type material. Specimens described by Smith (1908) and deposited in the "Entomological Museum of Stanford University" have long been considered to be lost (e.g., Coyle 1974 Smith's (1908) drawings and documentation of locality data for the species, I am reasonably confident that designation of this specimen as the neotype is consistent with what is known of the former name-bearing type. The locality from which the neotype was collected is ~20km to the west of Smith's type locality, described as "Stanford Estate" near Stanford University; considerable development has occurred in this region over the last century and specimens from the direct vicinity of Stanford University are not available. Smith noted collecting specimens, for the series on which A. stanfordianus was described, from points to the west below ~121m in elevation. The carapace length and width for the neotype are noted in the variation section below (enclosed in brackets [ ]) and a complete set of measurements are archived in the Dryad Data Repository at doi: 10.5061/dryad.3b95n; specimen coloration is similar to that illustrated in figure 110. As noted above, GenBank accession numbers EU570032 (12S-tRNA-val-16S) and EU569895 (18S (partial)-ITS1-5.8S-ITS2) are attributed to this specimen. Diagnosis. Individuals of this species are particularly difficult to distinguish morphologically (Figs 106-112) from A. angelinajolieae specimens but were diagnosed on the basis of a unique set of mtDNA nucleotide substitutions documented in Bond and Stockman (2008; but see discussion below). The species is separated geographically from A. angelinajolieae by the Salinas River Valley and is found only in inland habitats whereas A. miwok is found in coastal dunes. Aptostichus miwok is much lighter in color than A. stanfordianus (Figs 106,110,113,114).
Distribution and natural history. Aptostichus stanfordianus is distributed widely throughout the Coastal Ranges of central California, bounded to the east by the Central Valley (Map 10). The greatest concentration of populations appears to be centered in the Santa Cruz Mountains and the Diablo and Gabilan Ranges with additional populations in the Sonoma and Howell Mountains to the north. The DM for A. stanfordianus (Map 11) corresponds closely to the known distribution of the species with the exception of areas of high probability of occurrence that overlaps considerably with the predicted distribution of A. angelinajolieae but likewise is separated from this species by an area of low probability of occurrence across the Salinas Valley. Also, populations found on the eastern facing slopes of the Coastal Range are found in areas of a low probability of occurrence. Like A. angelinajolieae, this species is found along damp, north-facing steep banks and road cuts. Populations of this species are found in a number of ecoregion types including California coastal chaparral and shrub, coastal range open woodland and shrub, coniferous forest, coastal steppe, mixed forest and redwood forest. Males have been collected early fall through late winter (September-March).
Conservation status. Aptostichus stanfordianus is widespread and abundant throughout its distribution and thus is likely classified as secure. Nevertheless, its dis-tribution throughout the San Francisco Bay region has likely resulted in its extirpation from many localities; specimens from Smith's (1908) type locality have not been collected in many years.
Maps 10, 11. Aptostichus stanfordianus Smith, 1908. 10 distribution of known specimens 11 predicted distribution; cooler colors-blue shades-represent areas of high probability of occurrence, warmer colorsyellow and orange shades-represent areas of low probability of occurrence. Bond and Stockman 2008). Based on the evidence available at the time, Bond and Stockman (2008) considered the two A. stanfordianus clades to comprise a single ecologically interchangeable species; that is, the two sister lineages (no longer retained as such in our more recent analysis, see comments below) overlapped in their predicted distributions and thus were ecologically equivalent (not adaptively diverged).

Species concept applied. Cohesion (sensu
Remarks. Although cohesion species concept criteria were applied in the formulation of this species the subsequent addition of molecular data for more populations seems to have clouded the picture. The new data indicate that A. stanfordianus, as currently delineated, may comprise at least two distinct, unrelated lineages, within the Atomarius Sibling Species Complex (Fig. 28). As such the current diagnosis and delimitation will require reconsideration in the future if these two lineages remain genealogically exclusive under further scrutiny. Etymology. The specific epithet is patronym in honor of Daniel Tripp in recognition of the Tripp family support of biodiversity research and scholarship at East Carolina University, Greenville, North Carolina.
Diagnosis. Morphological differences, particularly secondary sexual characteristics , between A. dantrippi and other geographically proximate species of the Atomarius Sibling Species Complex are subtle. First, A. dantrippi male and female individuals are found only in far inland habitats but tend to be much lighter in coloration (Fig. 118) than other inland species (A. atomarius, A. angelinajolieae, and A. stanfordianus) and thus superficially resemble coastal dune species A. miwok and A. stephencolberti. Spermathecae have a very elongate lateral lobe that is directed anteriorly whereas the secondary lobe in other taxa is directed more posterior-laterally (Fig.  119). The species is restricted in distribution to Kern County (California) and does not overlap with any closely related Atomarius Sibling Species Complex taxa (Map 12).
Variation ( GenBank accessions. 16S-tRNAval-12S: EU569911, EU569912, JX103294-JX103300. Distribution and natural history. Aptostichus dantrippi as currently defined is distributed primarily throughout Kern County with a few specimens taken from the Temblor Range along the western border with San Luis Obispo County (Map 12). The distribution essentially "rings" the ranges that bound the southernmost extent of the Central Valley and includes the San Emigdio, Tehachapi, and Greenhorn Mountains. The species is mostly restricted to the south valley alluvium and basins, Sierran steppe and mixed and coniferous forests ecoregions of Kern County (Map 12). The only known male specimen was collected during late fall (October). The DM prediction corresponds closely to the known distribution but predicts a high probability of occurrence along the Transverse Ranges. Conversely, the Bakersfield locality along the banks of the Kern River is located in an area of relatively low probability of occurrence; it is likely that this population is relictual given the nature and paucity of the habitat at this location.
Conservation status. The status of A. dantrippi appears to be relatively secure; the species is widespread and abundant. However, the type locality, along the banks of the Kern River, in Bakersfield, California is disturbed and has been highly impacted by proximal development of the last quarter century and thus the species is likely to be locally vulnerable.
Species concept applied. Morphological/phylogenetic. As noted below the molecular data support the hypothesis that these populations constitute a single evolutionary lineage that has subtle morphological differences that distinguish it from sibling species.
Remarks. I have included additional Kern County specimens from the El Paso Mountain and Tehachapi Mountains as part of the A. dantrippi species hypothesis. Specimens from both of these outlying populations appear to be mostly consistent, morphologically, with those specimens collected from the type locality with the exception of the two specimens collected from Water Canyon; they appear to have more prominent abdominal markings and a slightly darker cephalothorax than the type specimens. Molecular data to date obtained from specimens collected just west of the Tehachapi's corroborate the hypotheses that these populations be included as A. dantrippi despite their somewhat divergence coloration.
Etymology. The specific epithet is a patronym in honor of Mr. Penn Jillette, freethinker and advocate of scientific skepticism.
Diagnosis. Males (Fig. 120) can be diagnosed from all known species of Aptostichus by having a unique spination pattern on the distal most aspect of tibia I consisting of a few elongate spines (TSrd 3-5) that do not overlap (Figs 121-125). This spination pattern is similar to A. atomarius (Figs 69-75); however, male A. pennjillettei individuals are smaller and much lighter in color (Fig. 120).
Variation ( Diagnosis. Males (Fig. 127) can be distinguished from all known species of Aptostichus by having a metatarsal I mating apophysis that forms a distinct knob . Females can potentially be recognized by having a large number of labial cuspules, > 8 that tend to form at least two distinctive rows. However, some Atomarius Sibling Species Complex individuals also have many labial cuspules but not forming two distinct rows.
Variation ( Diagnosis. Males (Fig. 134) can be distinguished having a distinctive row of spines on the prolateral surface of patella I (Figs 136, 138, 139). Females can be tentatively distinguished from all species, except some A. atomarius individuals, by having a large number of anterior margin denticles (ANTd= 8).
Variation ( v.1972 [AP544, 1juv, CAS]. Distribution and natural history. Aptostichus nateevansi is known primarily from Los Angeles County, Channel Islands of Santa Catalina and San Clemente (see comments below regarding the Alameda County specimen). The primary habitat is California coastal chaparral forest and shrub.
Conservation status. Few specimens of this species have ever been collected, and none within the last quarter century; it is known from only a few localities. The Catalina Island Conservancy manages most of Santa Catalina Island and the United States Navy owns San Clemente Island which may afford the species some protection. Nevertheless, I would consider the status of this species likely imperiled due to low abundance and rarity in collections.

Remarks.
Despite the geographical distance that separate the type locality and Alameda County, the anomalous specimen from the Sunol Regional Wilderness area is placed as part of the A. nateevansi species construct because the mating clasper and somatic morphology of the specimen is indistinguishable from those of other specimens. I have little doubt that this is a related, yet disjunct sister species (like A. chiricahua, below), but have chosen to conservatively wait until more specimens are available to set the Alameda County specimen aside as a separate species. Etymology. The specific epithet is a noun taken in apposition from the type locality, the Chiricahua Mountains of southeastern Arizona.

Aptostichus chiricahua
Diagnosis. Males can be diagnosed on the basis of a unique conformation of the tibia leg I, spination pattern which comprises numerous spines on the prolateral and distal surfaces (Figs 142-144). This spination pattern is most similar to the Channel Islands species A. nateevansi, however the A. chiricahua type specimen has considerably more spines, two rows, along the distal, prolateral aspects of the mating clasper tibia. A considerable geographic distance separates Aptostichus chiricahua and A. nateevansi. The geographical proximate species, A. edwardabbeyi, has dissimilar mating clasper morphology and has a distinct offset prolateral rastellar spine and thus is a Hesperus group species.
Variation. Known only from the type specimen. Description of female. Known only from male specimens. Material examined. Known only from the type material. Distribution and natural history. Aptostichus chiricahua is known only from a single specimen taken from the type locality in Arizona, Cochise Co., Portal (Map 1). Despite extensive collecting efforts in the area female burrows have never been observed. Based on the paucity of specimens, the species may be quite rare.
Conservation status. Undetermined but likely to be imperiled given its restricted distribution and rarity in collections.
Remarks. As noted above in the description of A. nateevansi, A. chiricahua has a mating clasper that is very similar to the California Channel Island species and thus may be closely related despite the disjunct distribution. Etymology. The specific epithet is a patronym in honor of Wendell Icenogle who has collected many of the Aptostichus types and has studied this group's natural history for many years. I am incredibly grateful to Wendell for his assistance, sage advice, patience, and friendship over many years; he has pointed out to me that he was collecting Aptostichus before I was born.

Aptostichus icenoglei
Diagnosis. Males (Fig. 146) can be diagnosed on the basis of a unique conformation of the tibia I mating apophysis and TSrd spination pattern (Figs 147, 149). The A. icenoglei tibial I apophysis (Figs 147, 149) is rectangular in shape and bears a distal spine. In all other Aptostichus species the tibial I apophysis is triangular, rounded, or absent, with the exception of A. cabrillo which has a similar rectangular apophysis (Fig.  160). A. icenoglei (Fig. 149) and A. cabrillo (Fig. 160) males can be differentiated on the basis of the TSrd spination pattern. The TSrd of A. icenoglei consists of no more than 3 non-overlapping spines (usually 2), whereas the TSrd of A. cabrillo is always greater than 4 overlapping spines. Female A. icenoglei specimens tend to be darker in coloration, larger (Cw > 5.50) and with fewer prolateral tibial spines on leg III (TBs < 4) than A. cabrillo (Figs 162, 164). Females are distinguished from the sympatric species A. hesperus by lacking contiguous sigilla (see that species' diagnosis) and A. cahuilla by virtue of its much larger size. Distinguishing female A. icenoglei (Fig. 151) and A. atomarius is problematic. Although their sampled distributions overlap, the sternum width to length ratio tends to be smaller in A. icenoglei (i.e., the sternum of A. icenoglei tends to be more narrow). Additionally, the lateral spermathecal base of A. atomarius is developed into a more distinctive auxiliary bulb that extends below (posteriorly) beyond, the lateral base. The secondary bulb of A. icenoglei is smaller and does not extend below the lateral base (Figs 152-155). As noted in the diagnosis of A. atomarius, A. icenoglei specimens in life tend to be much darker in coloration (Fig. 156).

Diego area (San Ysidro and Jamul Mountains and points north of the city). The DM (Map 15) indicates that considerable suitable habitat likely can be found in the areas surrounding San Diego and throughout the Santa Ana and San Jacinto
Mountains. Interestingly the model shows the Transverse Ranges to the north and west of the Los Angeles Basin to be an area of lower probability. Given genetic structuring in populations and diversity of habitat it may very well be likely that A. icenoglei as defined here comprises more than one species. Primary habitat types for this species include coastal chaparral forest and shrub and coastal range open woodland shrub and coniferous forest. Based on pitfall trap records, male dispersal is wide ranging (August-May), however, most wandering males at lower altitudes appear to be taken during the early winter months of November-January likely associated with the winter rains.
Conservation status. The status of this species is likely secure given how abundant it is in collections and how widespread it is geographically.
Species concept applied. Morphological/Phylogenetic. Remarks. Despite some subtle differences, female A. icenoglei specimens can be difficult to distinguish from A. atomarius; juveniles are very problematic; molecular data were used to place many specimens (adults and juveniles) collected over the course of this study. As discussed above, A. icenoglei as currently defined is found in a diversity of habitats across a considerable geographical range. The ~20 mtDNA sequences thus far collected for the species show considerable structuring that is consistent with cryptic species complexes hypothesized for other Aptostichus species. As such this taxon will likely be further divided at some point in the future on the basis of more detailed molecular and ecological studies. Etymology. The specific epithet is a noun taken in opposition taken from the type locality, Cabrillo National Monument, named in honor of Juan Rodríguez Cabrillo one of the first European explorers of the North American west coast.
Diagnosis. Aptostichus cabrillo most closely resembles A. icenoglei specimens and are differentiated from that species in its diagnosis (above).
Variation ( the coast. Failure to predict the occurrence of some of the outlying localities to the east may suggest that some of those specimens may have been misidentified-however, many of these are males that are easy to distinguish from A. icenoglei. Most male specimens have been collected during the summer months (June-September) with a few taken from pitfalls in October, November and January.
Conservation status. Because this species is generally rare in collections and restricted in distribution to an area that is highly impacted by development, I consider its status to be vulnerable.
Variation. Known only from the type specimen. Distribution and natural history. Aptostichus isabella is known only from a single specimen collected from the type locality (Map 1) in Kern Co., Piute Mountains; the habitat in the region is primarily classified as Sierran steppe, mixed coniferous forest.
Conservation status. Undetermined. Species concept applied. Morphological. Remarks. Although based on a single specimen, the morphology of this hypothesized species is significantly divergent, and represents an interesting form such that recognizing it as a nominal taxon is warranted. Etymology. The specific epithet is a patronym in honor of John Muir, one of the first European explorers to visit Yosemite Valley, and to subsequently fight for its preservation.

Aptostichus muiri
Diagnosis. Males of this species are similar to those of A. atomarius complex individuals, however A. muiri has fewer TSrd spines and a more slender palpal tibia . They can be distinguished from all other species of Aptostichus by their unique tibia I spination pattern. The female paratype of this species, collected not far from the type locality, is tentatively placed as a conspecific with the male holotype. This female specimen can be distinguished from A. atomarius by having fewer labial cuspules and a secondary spermathecal bulb (Fig. 173) that is much smaller than that observed for most putative A. atomarius specimens.
Variation ( Conservation status. The conservation status of this species is likely to be secure due to its abundance and widespread distribution; however, may be locally vulnerable (e.g., Sutter Butte locality).
Species concept applied. Morphological/Phylogenetic. Remarks. Originally thought to be rare, only a few specimens were originally known from the Hopland Field Station locality, collecting efforts in recent years have recovered considerably more specimens and have significantly extended the known distribution of the species. Diagnosis.  and male  A. hesperus can be distinguished from all other Aptostichus species by having posterior sternal sigilla that are positioned mid -ventrally and are either very closely positioned, or contiguous (Fig.  188). The sigilla of other Aptostichus species are distinctly separated and tend to be positioned more posteriorly. A longer palpal bulb length and greater PTw/PTl ratio (Figs 195,196) also help to distinguish this species from A. atomarius, A. cahuilla and A. icenoglei that potentially occur sympatrically with A. hesperus. All Hesperus group taxa have an offset rastellar spine (Fig. 189).
Descriptions. Described by Chamberlin (1919: 1-2 Chamberlin, 1919. 20 distribution of known specimens 21 predicted distribution; cooler colors-blue shades-represent areas of high probability of occurrence, warmer colorsyellow and orange shades-represent areas of low probability of occurrence. [AP692, 1♀, AUMNH]; NE Perris Reservoir, 33.8666 -117.1938 1 , 533m, USGS-BRD San Diego Sta. 1.ii.1999 [AP925, 1♂, CAS]; Hwy 79, ~6km S Beaumont, N facing slope small ravine, 33.87 -116.9963 1 , 655m, J Bond 19.i.1997 more prevalent throughout open woodland shrub habitat in the southwestern extent of San Bernardino County; the species has not been collected in the areas of higher probability to the south in San Diego County. Although a few males have been recovered from pitfall traps in the spring and summer, the majority of wandering males have been collected during late fall and winter months (October-February).
Conservation status. This species is relatively abundant across its range thus the conservation status of A. hesperus is likely secure.
Species concept applied. Morphological/Phylogenetic. Remarks. Aptostichus hesperus is one of the easier species to identify because of its unique sternal sigilla morphology and its range is relatively restricted in Orange and Riverside Counties. However, all male specimens collected as part of the USGS survey in the southernmost extent of the species distribution in Riverside County lack a foveal groove. Although this form seems anomalous, the fact that multiple individuals from a number of populations share it suggests that it may be a diagnostic feature that would set these populations aside as a separate species. However, I have conservatively included these specimens as part of the A. hesperus hypothesis until molecular data are available to confirm that these morphological distinct populations are an exclusive lineage. Types. Male holotype (MY3779) and three male paratypes (AP1279) from California, San Diego County, Anza-Borrego Desert State Park (ABSP), 0.4km N Hayden Spring, 32.71045 -116.11705 1 , 350m, coll. M. Hedin 14-15.x.2000; female paratype (AP675) from ABSP, along HWY 78 in wash by road, 33.13360 -11634083 1 , coll. J. Bond 12.xii.1998;deposited in AUMNH. Etymology. The specific epithet is a patronym in honor of the Hedin family, Marshal, Robin, Lars, and Molly.

Aptostichus hedinorum
Diagnosis. Males (Fig. 197) can be diagnosed on the basis of a unique conformation of the distal most spination pattern of tibia I, which consists of 2-3 long spines that typically do not overlap (Fig. 198). This spination pattern is most similar to A. icenoglei, however A. hedinorum males lack a rectangular mating apophysis, are lighter in coloration, have very light dorsal abdominal markings or lack markings altogether, and have a prolaterally offset rastellar spine.
Variation ( Etymology. The specific epithet is a noun in apposition taken from the Cahuilla Native American Tribal Group, which once resided in Southern California. Diagnosis. Males (Fig. 204) can be diagnosed on the basis of a unique conformation of the distal -most spination pattern of tibia I which consists of 5-9 short spines that are always overlapping (Figs 205, 208). This spination pattern is most similar to A. derhamgiulianii, however the retrolateral cymbium surface of A. derhamgiulianii bears a number of small, distinct spines, whereas that of A. cahuilla does not. Additionally, the MA4/MF4 ratio (Fig. 19) of A. derhamgiulianii is greater than that of A. cahuilla (i.e., the overall length of tarsus IV is greater for A. derhamgiulianii). Females can be distinguished from those of other known sympatric species of Aptostichus (A. icenoglei, A. hesperus, and A. atomarius) simply by their small size (Cl < 4.6). Additional features that distinguish females of this species from others that are closely related (A. hesperus and A. aguacaliente) is the presence of smaller sigilla that tend to be more widely spaced. Males can be further diagnosed on the basis of a greater PTw/PTl ratio (Fig. 23).
Variation ( Distribution and natural history. Aptostichus cahuilla is known from only from a few localities in Riverside County and one in southwestern San Bernardino County. Experience collecting this species indicates that it is found primarily in chaparral habi-Maps 23, 24. Aptostichus cahuilla Bond sp. n. 23 distribution of known specimens 24 predicted distribution; cooler colors-blue shades-represent areas of high probability of occurrence, warmer colors-yellow and orange shades-represent areas of low probability of occurrence. tat but is considerably less abundant than the species with which it is sympatric (e.g., A. atomarius, A. icenoglei, and A. hesperus).
Conservation status. The conservation status of A. cahuilla is likely to be considered imperiled; it is rare in collections, abundance is very low, and it is relatively restricted in distribution.
Species concept applied. Morphological/Phylogenetic. Etymology. The specific epithet is a noun in apposition taken from the name of the legendary surf break, "Killer Dana", that once graced the shore of Dana Point. The break was destroyed in the mid 1960's by the construction of the breakwater for Dana Point Harbor.

Aptostichus killerdana
Diagnosis. Males can be distinguished from other known related species of Aptostichus (e.g., A. cahuilla) by virtue of a unique tibia I TSrd spination pattern that comprises only a few spines (Fig. 210). In contrast, the spination pattern of A. cahuilla is formed of many overlapping distal spines. Females (Fig. 213) can be distinguished on the basis of having long median spermathecal stalks that do not curve as extensively and a median bulb that is larger (Fig. 214) than that of A. cahuilla; specimens also tend to have a larger number of labial cuspules (> 3).
Variation. Known only from the type specimen. Material examined. Distribution and natural history. Aptostichus killerdana is known only from the type locality in Orange County. The species was collected from a relatively low-lying, riparian habitat in the time interval from 1969-1971. Some point thereafter the area was developed and is now Monarch Beach Golf Links; the habitat was cleared and is now a golf course. Although classified as California coastal chaparral and scrub, photographs of the area prior to development seem to indicate that it was a relatively unique and pristine coastal riparian habitat. The location was also the southernmost known locality for Apomastus kristenae Bond, 2004, likewise a species that seems to have extirpated from the area. Extensive sampling in the low-lying areas around and above the golf resort has to date proven unsuccessful.
Species concept applied. Aptostichus killerdana is presumed extinct. Etymology. The specific epithet is a noun in apposition taken from the Serrano Native American Tribal group, which once resided throughout what are now the California counties of Riverside and San Bernardino.
Diagnosis. Males (Fig. 215) are easily distinguished from the other known sympatric species of Aptostichus, A. bonoi, by lacking spines on the ventral surface of tarsus I (Fig. 216). The TSrd spination of A. serrano (Fig. 216) is most similar to that of A. atomarius, however male A. serrano individuals can be distinguished by having a retrolaterally offset rastellar spine. Female A. serrano individuals can be distinguished from A. atomarius females by virtue of their smaller size and a rastellar configuration similar to that of the males. Male and females are both lighter in coloration and lack the distinct mottled striping of the non-desert species (Fig. 215).
Variation ( tal plate removed, cleared in trypsin, stored in microvial with specimen. General coloration. Carapace, legs, chelicerae, yellowish brown 10YR 5/4. Abdomen uniform pale brown 10YR 6/3, markings similar to males; recently collected specimens slightly darker in coloration. Cephalothorax. Carapace 4.05 long,3.60 wide, generally glabrous with light thin setae; generally smooth surface, pars cephalica moderately elevated. Fringe lacks setae. Foveal groove deep, slightly procurved. Eye group slightly elevated on low mound. AER slightly procurved, PER slightly recurved. PME-AME subequal diameter. Sternum widest at coxae II/III, moderately setose, STRl 2.63, Conservation status. The conservation status of A. serrano is considered to be secure because it is widespread and found in areas that are generally well protected (e.g., Joshua Tree National Park Etymology. The specific epithet is a noun in apposition taken from the Agua Caliente Band of the Cahuilla Native American Tribal group of Palm Springs, California. Diagnosis. Males (Fig. 220) of this species can be diagnosed on the basis of a unique conformation of the spination pattern of tibia I which consists of 3-5 long spines, sometimes overlapping, and by having a low tibia I apophysis that bears a spine (Figs 221, 223). Females can be distinguished by having a median spermathecal stalk that is sinuous and 8-9 times longer than wide (Figs 225-227). Males and females have features that are similar to A. hesperus: large sternal sigilla that are midventrally positioned and a rastellum that consists of at least 6 enlarged spines with one offset prolaterally. However, A. aguacaliente sigilla are not contiguous and this species' cephalothorax and abdominal coloration is very light (Figs 220, 224). Aptostichus hesperus coloration is much darker with a more distinctive abdominal banding pattern. Aptostichus aguacaliente males also tend to be smaller in size than A. hesperus males; however there is no discontinuous size difference between females of these two species.
Variation (10). Cl 5. 5.82±0.19;4.87±0.19;3.61±0.15;3.10±0.12;1.13±0.05;0.69±0.02;14.40±0.53;6.80±0.33;8.70±0.52;4.10±0.28. Material examined: United States: California: Imperial Co.: 12.9km SE Niland,between Coachella Canal & Railroad,26m,W Icenogle,T Valley (Map 27). County records comprise San Bernardino, Riverside, and Imperial. The DM (Map 28) appears to considerably overpredict the occurrence of A. aguacaliente in areas to the west in Riverside County and into eastern San Diego County but Maps 27, 28. Aptostichus aguacaliente sp. n. 27 distribution of known specimens 28 predicted distribution; cooler colors-blue shades-represent areas of high probability of occurrence, warmer colors-yellow and orange shades-represent areas of low probability of occurrence. otherwise corresponds to the known distribution. Based on the DM, it was likely that the species was more widely distributed throughout the Imperial Valley and areas to its north prior to the extensive agricultural development that has occurred in the region. Males appear to wander in the late winter, early spring, January-February. Female burrows can be detected during the winter months often after soaking rains when individuals extend their burrow leaving a small mound of soil at the burrow entrance.
Conservation status. The conservation status of A. aguacaliente is likely classified as secure. However, the species is presumed to be extirpated from the type locality (Windy Point, Palm Springs) as a consequence of recent construction of a golf course and housing development.
Species concept applied. Morphological/Phylogenetic. Etymology. The specific epithet is a noun in apposition taken from the Chemehuevi Band of the Southern Paiute Native American People.
Diagnosis. Males (Fig. 228) can be diagnosed from all known species of Aptostichus by having many spines on metatarsus I that form two distinct rows and by having a linear row of multiple spines on the prolateral surface of tibia I (Figs 230-234). Males of all other known species of Aptostichus have a single row of very few spines on metatarsus I and/or have very many spines dispersed across the prolateral surface of tibia I or have only three spines composing the row.
Distribution and natural history. Aptostichus chemehuevi is known from only three Mojave Desert localities in San Bernardino County (Map 25); despite extensive collecting efforts at the type locality females have never been collected thus little is known of this species natural history. Males appear to disperse during the winter months, November-February. This species is considered to be syntopic with A. elisabethae.
Conservation status. Although little information is available, the conservation status of A. chemehuevi is likely imperiled (also see discussion of A. elisabethae) given its paucity of specimens in collections and distribution restricted to three locations.

Aptostichus sarlacc
Etymology. The specific epithet is a noun in apposition taken from the fictional creature in George Lucas' science fiction saga, Star Wars: Return of the Jedi.
Diagnosis. Males can be distinguished from other known closely related species of Aptostichus (e.g., A. cahuilla, A. aguacaliente) by having a long curved metatarsus IV relative to femur IV length and by having an abdomen devoid of any dorsal markings (Fig. 236). This species can be distinguished from geographical proximate members of the Simus species group, with similarly long fourth tarsi and by having a longer, more slender palpal tibia (Figs 241, 242). The distribution of A. sarlacc is distributed considerably further to the north of the aforementioned Hesperus species group taxa.
Description of male holotype. Specimen preparation and condition. Specimen collected dead from pitfall trap, preserved 70% EtOH. Coloration likely faded. Pedipalp, leg I left side removed, stored in vial with specimen. General coloration. Carapace, chelicerae, legs strong brown 7.5YR 4/6. Abdomen uniform very pale brown, lacking distinct dorsal markings (e.g., paratype coloration pattern, Fig. 236). Cephalothorax. Carapace 3.41 long, 2.95 wide, glabrous with only sparse thin black setae, stout black bristles along fringe; surface smooth, pars cephalica elevated. Fringe, posterior margin with black bristles. Foveal groove deep, moderately procurved. Eyes on low mound. AER slightly procurved, PER slightly recurved. PME, AME subequal diameter. Sternum moderately setose, STRl 1.90, STRw 1.62. Posterior sternal sigilla small, positioned towards lateral margin, anterior sigilla pairs small, oval, marginal. Chelicerae with distinct anterior tooth row comprising 5 teeth, posterior margin with patch of very small denticles. Palpal endites with patch of small cuspules on proximal, inner margin, labium with 3 small cuspules, LBw 0.60, LBl 0.29. Rastellum consists of 6 stout spines, 2 offset prolaterally. Abdomen. Setose, heavy black setae intermingled with fine black setae. Legs.   Description of female. Known only from male specimens. Material examined. Known only from the type material. Distribution and natural history. Little is known about this species; it is very rare in collections and is only known from two specimens collected in the Mojave Desert in Inyo, Kern and San Bernardino Counties (Map 29).
Conservation status. This species is rare in collections and is known from only two localities; its status is considered imperiled.

Aptostichus derhamgiulianii
Diagnosis. Males of this species can be distinguished by having the following unique combination of features: a wide sternum, a rastellum with a single offset retrolateral spine, PME's smaller in diameter than AME's, multiple TSrd spines that overlap (Figs 244,247,248), and spines on the retrolateral surface of the cymbium (Figs 246,248). The overlapping TSrd spination pattern is similar to that of A. cahuilla, however, the spines on tibia I appear to be distributed more along the distal ventral surface in A. derhamgiulianii than A. cahuilla.
Distribution and natural history. Aptostichus derhamgiulianii is known from only a few male specimens, two of which were collected from pitfall traps during December (the other July), from sand dune habitats of the eastern foothills and ranges of the Mojave Desert (Map 29) in Inyo and Mono Counties.
Conservation status. This species is rare in collections and is known from only a few localities; its status is considered imperiled.
Distribution and natural history. Aptostichus mikeradtkei is distributed primarily along the coast in San Diego County (Map 30); the primary habitat type where it has been collected is characterized as coastal chaparral and shrub. Males appear to disperse early through mid-late winter during November-February. The DM for the species indicates that its distribution likely extends further up the coast and into Orange County.
Conservation status. Based on its abundance and relatively large number of populations sampled, the conservation status of A. mikeradtkei is likely secure.
Diagnosis. Males can be diagnosed on the basis of a unique conformation of the retrolateral distal-most spination pattern of tibia I, which comprises 8-10 short overlapping spines (Fig. 263). This spination pattern is most similar to A. cahuilla, however A. anzaborrego males are lighter in coloration, have very light dorsal abdominal markings (Fig. 262), and have numerous spines on the prolateral surface tibia and patella I (Fig. 264).
Diagnosis. Males can be differentiated from all other Aptostichus species on the basis of a unique conformation of the retrolateral distal-most spination pattern of tibia I, which comprises 3-6 spines arranged in a distinct cluster, a low rounded metatarsal mating apophysis that bears a single strong spine, and a convex shaped (curved) tarsus (Figs 266,269,272); all other known species lack this combination.
Variation ( Conservation status. Aptostichus simus is generally abundant at some localities along the California coast but has been almost entirely extirpated from many beaches in Southern California. For example, the species is very rare at the type locality, Silver Strand State Beach. Moreover, the species is particularly vulnerable to invasive plant species (e.g., ice plant, Carpobrotus edulis) and is highly structured genetically across its distribution thus many populations contain unique alleles (Bond et al. 2001). Consequently, I would consider this species to be vulnerable or imperiled due to its low abundance at many localities and extreme structuring.
Species concept applied. Morphological/Phylogenetic. Remarks. As discussed by Bond et al. (2001) the species hypothesis presented here likely represents 2-3 additional species, however, further work is needed before we fully understand the composition and limits of this taxon.  (Figs 285,286,288,289,291), darker coloration (non-desert adapted). The long leg I ventral tibial spine arrangement (Fig. 291) is similar to A. elisabethae, however, the palpal embolus of A. satleri is serrated whereas A. elisabethae is not. Aptostichus fornax, A. lucerne, and A. elisabethae are all much lighter in general coloration and lack distinct abdominal markings; A. satleri is much darker and has distinct chevron markings.
Description of male holotype. Specimen preparation and condition. Specimen collected from pitfall trap, preserved in 80% EtOH; legs III, IV removed, stored as tissues. Coloration in generally pristine condition. Pedipalp, leg I left side removed, stored in vial with specimen. General coloration. Carapace, chelicerae, dark brown 10YR 3/3. Abdomen brown 10YR 5/3, with distinct chevron markings. Cephalothorax. Carapace 4.60 long, 3.76 wide, lightly hirsute; stout black bristles along fringe; surface smooth, pars cephalica elevated. Fringe, posterior margin with black bristles. Foveal groove deep, recurved. Eyes on low mound. AER slightly procurved, PER slightly recurved. PME, AME subequal diameter. Sternum moderately setose, STRl 2.53, STRw 2.17. Posterior sternal sigilla small in size, widely separated, anterior sigilla pairs small, oval, marginal. Chelicerae with distinct anterior tooth row comprising 4 teeth, posterior margin with patch of small denticles. Palpal endites, labium lack cuspules, LBw 0.68, LBl 0.51. Rastellum consists of 10 stout spines not on prominent mound. and lacks the distinct abdominal markings (Fig. 292) of A. satleri. Females can be distinguished by having a sternum that is almost as long as it is wide and a rastellum composed of at least 8 large spines.
Distribution and natural history. Aptostichus elisabethae is known from Mojave Desert habitat at two localities in San Bernardino and Inyo Counties (Map 33). Based on limited pitfall trap data males appear to disperse November-February. The habitat and terrain at the type locality, Pisgah Crater, is the most extreme I encountered for any Aptostichus species. The Pisgah Crater locality is the site of a young volcanic cinder cone from which basaltic lava flows once extended for a considerable distance out from the vent source (Fig. 6). Female burrows, during winter months are visible by way of small soil mounds at the burrow entrance. Like other species, we presume that these mounds are formed when individuals extend their burrows during the rainy reason. Despite observing a number of "mounds" at the type locality during one collecting expedition in January of 1997, I was only able to collect two specimens from their burrows. Burrows were deep (15-20 cm) and unusually complicated with numerous side chambers and long horizontal below ground extensions that were often >10cm in length.
Conservation status. The conservation status of A. elisabethae would likely be considered vulnerable or imperiled; it is rare in collections, abundance is low, and it is relatively restricted in distribution (see comments below regarding Inyo County locality). The type locality is the site of a quarry (not presently active) where hectorite and volcanic cinders are mined.
Species concept applied. Morphological. Remarks. I have included the single specimen from Inyo County as part of the A. elisabethae hypothesis. Although this specimen is similar to A. elisabethae it is sufficiently different to lead me to believe that if more specimens were available it would likely be considered a separate species. However, at this time I have conservatively decided to group these specimens as a single species. The female paratype, the only known female specimen collected for the species has very lightly sclerotized spermathecae and as such may not be fully mature. Etymology. The specific epithet is a noun taken in apposition and refers to the hot climate in which this species is found. Fornax is a southern constellation; the name is Latin for furnace. In Roman mythology Fornax is the goddess of the hearth.
Diagnosis. Males can be distinguished by a palpal tibia with a retrolateral patch of small spines and at least one large, stout spine (Fig. 303, 302) and numerous spines on the retrolateral surface of tibia II; A. elisabethae lacks the palpal spine and tibia II retrolateral spines. The enlarged palpal spine is shared by a number of Sierra species group taxa; however, these species lack the proximal -ventral metatarsus I excavation that differentially characterizes A. fornax. Aptostichus fornax specimens lack the serrated embolus of other Simus group species (A. simus, A. lucerne, A. satleri).
Variation. Known only from the type specimen. Material examined. Known only from the type material. Distribution and natural history. Known only from the type locality in Inyo County, characterized as Mojave Desert habitat.
Conservation status. The conservation status of A. fornax is likely to be imperiled given its very restricted distribution in Death Valley National Park and paucity of specimens collected.
Species concept applied. Morphological. Diagnosis. Males can be distinguished by having long ventral spines on tibia I like those of A. elisabethae (Figs 304,305,308,309,310). However, the tibia I prolateral spination is denser (TSp 17-19 vs. 8-16 in A. elisabethae) and the embolus of A. lucerne is serrated (Fig. 306), whereas that of A. elisabethae is not.
Variation ( Distribution and natural history. Aptostichus lucerne is known from only the two male type specimens collected from the type locality in San Bernardino, characterized as Mojave Desert habitat.
Conservation status. The conservation status of A. lucerne is likely to be critically imperiled or presumed extinct. The species has not been seen since the type specimens were collected in 1957. Efforts to collect A. lucerne over the past decade, from the putative type locality, have proved unsuccessful; the area has been highly impacted by development.
Species concept applied. Morphological. Remarks. The locality label of the type specimens is somewhat dubious, labeled only as "Deadman Point, San Bernardino", and thus requires collecting of more specimens to confirm that the Apple Valley junction determination as the type locality is correct. terior two pairs noticeably more slender than posterior pairs. Leg I 12.55 long. Tarsus I with 7 trichobothria arranged in staggered row, distal aspect of row interspersed with setae. Legs I, II with light scopulae on tarsus, metatarsus; light scopulae on distal aspect tarsus legs III, IV. PTLs 30, TBs 7. Rudimentary preening comb on retrolateral distal surface, tarsus-metatarsus joint, of metatarsus IV; well developed, wide preening comb on leg III. Spermathecae. 2 short, heavily sclerotized, simple spermathecal bulbs; basal extension small (Fig. 315).
Distribution and natural history. Known only from the type locality in the Covington Flat area of Joshua Tree National Park (Map 33). The habitat is higher altitude Mojave Desert and is considerably more vegetated than lower altitude areas. Based on the limited data available, males disperse during late fall through early winter (September-November).

Aptostichus fisheri
Etymology. The specific epithet is a noun in apposition taken from the type locality, Cajalco Canyon.

Diagnosis.
Male and female A. cajalco can be diagnosed from all other Simus group species by having a round sternum that is approximately as wide as it is long; all other species have a sternum that is more typical (widest at coxae III-IV junction).
Description of male holotype. Specimen preparation and condition. Specimen collected from pitfall trap, preserved in 80% EtOH. Coloration in good condition. Pedipalp, leg I left side removed, stored in vial with specimen. General coloration. Carapace, chelicerae, legs yellowish red 5YR 4/6. Abdomen uniform brown 7.5YR 4/3, distinct Species concept applied. Morphological. Conservation status. As a consequence of its very restricted distribution and apparently low abundance the conservation status of A. cajalco would likely be characterized as imperiled.
Etymology. The specific epithet is a noun taken in apposition from the location of the type locality in the Sierra Nevada mountain range.
Diagnosis. All known male specimens of the Sierra species group can be distinguished from all other species of Aptostichus by virtue of having a long slender metatarsus I which lacks a ventral/proximal excavated area. Aptostichus sierra males can be distinguished from others in the Sierra species group by virtue of their large size, by having a broader sternum, and unique leg I spination pattern (Figs 333,334,336).
Variation. Known only from the type specimen. Description of female. Known only from male specimens. Material examined. Known only from the type specimen. Distribution and natural history. Aptostichus sierra is known only from the type specimen from Fresno County, collected in a pitfall trap in September. The habitat type is characterized as Sierran Steppe, Mixed Coniferous Forest, and Alpine Meadow.
Conservation status. The conservation status of A. sierra is likely to be characterized as imperiled due to its rarity and restricted distribution.
Species concept applied. Morphological. Remarks. Despite extensive searching in the areas around the type locality over the past decade, I have been unable to recover a single A. sierra specimen. This species is either very rare or I have been unable to pinpoint its exact microhabitat.
Diagnosis. Male of this species can be distinguished from others in the Sierra species group by their elongate sternum, strongly curved tarsus and unique tibia I prolateral spination pattern comprising > 31 spines.
Description of male holotype. Specimen preparation and condition. Specimen presumed to have been collected from pitfall trap, preserved in 70%EtOH. Coloration faded; abdomen extremely faded, collapsed. Pedipalp, leg I left/right side removed, stored in vial with specimen. General coloration. Carapace, chelicerae, legs strong brown 7.5YR 4/6. Abdomen uniform light brown 7.5YR 6/3, with mottled chevron striping. Cephalothorax. Carapace 5.31 long, 4.00 wide, generally glabrous with very light white setae intermingled with few thin black setae, stout black bristles along fringe; surface smooth, pars cephalica elevated. Fringe, posterior margin with black bristles. Foveal groove deep, strongly re-curved. Eyes on low mound. AER slightly procurved, PER slightly recurved. PME, AME subequal diameter. Sternum moderately setose, STRl 3.53, STRw 1.88; very thin. Posterior sternal sigilla small, positioned marginally, not contiguous, anterior sigilla pairs very  Etymology. The specific epithet is a patronym in honor of the American photographer and photojournalist Dorothea Lange (1895-1965); best known for her photo documentation work for the Farm Security Administration during the American Great Depression.
Diagnosis. Aptostichus dorothealangeae can be distinguished from all other species by having the characteristics described for all Sierra group species in the diagnosis of A. sierra and lacking a strongly curved tarsus I and by having a TSp spination pattern that is offset proximally (Fig. 344) Etymology. The specific epithet is a patronym in honor of labor and civil rights leader César Chávez .
Diagnosis. Male of A. chavezi can be distinguished from all other Sierra group species on the basis of a unique tibia I spination pattern that is most similar to that of its hypothesized and geographically proximate sister species A. dorothealangeae. Aptostichus chavezi males can be differentiated from A. dorothealangeae males by having a far greater number of spines on the prolateral surface of tibia I ( Fig. 348; 26 vs. 12-16). Females of A. chavezi and A. dorothealangeae are very similar in appearance, however, A. chavezi specimens are, on average, larger (Cl 5.28 vs. 4.56) and tend to have more patella III prolateral spines (11-20 vs. 7-10). The known distributions of these two species do not overlap.
Description of male holotype. Specimen preparation and condition. Specimen presumed collected from pitfall trap, preserved in 70%EtOH. Coloration slightly faded. Pedipalp, leg I right side removed, stored in vial with specimen; leg I left side missing. General coloration. Carapace, chelicerae, legs yellowish red 5YR 4/6. Abdomen brown, 7.5YR 4/3; distinct dorsal mottled striping pattern. Cephalothorax. Carapace 4.40 long,3.47 wide, lightly hirsute with thin white setae intermingled with thin black setae, stout black bristles along fringe; surface smooth, pars cephalica elevated. Fringe, posterior margin with black bristles. Foveal groove deep, strongly recurved. Eyes on low mound. AER, slightly procurved, PER recurved. PME, AME subequal diameter. Sternum moderately setose, STRl 2.45, STRw 1.84; elongate. Posterior sternal sigilla small, positioned laterally, anterior sigilla pairs small, oval, marginal. Chelicerae with distinct anterior tooth row comprising 5 teeth, posterior margin with single row of small denticles. Palpal endites with patch of small cuspules on proximal, inner margin, labium with 2 cuspules, LBw 0.58, LBl 0.27. Rastellum consists of 4 stout spines not on prominent mound. Abdomen. Setose, heavy black setae intermingled with fine black setae. Legs. Distribution and natural history. Aptostichus chavezi is distributed predominantly throughout Tulare and Fresno Counties (Fig. 34) in the Sierra Nevada foothills. The locality further to the north in Fresno County, not predicted in the DM (Fig. 35) may be a fifth, closely related Sierra group species. Because only a single specimen is known I have chosen to be conservative and include this specimen as part of the A. chavezi hypothesis until males become available. The habitat type throughout this species range is characterized as Sierran steppe, mixed and coniferous forest. Based on the single male specimen, it appears that males are late winter dispersers (March).
Conservation status. Based on its widespread distribution and general abundance in collections, this species would likely be considered secure.

Acknowledgements
This work was supported by National Science Foundation grant DEB 0315160. I am grateful to the following individuals and institutions for specimen loans: Charles Griswold and Darrell Ubick (Californian Academy of Sciences), Norman Platnick and Lou Sorkin (American Museum of Natural History), Laura Leibensperger (Museum of Comparative Zoology), Petra Sierwald (The Field Museum of Natural History), Rick Vetter (University of California Riverside), Christine Rollard (Muséum National D'Histoire Naturelle, Paris), Scott Williams, and Mel Thompson. A taxonomic project of this scope and size would not be possible without the collecting assistance of numerous individuals, friends, and colleagues: Jordan Satler, Jim Starrett, Casey Richart, Dean Leavitt, Paul Marek, Tom Prentice, Chad Spruill, David Beamer, Amy Stockman, Cody Will, the late Vince Roth, and many others. Fieldwork in California State Parks and Joshua Tree, Pinnacles, Yosemite, and Death Valley National Parks was facilitated through the availability of collecting permits to colleagues and myself. I am forever in the debt of three individuals-Brent Opell, Wendell Icenogle, and Marshal Hedin. Brent Opell was my Ph.D. advisor when I started to work on Aptostichus in 1995; he was an incredibly patient mentor, good friend, and colleague. Wendell Icenogle spent countless hours in the field with me and patiently taught me how to find these spiders and get them out of the ground without harming them. I dare say that Wendell will find this revision lacking in many of its attributes but hope that he will find some aspects of it worthy of his efforts and that it provides an initial foray into learning more about this fascinating and diverse group of spiders. Marshal Hedin has been a tremendous friend, collaborator, and colleague over the past 20 years and has collected many of the specimens that have served to significantly improve our knowledge of Aptostichus species diversity and distribution. The substantial pitfall collecting efforts of Robert Fisher (USGS) significantly enhanced our knowledge of Aptostichus species' distributions; I am grateful to Dr. Fisher for making these specimens available to the project. Although they probably do not remember given the exceptional amount of time that has passed, Jamel Sandidge, Sarah Crews, and Stacey Smith helped to database and georeference many specimens early in this project-at the time georeferencing entailed topographic maps (Google Earth had yet to be developed) and databasing was a note card collection. My thanks to Chris Hamilton and Rebecca Godwin; they assisted me in the final preparation of this manuscript. The comments of Brent Hendrixson, Marshal Hedin, and Charles Griswold, and Miquel Arnedo helped to improve the manuscript. Finally my gratitude to my family, Kristen and Elisabeth Bond, for their support and patiently suffering my preoccupation with completing this revision over the last couple of years; both remain as a firm reminder of things that are most important.