A total of 26 female, 5 male, 7 nymphal, and 21 larval ticks, not used for pathogen detection during the 2014–2018 surveys, was examined and used for these descriptions. The map in Fig. 1 illustrates the location of collection sites. All ticks were collected from M. c. scirpensis, with the exception of 5 larvae from M. musculus, two nymphs from M. c. vallicola, and 2 females from R. megalotis (Table 1).

Ticks were cleaned with household detergent in water (1: 9) and examined with a Nikon SMZ25 stereomicroscope (Nikon Instruments; Inc. Melville; NY), which was also used to take measurements (in millimeters for adults and nymphs and micrometers for larvae, given as range followed by mean and standard deviation in parentheses). Scanning electron microscope images were taken with a JEOL JSM-6610LV (JEOL USA, Inc.; Peabody, MA). Macroscopic images of adults, nymphs, and slide mounted larvae were generated with a BK Plus Lab System (Visionary Digital; Los Angeles, CA). The stacking images of the larvae were used to create hand drawn composite illustrations, as most larval ticks were damaged to the point that good SEM or macroscopic images of intact whole specimens could not be obtained.

DNA was extracted from 8 specimens of the new tick species (4 adults, 1 nymph, and 3 larvae) (Table 2). The exoskeletons of all ticks used for extractions were kept as voucher specimens by following previously described methods (Beati and Keirans, 2001; Beati et al., 2012). When possible, four different gene fragments (12S rDNA, 16S rDNA, COI, and ITS2) were amplified and sequenced for each tick (Beati and Keirans, 2001; Beati et al., 2012; Folmer et al., 1994; Mangold et al., 1998). In addition, the same genes were amplified and sequenced from available closely related species of Ixodes for comparison purpose. Also, 18S rDNA and 28S rDNA (Klompen et al., 2000) sequences were obtained from samples of the new tick species. Sequences were manually aligned with Mesquite 3.6 (Maddison and Maddison, 2018). Each data set was analyzed by maximum parsimony (MP) and maximum likelihood (ML) with PAUP (Swofford, 2000) and by Bayesian inference analysis (BA) using MrBayes 3.2.4 (Huelsenbeck and Ronquist, 2001; Ronquist et al., 2011). Branch support was assessed by bootstrap analysis (1000 replicates) with PAUP for MP and ML. MP heuristic searches were performed by branch-swapping using the tree bisection-reconnection (TBR) algorithm. Maximum likelihood distances were calculated after the nucleotide substitution model best fitting the data was selected by JModeltest v.2.1.7 (Darriba et al., 2012). The best model was used to calculate pairwise distances by using PAUP. Two runs with four chains each were run simultaneously for BA analyses (1,000, 000 generations). Trees were sampled every 100 iterations. Trees saved before the average standard deviation of split fragments converged to a value < 0.01 were discarded from the final sample. When necessary, the number of generations was increased so that the number of discarded samples would not exceed 25% of the total sampled trees. The 50% majority-rule consensus tree of the remaining trees was inferred, and posterior probabilities recorded for each branch.

Ixodes (Ixodes) mojavensis Backus & Beati, new species (Figs. 2, 6A and B)

The name Ixodes mojavensis has been registered with ZooBank according to the International Commission of Zoological Nomenclature. LSID: urn:lsid:zoobank.org:act:F71B8BD4-CEEA-4F47-AF02-D7B808BA 1BF7.

Note: all examined specimens were partially engorged and, therefore, body length and width will be overestimated in females, nymphs, and larvae.

Female (Figs. 2A–F, 6A and B)

Material analyzed (U.S. National Tick Collection USNMENT accession number; followed by the UC Davis [UCD] laboratory collection number): USNMENT00981933 UCD5706; USNMENT00981927 UCD5588; USNMENT00981850 UCD5571; USNMENT00981851 UCD5555; USNMENT00981854 UCD5591; USNMENT00981855 UCD5704; USNMENT00981788 UCD5840; USNMENT00981789 UCD5843; USNMENT00981929 UCD5611; USNMENT00981852 UCD 5570; USNMENT00981853 UCD5572; USNMENT00981848 UCD5724; USNMENT00981856 UCD5708 = HOLOTYPE; USNMENT00981785 UCD5698 (Table 1)

Body (Figs. 2A and B, 6A and B): oval, reddish-brown; body length from palpal apices to posterior margin 1.63 to 5.48 (3.54 ± 1.03); body width 0.83 to 2.78 (1.80 ± 0.52); idiosoma with homogeneously distributed, dense setation (Figs. 2A, 6B), setae whitish of moderate length 0.05–0.10 (0.07 ± 0.01); marginal groove lining idiosoma and reaching scutum edge at its widest point (Fig. 2A). Scutum: Oval, longer (from tip of scapulae to posterior margin) 0.93 to 1.30 (1.13 ± 0.10) than wide 0.75 to 1.04 (0.91 ± 0.08), length: width ratio 0.3, with few sparse whitish setae 0.01–0.11 (0.06 ± 0.03) mostly along anterolateral edges and anterior central field; scapulae pointed; lateral carinae present and slightly elevated; cervical grooves starting behind cornua as deep short triangular pits; extending into shallow but visible, somewhat shagreened cervical fields, first converging and then diverging posteriorly reaching about two thirds of scutal length, not reaching scutal margin; punctuation fine and shallow slightly deeper along anterolateral edge (Figs. 2A, 6B). Capitulum: length from tip of cornua to tip of hypostome 0.63 to 0.81 (0.73 ± 0.06); basis capituli (Fig. 2C) length from tip of cornua to cheliceral insertion 0.26 to 0.36 (0.30 ± 0.03); width 0.39 to 0.49 (0.43 ± 0.03), triangular-shaped, chaeliceral insertion marked by transversal line; cornua present, small, length 0.03 to 0.05 (0.04 ± 0.01), triangular shaped with a somewhat truncated tip; porose areas large, width 0.11 to 0.15 (0.12 ± 0.01), length 0.07 to 0.12 (0.10 ± 0.01), subtriangular, placed in distinct depressions, separated by v-shaped shallow groove, distance between areas 0.07 to 0.1 (0.08 ± 0.01) and outlined externally by ridge. Palps elongate; palpal article I small, length 0.03 to 0.08 (0.05 ± 0.01), width 0.06 to 0.09 (0.08 ± 0.01), dorsal or ventral projections absent; palpal article II length 0.28 to 0.35 (0.32 ± 0.03), width 0.12 to 0.16 (0.14 ± 0.01), widest point close to suture with palpal article III; palpal article III length 0.20 to 0.26 (0.23 ± 0.02), width 0.11 to 0.15 (0.13 ± 0.01). Ventrally, basis capituli (Fig. 2D): auriculae present, length 0.03 to 0.05 (0.04 ± 0.01), pointed, posteriorly directed; transverse suture visible; posterior part of the basis capituli not constricted; posterior margin rounded; hypostome elongated (Fig. 2D), length from insertion to rounded apex 0.36 to 0.53 (0.42 ± 0.06), dentition 4:4 near crown, 3:3 down to hypostomal mid-length; then 2:2. Venter (Fig. 2B–D): Anal grove anterior to anus and reaching posterior margin of body at perpendicular angles; anal valves with 3 pairs of setae; genital aperture situated between coxa IV; genital groove reaching posterior margin. Body with homogeneously distributed fine whitish setae 0.02–0.07 (0.04 ± 0.02); absent along genital groove (Figs. 2B, 6A). Legs: trochanters with no spurs; syncoxa present on coxa I and II; coxa I with 2 pointed spurs, internal twice as long as external, barely reaching anterior edge of coxa II; coxa II with short, triangular shaped external spur joined to inconspicuous internal spur by syncoxa; coxa III-IV with short, rounded external spur extending medially into sclerotized ridge (Figs. 2B, 6A). Tarsus I length 0.40 to 0.63 (0.51 ± 0.07) (Fig. 2F); metatarsus I length 0.26 to 0.36 (0.31 ± 0.02); tarsus IV length 0.32 to 0.54 (0.44 ± 0.08); metatarsus IV length 0.29 to 0.48 (0.36 ± 0.06). Spiracular plates (Fig. 2E) subcircular, longitudinal length 0. 21 to 0.30 (0.27 ± 0.03), transversal length 0.24 to 0.33 (0.30 ± 0.03).

Male (Figs. 3A–F, 6C and D):

Material analyzed: USNMENT00981855 UCD5705; USN-MENT00981785 UCD5699 (mating). USNMENT00981815 UCD5672 = ALLOTYPE; USNMENT00981925 UCD5569; USNMENT00981934 UCD5715.

Body (Figs. 3A–C, 6C and D): Dark brown, oval, length 1.82 to 2.09 (1.96 ± 0.12) from palpal apices to posterior margin; width 0.96 to 0.1.06 (1.01 ± 0.04). Conscutum: marginal groove reaching level of coxa II; setation sparse, fine, of moderate length 0.03–0.09 (0.07 ± 0.02), denser along lateral marginal fold; cervical grooves fine and shallow first slightly converging, then diverging in anterior third of conscutum; 3–4 lateral shallow but visible depressions at mid-length; punctuation large, shallow in median field, deeper along marginal groove; finer anterolaterally, in posterior forth of the conscutum and on marginal fold; posterior marginal fold creased; scapulae with blunt point (Figs. 3A, 6D). Capitulum: length from tip of cornua to tip of hypostome 0.46 to 0.55 (0.50 ± 0.06); dorsal basis capituli (Fig. 3D) length from tip of cornua to cheliceral insertion 0.2 to 0.28 (0.23 ± 0.04), roughly triangular shaped, narrowed posteriorly, extending smoothly into hypostome, width 0.21 to 0.32 (0.27 ± 0.05), punctate, with triangular, pointed cornua, cornua length 0.02 to 0.04 (0.03 ± 0.01); edge separating cornua straight. Ventrally (Fig. 3F), basis subtriangular with transversal rounded ridge joining triangular-shaped postero-laterally directed auriculae, auriculae length 0.02–0.05 (0.03 ± 0.02); palps inserted in antero-lateral extension of basis capituli. Hypostome slightly shorter than palps 0.22 to 0.27 (0.25 ± 0.03), notched apically; lateral denticles as posterolaterally directed sharp large triangles (on 1 or sometimes 2 files, and 4 rows), separated by crenulated ridges (7–8 recognizable rows). Palps clublike; palp I with no spurs, length 0.03 to 0.05 (0.04 ± 0.01), width 0.05 to 0.06 (0.004 ± 0.0); palp II length 0.11 to 0.15 (0.13 ± 0.02), width 0.11 to 0.15 (0.13 ± 0.02); palp III length 0.11 to 0.14 (0.13 ± 0.01), width 0.11 to 0.15 (0.13 ± 0.02). Venter (Fig. 3B and C): Anal groove anterior to anus; converging slightly towards posterior margin of body; fine whitish setae 0.03–0.08 (0.06 ± 0.01) densely and uniformly distributed; genital plate notched posteriorly; punctation large and shallow in median and genital plates, finer and deeper elsewhere, in particular around spiracular plates; genital aperture at level of posterior margin of coxa III, anal valves with 3 pairs of setae. Spiracular plates oval (not illustrated), elongated, longitudinal length 0.23 to 0.25 (0.24 ± 0.01), width 0.18 to 0.19 (0.19 ± 0.01, only two measurements). Legs: spurs absent from trochanters; coxa I and II with syncoxa and with two spurs; internal and external spurs on coxa I and II short ending in rounded points almost equal in length; external spur on coxa III short, round more conspicuous than internal spur; external spur of coxa IV short and round extending medially into sclerotized ridge (Figs. 3B and C, 6C). Tarsus I (Fig. 2F) length 0.25 to 0.41l (0.37 ± 0.07) (Fig. 3F); metatarsus I length 0.1 to 0.2 (0.15 ± 0.04); tarsus IV length 0.25 to 0.29 (0.27 ± 0.03; only 2 measurements); metatarsus IV length 0.16 to 0.23 (0.19 ± 0.05; only 2 measurements).

Nymph (Figs. 4A–G, 6E and F):

Material analyzed: USNMENT00981926 UCD5581, USN-MENT00981826 UCD5596; USNMENT00981928 UCD5597; USN-MENT00981825 UCD5584; USNMENT00981847 UCD5696; USNMENT00981817 UCD5678; USNMENT00981827 UCD5626; USN-MENT00981818 UCD5694; USNMENT00981819 UCD5686; USNMENT00981787 UCD5888.

Body (Figs. 4A and B, E, 6E and F): Outline overall oval, length from palpal apices to posterior margin 1.26 to 2.21 (1.81 ± 0.34); width 0.83 to 1.44 (1.15 ± 0.22); widest at level of coxa IV; Soma homogeneously setate; setae 0.04 to 0.06 (0.05 ± 0.01). Scutum (Fig. 4A): Oval-shaped, length 0.54 to 0.85 (0.63 ± 0.10), width 0.48 to 0.8 (0.57 ± 0.10) with scattered fine and shallow punctation and scattered short fine setae 0.01–0.02 (0.02 ± 0.01); lateral carinae moderately elevated (variable between specimens); cervical groove well defined, first converging and then diverging, reaching posterolateral margins of scutum, cervical field shallow. Capitulum (Fig. 4C and D): Length from tip of cornua to tip of hypostome 0.63 to 0.81 (0.73 ± 0.06); basis capituli length from from tip of cornua to insertion of chelicerae 0.13 to 0.17 (0.15 ± 0.02), width 0.21 to 0.35 (0.25 ± 0.04), dorsally subtriangular extending smoothly into the chelicerae with triangular, pointed, posteriorly directed cornua length 0.02 to 0.04 (0.03 ± 0.01); line joining cornua straight; chaelicheral insertion marked by transversal line; palpi elongate; suture between articles II and III distinct; palpal article one with ventral roundish plate, length 0.03 to 0.05 (0.04 ± 0.01), width 0.04 to 0.06 (0.05 ± 0.01); palp II length 0.15 to 0.23 (0.17 ± 0.03); width 0.06 to 0.11 (0.08 ± 0.02); palp III 0.12 to 0.20 (0.14 ± 0.03); width 0.07 to 0.11 (0.08 ± 0.01). Ventrally, basis with well-defined posteriorly directed triangular auriculae (length 0.03 to 0.05; 0.04 ± 0.01), constricted posterior to auriculae with no visible suture line, posterior margin rounded; hypostome lanceolate, apically rounded, length 0.22 to 0.37 (0.28 ± 0.05); dental formula 3:3 over the 6–7 apical rows, then 2:2 (3–4 additional rows) to the insertion of the hypostome, lateral files with much larger pointed triangular denticles than median ones. Venter (Figs. 4B and E, 6F): Body setate, setae scattered uniformly but absent from discernible future genital groove, length 0.04–0.06 (0.05 ± 0.01), longer between coxa I; anal groove curving around anus and joining posterior margin at a perpendicular angle; spiracular plates (Fig. 4F) subcircular length 0.11 to 0.13 (0.12 ± 0.01), width 0.12 to 0.16 (0.14 ± 0.01). Legs. Trochanters lacking spurs. Coxa I-II with 2 spurs, spurs in coxa I of similar length, rounded at apex; internal spurs shorter than external in coxa II-III decreasing in size; external spurs triangular and rounded; coxa IV with single short triangular, rounded, external spur, shorter than external spur in coxa III. Tarsus I (Fig. 4G) length 0.26 to 0.42 (0.32 ± 0.05); metatarsus I length 0.09 to 0.17 (0.12 ± 0.03; 3 specimens), tarsus IV length 0.23 to 0.26 (0.24 ± 0.02); metatarsus IV length 0.14 to 0.15 (0.15 ± 0.01; 3 specimens).

Larvae (Fig. 5A–F)

Material examined: USNMENT00981827 UCD5741; USN-MENT00981829 UCD5633; USNMENT00981830 UCD5740; USN-MENT00981831 UCD5745; USNMENT00981832 UCD5634; USNMENT00981833 UCD5632; USNMENT00981834 UCD5647; USN-MENT00981845 UCD5873; USNMENT00981846 UCD5874, UCD5875, UCD5876, UCD5877, and UCD5878. Terminology for larval chaetotaxy follows Clifford and Anastos (1960), and Clifford et al., (1961, 1973).

Body: (Fig. 5A): subcircular, length from tip of scapulae to posterior edge from 750.01 to 1377.78 (961.61 ± 190.25), widest near midlength 506.67 to 700.02 (626.93 ± 96.04). Sensilla sagittiformia (large wax glands) absent. Dorsal setae 10–12 pairs; 4 central dorsal setae, CD1 from 0.026 to 0.032 (0.029 ± 0.002), CD2 0.024 to 0.036 (0.030 ± 0.005); 7–8 marginal dorsal pairs, MD1 0.034 to 0.045 (0.040 ± 0.04), MD7 or MD8 0.032 to 0.037 (0.035 ± 0.002); 1 pair of supplementary setae 0.021 to 0.027 (0.025 ± 0.003). Scutum (Fig: 5A): length 433.33 to 457.78 (450.41 ± 8.64), breadth 487.67 to 514.29 (503.13 ± 8.57), outline broadly oval with posterolateral margins slightly concave; cervical grooves distinct but shallow, first converging then diverging posteriorly, almost reaching scutal margins (not visible in mounted specimens); 5 pairs of setae, SC1 0.013 to 0.020 (0.016 ±0.003), SC2 0.018 to 0.028 (0.022 ± 0.005), SC3 0.011 to 0.024 (0.018 ± 0.05), SC4 0.18 to 0.027 (0.022 ± 0.004), SC5 0.014 to 0.027 (0.021 ± 0.006). Capitulum (Fig. 5B, D): dorsal length from palpal apices to tip of cornua from 229.63 to 249.37 (237.84 ± 7.37), length from cheliceral insertion to tip of cornua from 82.22 to 89.78 (86.01 ± 2.45), width of basis capituli from 127.14 to 136.67 (133.07 ± 2.85). Basis capituli with straight posterior margin; lateral margins notched under insertion of palpal article I, cornua pointed and posterolaterally directed as extensions of slightly raised ridges, width at tips of cornua not exceeding width of tips of scapulae. Basis capituli ventrally constricted posterior to blunt posteriorly directed auriculae, posterior margin straight. Post-hypostomal setae 2 pairs, PH1 0.006 to 0.016 (0.010 ± 0.005), PH2 0.006 to 0.013 (0.009 ± 0.002). Palps elongated 154.29 to 171.46 (162.18 ± 4.88) with 4 sensilla, Palp I 21.43 to 27.78 (25.15 ±2.05) long by 25.71 to 30.00 (28.13 ±1.48) broad; palp II (85.71 to 98.57 (91.90 ± 4.10) long by 35.36 to 41.43 (38.43 ±1.80) broad, palp III 40.00 to 50.34 (45.12 ± 3.13) long by 37.33 to 42.86 (40.33 ±1.55) broad; setae absent from article I, 3 ventral and 8 dorsal setae on segment II and II combined, suture between segments II and III barely visible ventrally, absent dorsally; article IV with approximately 9 setae. Hypostome length 147.41 to 159.59 (151.82 ± 8.33), arising from anterior median extension of basis capituli, toothed portion covering approx. ¾ of hypostomal length; dental formula below crown 3:3 in first 2–3 rows, then 2:2; file 1 with ca. 9–10 denticles, file 2 with ca. 8–9 denticles, file 3 with ca. 2–3 denticles. Venter (Fig. 5D): Ventral setae: 13 pairs plus 1 pair on anal valves; 3 pairs of sternals, ST1 0.022 to 0.038 (0.032 ± 0.006), ST2 0.020 to 0.035 (0.030 ± 0.005), ST 3 0.013 to 0.035 (0.024 ± 0.007); 2 pairs of preanals PA1 0.016 to 0.020 (0.019 ± 0.002), PA2 0.016 to 0.023 (0020 ± 0.004); 4 pairs of premarginals 0.015 to 0.027 (0.019 ± 0.003), 4 pairs of marginal ventrals MV1 0.020 to 0.025 (0.024 ± 0.002) and MV4 0.023 to 0.027 (0.025 ± 0.002). Legs (Fig. 5C, E, F): Coxa I with broad triangular internal spur rounded at tip, narrower pointed, triangular, external spur; coxa II with internal rounded ridge-like thickening and narrow triangular rounded external spur; coxa III with no internal and inconspicuous external squarish ridge somewhat representing external spur; coxal setae 3 on coxa I, 2 on coxa II, 2–3 on coxa III. Tarsus I (Fig. 5E) length 135.71 to 178.57 (153.87 ± 10.91), Haller’s organ as in Fig. 5F with 5 setae in anterior pit, 4 pre-halleral and 4 posthalleral setae; tarsus IV from 136.78 to 187.51 (160.17 ± 17.39).

Type Data: Holotype female from M. c. scirpensis, Amargosa Valley, CA, United States of America (35.8610 °N, −116.2421 °W), collected on May 12, 2016 by Austin Roy. Deposited in the U.S. National Tick Collection (USNMENT00981856). Allotype male from M. c. scirpensis, Amargosa Valley, CA, United States of America (35.8742 °N, −116.2337 °W) on February 20, 2017 by Austin Roy. Deposited in the U.S. National Tick Collection (USNMENT00981815). Paratype adults, nymphs, and larvae as listed in Table 1.

As is demonstrated by the molecular analyses (see below), I. mojavensis is closely related to taxa that feed on both rodents and birds. Because host associations have yet to be fully explored for I. mojavensis, the possibility of it being carried by birds along the flyway from Central America to the Great Basin cannot be dismissed. Therefore, at least for adults, species relationships are described for North and Central American species of the subgenus Ixodes (Augustson, 1939; Bermudez at al., 2018; Cooley, 1944, 1945; Cooley and Kohls, 1938, 1942, 1943, 1945; Guzmán-Cornejo and Robbins, 2010; Keirans and Clifford, 1978; Keirans and Eckerlin, 2005; Kohls, 1953, 1956; Kohls and Clifford, 1962, 1964, 1966). For the immature stages, comparisons are limited to species of the U.S (Clifford et al., 1961; Durden and Keirans, 1996a; Keirans et al., 1996; Kleinjan and Lane, 2008; Kohls and Clifford, 1964; Oliver et al., 1987; Smith and Gouck, 1947).

Females: I. mojavensis females differ from I. minor (Neumann, 1902; Smith and Gouck, 1947; Keirans and Clifford, 1978) by auriculae not curving medially, absence of spines on palpal article I; porose area well defined, surrounded by a visible ridge and delimited medially by a fine longitudinal groove. Also, the number of denticle rows are 3 (inner file), 6 (median file), 10–11 (2 external files) rather than 5, 7, 10 and the scutum is almost lacking punctuation, while the scutum of I. minor has deep and large punctations in its posterior half. I. mojavensis and Ixodes muris Bishopp and Smith, 1937, both have posteriorly projecting auriculae, but these are proportionally shorter in I. mojavensis; porose areas are not as shallow as in I. muris; hypostome with 4 and not 3 files of denticles and with less rows (10 vs. 15), hypostome rounded apically and not pointed (Bishopp and Smith, 1937; Cooley and Kohls, 1945; Keirans and Clifford, 1978). When compared with Ixodes dentatus Marx, 1899, I. mojavensis has fewer hypostomal denticle files (4 vs. 5), inconspicuous scutal punctation, and palpal article I without ventral spur (Cooley and Kohls, 1945; Keirans and Clifford, 1978; Neumann, 1899, Smith, 1940). In addition, more succinctly, I. mojavensis can be differentiated from the other North and Central American members of the subgenus Ixodes Latreille, 1795 (Clifford et al., 1973) by the following characters: very long and wide external spur on coxa I (Ixodes loricatus Neumann, 1899 and Ixodes luciae Sénevet, 1940); auriculae absent, ridge-like, or rounded (Ixodes affinis Neumann, 1899, Ixodes guatemalensisKohls, 1956, Ixodes jellisoni Cooley and Kohls, 1938, I. loricatus, I. luciae, Ixodes pacificus Cooley and Kohls, 1943, Ixodes rubidus Neumann, 1901, Ixodes scapularis Say, 1821, Ixodes tamaulipas Kohls and Clifford, 1966, Ixodes tancitarius Cooley and Kohls, 1942, Ixodes tapirus Kohls, 1956, and Ixodes tecpanensis Kohls, 1956); auriculae either like laterally extending hooks (Ixodes dentatus Marx, 1899), or curved (Ixodes bequaerti Cooley and Kohls, 1945, Ixodes boliviensis Neuamnn, 1904, Ixodes cuernavacensis Kohls and Clifford, 1966, Ixodes eadsi Kohls and Clifford, 1964, Ixodes mexicanus Cooley and Kohls, 1942, Ixodes pomerantzi Kohls, 1956, Ixodes sinaloa Kohls and Clifford, 1966, Ixodes spinipalpis Hadwen and Nuttall, 1916, Ixodes tovari Cooley, 1945, Ixodes venezuelensis Kohls, 1953). The absence of spur or pointed processes on palpal article I will differentiate I. mojavensis from Ixodes bocatorensis Apanaskevitch and Bermudez, 2017, I. dentatus, I. jellisoni, I. pacificus, I. pomerantzi, Ixodes peromysci Augustson, 1939, I. spinipalpis, Ixodes tiptoni Kohls and Clifford, 1962, and I. tovari.

Males: I. mojavensis, unlike I. minor (Keirans and Clifford, 1978; Neumann, 1902; Smith and Gouck, 1947), has a straight posterior margin of the basis capituli, blunter auriculae without a sharp point, missing ventral spur on palp I. The pseudoscutum is visible, but not concave, nor heavily punctate; dorsal setation is scant and scattered, punctuation in posterior half of scutum is of moderate size and shallow; the pregenital plate is notched posteriorly, and the median plate is flat posteriorly, not pointed; the punctuation on the median plate is denser (over 70–90 vs. 50–60), shallower and finer; ventral setation is finer. When compared with I. muris (Bishopp and Smith, 1937; Keirans and Clifford, 1978), the scutum of I. mojavensis is less punctate in the anterior half (over the conscutum which is visible in both species, convex in I. muris but not in I. mojavensis), the auriculae are more visible and well-defined and cornua are present, the ventral median plate is flat posteriorly rather than pointed, and the spiracular plates are distinctly elongated (subcircular in I. muris). The males of I. dentatus (Cooley and Kohls, 1945; Keirans and Clifford, 1978; Smith, 1940) can be differentiated from I. mojavensis by the larger scutal punctations, denser and deeper and by the presence of a very long internal spur on coxa I reaching over mid length of coxa II, by the absence of an apical notch on the hypostome, by more rows of hypostomal denticles (about 11 vs. 8) and the proximal denticle rows not terminating with an external large posteriorly directed tooth as in I. mojavensis. Distinct pointed cornua distinguish I. mojavensis from I. affinis, I. bocatorensis, I. boliviensis, I. eadsi, I. guatemalensis, I. pacificus, I. scapularis, and I. tapirus. As for females, the males of I. loricatus and I. luciae have long external spurs on coxa I, while I. mojavensis has two subequal short spurs. The hypostome of I. dentatus is rounded with diagonally arranged crenulations each with 4 denticles and not notched with larger external denticles like I. mojavensis. The hypostome of I. pomerantzi is also not notched. Scutal punctations are shallower than in I. spinipalpis, I. eadsi, and I. affinis. The male of I. jellisoni, and I. spinipalpis are characterized by a spur on palpal article I which is absent in I. mojavensis. I. peromysci can be differentiated from I. mojavensis by finer and homogeneous punctation and denser setation on conscutum. I. tovari has a very elongate and lanceolate hypostome, very unlike the short, notched hypostome of I. mojavensis.

Nymphs: The nymph of I. mojavensis differs from I. minor by the shape of the basis capituli which does not extend posterolaterally, by having shorter, less massive auriculae, and less conspicuous cervical grooves; also, unlike in I. minor, the external files of hypostomal denticles in I. mojavensis are much larger than the internal ones. The nymph of I. dentatus differs from I. mojavensis by an almost round scutum with deep punctations in its posterior portion, by a posterolaterally extending dorsal basis capituli, and hypostomal dentition 4:4. The nymph of I. muris is characterized by wider auriculae, wider cornua, longer scutal setae, by the absence of internal spurs on coxa II and III, and by a pointed hypostome. The presence of well-defined, rather than round and, or inconspicuous auriculae differentiates I. mojavensis from I. affinis, I. jellisoni, I. peromysci, I. pacificus, and I. spinipalpis, and the absence of curved auriculae from I. eadsi. Unlike in I. mojavensis which has fairly straight external edges, the basis capituli of I. tovari extends poster-olaterally; I. tovari also has longer, pointed external spurs on coxa I-IV. I. scapularis differs from I. mojavensis by a sinuous, rather than straight posterior margin of the basis capituli, and by the absence of internal spurs on coxa II-III.

Larvae. I. dentatus, I. jellisoni, I. muris, I. scapularis, I. pacificus, and I. tovari have more than 2 pairs of central dorsal setae. I. peromysci lacks supplementary setae. Unlike I. mojavensis, I. affinis has a well-defined, pointed external spur on coxa III. I. mojavensis and I. minor larvae are difficult to differentiate; nevertheless, the idiosomal setae in I. minor are markedly longer (Md1 mean 0.073 vs. 0.040; Md7 average 0.057 vs. 0.035) and the hypostomal files carry more denticles than I. mojavensis. I. dentatus has weak inconspicuous auriculae, while auriculae in I. mojavensis are well-defined. The basis capituli of I. spinipalpis is distinctly broader than long behind the hypostome and widening into posterolaterally extending sharp cornua and the auriculae are notched. Ixodes eadsi has auriculae that are triangular, pointed and better defined than I. mojavensis.

Distribution and hosts: I. mojavensis is reported so far only from the Amargosa and the Owens Valley of California where it was collected mainly from M. c. scirpensis. Less often it has been collected from M. c. vallicola, M. musculus, and R. megalotis.

Sequences generated for this study were submitted to GenBank (Table 2). Accession numbers are in parentheses: 12S rDNA (MT840315–MT840331 and MT898578–MT898587); 16S rDNA (MT840295–MT840309); COI (MT906024–MT906040); ITS2 (MT880311–MT880332); 28S rDNA (MT897884–MT897893); 18S rDNA (MT860474–MT860481).