Introduction

The American continent belongs to two zoogeographical areas (Nearctic and Neotropical), and there are more than 100 described genera of chiggers so far [1]. One of the most studied and reported genera for the Nearctic region was Euschoengastia Ewing, 1938. Although the genera appear to be stable, by revising literature and types within this genus, Euschoengastia seems not to be one such genus.

This genus has historically included species mainly based on the presence of a pair of expanded prodorsal trichobothria [2]. So, after examining the types, different characters were found separating Euschoengastia latchmani Brennan and Yunker, 1964 and Euschoengastia obscura Wrenn and Loomis, 1974 from Euschoengastia. Here, we are redescribing these two species and proposing Goffacarus n. gen. to reallocate these species. These two species are the only ones in Euschoengastia with striations in the prodorsal sclerite [3, 4].

Materials and Methods

After an inspection and examination to the Acari Collection in the U.S. National Entomology Collection, Smithsonian Institution (USNM), the types of Euschoengastia latchmani and Euschoengastia obscura were found and herein redescribed. This collection is currently located in the Systematic Entomology Laboratory (BARC-USDA-ARS), Beltsville, MD, USA (informally known as Smithsonian National Chigger Collection). The official acronym used to enumerate each slide is USNMENT, according to Bassini-Silva et al. [5].

A literature survey was carried out for all species identified as Euschoengastia. The type species within this genus were examined, if available, and only after this exhaustive study, we came with the results of the present study. The types available and examined were listed in the type catalog by Bassini-Silva et al. [5].

The drawings were made using a ZEISS Axioskop 2 microscope with DIC and Phase Contrast. Measurements and photographs of the specimens were made using a ZEISS AXIO Imager.D1 with an attached ZEISS AxioCam ICc 5 digital camera. Extended focal range images were processed with AxioVision SE64 Rel. 4.9.1 SP1 software. The figures were prepared with Adobe Photoshop v. 13.0 and Inkscape v.1.0.1.

The terminology of the opisthosomal and prodorsal sclerite setae follow Grandjean [6] with adaptations by Kethley [7]. Also, we are using Grandjean [8, 9] for the specialized setae on the legs and palps.

Systematics

Trombiculidae Ewing, 1944

Goffacarus Bassini-Silva, Jacinavicius and Welbourn, n. gen.

Type species. Euschoengastia latchmani Brennan and Yunker, 1964.

Diagnosis. Larva. Palptarsus with seven branched setae and a basal solenidion; odontus trifurcate; cheliceral blade with tricuspid cap; eyes 2/2 without ocular sclerite; prodorsal sclerite subrectangular and striated; with pair of expanded trichobothria (si) and five normal setae (vi, 2 ve, and 2 se); se setae on prodorsal sclerite; Fe I–III each divided into basifemur and telofemur; coxal fields unisetose; pretarsal empodium without onychotriches; Ge I with two solenidia (σ); Ge II and III each with one solenidion (σ); Ta I and II each with subterminal eupathidium (ζ and ζ”); Ta I with dorsal eupathidium (ζ’) and companion seta (z); Ti III without solenidion (φ).

Differential diagnosis. The new genus is similar to Euschoengastia in having seven branched setae on the palptarsus, a single sigma (σ) on Ge II and III, and the absence of φ on Ti III. However, it can be differentiated from Euschoengastia, in having a 3-pronged odontus (vs. multi-pronged odontus) and striations on the prodorsal sclerite (vs. absence of striations). In addition, the new genus is similar to Neoschoengastia Ewing, 1929 and Megaschoengastia Vercammen-Grandjean, 1960, by having striations on the prodorsal sclerite that changes the posterior margin, but differs in having 1 σ on Ge II (vs. two or more σ on Ge II), absence of φ on Ti III (vs. present) and presence of companion seta (z) (vs. absence).

Etymology. The new genus, ‘Goffacarus’, is named in honor of Dr. Lee Goff, for his contributions to the taxonomy of chiggers worldwide, combined with the word ‘mite’ in the new Latin word, ‘acarus’.

Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.

Euschoengastia latchmani Brennan and Yunker [3], p. 311; Vercammen-Grandjean [10], p. 97; Wrenn and Loomis [4], p. 241; Wrenn [2], p. 222; Walters et al. [11], p. 13 (Tables 1, 2, 3 and 4).

Table 1 Standard measurements of the types of Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.
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Table 2 Standard measurements of the types of Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.
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Table 3 Standard measurements of the types of Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.
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Table 4 Standard measurements of the types of Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.
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Diagnosis. Palpfemur and palpgenu each with single branched seta; palptibia with three setae, branched dorsal and ventral setae and a nude lateral seta; adoral (cs) setae branched; prodorsal sclerite with an expanded obovate trichobothria (si), proximal half of the expanded portion with scale-like setules, that gradually increase in size to the middle of the expanded part then disappear on the distal half, 105–114 opisthosomal setae including the C row with 15–16 setae; D row with 12 setae; and 46–50 ventral setae; base famulus (ε) on Ta I and II distal and proximal to solenidion (ω), respectively.

Redescription. Larvae (holotype and with the range for six paratypes in parentheses). Gnathosoma—fPp = B/B/BNB/7Bω; odontus trifurcate; cheliceral blade with tricuspid cap; gnathobase with a few punctuations, subcapitular (bs) and adoral (cs) setae branched (Figs. 1A, B). Idiosoma—eyes 2/2, subequal, without ocular plate; prodorsal sclerite subrectangular with striations on posterior half; anterior and lateral prodorsal sclerite slightly sinuous, posterior margin broadly convex (Figs. 2 and 9A, C), with pair of expanded obovate trichobothria (si), with rounded scale-like setules that increase in size toward the middle of the expanded portion then disappear on the distal half, and five branched normal setae [pair of ve (= AL) seta, single vi (= AM) seta and pair of se (= PL) seta]; ve ≥ se > vi > si. Opisthosoma (Fig. 3A, B) with 110 (105–114) setae; dorsal opisthosoma with 63 (59–64) setae, C row with 16 (15–16) irregularly placed setae, D row with six pairs of setae, E, F and H rows merged, with 35 (32–36) setae; ventral opisthosomal with 47 (46–50) setae of which 26 are anterior to anus and 21 (20–24) are posterior. Two pairs of sternal setae (1a, 3a) between coxal fields I and III. Legs—femur of legs I–III each divided into basifemur and telofemur, each leg terminated with paired claws, and claw like empodium without onychotriches, coxal fields with a few punctuations; Leg I—coxal field seta 1b branched (1B); trochanter 1B; basifemur 1B; telofemur 5B; genu 4B, 2σ and κ; tibia 7B, 2φ and κ; tarsus 22B with ω, ε, dorsal eupathidium (ζ’) with companion seta (z) and subterminal eupathidium (ζ”), base of famulus (ε) distal to solenidion (ω) (Fig. 4A). Leg II—coxal field seta 2b (1B); trochanter 1B; basifemur 2B; telofemur 4B; genu 3B, σ; tibia 6B, 2 φ; tarsus 16B with ω, ε and subterminal eupathidium (ζ), base of ε proximal to ω (Fig. 4B). Leg III—coxal field seta 3b (1B); trochanter 1B; basifemur 2B; telofemur 3B; genu 3B, σ, tibia 6B; tarsus 14B (Fig. 4C).

Fig. 1
figure 1

Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.; A—dorsal view of gnathosoma; B—ventral view of palp. Symbols: ω = solenidion on palptarsus; Odo = odontus; cs = adoral setae; bs = subcapitular setae. Scales: A and B 50 μm

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Fig. 2
figure 2

Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.; prodorsal sclerite. Symbols: ve = external vertical setae; se = external scapular setae; vi = internal vertical setae; si = internal scapular setae (trichobothria). Scales: 20 μm

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Fig. 3
figure 3

Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.; A—dorsal view of idiosoma; B—ventral view of idiosoma. Solid circles = ventral setae; open circles = dorsal setae; Symbols: c1–c8 = C row setae; d1–d6 = D row setae; 1a = anterior sternal setae; 3a = posterior sternal setae; 1b = coxal field I seta; 2b = coxal field II seta; 3b = coxal field III seta. Scales: A and B 100 μm

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Fig. 4
figure 4

Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.; A—Leg I; B—Leg II; C—Leg III; Solid circles = ventral leg setae; open circles = dorsal leg setae; Symbols: ζ’ = dorsal eupathidium on Ta I; ζ” and ζ = subterminal eupathidium on Ta I; ω = solenidion on Ta I and II; σ, σ’, σ" = solenidia on Ge I-III; κ = microsetae on Ge and Ti I; φ', φ" = solenidia on Ti I-II; ε = famulus on Ta I and II; 1b = coxal field I seta; 2b = coxal field II seta; 3b = coxal field III seta. Scales: A–C 50 μm

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Type material. HOLOTYPE: larva (USNMENT01757381); Sonora County, California State, USA; 13 Feb. 1963; ex Equus caballus L. (Perissodactyla: Equidae); original number: RML 38601. PARATYPES: six larvae (USNMENT01757382, USNMENT01757383, USNMENT0175784, USNMENT01757385, USNMENT01757386, USNMENT01757387), same data as holotype.

Type depository. USNM (holotype and six paratypes) and FMNH (two paratypes).

Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.

Euschoengastia radfordi: Loomis and Bunnell [12], p. 183; Loomis and Somerby [13], p. 223 (in part); Euschoengastia obscura Wrenn and Loomis [4], p. 244; Wrenn [2], p. 222; Walters et al. [11], p. 16 (Tables 5, 6, 7 and 8).

Table 5 Standard measurements of the types of Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.
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Table 6 Standard measurements of the types of Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.
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Table 7 Standard measurements of the types of Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.
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Table 8 Standard measurements of the types of Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.
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Diagnosis. Palpfemur and palpgenu each with single branched seta; palptibia with three setae, branched dorsal and ventral setae and a nude lateral seta; adoral (cs) setae branched; prodorsal sclerite with a capitate expanded trichobothria (si), the expanded portion with scale-like setules, that gradually increase in size distally; 130 or 132 opisthosomal setae including the C row with 20 setae; D row with 14 setae; and 62 or 64 ventral setae; base famulus (ε) on Ta I and II distal and proximal to solenidion (ω), respectively.

Redescription. Larvae (holotype and one paratype). Gnathosoma—fPp = B/B/BNB/7Bω; odontus trifurcate; cheliceral blade with tricuspid cap; gnathobase with a few punctuations, subcapitular (bs) and adoral (cs) setae branched (Fig. 5A, B). Idiosoma—eyes 2/2, anterior lens larger, without ocular plate; prodorsal sclerite subrectangular with a few punctuations in the middle and striations on the posterior half; anterior and lateral, margins slightly sinuous, posterior margin broadly convex (Figs. 6 and 9B and D), with pair of capitate trichobothria (si), with pointed scale-like setules that gradually increase in size distally, and 5 branched normal setae [pair of ve (= AL) seta, single vi (= AM) seta and pair of se (= PL) seta]; se > ve > vi > si. Opisthosoma (Fig. 7A, B) with 130 (132 in paratype) setae; dorsal opisthosomal with 68 setae, C row with 20 irregularly placed setae, D row with seven pairs of irregularly placed setae, E, F and H rows merged, with 34 setae pairs of setae and 62 (64 in paratype) ventral opisthosomal setae with 34 setae anterior to anus and 28 (30 in paratype) setae posterior. Two pairs of sternal setae (1a, 3a) between coxal fields I and III. Legs—femur of legs I–III each divided into basifemur and telofemur, each leg terminated with paired claws, and claw like empodium without onychotriches, coxal fields with a few punctuations; Leg I—coxal field seta 1b branched (1B); trochanter 1B; basifemur 1B; telofemur 5B; genu 4B, 2σ and κ; tibia 7B, 2φ and κ; tarsus 22B with ω, ε, dorsal eupathidium (ζ’) with companion seta (z) and subterminal eupathidium (ζ”), base of famulus (ε) distal to solenidion (ω) (Fig. 8A). Leg II—coxal field seta 2b (1B); trochanter 1B; basifemur 2B; telofemur 4B; genu 3B, σ; tibia 6B, 2φ; tarsus 16B with ω, ε and subterminal eupathidium (ζ), base of ε proximal to ω (Fig. 8B). Leg III—coxal field seta 3b (1B); trochanter 1B; basifemur 2B; telofemur 3B; genu 3B, σ, tibia 6B; tarsus 15B (Fig. 8C).

Fig. 5
figure 5

Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.; A—dorsal view of gnathosoma; B—ventral view of palp. Symbols: ω = solenidion on palptarsus; Odo = odontus; cs = adoral setae; bs = subcapitular setae. Scales: A and B 50 μm

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Fig. 6
figure 6

Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.; prodorsal sclerite. Symbols: ve = external vertical setae; se = external scapular setae; vi = internal vertical setae; si = internal scapular setae (trichobothria). Scales: 20 μm

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Fig. 7
figure 7

Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.; A—dorsal view of idiosoma; B—ventral view of idiosoma. Solid circles = ventral setae; open circles = dorsal setae; Symbols: c1–c10 = C row setae; d1–d7 = D row setae; 1a = anterior sternal setae; 3a = posterior sternal setae; 1b = coxal field I seta; 2b = coxal field II seta; 3b = coxal field III seta. Scales: A and B 100 μm

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Fig. 8
figure 8

Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.; A—Leg I; B—Leg II; C—Leg III; Solid circles = ventral leg setae; open circles = dorsal leg setae; Symbols: ζ’ = dorsal eupathidium on Ta I; ζ” and ζ = subterminal eupathidium on Ta I; ω = solenidion on Ta I and II; σ, σ’, σ" = solenidia on Ge I-III; κ = microsetae on Ge and Ti I; φ', φ" = solenidia on Ti I-II; ε = famulus on Ta I and II; 1b = coxal field I seta; 2b = coxal field II seta; 3b = coxal field III seta. Scales: A–C 50 μm

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Type material. HOLOTYPE: larva (USNMENT01758568); Joshua Tree National Park Riverside County, California State, USA; 17 Mar. 1963; ex Dipodomys merriami Mearns (Rodentia: Heteromyidae); H. S. Logsdon coll.; original number: HSL 630317. PARATYPE: 1 larva (USNMENT01758569); same data as holotype.

Type depository. USNM (holotype and paratype).

Discussion

Euschoengastia latchmani was described from horses, dogs, the black-tailed jackrabbit, Lepus californicus Gray, 1837 (Lagomorpha: Leporidae), and the golden-crowned sparrow, Zonotrichia atricapilla (Gmelin, 1789) (cited as Zonotrichia coronata) in California, USA [3]; while E. obscura was described from cricetid and heteromyid rodents in California, the USA, and Baja California Norte, Mexico [4]. The heteromyd host records include: Baja California Norte host was the agile kangaroo rat, Dipodomys agilis Gambel, 1848, and the California hosts include the San Diego pocket mouse, Chaetodipus fallax (Merriam, 1889) (cited as Perognathus fallax); the long-tailed pocket mouse, Chaetodipus formosus (Merriam, 1889) (cited as Perognathus formosus); the Merriam's kangaroo rat, Dipodomys merriami Mearns, 1890; the Stephens' kangaroo rat, Dipodomys stephensi (Merriam, 1907); the little pocket mouse, Perognathus longimembris (Coues, 1875); and cricetid host records includes: the dusky-footed woodrat, Neotoma fuscipes Baird, 1858; the desert woodrat, Neotoma lepida Thomas, 1893; the cactus mouse, Peromyscus eremicus (Baird, 1858); and the pinyon mouse, Peromyscus truei (Shufeldt, 1885) [4].

After examining all Euschoengastia types and conducting an exhaustive bibliographic review, we concluded G. latchmani n. comb. and G. obscura n. comb. represented a new genus, represented by having unique combination of characters (e.g. 3-pronged odontus and striations on the prodorsal sclerite) that may these two species different from the rest of Euschoengastia.

Both species share generic characteristics, but they can be separated by the following characters: G. latchmani n. comb. has obovate si setae, with rounded scale-like setules, C row with 15–16 dorsal opisthosomal setae, and D row with 12 setae. In comparison, G. obscura has capitate se setae, with pointed scale-like setules, C row with 20 dorsal opisthosomal setae, D row with 14 setae.

Some differences between the original descriptions include discrepancies in the numbers of dorsal and ventral opisthosomal setae in both species. Goffacarus latchmani n. comb. was described with 101 opisthosomal setae, we observed 110 setae in the holotype, with a range of 105–114 in the paratypes. Goffacarus obscura n. comb. was described with 137 opisthosomal setae, we observed 130 (holotype) and 132 (paratype) setae.

Some discrepancies and omissions in the measurements were observed in Brennan and Yunker’s [3] description of G. latchmani n. comb. They did not provide measurements of the legs, sternal or ventral opisthosomal setae and did not provide the complete schematic drawing of the legs, gnathosoma or the dorsal and ventral opisthosomal setal arrangement. The original description [4] of G. obscura n. comb. was more detailed, but the complete schematic drawings of the legs and the arrangement of the dorsal and ventral opisthosomal setae were omitted. While metric data were provided for G. obscura n. comb., we noticed differences in the ve, si, 1a setal lengths, as well as the dorsal and ventral opisthosomal setae. These differences are shown in Tables 5 and 8. In the present study, the missing measurements and drawings were provided for both species along with their microscopic images.

Despite being presented in the wide diagnosis provided by Wrenn [2] with the following consideration: “cuticular striae usually not encroaching over posterior portion of scutum”, the ornamentation of the prodorsal sclerites when changes and/or make it difficult to observe the line of the posterior margin (Fig. 9) become a stable and useful structure in differentiating genera, in the same way that it is used to separate genera as Neoschoengastia Ewing, 1929 and Megaschoengastia Vercammen-Grandjean, 1960. In this case, the marked striations change the margins, changing the shape of the prodorsal sclerite, consequently these striations help to separate Goffacarus n. gen. from Euschoengastia. It is important to highlight that the present study is part of a systematic review of Euschoengastia made by us that has always been necessary over the years.

Fig. 9
figure 9

Phase Contrast and DIC images of the prodorsal sclerite of Goffacarus Bassini-Silva, Jacinavicius and Welbourn, n. gen. A and C—Goffacarus latchmani (Brennan and Yunker, 1964) n. comb.; B and D—Goffacarus obscura (Wrenn and Loomis, 1974) n. comb.; Symbols: ve = external vertical setae; se = external scapular setae; vi = internal vertical setae; si = internal scapular setae (trichobothria). Scales: A–D 20 μm

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