# A new mite species Fagacarus absalom sp. n. (Astigmata: Acaridae) from the Eastern Palearctic, with 18 rRNA molecular barcodes

Pavel B Klimov, Vasiliy B Kolesnikov, Alexander A Khaustov, Barry M Oconnor

<figure><img src="image_1.png" /></figure>

## To cite this version:

Pavel B Klimov, Vasiliy B Kolesnikov, Alexander A Khaustov, Barry M Oconnor. A new mite species Fagacarus absalom sp. n. (Astigmata: Acaridae) from the Eastern Palearctic, with 18 rRNA molecular barcodes. Acarologia, 2024, 64 (2), pp.542-553. 10.24349/0j5b-083x. hal-04582884

HAL Id: hal-04582884

https://hal.science/hal-04582884

Submitted on 22 May 2024

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# A new mite species Fagacarus absalom sp. n. (Astigmata: Acaridae) from the Eastern Palearctic, with 18 rRNA molecular barcodes

Pavel B Klimov, Vasiliy B Kolesnikov, Alexander A Khaustov, Barry M Oconnor

► To cite this version:

Pavel B Klimov, Vasiliy B Kolesnikov, Alexander A Khaustov, Barry M Oconnor. A new mite species Fagacarus absalom sp. n. (Astigmata: Acaridae) from the Eastern Palearctic, with 18 rRNA molecular barcodes. Acarologia, 2024, 64 (2), pp.542-553. 10.24349/0j5b-083x. hal-04582884

HAL Id: hal-04582884

https://hal.science/hal-04582884v1

Submitted on 22 May 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
Acarologia

Open Science
in Acarology

# A new mite species *Fagacarus absalom* sp. n. (Astigmata: Acaridae) from the Eastern Palearctic, with 18 rRNA molecular barcodes

Pavel B. Klimov ID a,b, Vasiliy B. Kolesnikov ID a, Alexander A. Khaustov ID a, Barry M. OConnor ID c,d

## Original research

### ABSTRACT

The genus *Fagacarus* (Acari: Acaridae) characterized by long pectinate dorsal setae and heavily sclerotized and ornamented idiosoma is unmistakably recognizable in the subfamily Rhizoglyphinae. Mites of this genus live inside fallen tree trunks and have been only occasionally collected. However, it is increasingly likely that these mites are more widespread than previously believed. The single described species, *Fagacarus verrucosus*, is known from the USA (Indiana and Michigan); two undescribed species were reported from North America (Colorado) and the Western and Eastern Palearctic. The deutonymphal stage of *Fagacarus* is known, but it has never fully described. The paper presents description of a new species, *Fagacarus absalom* sp. n., based on adults and deutonymphs found in the Russian Far East. The new species differs from *F. verrucosus* by the length of seta *d* IV (female) and solenidia (σ II) of legs, the shape of posterior apodemes II in adults and pseudanal setae *ps*₁,₂ and the dorsal crista of tarsus IV in males. The uncorrected 18S rDNA genetic distance between *F. absalom* sp. n. and *F. verrucosus* is 1.52%, which is sufficient to delimit the two species based on this slowly evolving nuclear gene.

**Keywords** Astigmatid mites; morphology; Russian Far East; taxonomy; heteromorphic deutonymph

**Zoobank** http://zoobank.org/65BD239E-46D0-45A5-A7DD-9F4ACB8403DF

### Introduction

Mites of the genus *Fagacarus* Fain et Norton, 1979 (Acari: Acaridae: Rhizoglyphinae) feed on white rot fungi growing between the sapwood and heartwood layers in fallen tree trunks at an advanced stage of decay (PBK pers. obs.). As these mites occupy a hidden and very specialized ecological niche, they are only occasionally collected. A single described species, *Fagacarus verrucosus* Fain et Norton, 1979, is known from the USA (Indiana, Michigan), while undescribed species have been reported from both the Nearctic (Colorado, USA) and Western and Eastern Palearctic realms (Bugrov, 1997; Klimov, 2000; Klimov and Tolstikov, 2011). It is very likely that the genus *Fagacarus* may be actually more common, diverse, and broadly distributed.

The genus *Fagacarus* is characterized by a remarkably distinct external morphology, exemplified by long pectinate dorsal setae and a heavily sclerotized and ornamented idiosoma. In contrast, most other mites of the acarid subfamily Rhizoglyphinae typically have a smooth

Received 30 October 2023

Accepted 06 April 2024

Published 19 April 2024

Corresponding author

Pavel B. Klimov ID:
pklimov@purdue.edu

Academic editor

Akashi Hernandes, Fabio

https://doi.org/10.24349/0j5b-083x

ISSN 0044-586X (print)

ISSN 2107-7207 (electronic)

<figure><img src="image_3.png" /></figure>

Klimov P. B. et al.

Licensed under

Creative Commons CC-BY 4.0

<footnote>ᵃX-BIO Institute, Tyumen State University, Tyumen, Russia.</footnote>

<footnote>ᵇPurdue University, Lilly Hall of Life Sciences, West Lafayette, Indiana, USA.</footnote>

<footnote>ᶜDepartment of Ecology.</footnote>

<footnote>ᵈEvolutionary Biology, University of Michigan, 3600 Varsity Drive, Ann Arbor, MI 48109, USA.</footnote>
Acarologia

Open Science
in Acarology

# A new mite species *Fagacarus absalom* sp. n. (Astigmata: Acaridae) from the Eastern Palearctic, with 18 rRNA molecular barcodes

Pavel B. Klimov IDa,b, Vasiliy B. Kolesnikov IDa, Alexander A. Khaustov IDa, Barry M. OConnor Id,c,d

## Original research

### ABSTRACT

The genus *Fagacarus* (Acari: Acaridae) characterized by long pectinate dorsal setae and heavily sclerotized and ornamented idiosoma is unmistakably recognizable in the subfamily Rhizoglyphinae. Mites of this genus live inside fallen tree trunks and have been only occasionally collected. However, it is increasingly likely that these mites are more widespread than previously believed. The single described species, *Fagacarus verrucosus*, is known from the USA (Indiana and Michigan); two undescribed species were reported from North America (Colorado) and the Western and Eastern Palearctic. The deutonymphal stage of *Fagacarus* is known, but it has never fully described. The paper presents description of a new species, *Fagacarus absalom* sp. n., based on adults and deutonymphs found in the Russian Far East. The new species differs from *F. verrucosus* by the length of seta *d* IV (female) and solenidia (σ II) of legs, the shape of posterior apodemes II in adults and pseudanal setae *ps*₁,₂ and the dorsal crista of tarsus IV in males. The uncorrected 18S rDNA genetic distance between *F. absalom* sp. n. and *F. verrucosus* is 1.52%, which is sufficient to delimit the two species based on this slowly evolving nuclear gene.

**Keywords** Astigmatid mites; morphology; Russian Far East; taxonomy; heteromorphic deutonymph

**Zoobank** http://zoobank.org/65BD239E-46D0-45A5-A7DD-9F4ACB8403DF

### Introduction

Mites of the genus *Fagacarus* Fain et Norton, 1979 (Acari: Acaridae: Rhizoglyphinae) feed on white rot fungi growing between the sapwood and heartwood layers in fallen tree trunks at an advanced stage of decay (PBK pers. obs.). As these mites occupy a hidden and very specialized ecological niche, they are only occasionally collected. A single described species, *Fagacarus verrucosus* Fain et Norton, 1979, is known from the USA (Indiana, Michigan), while undescribed species have been reported from both the Nearctic (Colorado, USA) and Western and Eastern Palearctic realms (Bugrov, 1997; Klimov, 2000; Klimov and Tolstikov, 2011). It is very likely that the genus *Fagacarus* may be actually more common, diverse, and broadly distributed.

The genus *Fagacarus* is characterized by a remarkably distinct external morphology, exemplified by long pectinate dorsal setae and a heavily sclerotized and ornamented idiosoma. In contrast, most other mites of the acarid subfamily Rhizoglyphinae typically have a smooth

Received 30 October 2023

Accepted 06 April 2024

Published 19 April 2024

Corresponding author

Pavel B. Klimov ID:
pklimov@purdue.edu

Academic editor

Akashi Hernandes, Fabio

https://doi.org/10.24349/0j5b-083x

ISSN 0044-586X (print)

ISSN 2107-7207 (electronic)

<figure><img src="image_2.png" /></figure>

Klimov P. B. et al.

Licensed under

Creative Commons CC-BY 4.0

<footnote>ªX-BIO Institute, Tyumen State University, Tyumen, Russia.</footnote>

<footnote>ᵇPurdue University, Lilly Hall of Life Sciences, West Lafayette, Indiana, USA.</footnote>

<footnote>ᶜDepartment of Ecology.</footnote>

<footnote>ᵈEvolutionary Biology, University of Michigan, 3600 Varsity Drive, Ann Arbor, MI 48109, USA.</footnote>
idiosomal cuticle and smooth and short dorsal setae. Based on these distinct (but arguably autapomorphic and homoplastic) character states, the genus *Fagacarus* was first placed in a new subfamily Fagacarinae in the family Acaridae (Fain and Norton, 1979). However, cladistic analyses based on both adult and deutonymphal morphological characters demonstrated close relationships of *Fagacarus* with the genera *Schwiebea* Oudemans, 1916 and *Thyreophagus* Rondani, 1874 in the subfamily Rhizoglyphinae Oudemans, 1923 (Klimov, 2000). Subsequently, a refined analyses showed sister-group relationships of only two genera, *Fagacarus* and *Schwiebea* (Klimov and OConnor, 2003). This placement of *Fagacarus* among rhizoglyphine lineages was further supported by the discovery of heavily sclerotized and “hairy” adults of *Schwiebea koerneri* Türk et Türk, 1957 (Wurst, 2002), suggesting that these conspicuous character states also occur in other species of the subfamily Rhizoglyphinae and are not restricted only to the genus *Fagacarus*.

Here, we describe both adults and a heteromorphic deutonymph of a new species, *Fagacarus absalom sp. n.*, from the Russian Far East and provide renewed diagnosis of the genus.

## Material and methods

Tree trunks at an advanced stage of decay (almost no bark, wood is brown color, can be easily broken in pieces) were examined in the field. Specimens were collected by hand from colonies of white rot fungi growing between the sapwood and heartwood layers.

The terminology of idiosomal chaetotaxy follows Griffiths *et al.* (1990) and the terminology of the palp and leg chaetotaxy follows that of Grandjean (1939) and Griffiths (1970) with minor corrections to coxal setation by Norton (1998). The terminology of the spermatheca follows that of Witaliński *et al.* (1990) and Klimov and OConnor (2008). All measurements are in micrometres (µm).

We sequenced the small subunit ribosomal RNA (18S rRNA) in two species, *Fagacarus absalom* sp. n. (BMOC 01-0922-004.AD489, see below) and *Fagacarus verrucosus* (USA: Michigan, Lake Co., 3.5mi WSW Irons, Driftwood Valley Recreation Area, decayed log, 01 Oct 2000, B.M. OConnor, P. B. Klimov, 44°07′54″N 85°59′54″W, BMOC 00-1001-004.AD313). DNA extraction and sequencing were done as described previously (Klimov and OConnor, 2013). Genetic distances were calculated in PAUP v.4a168 (Swofford, 2022) as follows: begin paup; dset distance = p; savedist format = tabtext undefined = asterisk file = 1_p distances.tab; dset distance = k2p; savedist format = tabtext undefined = asterisk file = 2_k2p distances.tab; end; 18S rRNA sequences were deposited into the NCBI GenBank database, accession IDs: OR644287-OR644288.

## Taxonomy

**Family Acaridae Latreille, 1802**

**Subfamily Rhizoglyphinae Oudemans, 1923**

**Genus *Fagacarus* Fain et Norton, 1979**

Type species: *Fagacarus verrucosus* Fain et Norton, 1979, by original designation.

**Diagnosis** — *Adults*. Chelicera with one setae; subcapitulum with paired hemispherical filter apparatus at sides of oral opening well developed, with oblique rows of spines. Grandjean's organ reduced; dorsal setae long, rounded in cross-section, heavily barbed; setae *ve*, *f*₂ and *c*₃ absent, other idiosomal (*vi*, *se*, *si*, *c*₁, *c*₂, *c*ₚ, *d*₁, *e*₁, *d*₂, *e*₂, *h*₁, *h*₂, *h*₃) setae present. Cuticle dorsally and in part ventrally with numerous raised protuberances forming a reticulate pattern. Tarsal setae *ba* I-II spiniform, situated near *ω*₁; setae ~*aa* absent. Genua I with two solenidia. Genual setae *nG* III absent. *Female*. copulatory opening separated from anus by distance greater than half of anus length. *Male*. genital apparatus located between tarsi IV, with widened
idiosomal cuticle and smooth and short dorsal setae. Based on these distinct (but arguably autapomorphic and homoplastic) character states, the genus *Fagacarus* was first placed in a new subfamily Fagacarinae in the family Acaridae (Fain and Norton, 1979). However, cladistic analyses based on both adult and deutonymphal morphological characters demonstrated close relationships of *Fagacarus* with the genera *Schwiebea* Oudemans, 1916 and *Thyreophagus* Rondani, 1874 in the subfamily Rhizoglyphinae Oudemans, 1923 (Klimov, 2000). Subsequently, a refined analyses showed sister-group relationships of only two genera, *Fagacarus* and *Schwiebea* (Klimov and OConnor, 2003). This placement of *Fagacarus* among rhizoglyphine lineages was further supported by the discovery of heavily sclerotized and “hairy” adults of *Schwiebea koerneri* Türk et Türk, 1957 (Wurst, 2002), suggesting that these conspicuous character states also occur in other species of the subfamily Rhizoglyphinae and are not restricted only to the genus *Fagacarus*.

Here, we describe both adults and a heteromorphic deutonymph of a new species, *Fagacarus absalom sp. n.*, from the Russian Far East and provide renewed diagnosis of the genus.

## Material and methods

Tree trunks at an advanced stage of decay (almost no bark, wood is brown color, can be easily broken in pieces) were examined in the field. Specimens were collected by hand from colonies of white rot fungi growing between the sapwood and heartwood layers.

The terminology of idiosomal chaetotaxy follows Griffiths *et al.* (1990) and the terminology of the palp and leg chaetotaxy follows that of Grandjean (1939) and Griffiths (1970) with minor corrections to coxal setation by Norton (1998). The terminology of the spermatheca follows that of Witaliński *et al.* (1990) and Klimov and OConnor (2008). All measurements are in micrometres (μm).

We sequenced the small subunit ribosomal RNA (18S rRNA) in two species, *Fagacarus absalom sp. n.* (BMOC 01-0922-004.AD489, see below) and *Fagacarus verrucosus* (USA: Michigan, Lake Co., 3.5mi WSW Irons, Driftwood Valley Recreation Area, decayed log, 01 Oct 2000, B.M. OConnor, P. B. Klimov, 44°07′54″N 85°59′54″W, BMOC 00-1001-004.AD313). DNA extraction and sequencing were done as described previously (Klimov and OConnor, 2013). Genetic distances were calculated in PAUP v.4a168 (Swofford, 2022) as follows: begin paup; dset distance = p; savedist format = tabtext undefined = asterisk file = 1_p distances.tab; dset distance = k2p; savedist format = tabtext undefined = asterisk file = 2_k2p distances.tab; end; 18S rRNA sequences were deposited into the NCBI GenBank database, accession IDs: OR644287-OR644288.

## Taxonomy

### Family Acaridae Latreille, 1802

### Subfamily Rhizoglyphinae Oudemans, 1923

### Genus *Fagacarus* Fain et Norton, 1979

Type species: *Fagacarus verrucosus* Fain et Norton, 1979, by original designation.

**Diagnosis** — *Adults*. Chelicera with one setae; subcapitulum with paired hemispherical filter apparatus at sides of oral opening well developed, with oblique rows of spines. Grandjean's organ reduced; dorsal setae long, rounded in cross-section, heavily barbed; setae *ve*, *f*₂ and *c*₃ absent, other idiosomal (*vi*, *se*, *si*, *c*₁, *c*₂, *c*ₚ, *d*₁, *e*₁, *d*₂, *e*₂, *h*₁, *h*₂, *h*₃) setae present. Cuticle dorsally and in part ventrally with numerous raised protuberances forming a reticulate pattern. Tarsal setae *ba* I-II spiniform, situated near *ω*₁; setae ~*aa* absent. Genua I with two solenidia. Genual setae *nG* III absent. *Female*. copulatory opening separated from anus by distance greater than half of anus length. *Male*. genital apparatus located between tarsi IV, with widened
posterior part. Anal suckers vestigial, *ad*₁ and *ad*₂ minute or reduced to alveoli; *ps*₃ situated at anterior level of anus. Tarsus IV with a dorsal crista.

*Heteromorphic deutonymph.* Gnathosoma with one pair basal setae on dorsal sides, palpal remnants without setae. Setae *ve* absent. Setae *si*, *c*₁, *d*₁, *e*₁ and *h*₁ longer than other dorsal setae. Setae *1a*, *3a*, *4a* conoidal. Coxal fields II and III closed. Sternum long, free. Ventrum present. Attachment organ with conoidal setae *ps*₂ situated at posterior level of central suckers *ad*₁+₂, posterior to midline of *ad*₁+₂ and anterior to *ps*₁. Bases of conoidal setae *ps*₁ and *ps*₂ with long subcuticular sclerites, distinctly extending beyond the posterior level of attachment organ. On tarsus I, solenidion ω₃ situated in common field with solenidion ω₁; setae *ba* I and *aa* absent. Tarsal seta *e* I with very large, triangle-shaped tip; *e* II needle-like, shorter than claw; *e* III-IV spiniform. Tarsal setae *p*, *q* III and IV with attenuate tips. On genu III, setae *nG* III and solenidion σ III absent.

**Remarks** — The genus *Fagacarus* is similar to the genus *Schwiebea* sharing the following character states. *Adults:* Grandjean's organ is reduced; setae *ve*, *c*₃ and *f*₂ are absent; tarsal setae *r* IV, *gT* I-II and *hT* I-II are spiniform; tarsal setae *aa* are absent; tarsal setae *ba* I-II spiniform, situated at base of tarsus, adjacent to ω₁; tarsal setae *e* I-II are spiniform, massive. *Female:* adanal setae *ad* are absent; tarsal setae *la* I-II are spiniform; tarsal setae *ra* and *la* I-II are subterminal. *Male:* the genital apparatus is posterior to anterior apodemes IV and close to the anus; tarsal setae *f* I-II are simple; solenidion φ IV is spiniform. *Heteromorphic deutonymph:* setae *ve* are absent; tarsal setae *aa* absent; solenidion σ III is absent.

The genus *Fagacarus* differs from *Schwiebea* by the following character states. *Adults:* the subcapitulum has paired, hemispherical structures representing a filter apparatus (absent in *Schwiebea*); the dorsal setae are heavily barbed (smooth or very finely barbed in *Schwiebea koerneri*); the dorsal body is covered with raised, sclerotized protuberances (smooth in most *Schwiebea*, pitted in *S. koerneri*, or with small network of protuberances in nymphal stages of *S. koerneri*). *Male:* the opisthosomal shield is absent (present in *Schwiebea*); the anal suckers are vestigial (well developed in *Schwiebea*); adanal seate *ad*₁ and *ad*₂ are minute or alveolar (*ad*₁ and *ad*₂ or their alveoli absent in *Schwiebea*). *Heteromorphic deutonymph:* dorsal setae *si*, *c*₁, *d*₁, *e*₁ and *h*₁ are longer that other dorsal setae (subequal in *Schwiebea*); palps of gnathosoma without setae (with a pair of setae in *Schwiebea*); tarsal setae *e* I with a very large, triangle-shaped tips (setae *e* I rounded, not triangle-shaped in *Schwiebea*).

**Fagacarus absalom Klimov, Kolesnikov et OConnor, sp. n.**

Zoobank: D81AB2F8-CCE7-4511-9AEA-A248C4FF94FF

**Type material**

**Holotype female** — RUSSIA: Primorskiy Kray, Ussuriysky District, Kaymanovka village, banks of Barsukovka stream, inside rotten stump of a deciduous tree (between sapwood and heartwood layers), on edge of colony of white rot fungi, 7 Oct 1998, coll. P.B. Klimov (slide #1.1).

Paratypes: 5 females – same slide as holotype; Paratypes: 1 female, 2 males – same data, slide#1.2; 3 females, 7 males – same data, slide#1.3; 3 females, 5 males – same data, slide#1.4; 8 females, 5 males – same data, slide#1.5; 12 females, 3 males – same data, slide#1.6. 1 heteromorphic deutonymph – RUSSIA: Primorskiy Kray, Khasanskiy rayon, Kedrovaya pad’ reserve, fallen log with *Lasius niger* (Hymenoptera, Formicidae), 29 Apr 1999, coll. P.B. Klimov (mounted 21 Mar 2000) (slide #2.2); 2f – same data, slide #2.2.

**Non-type material** — Immatures (not counted) – slides 1.3, 1.6; 1 TN – slide 1.4, 1 TN – slide #2.2; 1 TN – slide #2.3.

**Type deposition** — Holotype and paratypes (slides #1.6, 2.3) are deposited in the Zoological Institute, Russian Academy of Sciences, Saint Petersburg, Russia (ZISP). The remaining paratypes (slides #1.1-1.5, 2.1, 2.2) are deposited in the University of Michigan, Museum of Zoology, Ann Arbor, Michigan, USA (UMMZ).
posterior part. Anal suckers vestigial, *ad*₁ and *ad*₂ minute or reduced to alveoli; *ps*₃ situated at anterior level of anus. Tarsus IV with a dorsal crista.

*Heteromorphic deutonymph.* Gnathosoma with one pair basal setae on dorsal sides, palpal remnants without setae. Setae *ve* absent. Setae *si*, *c*₁, *d*₁, *e*₁ and *h*₁ longer than other dorsal setae. Setae *la*, *3a*, *4a* conoidal. Coxal fields II and III closed. Sternum long, free. Ventrum present. Attachment organ with conoidal setae *ps*₂ situated at posterior level of central suckers *ad*₁+₂, posterior to midline of *ad*₁+₂ and anterior to *ps*₁. Bases of conoidal setae *ps*₁ and *ps*₂ with long subcuticular sclerites, distinctly extending beyond the posterior level of attachment organ. On tarsus I, solenidion ω₃ situated in common field with solenidion ω₁; setae *ba* I and *aa* absent. Tarsal seta *e* I with very large, triangle-shaped tip; *e* II needle-like, shorter than claw; *e* III-IV spiniform. Tarsal setae *p*, *q* III and IV with attenuate tips. On genu III, setae *nG* III and solenidion σ III absent.

**Remarks** — The genus *Fagacarus* is similar to the genus *Schwiebea* sharing the following character states. *Adults:* Grandjean's organ is reduced; setae *ve*, *c*₃ and *f*₂ are absent; tarsal setae *r* IV, *gT* I-II and *hT* I-II are spiniform; tarsal setae *aa* are absent; tarsal setae *ba* I-II spiniform, situated at base of tarsus, adjacent to ω₁; tarsal setae *e* I-II are spiniform, massive. *Female:* adanal setae *ad* are absent; tarsal setae *la* I-II are spiniform; tarsal setae *ra* and *la* I-II are subterminal. *Male:* the genital apparatus is posterior to anterior apodemes IV and close to the anus; tarsal setae *f* I-II are simple; solenidion φ IV is spiniform. *Heteromorphic deutonymph:* setae *ve* are absent; tarsal setae *aa* absent; solenidion σ III is absent.

The genus *Fagacarus* differs from *Schwiebea* by the following character states. *Adults:* the subcapitulum has paired, hemispherical structures representing a filter apparatus (absent in *Schwiebea*); the dorsal setae are heavily barbed (smooth or very finely barbed in *Schwiebea koerneri*); the dorsal body is covered with raised, sclerotized protuberances (smooth in most *Schwiebea*, pitted in *S. koerneri*, or with small network of protuberances in nymphal stages of *S. koerneri*). *Male:* the opisthosomal shield is absent (present in *Schwiebea*); the anal suckers are vestigial (well developed in *Schwiebea*); adanal seate *ad*₁ and *ad*₂ are minute or alveolar (*ad*₁ and *ad*₂ or their alveoli absent in *Schwiebea*). *Heteromorphic deutonymph:* dorsal setae *si*, *c*₁, *d*₁, *e*₁ and *h*₁ are longer that other dorsal setae (subequal in *Schwiebea*); palps of gnathosoma without setae (with a pair of setae in *Schwiebea*); tarsal setae *e* I with a very large, triangle-shaped tips (setae *e* I rounded, not triangle-shaped in *Schwiebea*).

**Fagacarus absalom Klimov, Kolesnikov et OConnor, sp. n.**

Zoobank: D81AB2F8-CCE7-4511-9AEA-A248C4FF94FF

**Type material**

**Holotype female** — RUSSIA: Primorskiy Kray, Ussuriysky District, Kaymanovka village, banks of Barsukovka stream, inside rotten stump of a deciduous tree (between sapwood and heartwood layers), on edge of colony of white rot fungi, 7 Oct 1998, coll. P.B. Klimov (slide #1.1).

Paratypes: 5 females – same slide as holotype; Paratypes: 1 female, 2 males – same data, slide#1.2; 3 females, 7 males – same data, slide#1.3; 3 females, 5 males – same data, slide#1.4; 8 females, 5 males – same data, slide#1.5; 12 females, 3 males – same data, slide#1.6. 1 heteromorphic deutonymph – RUSSIA: Primorskiy Kray, Khasanskiy rayon, Kedrovaya pad’ reserve, fallen log with *Lasius niger* (Hymenoptera, Formicidae), 29 Apr 1999, coll. P.B. Klimov (mounted 21 Mar 2000) (slide #2.2); 2f – same data, slide #2.2.

**Non-type material** — Immatures (not counted) – slides 1.3, 1.6; 1 TN – slide 1.4, 1 TN – slide #2.2; 1 TN – slide #2.3.

**Type deposition** — Holotype and paratypes (slides #1.6, 2.3) are deposited in the Zoological Institute, Russian Academy of Sciences, Saint Petersburg, Russia (ZISP). The remaining paratypes (slides #1.1-1.5, 2.1, 2.2) are deposited in the University of Michigan, Museum of Zoology, Ann Arbor, Michigan, USA (UMMZ).
## Description

**Female** — (Figures 1A, B, 2A–H, 3B, C, 6A). Subcapitulum (57 × 38, holotype) elongated, trapezoid, lateral sides straight, strongly converging towards apex, at base, with two pairs of weakly sclerotized fields (muscle attachment sites). Paired filter apparatus at sides of oral opening well developed, forming dense hemispherical structures with oblique rows of spines. Subcapitulum with 1 pair of filiform setae *h* and short setae *a*. Palps with setae *sup* and *cm*; supracoxal seta (*elcp*) absent. Palp solenidion ω rod-shaped; *ul'* and *ul''* present, minute, button-shaped. Chelicerae (55) elongated, twice as long as height, with one distal sharp tooth and seta *cha*.

Idiosoma, length × width, 287 × 175 (holotype), 276–347 × 160–187 (paratypes, n=21), length / wide ratio 1.53–1.90 (n=12). Propodosoma 88, hysterosoma 199, ratio of hysterosoma/propodosoma 2.26 (n=1). Cuticle pigmented, not forming distinct shields or shield. Dorsolateral idiosoma with raised protuberances (sometimes conical and spiniform in shape); on dorsal hysterosoma, these protuberances form a network consisting of 4-6-sided polygons; central part of dorsum has two pairs of curved and heavily sclerotized ridges at level of scapular setae; on middorsal propodosoma, pattern is weakly developed; lateral propodosoma and hysterosoma with irregular protuberances, not forming clear pattern. Idiosoma smooth ventrally, except for posterolateral hysterosoma and transverse area at level of posterior coxal apodemes II, which covered by small, conical protuberances. Dorsal sejugal furrow well developed.

Grandjean's organ not observed. Supracoxal seta of leg I (*scx*) 28, smooth, long, nearly spiniform. Dorsal setae heavily barbed, thick, rounded in cross section, situated on protuberances (except for *vi*, *scx*, *h*<sub>3</sub>). External scapular setae *se* anterior to posterior propodosomal shield ridges; *si* posterior to *se*, 1.5 times shorter than *se*. Dorsal setae *c*<sub>1</sub> and *c*<sub>2</sub> at anterior margin of hysterosoma. Setae *c*<sub>3</sub>,*f*<sub>2</sub> and *ve* absent. Length of setae *vi* 41, *se* 73, *si* 48, *c*<sub>1</sub> 63, *c*<sub>2</sub> 44, *c*<sub>p</sub> 67, *d*<sub>1</sub> 104, *d*<sub>2</sub> 61 *e*<sub>1</sub> 79, *h*<sub>1</sub> 70, *h*<sub>2</sub> 56, *h*<sub>3</sub> 34 (n=1). Distance *vi-vi* 13, *se-se* 63, *si-si* 21, *c*<sub>1</sub>-*c*<sub>1</sub> 44, *d*<sub>1</sub>-*d*<sub>1</sub> 20, *e*<sub>1</sub>-*e*<sub>1</sub> 27, *h*<sub>1</sub>-*h*<sub>1</sub> 41. Cupules *ip* situated ventrally, approximately between insertion points of legs III-IV, *ih* situated on sides of anterior end of anus, cupules *ia* and *im* not observed. Opisthonotal gland openings *gla* situated on cuticular protuberances, slightly anterior to *e*<sub>2</sub>. Anterior coxal apodemes I fused to form sternum, other coxal apodemes free, posterior coxal apodeme IV absent. Coxal fields I-IV with large sclerotized areas. Distance between posterior end of posterior coxal apodemes II and free tip of anterior coxal apodemes III shorter than length of the latter. Ovipore wide, in form of an inverted Y; situated between coxal fields III-IV. Coxisternal setae 1a, 3a, 4a, 4b and genital setae *g* subequal in length, filiform; setae *g* anteriad of setae 4a. Genital papillae well sclerotized and pigmented, rounded; distal tip rounded, with pigmented cap; proximal part slightly narrowed forming a neck. Anus shifted from posterior edge of body by more than 3/4 of its length. Setae *ps* and *ad* absent. Copulatory opening ventral, near posterior margin of body (separated from anus by a distance greater than half of anus length); inseminatory canal of spermatheca long, and widened near spermatheca (diameter 1.6); spermatheca spherical (18.9), pigmented and sclerotized; efferent ducts in form of elongated V-like funnels (5.6 × 1.9).

Legs I-IV short, legs length (without empodium) 99, 90, 90 and 120 (n=1). Pretarsi with claws attached to condylophores. Leg setation: trochanters 1–1–1–0, femora 1–1–0–1, genua 2(2)–2(1)–0(1)–0, tibiae 2(1)–2(1)–1(1)–1(1), tarsi 12(3+ε)–12(1)–10–10. Trochanters I–III with filiform setae (*pR* I–II, *sR* III). Femoral setae *vF* I–II and *wF* IV filiform. Genual setae *cG* I–II short, spiniform, *mG* I–II robust, sword-shaped, *nG* III absent. Tibial setae *gT* I–II spiniform, *hT* I–II and *kT* III robust, sword-shaped, *kT* IV slightly sword-shaped. Tarsi I–II without foliate setae, setae *ba* and *e* robust, spiniform (at least 1/2 of claw length), *ba* situated near ω₁; *wa* and *la* spiniform; *d*, *f*, *ra* filiform, *d* and *f* shorter than tarsus, *ra* slightly widened basally; *s*, *v*, *u*, *p* and *q* spiniform, *p* I and *q* II shorter than other spiniform setae. Tarsi III-IV without foliate setae; setae *w*, *e*, *r*, *s*, *u*, *v*, *p* and *q* spiniform; *d* and *f* filiform, shorter than tarsus, *p* and *u* larger than *q* and *v*. Solenidion ω₁ I bacilliform, thin, slightly curved, slightly widened apically, reaching level of seta *e*; ω₂ I anterolaterad ω₁ I, bacilliform, about 5 times shorter than
## Description

**Female** — (Figures 1A, B, 2A–H, 3B, C, 6A). Subcapitulum (57 × 38, holotype) elongated, trapezoid, lateral sides straight, strongly converging towards apex, at base, with two pairs of weakly sclerotized fields (muscle attachment sites). Paired filter apparatus at sides of oral opening well developed, forming dense hemispherical structures with oblique rows of spines. Subcapitulum with 1 pair of filiform setae *h* and short setae *a*. Palps with setae *sup* and *cm*; supracoxal seta (*elcp*) absent. Palp solenidion ω rod-shaped; *ul'* and *ul''* present, minute, button-shaped. Chelicerae (55) elongated, twice as long as height, with one distal sharp tooth and seta *cha*.

Idiosoma, length × width, 287 × 175 (holotype), 276–347 × 160–187 (paratypes, n=21), length / wide ratio 1.53–1.90 (n=12). Propodosoma 88, hysterosoma 199, ratio of hysterosoma/propodosoma 2.26 (n=1). Cuticle pigmented, not forming distinct shields or shield. Dorsolateral idiosoma with raised protuberances (sometimes conical and spiniform in shape); on dorsal hysterosoma, these protuberances form a network consisting of 4-6-sided polygons; central part of dorsum has two pairs of curved and heavily sclerotized ridges at level of scapular setae; on middorsal propodosoma, pattern is weakly developed; lateral propodosoma and hysterosoma with irregular protuberances, not forming clear pattern. Idiosoma smooth ventrally, except for posterolateral hysterosoma and transverse area at level of posterior coxal apodemes II, which covered by small, conical protuberances. Dorsal sejugal furrow well developed.

Grandjean's organ not observed. Supracoxal seta of leg I (scx) 28, smooth, long, nearly spiniform. Dorsal setae heavily barbed, thick, rounded in cross section, situated on protuberances (except for *vi*, *scx*, *h*<sub>3</sub>). External scapular setae *se* anterior to posterior propodosomal shield ridges; *si* posterior to *se*, 1.5 times shorter than *se*. Dorsal setae *c*<sub>1</sub> and *c*<sub>2</sub> at anterior margin of hysterosoma. Setae *c*<sub>3</sub>,*f*<sub>2</sub> and *ve* absent. Length of setae *vi* 41, *se* 73, *si* 48, *c*<sub>1</sub> 63, *c*<sub>2</sub> 44, *c*<sub>p</sub> 67, *d*<sub>1</sub> 104, *d*<sub>2</sub> 61 *e*<sub>1</sub> 79, *h*<sub>1</sub> 70, *h*<sub>2</sub> 56, *h*<sub>3</sub> 34 (n=1). Distance *vi-vi* 13, *se-se* 63, *si-si* 21, *c*<sub>1</sub>-*c*<sub>1</sub> 44, *d*<sub>1</sub>-*d*<sub>1</sub> 20, *e*<sub>1</sub>-*e*<sub>1</sub> 27, *h*<sub>1</sub>-*h*<sub>1</sub> 41. Cupules *ip* situated ventrally, approximately between insertion points of legs III-IV, *ih* situated on sides of anterior end of anus, cupules *ia* and *im* not observed. Opisthonotal gland openings *gla* situated on cuticular protuberances, slightly anterior to *e*<sub>2</sub>. Anterior coxal apodemes I fused to form sternum, other coxal apodemes free, posterior coxal apodeme IV absent. Coxal fields I-IV with large sclerotized areas. Distance between posterior end of posterior coxal apodemes II and free tip of anterior coxal apodemes III shorter than length of the latter. Ovipore wide, in form of an inverted Y; situated between coxal fields III-IV. Coxisternal setae 1a, 3a, 4a, 4b and genital setae *g* subequal in length, filiform; setae *g* anteriad of setae 4a. Genital papillae well sclerotized and pigmented, rounded; distal tip rounded, with pigmented cap; proximal part slightly narrowed forming a neck. Anus shifted from posterior edge of body by more than 3/4 of its length. Setae *ps* and *ad* absent. Copulatory opening ventral, near posterior margin of body (separated from anus by a distance greater than half of anus length); inseminatory canal of spermatheca long, and widened near spermatheca (diameter 1.6); spermatheca spherical (18.9), pigmented and sclerotized; efferent ducts in form of elongated V-like funnels (5.6 × 1.9).

Legs I-IV short, legs length (without empodium) 99, 90, 90 and 120 (n=1). Pretarsi with claws attached to condylophores. Leg setation: trochanters 1–1–1–0, femora 1–1–0–1, genua 2(2)–2(1)–0(1)–0, tibiae 2(1)–2(1)–1(1)–1(1), tarsi 12(3+ε)–12(1)–10–10. Trochanters I–III with filiform setae (*pR* I–II, *sR* III). Femoral setae *vF* I–II and *wF* IV filiform. Genual setae *cG* I–II short, spiniform, *mG* I–II robust, sword-shaped, *nG* III absent. Tibial setae *gT* I–II spiniform, *hT* I–II and *kT* III robust, sword-shaped, *kT* IV slightly sword-shaped. Tarsi I–II without foliate setae, setae *ba* and *e* robust, spiniform (at least 1/2 of claw length), *ba* situated near ω₁; *wa* and *la* spiniform; *d*, *f*, *ra* filiform, *d* and *f* shorter than tarsus, *ra* slightly widened basally; *s*, *v*, *u*, *p* and *q* spiniform, *p* I and *q* II shorter than other spiniform setae. Tarsi III-IV without foliate setae; setae *w*, *e*, *r*, *s*, *u*, *v*, *p* and *q* spiniform; *d* and *f* filiform, shorter than tarsus, *p* and *u* larger than *q* and *v*. Solenidion ω₁ I bacilliform, thin, slightly curved, slightly widened apically, reaching level of seta *e*; ω₂ I anterolaterad ω₁ I, bacilliform, about 5 times shorter than
<figure><img src="image_4.png" /><figcaption>**Figure 1** *Fagacarus absalom* sp. n., female (A, B) and male (C, D): A, C – ventral view; B, D – dorsal view.</figcaption></figure>
<figure><img src="image_3.png" /><figcaption>**Figure 1** *Fagacarus absalom* sp. n., female (A, B) and male (C, D): A, C – ventral view; B, D – dorsal view.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Figure 2** *Fagacarus absalom sp. n.*, female (A–H) and male (I, J): A–D – legs I–IV, posterior (I, II) and anterior (III, IV) views; E–H – tarsus I–IV, anterior (I, II) and posterior (III, IV) views; I – leg IV, anterior view; J – tarsus IV, posterior view.</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**Figure 2** *Fagacarus absalom sp. n.*, female (A–H) and male (I, J): A–D – legs I–IV, posterior (I, II) and anterior (III, IV) views; E–H – tarsus I–IV, anterior (I, II) and posterior (III, IV) views; I – leg IV, anterior view; J – tarsus IV, posterior view.</figcaption></figure>
<figure><img src="image_6.png" /></figure>

**Figure 3** *Fagacarus absalom* sp. n., female (B, C) and male (A, D, E): A – chelicera; B – gnathosoma, ventral view; C – spermatheca; D – genital capsule.

$\omega_1$ I; $\omega_3$ I curved, with rounded tip, not reaching half of claw; famulus $\epsilon$ short. Solenidion $\omega$ II well expanded apically in comparison with $\omega_1$ I. Solenidion $\phi$ I long, tapering; $\phi$ II shorter than $\phi$ I, projecting slightly beyond apex of tarsus; $\phi$ III and IV short, tapering, shorter than tibia. Solenidia $\sigma'$ and $\sigma''$ I distinctly longer than tibia, $\sigma'$ slightly longer than $\sigma''$; $\sigma$ II distinctly longer than tibia, with rounded tip; $\sigma$ III curved, with rounded tip, shorter than genu III.

**Male** — (Figures 1C, D, 2I, J, 3A, D, E, 6B). Gnathosoma as in a female. Subcapitulum 51 × 35 (n=1). Chelicerae 44 (n=1).

Idiosoma, length × wide, 287–237 × 140 – 176 (n=13), length / wide 1.54-1.92 (n=12).

Propodosomal length 85, hysterosomal length 158, ratio of hysterosoma/propodosoma 1.86 (n=1). Iddiosomal cuticle as in female; distinct shields or sclerites absent. Sejugal furrow present. Grandjean's organ absent. Dorsal setae as in female; length of setae *scx* 25, *vi* 34, *se* 56, *si* 38, *c*₁ 66, *c*₂ 36, *c*ₚ 50, *d*₁ 82, *d*₂ 53 *e*₁ 61, *h*₁ 56, *h*₂ 41, *h*₃ 27 (n=1). Distance *vi-vi* 13, *se-se* 60, *si-si* 20, *c*₁-*c*₁ 27, *d*₁-*d*₁ 21, *e*₁-*e*₁ 25, *h*₁-*h*₁ 30. Opisthonotal gland opening *gla*, cupules and apodemes as in female. Setae *g* slightly anteriad of setae *4a*. Genital apparatus between apodemes IV and close to anus. Aedeagus rod-shaped, slender, not curved, not protruding beyond the edge of genital capsule. Genital papillae as in a female. Anus shifted from posterior margin of body by more than 3/4 of its length. Anal suckers vestigial. Cuticle posteriad of anus with irregular small papillae. Setae (*ps*) present: *ps*₁ (4) and *ps*₂ (3) situated posteriad of anus, short, slightly spiniform, distance *ps*₂-*ps*₂ longer than distance *ps*₁-*ps*₁; *ps*₃ situated near anterior sides of anus, filiform, slightly longer than *ps*₁ and *ps*₂. Setae *ad*₁-₂ adjacent to each other, situated on anal suckers, *ad*₁ very short, *ad*₂ represented by alveoli.

Legs I–III as in a female, except solenidion $\omega_3$ I thickened, almost reaching tip of claw. Trochanter and femur IV as in female. Tibia IV with slightly sword-shaped seta *kT* IV. Tarsus IV with dorsal crista, seta *f* filiform, situated anteriad of crista; setae *d* and *e* represented by
<figure><img src="image_5.png" /></figure>

**Figure 3** *Fagacarus absalom* sp. n., female (B, C) and male (A, D, E): A – chelicera; B – gnathosoma, ventral view; C – spermatheca; D – genital capsule.

$\omega_1$ I; $\omega_3$ I curved, with rounded tip, not reaching half of claw; famulus $\epsilon$ short. Solenidion $\omega$ II well expanded apically in comparison with $\omega_1$ I. Solenidion $\phi$ I long, tapering; $\phi$ II shorter than $\phi$ I, projecting slightly beyond apex of tarsus; $\phi$ III and IV short, tapering, shorter than tibia. Solenidia $\sigma'$ and $\sigma''$ I distinctly longer than tibia, $\sigma'$ slightly longer than $\sigma''$; $\sigma$ II distinctly longer than tibia, with rounded tip; $\sigma$ III curved, with rounded tip, shorter than genu III.

**Male** — (Figures 1C, D, 2I, J, 3A, D, E, 6B). Gnathosoma as in a female. Subcapitulum 51 × 35 (n=1). Chelicerae 44 (n=1).

Idiosoma, length × wide, 287–237 × 140 – 176 (n=13), length / wide 1.54-1.92 (n=12).

Propodosomal length 85, hysterosomal length 158, ratio of hysterosoma/propodosoma 1.86 (n=1). Iddiosomal cuticle as in female; distinct shields or sclerites absent. Sejugal furrow present. Grandjean's organ absent. Dorsal setae as in female; length of setae *scx* 25, *vi* 34, *se* 56, *si* 38, *c*₁ 66, *c*₂ 36, *c*ₚ 50, *d*₁ 82, *d*₂ 53 *e*₁ 61, *h*₁ 56, *h*₂ 41, *h*₃ 27 (n=1). Distance *vi-vi* 13, *se-se* 60, *si-si* 20, *c*₁-*c*₁ 27, *d*₁-*d*₁ 21, *e*₁-*e*₁ 25, *h*₁-*h*₁ 30. Opisthonotal gland opening *gla*, cupules and apodemes as in female. Setae *g* slightly anteriad of setae *4a*. Genital apparatus between apodemes IV and close to anus. Aedeagus rod-shaped, slender, not curved, not protruding beyond the edge of genital capsule. Genital papillae as in a female. Anus shifted from posterior margin of body by more than 3/4 of its length. Anal suckers vestigial. Cuticle posteriad of anus with irregular small papillae. Setae (*ps*) present: *ps*₁ (4) and *ps*₂ (3) situated posteriad of anus, short, slightly spiniform, distance *ps*₂-*ps*₂ longer than distance *ps*₁-*ps*₁; *ps*₃ situated near anterior sides of anus, filiform, slightly longer than *ps*₁ and *ps*₂. Setae *ad*₁-₂ adjacent to each other, situated on anal suckers, *ad*₁ very short, *ad*₂ represented by alveoli.

Legs I–III as in a female, except solenidion $\omega_3$ I thickened, almost reaching tip of claw. Trochanter and femur IV as in female. Tibia IV with slightly sword-shaped seta *kT* IV. Tarsus IV with dorsal crista, seta *f* filiform, situated anteriad of crista; setae *d* and *e* represented by
<figure><img src="image_7.png" /><figcaption>**Figure 4** *Fagacarus absalom* sp. n., heteromorphic deutonymph: A – dorsal view; B – ventral view.</figcaption></figure>

suckers (shifted to distal part of tarsus); other setae (w, r, s, u, v, p and q) spiniform. Solenidion φ of tibia IV shortened and thickened.

**Heteromorphic deutonymph** — (Figures 4, 5, 6C–E). Body rounded, 160 × 140, length/width ratio 1.1. Gnathosoma with elongated subcapitular remnant (slightly longer than wide, 12 × 7) and short palps (slightly longer than wide) with filiform apical palpal solenidia ω (25), and one pair of dorsobasal setae.

Dorsal idiosoma smooth, except regions of sejugal furrow and lateral sides of hysterosomal shield, which have lineate pattern. Length of hysterosoma (130), length of propodosoma (32) 4.0. Anterior propodosoma with rounded rostrum and convave sides. Ocelli absent. Setae *vi* short (4), filiform, smooth. Setae *ve* absent. Setae *se* (10) longer that *vi*, finely serrate at tips; setae *si* (18) longer that *se*, finely serrate; setae *si* posterior to *se*. Setae *scx* (9) with bifurcate
<figure><img src="image_6.png" /><figcaption>**Figure 4** *Fagacarus absalom* sp. n., heteromorphic deutonymph: A – dorsal view; B – ventral view.</figcaption></figure>

suckers (shifted to distal part of tarsus); other setae (w, r, s, u, v, p and q) spiniform. Solenidion φ of tibia IV shortened and thickened.

**Heteromorphic deutonymph** — (Figures 4, 5, 6C–E). Body rounded, 160 × 140, length/width ratio 1.1. Gnathosoma with elongated subcapitular remnant (slightly longer than wide, 12 × 7) and short palps (slightly longer than wide) with filiform apical palpal solenidia ω (25), and one pair of dorsobasal setae.

Dorsal idiosoma smooth, except regions of sejugal furrow and lateral sides of hysterosomal shield, which have lineate pattern. Length of hysterosoma (130), length of propodosoma (32) 4.0. Anterior propodosoma with rounded rostrum and convave sides. Ocelli absent. Setae *vi* short (4), filiform, smooth. Setae *ve* absent. Setae *se* (10) longer that *vi*, finely serrate at tips; setae *si* (18) longer that *se*, finely serrate; setae *si* posterior to *se*. Setae *scx* (9) with bifurcate
<figure><img src="image_8.png" /><figcaption>**Figure 5** *Fagacarus absalom* sp. n., heteromorphic deutonymph: A – leg I, dorsal view; B – tarsus I, ventral view; C – leg II, dorsal view; D – tarsus II, ventral view; E – leg III, ventral view; F – leg IV, ventral view; G – anal disk.</figcaption></figure>

tip. Hysterosomal setae $c_1$ (22), $d_1$ (25), $e_1$ (20) and $h_1$ (15) finely serrate; length of $d_1$ and $e_1$ shorter than distance between bases of $d_1-e_1$ and $e_1-h_1$, respectively. Setae $c_2$ (10), $c_p$ (7) and $d_2$ (7) shorter than $c_1$, $d_1$, $e_1$ and $h_1$, all somewhat finely serrate. Setae $e_2$ (6), $f_2$ (4), $h_2$ (6) and $h_3$ (10) smooth, shorter than $c_1$, $d_1$, $e_1$ and $h_1$ (setae $h_3$ longer than $e_2$, $f_2$ and $h_2$). Opisthonotal gland openings *gla* situated between $d_2$ and $e_2$. Cupules *ia* present, situated posterior to $c_2$.

Surface of coxal fields without any well-developed pattern. Anterior apodemes of coxal fields I fused, forming a sternum. Posterior end of sternum acute, not touching anterior apodemes II, ending near ends of anterior apodemes II; distance between its end and ventrogenial shield much shorter than its length. Coxal fields II and III closed, posterior apodemes II and anterior apodemes III adjacent. Anterior apodemes of coxal fields III not fused with each
<figure><img src="image_7.png" /><figcaption>**Figure 5** *Fagacarus absalom* sp. n., heteromorphic deutonymph: A – leg I, dorsal view; B – tarsus I, ventral view; C – leg II, dorsal view; D – tarsus II, ventral view; E – leg III, ventral view; F – leg IV, ventral view; G – anal disk.</figcaption></figure>

tip. Hysterosomal setae $c_1$ (22), $d_1$ (25), $e_1$ (20) and $h_1$ (15) finely serrate; length of $d_1$ and $e_1$ shorter than distance between bases of $d_1-e_1$ and $e_1-h_1$, respectively. Setae $c_2$ (10), $c_p$ (7) and $d_2$ (7) shorter than $c_1$, $d_1$, $e_1$ and $h_1$, all somewhat finely serrate. Setae $e_2$ (6), $f_2$ (4), $h_2$ (6) and $h_3$ (10) smooth, shorter than $c_1$, $d_1$, $e_1$ and $h_1$ (setae $h_3$ longer than $e_2$, $f_2$ and $h_2$). Opisthonotal gland openings *gla* situated between $d_2$ and $e_2$. Cupules *ia* present, situated posterior to $c_2$.

Surface of coxal fields without any well-developed pattern. Anterior apodemes of coxal fields I fused, forming a sternum. Posterior end of sternum acute, not touching anterior apodemes II, ending near ends of anterior apodemes II; distance between its end and ventrogenial shield much shorter than its length. Coxal fields II and III closed, posterior apodemes II and anterior apodemes III adjacent. Anterior apodemes of coxal fields III not fused with each
<figure><img src="image_9.png" /><figcaption>**Figure 6** *Fagacarus absalom* sp. n., female (A), male (B) and heteromorphic deutonymph (C-E), DIC photomicrographs: A, B – gnathosoma (arrows point to the filter apparatus); C – dorsal view; D – ventral view; E – dorsal setae *d*₁ and *e*₁.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Figure 6** *Fagacarus absalom* sp. n., female (A), male (B) and heteromorphic deutonymph (C-E), DIC photomicrographs: A, B – gnathosoma (arrows point to the filter apparatus); C – dorsal view; D – ventral view; E – dorsal setae *d*₁ and *e*₁.</figcaption></figure>
other, with a short gap between them. Anterior apodemes of coaxal fields IV fused to each other and connected to apodemes III. Ventrum present, not reaching anus. Setae 1a, 3a, 4a conoidal, well-developed; 4a situated posterior to g; 4b (3) and g (4) filiform. Setae c₃ (3) filiform, ventral, situated between transverse levels of trochanters II–III. Attachment organ 40 long, 48 wide (length/width ratio 0.8), situated near posterior edge of the body. Cuticular suckers present. Setae ps₁ and ps₂ conoidal; ps₂ situated posterior to midline of ad₁+₂ and anterior to ps₁; sclerites of ps₁ and ps₂ large, elongated. A pair of small refractile spots (ps₃) anterolaterad of median suckers (ad₁+₂). Suckers ad₃ round; ad₁+₂ much larger, consisting of paired vestigial alveoli surrounded by wide sclerotized border.

Legs I long (96), longer than half the body length; legs II-IV (71, 50 and 63, respectively) shorter than half the body length; all segments free, with dorsal and ventral longitudinal ridges near the setae. Leg setation: trochanters 1–1–1–0, femora 1–1–0–1, genua 2(1)–2(1)–0–0, tibiae 2(1)–2(1)–1(1)–1(1), tarsi 8(3+ε)–9(1)–8–8. Trochanters I–III each with filiform seta (pR I, II, sR III). Femoral setae vF I, II spiniform with attenuate tips, wF IV setiform. Genual setae mG I, II spiniform, sword-shaped; cG I, II spiniform, short; nG III absent. Tibial setae gT I–II and kT III, IV spiniform; setae hT I, II spiniform, sword-shaped, larger than other sword-shaped leg setae. All pretarsi with hooked empodial claws arising from tarsal apices and connected to short, paired condylophores. Tarsus I with 4 setiform setae (d, f, p and q), 3 spiniform setae (ra, la and wa) and 1 modified setae e (wide triangle-shaped tips). Tarsus II with 3 filiform setae (d, p and q), 5 spiniform setae (e, ba, ra, la and wa) and foliate seta f. Tarsi III, IV with 2 filiform setae (d and f') and 6 spiniform setae (e, p, q, w, e and s), with attenuate tips. Solenidia ω₁ I-II on tarsi I cylindrical, with rounded apices, situated in basal part of tarsus; solenidion ω₃ situated close to ω₁, longer than ω₁, cylindrical; solenidion ω₂ cylindrical, with rounded apex, shorter than ω₁. Famulus ε short, spiniform, adjacent to solenidion ω₁. Solenidia φ I, II tapering, shorter than tarsi; φ II, IV short, bacilliform. Genua I, II with single solenidion (σ), σ I, II elongate, cylindrical; σ I shorter than ω₂; σ II shorter than σ I; σ of genu III absent.

Diagnosis

*Fagacarus absalom* differs from *F. verrucosus* by the following character states: in adults, solenidion σ II reaches tarsus II (vs. not reaching in *F. verrucosus*), posterior coaxal apodemes II are curved (vs. nearly straight in *F. verrucosus*); in males, pseudanal setae ps₂ are smooth, situated at the posterior edge of the anus, not protruding beyond the posterior margin of the body (vs. barbed, posterior to this level, protruding in *F. verrucosus*), pseudanal setae ps₁ and ps₂ are slightly spiniform, about 5 times shorter than h₃ (vs. filiform, less than 2 times shorter in *F. verrucosus*), the dorsal crista of tarsus IV is about 3/4 of the height of tarsus IV (vs. about 1/2 in *F. verrucosus*); in females, setae d IV are shorter than tarsus IV (vs. slightly longer in *F. verrucosus*). Heteromorphic deutonymphs are known only for *Fagacarus absalom* and therefore cannot be compared with those of any other species of the genus *Fagacarus*.

Molecular identification

A NCBI BLAST search of both 18S rRNA sequences (*Fagacarus absalom* sp. n. and *F. verrucosus*) returned close matches with *Schwiebea pseudotsugae* (97.40–96.73%) and *Rhizoglyphus* sp. AP-2010 (97.26–96.78%), thus confirming our morphology-based placement of *Fagacarus* in the subfamily Rhizoglyphinae and as a sister lineage to *Schwiebea* (Klimov and OConnor, 2003). Uncorrected 18S rDNA genetic distance between *Fagacarus absalom* sp. n. and *F. verrucosus* was 1.52%. This distance is sufficient to delimit the two species, since 18 rDNA (a nuclear gene) evolves much slower than the COX1 gene (a mitochondrial gene) (Klimov at al. 2019).

Etymology

Absalom is a biblical figure known for his luxuriant, long hair, which is reminiscent of the long and barbed dorsal setae of *Fagacarus absalom*. This specific name is treated here as a nomen in apposition.
other, with a short gap between them. Anterior apodemes of coaxal fields IV fused to each other and connected to apodemes III. Ventrum present, not reaching anus. Setae 1a, 3a, 4a conoidal, well-developed; 4a situated posterior to g; 4b (3) and g (4) filiform. Setae c₃ (3) filiform, ventral, situated between transverse levels of trochanters II–III. Attachment organ 40 long, 48 wide (length/width ratio 0.8), situated near posterior edge of the body. Cuticular suckers present. Setae ps₁ and ps₂ conoidal; ps₂ situated posterior to midline of ad₁+₂ and anterior to ps₁; sclerites of ps₁ and ps₂ large, elongated. A pair of small refractile spots (ps₃) anterolaterad of median suckers (ad₁+₂). Suckers ad₃ round; ad₁+₂ much larger, consisting of paired vestigial alveoli surrounded by wide sclerotized border.

Legs I long (96), longer than half the body length; legs II-IV (71, 50 and 63, respectively) shorter than half the body length; all segments free, with dorsal and ventral longitudinal ridges near the setae. Leg setation: trochanters 1–1–1–0, femora 1–1–0–1, genua 2(1)–2(1)–0–0, tibiae 2(1)–2(1)–1(1)–1(1), tarsi 8(3+ε)–9(1)–8–8. Trochanters I–III each with filiform seta (pR I, II, sR III). Femoral setae vF I, II spiniform with attenuate tips, wF IV setiform. Genual setae mG I, II spiniform, sword-shaped; cG I, II spiniform, short; nG III absent. Tibial setae gT I–II and kT III, IV spiniform; setae hT I, II spiniform, sword-shaped, larger than other sword-shaped leg setae. All pretarsi with hooked empodial claws arising from tarsal apices and connected to short, paired condylophores. Tarsus I with 4 setiform setae (d, f, p and q), 3 spiniform setae (ra, la and wa) and 1 modified setae e (wide triangle-shaped tips). Tarsus II with 3 filiform setae (d, p and q), 5 spiniform setae (e, ba, ra, la and wa) and foliate seta f. Tarsi III, IV with 2 filiform setae (d and f') and 6 spiniform setae (e, p, q, w, e and s), with attenuate tips. Solenidia ω₁ I-II on tarsi I cylindrical, with rounded apices, situated in basal part of tarsus; solenidion ω₃ situated close to ω₁, longer than ω₁, cylindrical; solenidion ω₂ cylindrical, with rounded apex, shorter than ω₁. Famulus ε short, spiniform, adjacent to solenidion ω₁. Solenidia φ I, II tapering, shorter than tarsi; φ II, IV short, bacilliform. Genua I, II with single solenidion (σ), σ I, II elongate, cylindrical; σ I shorter than ω₂; σ II shorter than σ I; σ of genu III absent.

Diagnosis

*Fagacarus absalom* differs from *F. verrucosus* by the following character states: in adults, solenidion σ II reaches tarsus II (vs. not reaching in *F. verrucosus*), posterior coaxal apodemes II are curved (vs. nearly straight in *F. verrucosus*); in males, pseudanal setae ps₂ are smooth, situated at the posterior edge of the anus, not protruding beyond the posterior margin of the body (vs. barbed, posterior to this level, protruding in *F. verrucosus*), pseudanal setae ps₁ and ps₂ are slightly spiniform, about 5 times shorter than h₃ (vs. filiform, less than 2 times shorter in *F. verrucosus*), the dorsal crista of tarsus IV is about 3/4 of the height of tarsus IV (vs. about 1/2 in *F. verrucosus*); in females, setae d IV are shorter than tarsus IV (vs. slightly longer in *F. verrucosus*). Heteromorphic deutonymphs are known only for *Fagacarus absalom* and therefore cannot be compared with those of any other species of the genus *Fagacarus*.

Molecular identification

A NCBI BLAST search of both 18S rRNA sequences (*Fagacarus absalom* sp. n. and *F. verrucosus*) returned close matches with *Schwiebea pseudotsugae* (97.40–96.73%) and *Rhizoglyphus* sp. AP-2010 (97.26–96.78%), thus confirming our morphology-based placement of *Fagacarus* in the subfamily Rhizoglyphinae and as a sister lineage to *Schwiebea* (Klimov and OConnor, 2003). Uncorrected 18S rDNA genetic distance between *Fagacarus absalom* sp. n. and *F. verrucosus* was 1.52%. This distance is sufficient to delimit the two species, since 18 rDNA (a nuclear gene) evolves much slower than the COX1 gene (a mitochondrial gene) (Klimov at al. 2019).

Etymology

Absalom is a biblical figure known for his luxuriant, long hair, which is reminiscent of the long and barbed dorsal setae of *Fagacarus absalom*. This specific name is treated here as a nomen in apposition.
Distribution

Russia: Primorsky Krai.

Biology

These mites live inside rotten trunks of a deciduous tree (between sapwood and heartwood layers), on the edge of colony of white rot fungi. Associated astigmatan species included *Histiostoma* sp. aff *ruehmi* (Histiostomatidae), *Schwiebea* sp. aff *koerneri* (Acaridae).

Acknowledgements

This research was supported by the cooperative agreement No. FEWZ-2021-0004 from the
Russian Ministry of Science and Higher Education.

ORCID

Pavel B. Klimov ID https://orcid.org/0000-0002-9966-969X

Vasiliy B. Kolesnikov ID https://orcid.org/0000-0001-6177-7858

Alexander A. Khaustov ID https://orcid.org/0000-0002-0306-112X

Barry M. OConnor ID https://orcid.org/0000-0003-3361-7675

References

Bugrov S.A. 1997. [Free-living Astigmata (Acariformes) of the Moscow District fauna]. Zoologicheskij Zhurnal, 76: 147-156(in Russian)

Fain A., Norton R. A. 1979. *Fagacarus verrucosus* n. g., n. sp. (Acari, Astigmata) from decaying beech wood in the U.S.A. International Journal of Acarology, 5: 5-8. https://doi.org/10.1080/01647957908683160

Grandjean F. 1939. La chaetotaxie des pattes chez les Acaridiae. Bulletin de la Société Zoologique de France, 64: 50-60.

Griffiths D. A. 1970. A further systematic study of the genus *Acarus* L., 1758 (Acaridae, Acarina), with a key to species. Bulletin of the British Museum (Natural History). Zoology series, 19: 85-118.

Griffiths D. A., Atyeo W. T., Norton R. A., Lynch, C. A. 1990. The idiosomal chaetotaxy of astigmatid mites. Journal of Zoology, 220: 1-32. https://doi.org/10.1111/j.1469-7998.1990.tb04291.x

Klimov P. B. 2000. Notes on systematics, distribution and ecology of mites of the genus *Fagacarus* (Acariformes: Acaridae). Acarina, 8 (2): 105-115.

Klimov B. B., OConnor B. M. 2003. Phylogeny, historical ecology and systematics of some mushroom-associated mites of the genus *Sancassania* (Acari: Acaridae), with new generic synonymies. Invertebrate Systematics, 17 (4): 469-514. https://doi.org/10.1071/IS02050

Klimov B. B., OConnor B. M. 2008. Morphology, evolution, and host associations of bee-associated mites of the family Chaetodactylidae (Acari: Astigmata), with a monographic revision of North American taxa. Miscellaneous Publications Museum of Zoology University of Michigan.199: 1-243.

Klimov P. B., OConnor B. M. 2013. Is permanent parasitism reversible? - Critical evidence from early evolution of house dust mites. Systematic Biology, 62, 411-423. https://doi.org/10.1093/sysbio/syt008

Klimov P. B., Tolstikov A. V. 2011. Acaroid mites of Northern and Eastern Asia (Acari: Acaroidea). Acarina, 19 (2): 252-264.

Klimov P. B., Skoracki M., Bochkov A.V. 2019. Cox1 barcoding versus multilocus species delimitation: validation of two mite species with contrasting effective population sizes. Parasites & Vectors 12. https://doi.org/10.1186/s13071-018-3242-5

Norton R. A. 1998. Morphological evidence for the evolutionary origin of Astigmata (Acari: Acariformes). Experimental and Applied Acarology, 22: 559-594. https://doi.org/10.1023/A:1006135509248

Swofford D. L., 2022. PAUP*. Phylogenetic Analysis Using Parsimony (*and other methods). Version 4.0a168. Distributed by the author.

Witaliński W., Szlendak E., Boczek J. 1990. Anatomy and ultrastructure of the reproductive systems of *Acarus siro* (Acari: Acaridae). Experimental and Applied Acarology, 10: 1-31. https://doi.org/10.1007/BF01193970

Wurst E. 2022. Beitrag zur Revision der mitteleuropäischen Arten der Gattung *Schwiebea*. Verlag Grauer, Beuren and Stuttgart, 128 p.
Distribution

Russia: Primorsky Krai.

Biology

These mites live inside rotten trunks of a deciduous tree (between sapwood and heartwood layers), on the edge of colony of white rot fungi. Associated astigmatan species included *Histiostoma* sp. aff *ruehmi* (Histiostomatidae), *Schwiebea* sp. aff *koerneri* (Acaridae).

Acknowledgements

This research was supported by the cooperative agreement No. FEWZ-2021-0004 from the
Russian Ministry of Science and Higher Education.

ORCID

Pavel B. Klimov ID https://orcid.org/0000-0002-9966-969X

Vasiliy B. Kolesnikov ID https://orcid.org/0000-0001-6177-7858

Alexander A. Khaustov ID https://orcid.org/0000-0002-0306-112X

Barry M. OConnor ID https://orcid.org/0000-0003-3361-7675

References

Bugrov S.A. 1997. [Free-living Astigmata (Acariformes) of the Moscow District fauna]. Zoologicheskij Zhurnal, 76: 147-156(in Russian)

Fain A., Norton R. A. 1979. *Fagacarus verrucosus* n. g., n. sp. (Acari, Astigmata) from decaying beech wood in the U.S.A. International Journal of Acarology, 5: 5-8. https://doi.org/10.1080/01647957908683160

Grandjean F. 1939. La chaetotaxie des pattes chez les Acaridiae. Bulletin de la Société Zoologique de France, 64: 50-60.

Griffiths D. A. 1970. A further systematic study of the genus *Acarus* L., 1758 (Acaridae, Acarina), with a key to species. Bulletin of the British Museum (Natural History). Zoology series, 19: 85-118.

Griffiths D. A., Atyeo W. T., Norton R. A., Lynch, C. A. 1990. The idiosomal chaetotaxy of astigmatid mites. Journal of Zoology, 220: 1-32. https://doi.org/10.1111/j.1469-7998.1990.tb04291.x

Klimov P. B. 2000. Notes on systematics, distribution and ecology of mites of the genus *Fagacarus* (Acariformes: Acaridae). Acarina, 8 (2): 105-115.

Klimov B. B., OConnor B. M. 2003. Phylogeny, historical ecology and systematics of some mushroom-associated mites of the genus *Sancassania* (Acari: Acaridae), with new generic synonyms. Invertebrate Systematics, 17 (4): 469-514. https://doi.org/10.1071/IS02050

Klimov B. B., OConnor B. M. 2008. Morphology, evolution, and host associations of bee-associated mites of the family Chaetodactylidae (Acari: Astigmata), with a monographic revision of North American taxa. Miscellaneous Publications Museum of Zoology University of Michigan.199: 1-243.

Klimov P. B., OConnor B. M. 2013. Is permanent parasitism reversible? - Critical evidence from early evolution of house dust mites. Systematic Biology, 62, 411-423. https://doi.org/10.1093/sysbio/syt008

Klimov P. B., Tolstikov A. V. 2011. Acaroid mites of Northern and Eastern Asia (Acari: Acaroidea). Acarina, 19 (2): 252-264.

Klimov P. B., Skoracki M., Bochkov A.V. 2019. Cox1 barcoding versus multilocus species delimitation: validation of two mite species with contrasting effective population sizes. Parasites & Vectors 12. https://doi.org/10.1186/s13071-018-3242-5

Norton R. A. 1998. Morphological evidence for the evolutionary origin of Astigmata (Acari: Acariformes). Experimental and Applied Acarology, 22: 559-594. https://doi.org/10.1023/A:1006135509248

Swofford D. L., 2022. PAUP*. Phylogenetic Analysis Using Parsimony (*and other methods). Version 4.0a168. Distributed by the author.

Witaliński W., Szlendak E., Boczek J. 1990. Anatomy and ultrastructure of the reproductive systems of *Acarus siro* (Acari: Acaridae). Experimental and Applied Acarology, 10: 1-31. https://doi.org/10.1007/BF01193970

Wurst E. 2022. Beitrag zur Revision der mitteleuropäischen Arten der Gattung *Schwiebea*. Verlag Grauer, Beuren and Stuttgart, 128 p.