# Two new species of gall mites (Acariformes, Eriophyoidea) from ferns (Polypodiopsida) from South Africa and Vietnam

Philipp E Chetverikov, Charnie Craemer, Vladimir D Gankevich, Andrey T Kudryavtzev, Alexey G Desnitskiy, Thi Tuyet Nhung Le, Duc Viet Nguyen, Hoat Trinh Xuan

► To cite this version:

Philipp E Chetverikov, Charnie Craemer, Vladimir D Gankevich, Andrey T Kudryavtzev, Alexey G Desnitskiy, et al. Two new species of gall mites (Acariformes, Eriophyoidea) from ferns (Polypodiopsida) from South Africa and Vietnam. Acarologia, 2025, 65 (3), pp.868-886. 10.24349/9qu7-ilj8. hal-05311349

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Acarologia

Open Science
in Acarology

# Two new species of gall mites
(Acariformes, Eriophyoidea) from ferns
(Polypodiopsida) from South Africa and
Vietnam

Philipp E. Chetverikov ID a,b, Charnie Craemer ID c, Vladimir D. Gankevich ID d, Andrey T. Kudryavtzev d,e, Alexey G. Desnitskiy ID a, Thi Tuyet Nhung Le ID f, Duc Viet Nguyen ID f, Hoat Trinh Xuan ID f

## Original research

### ABSTRACT

The diversity of eriophyoid mites on ferns and conifers is notably lower than on angiosperms. To date, 40 eriophyoid mite species from 20 genera have been recorded on ferns. Most species belong to the eriophyid subfamilies Phyllocoptinae (45%), Eriophyinae (34%), and Nothopodinae (18%), while only one represents the diptilomioid subfamily Rhyncaphytoptinae. The greatest diversity occurs on the fern orders Polypodiales and Cyatheales, followed by Equisetales, Gleicheniales, and Schizaeales, whereas no eriophyoid taxa have been described from Marattiales. We describe two new Eriophyidae species from ferns: *Cymoptus ptisanis* n. sp., collected in South Africa from erinea on the lower surface of frond pinnae of *Ptisana salicifolia* (Schrad.) Senterre et Rouhan (Marattiales: Marattiaceae), and *Nothopoda vietnamensis* n. sp., collected in Vietnam from galls on fronds of *Nephrolepis cordifolia* (L.) C.Presl (Polypodiales: Nephrolepidaceae). Morphological descriptions of the new taxa are supplemented with partial *Cox1* (PV698368, PV698369) and 28S (PV711118, PV711119) gene sequences, photographs of host plant symptoms, and a series of images documenting stages of gall formation on *Nephrolepis*. In this paper we also propose relaxing the generic concept of *Cymoptus* Keifer 1946 (as *Aceria*-like eriophyines missing tibial seta *l'* I), question the synonymy of the poorly differentiated nothopodine genera *Floracarus* Keifer 1953 and *Nothopoda* Keifer 1951, and advocate for future comparative studies on gallogenesis induced by eriophyoids on ferns and angiosperms.

**Keywords** acariform mites; phytophagy; fern pests; gall formation

**Zoobank** http://zoobank.org/D48F0248-D9DF-47BB-83BE-D2A368788288

### Introduction

Eriophyoid mites (Eriophyoidea Nalepa, 1898) are an ancient lineage of highly host-specific phytoparasites closely related to soil mites of the family Nematalycidae Strenzke, 1954 (Bolton

Received 07 June 2025
Accepted 27 August 2025
Published 02 September 2025

Corresponding author
Philipp E. Chetverikov ID:
philipp-chetverikov@yandex.ru

Academic editor
Kreiter, Serge

https://doi.org/10.24349/9qu7-i1j8

ISSN 0044-586X (print)
ISSN 2107-7207 (electronic)

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

Chetverikov P. E. et al.

Licensed under
Creative Commons CC-BY 4.0

OPEN ACCESS

<footnote>a Saint Petersburg State University, Universitetskaya Nab. 7/9, St. Petersburg, 199034, Russia.</footnote>

<footnote>b Zoological Institute of Russian Academy of Sciences, Universitetskaya Nab. 1, Saint Petersburg, 199034, Russia.</footnote>

<footnote>c Landcare Research, 231 Morrin Road, Auckland, 1072, New Zealand.</footnote>

<footnote>d Zoological Institute of Russian Academy of Sciences, Universitetskaya Nab. 1, St. Petersburg, 199034, Russia.</footnote>

<footnote>e St. Petersburg State Agrarian University, Peterburgskoe shosse 2, Pushkin, St. Petersburg, 196601, Russia.</footnote>

<footnote>f Plant Protection Research Institute, 10 Pho Vien, Duc Thang ward, Bac Tu Liem district, Hanoi City, Vietnam.</footnote>
et al. 2017; Klimov et al. 2018, 2022). In extant ecosystems, they exhibit peak species richness on angiosperms, with significantly fewer representatives on conifers and ferns (Gerson 1996; Amrine et al. 2003). Evolutionary evidence indicates that eriophyoid mites originated as symbionts of ancient land plants, with their earliest associations likely occurring on now-extinct lineages such as seed ferns, progymnosperms, and proangiosperms (Sukhareva 1994; Sidorchuk et al. 2014; Klimov et al. 2025). The most morphologically archaic extant eriophyoids of the family Pentasetacidae Schliesske, 1985, which retain a complete set of plesiomorphic traits, are associated with ancient coniferous hosts in the genera *Araucaria* and *Cupressus* (Chetverikov et al. 2019). While theoretically, similar relict Eriophyoidea taxa could have persisted on ferns (Polypodiopsida), no pentasetacid-like eriophyoids have been documented on these hosts (Gerson 1996; Lotfollahi and de Lillo 2017). Recent molecular phylogenetic analyses – albeit limited in taxon sampling – suggest that fern-associated eriophyoid lineages evolved through secondary host shifts from non-fern hosts (Li et al. 2014; Chetverikov et al. 2023; Zhang et al. 2024).

At present, ~40 eriophyoid mites species from 20 genera (*Aceria*, *Acerimina*, *Aculus*, *Calacarus*, *Cosella*, *Cymeda*, *Dicolopodacus*, *Diphytoptus*, *Eriocaenus*, *Eriophyes*, *Esalquia*, *Floracarus*, *Jutarus*, *Leipothrix*, *Litaculus*, *Metaculus*, *Nothopoda*, *Phyllocoptes*, *Rhinophytopsus*, and *Stenacis*) are known from ferns (Petanović et al. 2015; Lotfollahi and de Lillo 2017; Chetverikov et al. 2023). The greatest generic diversity of fern-associated eriophyoid mites occurs on fern orders Polypodiales and Cyatheales, followed by Equisetales, Gleicheniales, and Schizaeales, whereas none have been described from Marattiales (Petanović et al. 2015). Most eriophyoid mite species inhabiting ferns belong to the subfamilies Phyllocoptinae (~45%), Eriophyinae (~34%), and Nothopodinae (~18%) of the family Eriophyidae. Only one species (*Rhinophytoptus plagiogyrus* Huang, 2001 from *Plagiogyria formosana* Christ) reperesents the family Diptilomiopidae. Approximately half of the known fern-associated eriophyid mite species are vagrants, causing no visible damage to their hosts. The other species induce various frond distortions (including marginal rolling, discoloration, thickening, and curling) or, more rarely, form erinea, galls, or witches' brooms (Gerson 1996; Lotfollahi and de Lillo 2017).

From 2017 to 2024, a series of expeditions were conducted to study the eriophyoid fauna of South Africa and Vietnam. These field surveys were organized by the ARC Plant Protection Research Institute (Roodeplaat, Gauteng, South Africa) and Plant Protection Research Institute (Hanoi, Vietnam) in collaboration with Saint-Petersburg State University (Russia). During these surveys, two new species of eriophyoid mites of the family Eriophyidae were discovered on ferns of the genera *Ptisana* (Marattiales) and *Nephrolepis* (Polypodiales). In this paper, we present descriptions of these species, supported by partial sequences of the mitochondrial *Cox1* and nuclear 28S rRNA genes, and photographs of the damage symptoms caused to the infested host plants. Additionally, we document the stages of gallogenesis on *Nephrolepis* through a series of sequential images.

# Material and methods

## Collection and morphological measurements

Eriophyoid mites were collected from ferns in South Africa (2017) and Vietnam (2023–2024) using a fine minute pin under a stereomicroscope. They were kept in Eppendorf tubes filled with 96% ethanol in a freezer at –20 °C prior to transport to the Zoological Institute of the Russian Academy of Sciences (ZIN RAS), where the mites were mounted in modified Berlese medium with iodine (Amrine and Manson 1996) and cleared on a heating block at 90 °C for 3 hours. The slide-mounted specimens were examined with differential interference contrast light microscopy (DIC LM) and phase contrast light microscopy (PC LM) in the Laboratory of Parasitic Arthropods of the ZIN RAS. In the species description, measurements of the holotype (female) are presented along with ranges based on measurements of paratype females; in the descriptions of males, only ranges are given. All measurements are given in micrometers (µm)
as lengths unless stated otherwise. The classification and terminology of eriophyoid genital
anatomy and external morphology follow that of Amrine *et al.* (2003); Chetverikov (2014),
and Lindquist (1996), respectively. Drawings of the mites were produced with the aid of a
video projector as described by Chetverikov (2016). Host plant taxonomy follows Senterre *et
al.* (2014) and Hovenkamp and Miyamoto (2005).

DNA extraction, PCR and sequencing

For DNA extraction, 1–3 mite specimens of each species were crushed with a fine pin in a 3 µL drop of distilled water on a cavity well microscope slide. The drop was then pipetted into a thin-walled PCR tube containing 20 µL of a 5% solution of Chelex® 100 Resin (Bio-Rad Laboratories, Inc., Hercules, California, USA) followed by two heating steps (5 min at 95 °C). The supernatant above the settled Chelex® granules was used as the DNA template for PCR to amplify a fragment of subunit I of the *Cox1* gene and the *DID2* fragment of the 28S rDNA gene. Thermal cycling profiles and primers (for both PCR and sequencing) followed those specified by Chetverikov and Bertone (2022). After amplification, 4.5 µL of each reaction product was mixed with 0.5 µL of SYBR Green I (Lumiprobe, Hannover, Germany) and analyzed by electrophoresis in a 1% agarose gel to assess product size and concentration. Sequencing was performed using BigDye Terminator v.3.1 chemistry in a 3500xl Genetic Analyzer (Applied Biosystems, Foster City, CA, USA).

Results

Family Eriophyidae Nalepa, 1898

Subfamily Eriophyinae Balepa, 1898

Tribe Aceriini Amrine & Stasny, 1994

Genus *Cymoptus* Keifer, 1946

**Remarks** — This genus is very close to the large genus *Aceria* Keifer, 1944. Unlike *Aceria*, *Cymoptus* lacks tibial seta *l'* I. Keifer (1946) and Amrine *et al*. (2003) reported that dorsal opisthosomal annuli in *Cymoptus* are smooth and sinuate, whereas ventral annuli are reinforced with spine-like microtubercles. These traits (undulation of annuli and spine-like shape of microtubercles) are variable at the species level, e.g. *Cymoptus bengalensis* Ghosh, Mondal and Chakrabarti, 1984 lacks annular undulation and spine-like microtubercles. Additionally, in various eriophyoid taxa deutogyne and protogyne forms of the same species differ in the shape of opisthosomal annuli and microtubercles (Manson and Oldfield 1996; Sukhareva and Chetverikov 2013). We propose relaxing the generic concept of *Cymoptus* by excluding characteristics of the opisthosomal annuli from its diagnosis, and treating *Cymoptus* as a taxon with all morphological traits typical of the genus *Aceria*, except for the absence of tibial seta *l'* I. Although future molecular phylogenetic studies may reveal non-monophyly of the “relaxed” *Cymoptus*, we consider this interpretation convenient for the systematics of Eriophyoidea.

**Type species** — *Cymoptus spiniventris* Keifer, 1946

**Species included** — Five (Table 1).

**Hosts** — Four *Cymoptus* spp. are known from eudicot angiosperms (Nothofagaceae, Euphorbiaceae, Lauraceae), and one species (*C. ptisanis* *n. sp.*) from ferns (Marattiaceae).

**Relation to hosts** — Except for one presumably vagrant species (*C. bengalensis*), the other four *Cymoptus* spp. are associated with one of two types of plant growth abnormalities: erineum (*C. spiniventris*, *C. ptisanis* *n. sp.*, *C. vieirai*) and withches' broom (*C. waltheri*).

**Deuterogyny** — Based on material from New Zealand, Manson (1984) reported deuterogyny in *C. waltheri* (Keifer, 1939). No data on deuterogyny in other *Cymoptus* spp.

**Distribution** — (Figure 1). Current data on the global distribution of *Cymoptus* spp. remain limited. Records include findings on native hosts in type localities in Argentina, India, Portugal,
<figure><img src="image_3.png" /></figure>

**Figure 1** Type localities of *Cymoptus* spp. (1–5), and nothopodines from *Nephrolepis* (6–8): 1 – *Cymoptus bengalensis* Ghosh, Mondal et Chakrabarti, 1984; 2 – *C. ptisanis* n. sp.; 3 – *C. spiniventris* Keifer, 1946; 4 – *C. vieirai* Carmona, 1988; 5 – *C. waltheri* (Keifer, 1939); 6 – *Floracarus biserratae* Huang, 2001; 7 – *F. footei* Keifer, 1953; 8 – *Nothopoda vietnamensis* n. sp. Introduction of *C. waltheri* from New Zealand to California (5) and interception of *F. biserratae* (7) from the Philippines to Hawaii are shown with arrows.

and South Africa, as well as one record from the USA, where *C. waltheri* was detected on *Nothofagus menziesii* introduced from New Zealand (Keifer 1939). Additionally, *C. waltheri* has been reported in New Zealand on native *Nothofagus* spp. (Manson 1984).

### Cymoptus ptisanis n. sp.

Zoobank: 32074337-C04A-45F0-B20C-5D90E2498CCE

Figures 2 – 5

<table><caption>**Table 1** List of species of the genus *Cymoptus* Keifer, 1946 of the world.</caption><thead><tr><td>Mite species</td><td>Host plant</td><td>Relation to host</td><td>Type locality</td><td>Reference</td></tr></thead><tbody><tr><td>C. bengalensis Ghosh, Mondal and Chakrabarti, 1984</td><td>Mallotus repandus (Rottler et Willd.) Muell. (Euphorbiaceae)</td><td>vagant on lower leaf surface</td><td>West Bengal, India</td><td>Ghosh et al. (1984)</td></tr><tr><td>C. ptisanis n. sp.</td><td>Ptisana salicifolia (Schrad.) Senterre et Rouhan (Marratiaceae)</td><td>in erineum around sporangia on lower surface of fronds</td><td>South Africa</td><td>this paper</td></tr><tr><td>C. spiniventris Keifer 1946</td><td>Nothofagus dombeyi (Mirb.) Oerst. (Nothofagaceae)</td><td>erineum on lower leaf surface</td><td>Argentina</td><td>Keifer (1946)</td></tr><tr><td>C. vieirai Carmona, 1988</td><td>Apollonias barbujana (Cav.) Bornm. (Lauraceae)</td><td>Inhabiting patches and felty erineum with Eriophyes barbujanae Carmona, 1988 on the lower leaf surface</td><td>Madeira Island, Portugal</td><td>Carmona (1988)</td></tr><tr><td>C. waltheri (Keifer, 1939)</td><td>Nothofagus menziesii Orst. (Nothofagaceae)</td><td>terminal stunting and branching, resulting in a heavy cluster of large, aborted buds (withches' broom)</td><td>California, USA</td><td>Keifer (1939)</td></tr></tbody></table>
<figure><img src="image_4.png" /><figcaption>**Figure 2** *Cymoptus ptisanis* n. sp. A – prodorsal shield, B and C – tarsal solenidia I (B) and II (C), D – tarsal empodium I, E and F – legs I (E) and II (F), H – female internal genitalia, I – male genital area. Scale bar: A – 20 µm; B, C, D, E, F, H – 5 µm; G, I – 10 µm.</figcaption></figure>

Female (n = 11)

**Idiosoma** elongate, vermiform, whitish, 143 (130–164), 49 (38–55) wide at level of seta c2.
**Prodorsal shield** semicircular, 19 (17–22), 30 (27–33) wide, without frontal lobe. Prodorsal shield ornamentation weak consisting of faint longitudinal lines (representing putative traces
of admedians and submedians) and a group of about 30–50 distinct microtuberules in the posteromedial part of prodorsal shield between tubercles of *sc*. Scapular setae *sc* 23 (19–26), 22 (21–23) apart, directed divergently posteriad. **Gnathosoma** directed anteriad and slightly downward, 18 (16–21), *ep* 2 (1–3), *d* 8 (6–10), *v* 2 (2–3); chelicera 15 (13–19).

**Leg I** 28 (25–31), femur 7 (6–8), *bv* 4 (3–6), genu 3 (3–5), *l'* 19 (17–22), tibia 5 (4–6), *l'* absent; tarsus 5 (4–6), *u'* 4 (3–6), *ft'* 4 (3–6), *ft''* 10 (8–14), *ω* 6 (5–7) with small subspherical knob; empodium 5–rayed, 4 (4–6). **Leg II** 27 (24–28), femur 6 (5–7), *bv* 3 (2–5), genu 3 (3–5), *l''* 7 (5–9), tibia 5 (4–5); tarsus 4 (4–6), *u'* 2 (2–3), *ft'* 4 (3–7), *ft''* 11 (7–16), *ω* 6 (5–7) with small subspherical knob; empodium 5–rayed, 4 (4–5).

**Infracapitular plate** subtriangular, rounded anteriorly, smooth, 10 (8–13), 10 (9–13) wide; the prosternal apodeme is indistinct in most specimens but appears forked posteriorly when clearly visible.

**Coxal plates** smooth or with several faint curved ridges. Setae *1b* 4 (3–6), 8 (7–11) apart, *1a* 15 (10–17), 10 (9–12) apart; *2a* 20 (17–25), 21 (20–25) apart; 6 (5–7) incomplete coxigenital annuli bearing tiny round microtubercles before epigynium.

**External genitalia.** Genital coverflap, smooth, narrow, 11 (9–13), 20 (19–23) wide; setae *3a* 3 (3–5), 12 (10–13) apart; pregenital plate (*sensu* Flechtmann *et al.* 2015) absent.

**Internal genitalia** (n=4). Spermathecae globose or tear-drop shaped, 5–8 in diameter; spermathecal tubes short, about 2–3, 2–3 wide, directed laterad; rudimentary spermathecal process (*sensu* Duarte *et al.* 2016), associated with spermathecal tube, present and about 1–2; longitudinal bridge 7–9, anterior (transverse) genital apodeme trapezoidal; oblique apodeme distinct.

**Opisthosoma** with 69 (63–75) dorsal and 70 (67–77) ventral annuli. Dorsal and ventral annuli with distinct oval microtubercles. Dorsally they are present on anterior 60 annuli, and absent on rear 9–10 annuli. Setal lengths: *c2* 29 (20–36), *d* 32 (26–40), *e* 5 (4–8), *f* 11 (11–14); *h1* 2 (1–2); *h2* 43 (38–50); 15 (11–17) annuli from rear shield margin to *c2*; 12 (9–12) annuli between *c2–d*; 12 (9–14) annuli between *d* and *e*; 24 (22–27) annuli between *e* and *f*; and 8 (8–11) annuli between *f* and *h2*.

## Male (n = 3)

**Idiosoma** fusiform, whitish, 119–126, 42–46 wide. **Prodorsal shield** 17–21, 27–31 wide. Prodorsal shield ornamentation similar to that in female. Scapular setae *sc* 19–20, 19–22 apart. **Gnathosoma** 16–18, *ep* 1–2, *d* 6–9, *v* 1–2; chelicera 11–16.

**Leg I** 25–30, femur 6–7, *bv* 3–4, genu 3–4, *l''* 14–20, tibia 4–5, *l'* absent; tarsus 4–5, *u'* 2–3, *ft'* 3–4, *ft''* 10–12, *ω* 6–7 with small subspherical knob; empodium 5–rayed, 4–5. **Leg II** 26–28, femur 5–7, *bv* 2–4, genu 3–4, *l''* 5–8, tibia 4–5; tarsus 3–4, *u'* 2–3, *ft'* 3–4, *ft''* 11–13, *ω* 6–8 with small subspherical knob; empodium 5–rayed, 4–5.

**Coxal plates** smooth, *1b* 2–3, 6–9 apart; *1a* 5–9, 9–11 apart; *2a* 15–18, 18–20 apart; 6–7 incomplete coxigenital annuli before epiandrium.

**External genitalia.** Genital area about 10–12, 14–16 wide; setae *3a* 3–4, 9–12 apart; *eu* about 0.5–1.

**Opisthosoma** with 61–68 dorsal and 61–64 ventral annuli microtuberculated similar to those in female. Setal lengths: *c2* 23–28, *d* 25–33, *e* 4–6, *f* 9–11, *h1* 2–3, *h2* 39–46; 9–14 annuli from rear shield margin to *c2*; 7–10 annuli between *c2–d*; 10–12 annuli between *d* and *e*; 20–24 annuli between *e* and *f*; 7–8 annuli between *f* and *h2*.

## Gen Bank data

PV698369 (*Cox1*, 1151 bp), PV711119 (28S, 1009 bp).

## Host plant

*Pitisana salicifolia* (Schrad.) Senterre and Rouhan (Polypodiopsida: Marattiales: Marratiaceae).
<figure><img src="image_5.png" /><figcaption>**Figure 3** DIC LM (A, B, C) and PC LM (D, E, F, G) photographs of *Cymoptus ptisanis* n. sp. A, B, and C – variation of prodorsal shield pattern in three females; D and E – dorsal (D) and ventral (E) view of female; F – female internal genitalia, G – semilateral view of nymph. Scale bar: A, B, C, G – 10 µm; D, E – 20 µm; F – 5 µm.</figcaption></figure>
**Relation to the host**

Mites live in brownish erinea, which they cause around synangia on lower surface of frond pinnae (Figure 4).

**Remarks** — Erinea were found exclusively around synangia of *P. salicifolia*, indicating that mites (a) can locate and distinguish these structures and (b) selectively target epidermal cells near synangia while ignoring other cells. Intriguingly, a similar ability to induce morphologically distinct galls in specific leaf zones is known in eriophyoid mites associated with angiosperms, for example, *Eriophyes* spp. galls on *Tilia* spp. (Soika and Kozak 2013). Our long-term observations suggest that eriophyoid mites very often move along veins and possibly recognize them when crossing. The mites' capacity to detect veins (via sensory structures on their distal leg segments and gnathosoma) and follow them may be key to locating precise regions on fern fronds or angiosperm leaves for inducing galls. Future experimental work should explore how eriophyoids identify suitable sites for gall induction. In *P. salicina*, colonization by *C. ptisanis* n. sp. produces a distinctive dark, ring-like epidermal area surrounding synangia (Figure 4D, arrows). A similar ring-like zone appears during early-stage chambered gall formation in certain angiosperms (e.g., *Betula* or *Alnus*; see fig. 1a, c in Desnitskiy *et al.* 2024). Whether these rings are structurally and genetically homologous remains unclear. Comparative histological and genetic studies of eriophyoid galls on ferns and angiosperms could resolve this question.

**Type locality**

SOUTH AFRICA: Mpumalanga Prov., near Sabie, Bridal Veil Falls, 25°04′55.2″S 30°43′29.2″E (Figure 5).

**Type material**

Holotype female in slide #M110-1, 18 paratypes on slide series #M110, collected on 14 November 2017 at the type locality, coll. P. Chetverikov, C. Craemer, S. Neser. Type material is deposited in Acarological collection of ZIN RAS.

**Etymology**

The species epithet *ptisanis* is an adjective, gender masculine, derived from the generic name of the host plant, *Ptisana*.

**Differential diagnosis**

Among other *Cymoptus* spp., the new species is closest to *C. waltheri* (Keifer, 1939). The main differences concern ornamentation of prodorsal shield and number of empodial rays. In *C. waltheri* a short median line is present in posterior half of the shield, the admedian lines are long and complete, the internal submedian lines converge anteriorly, the cuticle between tubercles of *sc* is smooth, and the empodium is 3-rayed (Keifer 1939, Plate LXXXIV). In *C. ptisanis* n. sp. median line is absent; submedian lines faint, non-converging; the cuticle between tubercles of *sc* with 30–50 distinct microtubercles; and the empodium is 5-rayed.

**Subfamily Nothopodinae Keifer, 1956**

**Tribe Nothopodini Keifer, 1956**

**Genus Nothopoda Keifer, 1951**

**Remarks on the generic diagnosis of Nothopoda** — This genus is poorly distinguished from another nothopodine genus, *Floracarus* Keifer, 1953. They differ only in the presence (in *Floracarus*) and absence in (*Nothopoda*) of a relatively small subtriangular frontal lobe of the prodorsal shield (Keifer 1953, p. 69; Amrine *et al.* 2003). Presence or absence of this structure is a weak discriminating character, also varying among members of different eriophyid genera
<figure><img src="image_6.png" /><figcaption>**Figure 4** Erinea around synangia on the lower surface of frond pinnae of the fern *Pisana salicifolia* caused by *Cymoptus ptisanis* n. sp. (photo - P. Chetverikov). Scale bar: A, C, E - 10 mm; B, D, F - 5 mm. Mites attack epidermal cells, causing the formation of a dark green ring surrounding synangia (Fig. 4D, arrows) followed by growth of trichomes, forming an erineum produced by the cells of the “dark ring” area (Fig. 4 A, C, arrows). Sometimes, two or more neighboring synangia are attacked (Fig. 4 B, D, E, F). Attacked synangia exhibit delayed development; they remain closed and often retain a green or yellowish color (Fig. 4 B, E, F) similar to young synangia, which are typically green or yellowish (Fig. 4F, asterisk), whereas mature, intact synangia are brownish and open for sporulation (Fig. 4 A, C asterisk).</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Figure 5** Type locality (A) of *Cymoptus ptisanis* n. sp. from the fern *Ptisana salicifolia* (B, arrows) along a small creek (A, C) near Bridal Veil Falls in South Africa (photo – P. Chetverikov).</figcaption></figure>

(e.g. in *Aceria* and *Eriophyes*). Recent phylogenies based on limited set of nothopodine taxa, did not support monophyly of *Nothopoda* and inferred *Floracarus* a basal taxon in a clade comprising three nothopodine genera – *Nothopoda*, *Cosella*, and *Floracarus* (Chetverikov *et al.* 2023). In this study, we follow the traditional concept of *Nothopoda* as a *Floracarus*-like taxon lacking a frontal lobe. However, future morphological revisions and molecular phylogenetic studies may confirm synonymy of *Nothopoda* and *Floracarus*.

**Nothopoda vietnamensis n. sp.**

Zoobank: B7C38800-01F0-4069-9D12-7785DBFE6615

Figures 6 – 7

**Female (n = 19)**

**Idiosoma** elongate, vermiform, white to slightly yellowish, 195 (170–241), 55 (50–62) wide at the level of seta c2. **Prodorsal shield** subtriangular, rounded and slightly notched anteriorly, 28 (24–30), 36 (30–40) wide, without frontal lobe. Prodorsal shield with variable linear ornamentation in medial part. Lateral parts of prodorsal shield with numerous microtubercles. Most commonly, the linear pattern is subsymmetrical and includes median line, two admedians, submedian I and a series of longitudinal and transversal lines. Median line entire, slightly sinuous, incomplete (absent in anterior 1/5 part of prodorsal shield). Admedians entire, complete, converging anteriorly. Usually three short transverse lines crossing median line are present between admedians. Submedian line I broken, consisting of two approximately equal fragments. Three to six short transverse lines present near anterior fragment of submedian I. Some females possess aberrant ornamentation of prodorsal shield with median line broken and additional transverse lines present and forming cells along anterior margin of prodorsal shield
<figure><img src="image_8.png" /><figcaption>**Figure 6** *Nothopoda vietnamensis n. sp.* A – prodorsal shield; B – female internal genitalia; C – ventral aspect of the female prosoma and external genitalia (dorsal leg setae not shown); D and E – legs II (D) and I (E), F – telosoma; G – tarsal empodium I, H and I – tarsal solenidia I (H) and II (I); J – lateral view of entire female. Scale bar: A, B, D, E – 10 µm; C – 15 µm; G, H, I – 5 µm; F – 20 µm, J – 30 µm.</figcaption></figure>

and between long lines (Figure 7). Scapular setae *sc* 9 (7–12), 21 (17–24) apart, directed dorsally and slightly posteriad. **Gnathosoma** directed anteriad and obliquely downward, 19 (18–23), *ep* 2 (1–3), *d* 2 (2–3), simple, *v* 2 (1.5–2); chelicerae 13 (11–14).

Leg I 35 (30–39), femur 9 (9–10), *bv* 5 (4–8), genu 4 (3–4), *l'* 23 (20–30), tibia absent
<figure><img src="image_9.png" /><figcaption>**Figure 7** Variation in ornamentation of prodorsal shield in six females of *Nothopoda vietnamensis n. sp.* (A–F) collected from the same gall, ventral view of a female prosome (G), and external female genitalia (H, I). Scale bar: A, B, C, D, E, F, G – 10 µm; H, I – 5 µm.</figcaption></figure>

(or fused with tarsus), *l'* absent; tarsus 7 (7–8), *u'* 2 (1–2), *ft'* 8 (4–10), *ft''* 19 (15–24), *ω* 7 (5–8) with small subspherical knob, displaced on medially; empodium 4-rayed, 5 (4–6) long.
**Leg II** 33 (29–36), femur 9 (8–9), *bv* 4 (3–5), genu 3 (3–4), *l''* 20 (17–26), tibia absent (or fused with tarsus); tarsus 7 (7–8), *u'* 2 (1–2), *ft'* 4 (3–6), *ft''* 19 (15–23), *ω* 7 (5–8) with small subspherical knob, commonly located in dorsal position above empodium; empodium 4-rayed, 5 (4–6) long.

**Infracapitular plate** suboval, rounded anteriorly, smooth or with indistinct small microtubercles, 7 (6–9), 11 (10–13) wide; prosternal apodeme absent.
**Coxal plates** with numerous small microtubercles. Setae 1b absent; 1a 9 (7–12), 9 (8–10) apart; 2a 20 (17–28), 21 (18–22) apart; 4 (3–7) incomplete coxigenital annuli bearing tiny, round microtubercles anterior to the epigynium.

**External genitalia.** Genital coverflap with a group of microtubercles in medio-proximal region and in most females with two paired symmetrically located transverse ridges near distal margin of coverflap (Figure 7 H), which in some individuals may be replaced by several thinner ridges (Figure 7 I), 11 (9–13), 20 (19–23) wide; setae 3a 5 (4–8), 16 (14–17) apart; basal part of epigynium and pregenital area with numerous tiny microtubercles.

**Internal genitalia (n=5).** Spermathecae globose, 6–8 in diameter; spermathecal tubes short, about 2–3, 1–3 wide, directed laterad; rudimentary spermathecal process (sensu Duarte *et al.* 2016), associated with spermathecal tube, present and about 0.5–1 long; longitudinal bridge 11–14, anterior (transverse) genital apodeme consists of two fragments separated with a notch, putatively situated within the transverse plane (orthogonal to the longitudinal body axis, as in cecidophyines); oblique apodeme distinct, sinuous, almost orthogonal to longitudinal bridge.

**Opisthosoma** with 73 (65–76) dorsal and 74 (68–79) ventral annuli. Dorsal and ventral annuli with distinct oval microtubercles. Setal lengths: c2 25 (20–30), d 43 (33–49), e 5 (4–7), f 16 (14–20); h1 2 (2–3); h2 48 (38–59); 8 (5–9) annuli from rear shield margin to c2; 14 (10–16) annuli between c2–d; 18 (15–19) annuli between d and e; 23 (20–25) annuli between e and f; and 9 (7–10) annuli between f and h2.

**Gen Bank data**

PV698368 (*Cox1*, 1161 bp), PV711118 (28S, 1005 bp).

**Host plant**

*Nephrolepis cordifolia* (L.) C.Presl (Polypodiales: Nephrolepidaceae).

**Relation to the host**

Mites live in galls on frond pinnae (Figures 8, 9).

**Remarks** — The gall formation process in *N. cordifolia* resembles the development of marginal leaf-rolling galls induced by eriophyoid mites on leaves of various dicotyledonous plants. These pathological morphogenetic processes in ferns and angiosperms may share elements of genetic developmental programs common across different phylogenetic lineages of land plants, which are exploited by gall-inducing mites. Remarkably, recent studies on regulatory gene expression in *Fragaria viridis* (Rosaceae) leaf galls caused by the eriophyoid mite *Fragariocoptes setiger* (Nalepa, 1894) (Eriophyoidae: Phytoptidae) revealed localized alterations in leaf epidermis dorsoventral polarity (Paponova *et al.* 2021). Future research should examine whether similar polarity changes occur in eriophyoid mite galls on other hosts, including ferns.

**Type locality**

VIETNAM: Tam Dao, near Silver waterfall (Figure 10), 21°27′13.2″N 105°38′38.1″E

**Type material**

**Holotype** — female in slide #V21-1, 25 paratypes on slide series #V21 and #V23, collected 22 February 2023 in type locality, coll. P. Chetverikov and Viet D. Nguyen. Type material deposited in Acarological collection of ZIN RAS.

**Additional material** — Numerous adults and immatures in slide series #V61 and #V62 collected 8 March 2024 in VIETNAM: Moc Chau, 20°50′56.7″N 104°39′55.4″E, coll. P. Chetverikov and Viet D. Nguyen.
<figure><img src="image_10.png" /><figcaption>**Figure 8** Fronds of *Nephrolepis cordifolia* damaged by *Nothopoda vietnamensis* n. sp. (photo – P. Chetverikov). A – some fronds may be completely deformed, B – typically only apical parts of pinnae are galled, C – unlike younger galls (arrow), which are open, older galls (arrowhead) are tightly closed, D – galls are usually more numerous in the basal (older) half of a frond, whereas the apical (younger) part is uninfested. Scale bar – 10 mm.</figcaption></figure>

## Etymology

The species epithet *vietnamensis*, gender feminine, is an adjective derived from “Vietnam”, indicating the country where the type locality of the new species is situated.
<figure><img src="image_11.png" /><figcaption>**Figure 9** Different developmental stages of the galls caused by *Nothopoda vietnamensis* n. sp. on fronds of a fern *Nephrolepis cordifolia* (photo - P. Chetverikov). Scale bar: A, B, E, F, G, H - 5 mm; C, D, J - 2 mm; I - 1 mm. A - dorsal view of damaged (arrow) and intact (arrowhead) lateral margin of pinna at the earliest step of gall development. B - enlargement of marginal lobes (ml) and radial ridges (arrowheads) in the infested area of pinna (dorsal view). C, D - beginning of the formation of the gall chamber on the ventral surface of pinna, the ridges (arrowheads) form carcass of the developing gall chamber, thin membranous film (mf) outlines the gall chamber margin. E, F, G - faster growing dorsal pinna tissues form irregularly shaped distal epidermal protuberances (dp); later proximal epidermal protuberances (pp) bearing trichomes appear. H, I - the internal topography of the gall becomes more complex due to formation of many secondary folds and growth of trichomes; J - closure of the gall edges and formation of a mature gall with chamber.</figcaption></figure>

Differential diagnosis

The new species, *Nothopoda vietnamensis* n. sp., is morphologically very close to *Floracarus footei* Keifer, 1953 (assigned to *Nothopoda* by Amrine and Stasny (1994)) and *F. biserratae* Huang, 2001. These three species have been recorded from Southeast Asia (Figure 1)
<figure><img src="image_12.png" /><figcaption>**Figure 10** Type locality of *Nothopoda vietnamensis* n. sp. from a fern *Nephrolepis cordifolia* (A) growing along the staircase (B) leading to the Silver Waterfall (C) in Vietnam (photo - P. Chetverikov).</figcaption></figure>

parasitizing ferns of the genus *Nephrolepis* (Polypodiales: Nephrolepidaceae) and causing presumably similarly shaped galls on pinnae (Table 2). Considering high morphological variability observed in *N. vietnamensis* n. sp. and possible synonymy of *Nothopoda* and *Floracarus* (see above), the three species discussed may either belong to one polymorphic widely distributed olygophagous species or represent a complex of geographically isolated species, discrimination of which is possible only based on DNA comparison. Because molecular data on *F. footei* and *F. biserratae* is unavailable, following morphological concept of species, here we treat the Vietnamese mites as a new taxon and differentiate it from *F. footei* and *F. biserratae* based on ornamentation of prodorsal shield, width of first three dorsal opisthosomal annuli and presence/absence of coxigenital annuli (Table 2, Figure 11).

**Acknowledgments**

We are grateful to Dr. Enrico de Lillo (Italy) for providing copies of rare taxonomic publications on eriophyoid mites and to Dr. Bruno Senterre (Biodiversity and Conservation Centre, University of Seychelles) for his help with plant identification. The light microscopy study was funded by the Zoological Institute of Russian Academy of Sciences (ZIN RAS project
<table><caption>**Table 2** Morphological differences between *Nothopoda vietnamensis* n. sp., *Floracarus footei* Keifer 1953 and *F. biserratae* Huang 2001.</caption><thead><tr><th>Character</th><th>Nothopoda vietnamensis n. sp.</th><th>Floracarus footei Keifer, 1953</th><th>Floracarus biserratae Huang, 2001</th></tr></thead><tbody><tr><td>Bifurcation of apical part of median line of prodorsal shield forming a small elliptical closed cell</td><td>Absent<br>(Figure 11 C)</td><td>Present<br>(Figure 11 B)</td><td>Absent<br>(Figure 11 A)</td></tr><tr><td>Number of transverse lines crossing median line</td><td>3 or more</td><td>2</td><td>2</td></tr><tr><td>Posterior part of submedian line I</td><td>connected anteriorly with neighbor lines</td><td>connected anteriorly with neighbor lines</td><td>separated anteriorly from neighbor lines</td></tr><tr><td>Coxigenital annuli between coxeae II and external genitalia</td><td>5–6</td><td>3–4</td><td>absent</td></tr><tr><td>Width of the first three dorsal annuli relative to other dorsal annuli</td><td>same</td><td>same</td><td>the first three dorsal annuli are three times wider than other annuli (Figure 11 A)</td></tr><tr><td>Number of dorsal opisthosomal annuli</td><td>69–79</td><td>69</td><td>74</td></tr><tr><td>Type locality</td><td>Northern Vietnam</td><td>"the Philippines, intercepted in quarantine at Honolulu, Hawaii"</td><td>Taiwan</td></tr><tr><td>Host plant</td><td>Nephrolepis cordifolia (L.) K. Presl</td><td>Nephrolepis sp.</td><td>Nephrolepis biserrata (Sw.) Schott</td></tr><tr><td>Relation to host</td><td>in galls on frond pinnae (Figures 8, 9)</td><td>"the mites make terminal galls on the frond branches"</td><td>"this species causes scrolling at the edge of the leaf"</td></tr><tr><td>Reference</td><td>this paper</td><td>Keifer 1953</td><td>Huang 2001</td></tr></tbody></table>

<figure><img src="image_13.png" /><figcaption>**Figure 11** Prodorsal shield ornamentation in three nothopodine species from *Nephrolepis* spp. A – *Floracarus biserratae* Huang 2001 (redrawn from original description), B – *Floracarus footei* Keifer 1953 (redrawn from original description), C – *Nothopoda vietnamensis n. sp.* Remarks: the first three wider dorsal opisthosomal annuli in *F. biserratae* (Figure 11 A), and position of *sc* in *F. footei* (Figure 11 B), may be unnatural and represent slide-mounting artifacts.</figcaption></figure>

# 125013001089-0). PCR and sequencing were conducted with the equipment of the “Development of Molecular and Cellular Technologies”, “The Bio-Bank”, and “Microscopy and Microanalysis» Resource Centers and supported by Saint Petersburg State University (Russia).

ORCID

Philipp E. Chetverikov https://orcid.org/0000-0003-1300-1486

Charnie Craemer https://orcid.org/0000-0002-9943-9595

Vladimir D. Gankevich https://orcid.org/0000-0003-4010-6240

Alexey G. Desnitskiy https://orcid.org/0000-0003-1141-1684

Thi Tuyet Nhung Le https://orcid.org/0000-0003-2624-3759

Duc Viet Nguyen https://orcid.org/0000-0002-7355-574X
Hoat Trinh Xuan https://orcid.org/0000-0002-2240-3922

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