# A comprehensive morphological descriptions of three marine water mites (Acari: Hydrachnidia: Pontarachnidae) from Hainan Island, China

Hai-Tao Li, Harry Smit, Bao-Xiang Zhan, Dao-Chao Jin, Jian-Jun Guo

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Hai-Tao Li, Harry Smit, Bao-Xiang Zhan, Dao-Chao Jin, Jian-Jun Guo. A comprehensive morphological descriptions of three marine water mites (Acari: Hydrachnidia: Pontarachnidae) from Hainan Island, China. Acarologia, 2025, 65 (3), pp.786-814. 10.24349/jiun-ayx5. hal-05206338

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Acarologia

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in Acarology

# A comprehensive morphological descriptions of three marine water mites (Acari: Hydrachnidia: Pontarachnidae) from Hainan Island, China

Hai-Tao Li ID<sup>a</sup>, Harry Smit ID<sup>b,c</sup>, Bao-Xiang Zhan ID<sup>a</sup>, Dao-Chao Jin ID<sup>a</sup>, Jian-Jun Guo ID<sup>a</sup>

## Original research

### ABSTRACT

This paper provides redescriptions of three pontarachnid species collected from the marine littoral of Hainan Island, China, i.e. *Litarachna curtipalpis* Smit, 2003, *L. thetis* Pešić & Smit, 2016, and *Pontarachna australis* Smit, 2003. *Litarachna curtipalpis* and *L. thetis* are recorded new for the Chinese fauna. Detailed morphological characters, including idiosoma coloration, gnathosomal structure, cheliceral claws, palps, and legs, were examined using optical microscopy and scanning electron microscopy (SEM).

**Keywords** new records; micrography; morphology; SEM; *Litarachna*; *Pontarachna*

## Introduction

The pontarachnid mites are the only family of the true water mites occurring in the marine habitats (Chatterjee *et al.* 2019). A few species are not directly marine, but inhabit nearby estuary or lakes (Cook 1986, 1996; Smit 2007; Pešić 2013). The family Pontarachnidae contains only two genera, *i.e.* *Pontarachna* Philippi, 1840 and *Litarachna* Walter, 1925, with 30 and 24 species respectively (Chatterjee *et al.* 2019; Montes-Ortiz *et al.* 2021).

Many experts use “peculiar” to describe this group because the presence of so-called “wheel-like acetabula” (Cook 1996; Smit and Alberti 2010; Chatterjee et al. 2019). Cook (1996) was aware of the significant phylogenetic value of this character. Smit and Alberti (2010) did careful observations with the help of SEM and TEM, and believed that this organ was used for osmoregulation. However, they were uncertain whether the wheel-like acetabula were homologues of the acetabula of freshwater mites. Taxonomists have paid more attention to the description of this character, but some other characters have not been given enough attention, especially the mouth parts. This to some extent limits our understanding of this group.

In China, three species have been reported, *i.e.* *Litarachna hongkongensis* Smit, 2002 (Hong Kong), *Pontarachna formosae* Lohmann, 1909 (Taiwan) and *Pontarachna australis* Smit, 2003 (Taiwan) (Pešić *et al.* 2008; Chatterjee *et al.* 2019; Jin *et al.* 2024). After recent collections from Hainan Island, we obtained three species, *i.e.* *Litarachna curtipalpis* Smit, 2003, *Litarachna thetis* Pešić & Smit, 2016 and *Pontarachna australis* Smit, 2003. More detailed characters were observed by camera, optical microscope and SEM, which will be discussed in this paper.

Received 01 June 2025

Accepted 04 August 2025

Published 05 August 2025

Corresponding author

Jian-Jun Guo ID: jjguo@gzu.edu.cn

Academic editor

Mąkol, Joanna

https://doi.org/10.24349/jiun-ayx5

ISSN 0044-586X (print)

ISSN 2107-7207 (electronic)

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

Li H.-T. *et al.*

Licensed under

Creative Commons CC-BY 4.0

<footnote><sup>a</sup> Institute of Entomology, Guizhou University, Scientific Observing and Experimental Station of Crop Pests in Guiyang, Ministry of Agricultural and Rural Affairs of the P. R. China, Guiyang 550025, P. R. China.</footnote>

<footnote><sup>b</sup> Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA Leiden, the Netherlands.</footnote>

<footnote><sup>c</sup> Museums Victoria Research Institute, Museums Victoria, Melbourne, Australia.</footnote>
**Material and methods**

The collection and preservation of water mites and preparation of slides followed Gu *et al.*
(2021). Micrographs of living watermite were taken by a Canon EOS R8 digital camera with a
Mitutoyo Plan NIR 10 lens, a Godox MF12 flash was used as the light source. Helicon Focus
(vers. 8.1.0) was used for image stacking. All optical microscope images, examinations and
measurements (given in µm) were made with a Nikon Ni-E (with Nikon DS-Ri2 camera). The
measurements method of idiosoma, genital field, excretory pore, gnathosoma, chelicera, palp
and legs followed Li *et al.* (2024). The treatments of SEM (scanning electron microscope)
referred to Li *et al.* (2022). All images were modified and grouped into plates in Adobe
Photoshop CS6.

The terminology and abbreviations used were updated from Jin (1997): a.s.l. = above sea
level, *A*₁ = preantennal glandularia, *A*₂ = postantennal glandularia, *Ae* = anterior extension, *C*₂
and *C*₄ = coxoglandularia 2 and 4, Cx-I–IV = coxae I–IV, El₁ = the first pair of eye lenses, El₂
= the second pair of eye lenses, *D*₁–*D*₄ = dorsoglandularia 1–4, I-L-1–6, *etc*. = the first–sixth
segment of the first leg, *etc.*, L = length, *L*₁–*L*₄ = lateroglandularia 1–4, Ma = medial apodeme,
*O*₁ = preocularia, *O*₂ = postocularia, P-1–5 = the first–fifth segments of the palp (from most
proximal to most distal), *So*₁–*So*₅ = slit organs 1–5, *V*₁–*V*₄ = ventroglandularia 1–4, W = width,
Wa = wheel-like acetabula.

The material is deposited in the Institute of Entomology, Guizhou University, Guiyang, P. R. China (GUGC).

**Systematics**

**Family Pontarachnidae Koenike, 1910**

**Genus *Litarachna* Walter, 1925**

*Litarachna curtipalpis* Smit, 2003 (Figs 1–10, 24A–B)

**Material examined**

4♂, 4♀, Lingshui Li Autonomous County, Hainan Province, P. R. China (18.41°N, 110.06°E, 2.8 m a.s.l.) (Fig. 1A), leg. Hai-Tao Li & Lu-Ping Zhao, 17-II-2025, Slides No. HN-PO-2025021701-2025021708.

**Habitat**

Coastal tidal flats, depth of water 0.5m, with a large amount of organic detritus at the bottom.
(Fig. 1B–D).

**Diagnosis**

Coxal field pink; first coxal plates separated medially; suture lines of Cx-II/III, and Cx-III/IV
incomplete; a pair of lateral platelets with three pores posterior to the gonopore; a pair of
wheel-like acetabula posteriorly to the genital field; P-2 having a large protrusion without seta
on the ventral margin; two long fine setae near a stout seta at the middle of the ventral margin
of P-4.

**Male** — Genital field with a sclerotized ring with a long anterior extension, and numerous (approximately 100) perigenital setae surrounding this ring.

**Female** — Pregenital sclerite arrow-shaped; postgenital sclerite lunate; an extra pair of wheel-like acetabula located posterior to the genital field.

**Description**

Living specimen: oval body color usually brownish-red (Fig. 2A, E–F), occasionally red (Fig. 2C–D), eye pigment obvious, coxal field pink (Fig. 2B).
<figure><img src="image_3.png" /><figcaption>**Figure 1** Locality and habitat of three pontarachnid mites, littoral of Lingshui Li Autonomous County, Hainan Province, P. R. China (18.41°N, 110.06°E, 2.8 m a.s.l.).</figcaption></figure>

**Male** (n=4) — In dorsal view: *A*₁ not visible; two pairs of El rounded (Fig. 3D), lying beneath the integument; idiosoma without sclerites (Fig. 3A). In ventral view: Cx-I separated medially; suture lines of Cx-II/III, and Cx-III/IV incomplete; medial apodeme of Cx-IV longer than lateral apodeme, *C*₄ in the middle between the apodemes; rounded *V*₃ much larger than other glandularia, without accompanying seta (Fig. 4C); genital field with a sclerotized ring bearing 4–5 pairs of setae and with a long anterior extension (Fig. 4A); numerous perigenital setae surrounded the genital field (Fig. 3E); a pair of lateral platelets with three pores posterior to the gonopore; a pairs of wheel-like acetabula posteriorly of the genital field (Fig. 3B, E).

Gnathosoma not fused with ACG with a short rostrum bearing two pairs of setae, apodeme located inside the idiosoma and appearing trapezoid in ventral view (Fig. 3F–G). Chelicera consisting of two segments (Fig. 3I); cheliceral claw having a narrow groove with fence-like structure, and dense minute seta-like projections in medial view (Fig. 5B); many teeth ventrally in lateral view (Fig. 5C). Palp five-segmented (Fig. 6A, E); P-1 with one dorsal seta; P-2 with 4–5 dorsal setae, and a large protrusion without seta ventrally (Fig. 6B, F); dorsal P-3 with a fine seta terminally; two long fine setae near a stout seta at the middle of the ventral margin of P-4, and a fine anteroventral seta (Fig. 6C, G); stout P-5 bearing six setae in total, with two stout claws, and two seta-like claws (Fig. 6D, H).

All legs simple, without modifications; claws well-developed and trifid, some nicks on the
<figure><img src="image_4.png" /><figcaption>**Figure 2** Micrographs of *Litarachna curtipalpis* Smit, 2003 habitus: (A) ♂ dorsal view; (B) ♂ ventral view; (C) ♀ dorsal view; (D) ♀ ventral view; (E) ♂ dorsal view; (F) ♀ dorsal view. Scale bars = 200 µm.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Figure 3** *Litarachna curtipalpis* ♂ (HN-PO-2025021701). Optical microscope photographs: (A) Dorsal view of idiosoma; (B) Ventral view of idiosoma; (C) Lateral view of idiosoma; (D) Eye lenses; (E) Genital field; (F) Lateral view of gnathosoma; (G) Ventral view of gnathosoma; (H) Lateral view of palp; (I) Lateral view of chelicera; (J) Ejaculatory complex. Scale bar A–C = 200 µm; scale bars D, E, F–J = 50 µm.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Figure 4** *Litarachna curtipalpis* A–C, *Litarachna thetis* D–G, *Pontarachna australis* H–I, SEM photographs: (A) ♂ genital field; (B) ♀ coxal groups; (C) ♀ *V*<sub>3</sub>; (D) ♂ genital field; (E) ♀ genital field; (F) ♀ medial chelicera claw; (G) ♀ lateral chelicera claw; (H) ♀ gnathosoma + cheliceral claws; (I) ♀ terminal of cheliceral claws.</figcaption></figure>

dorsal surface (Figs 5I; 7C, I; 8D). I–II–L with terminal “swimming setae” of the fourth and fifth segments (Fig. 7A–B, G–H); III–IV–L–4–5 with one and two terminal swimming setae, respectively (Figs 5G–H, 8).

**Female** (n=4) — In most aspects similar to male (Figs 9, 10). Sexual dimorphism exhibited in the following characters. Genital field situated between Cx-IV, pregenital sclerite arrow-shaped, postgenital sclerite lunate (Fig. 9E). An extra pair of wheel-like acetabula compared to males, located posterior to the genital field (Fig. 9B).

**Measurements**

**Male** (n=4) and **Female** (n=4) — See Table 1 for details.

**Remarks**

The diagnostic characters of the specimens from this study match the description of *L. curtipalpis* (Fig. 24A–B), a species known from Western Australia and Singapore (Smit 2003, 2009). However, this conclusion is only temporary, as the two localities are far apart. In the
<figure><img src="image_7.png" /><figcaption>**Figure 5** *Litarachna curtipalpis*, (A–F) ♀, (G–I) ♂, SEM photographs, captions as shown in each photos.</figcaption></figure>

future, DNA barcoding based research may provide us with new insights.

**Litarachna thetis Pešić & Smit, 2016 (Figs 11–19)**

**Material examined**

1♂, 3♀, Lingshui Li Autonomous County, Hainan Province, P. R. China (18.41°N, 110.06°E, 2.8 m a.s.l.) (Fig. 1A), leg. Hai-Tao Li & Lu-Ping Zhao, 17-II-2025, Slides No. HN-PO-2025021709-2025021712.

**Habitat**

Same as *Litarachna curtipalpis*.

**Diagnosis**

Coxal field amber-colored; Cx-I separated medially; suture lines of Cx-II/III incomplete, suture lines of Cx-III/IV complete; *V*₃ almost at the same level of the two pairs of wheel-like acetabula; P-2 with a shallow anteroventral extension; the two long ventral setae of P-4 not lying at the same level; claws of legs well-developed, usually five-branched, but sometimes 4-
<figure><img src="image_8.png" /><figcaption>**Figure 6** *Litarachna curtipalpis* ♂, characters of palps, SEM photographs, captions as shown in each photos.</figcaption></figure>

or 6-branched.

**Male** — Genital field with a sclerotized ring bearing four pairs of setae with an anterior extension, and numerous perigenital setae (approximately 130).

**Female** — Genital field situated between Cx-IV.
<figure><img src="image_9.png" /><figcaption>**Figure 7** *Litarachna curtipalpis*, characters of I–II-L, (A–C, G–I ♂, (D–F, J–L) ♀, SEM photographs, captions as shown in each photos.*</figcaption></figure>

**Description**

Living specimen: rounded body color red, eye pigment obvious, coxal field amber-colored (Fig. 11).

**Male** (n=1) — In dorsal view: *A*₁ not visible; El₁ larger than El₂ (Fig. 12D), lying beneath the integument; idiosoma without sclerites (Fig. 12A). In ventral view: Cx-I separated medially; suture lines of Cx-II/III incomplete, suture lines of Cx-III/IV complete; medial
<figure><img src="image_10.png" /><figcaption>**Figure 8** *Litarachna curtipalpis*, characters of IV-L, (A–E) ♂, (F–I) ♀, SEM photographs, captions as shown in each photos.</figcaption></figure>

apodeme of Cx-IV longer than lateral apodeme, *C*<sub>4</sub> close to the tip of the lateral apodeme; *V*<sub>3</sub> much larger than other glandularia, almost at the same level of the two pairs of wheel-like acetabula; genital field with a sclerotized ring bearing four pairs of setae with an anterior extension, and numerous perigenital setae (approximately 130) (Figs 4D, 12E); two pairs of wheel-like acetabula posteriorly of the genital field (Fig. 12B).

Gnathosoma not fused with ACG, with a short rostrum and two pairs of setae, apodeme located inside the idiosoma and appearing as a rectangle in the ventral view (see Fig. 18H–I of the female). Chelicera consisting of two segments (Fig. 12G); cheliceral claw having a deep groove, and a few teeth in medial view (see Fig. 4F of the female), and many teeth ventrally (see Fig. 4G of the female). Palp five-segmented (Fig. 12F); P-1 with one dorsal seta (Fig. 13A, E); P-2 with four dorsal setae, and a shallow anteroventral extension (Fig. 13B, F); P-3 dorsally with a fine terminal seta; two long ventral setae of P-4 not lying at the same level, and three dorsal setae located terminally (Fig. 13C, G); P-5 with six setae in total (Fig. 13D, H).

All legs simple, without modifications; claws well-developed, usually five-branched, but sometimes 4- or 6-branched, some nicks on the dorsal surface (Figs 14–16C, F; 17J, K). Only one “swimming setae” (but it’s not sure if it’s strictly speaking a swimming seta, as it’s noticeably thinner than the swimming setae of III–IV-L) on I-L-5 and II-L-5 (Figs 14–15A, D);
<figure><img src="image_11.png" /><figcaption>**Figure 9** *Litarachna curtipalpis* ♀ (HN-PO-2025021705). Optical microscope photographs: (A) Dorsal view of idiosoma; (B) Ventral view of idiosoma; (C) Lateral view of idiosoma; (D) Eye lenses; (E) Genital field; (F) Lateral view of palp; (G) Lateral view of gnathosoma; (H) Ventral view of gnathosoma; (I) Lateral view of chelicera. Scale bar A–C = 200 µm; scale bars D, E, F–I = 50 µm.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Figure 10** *Litarachna curtipalpis* ♀, characters of palps, SEM photographs, captions as shown in each photo.</figcaption></figure>

III–IV-L-4–5 with one and two terminal swimming setae, respectively (Figs 16A, D; 17A–C).

**Female** (n=3) — In most aspects similar to male (Figs 18–19). Genital field situated between Cx-IV and medial apodemes of Cx-IV longer than lateral apodemes, pregenital sclerite arrow-shaped, postgenital sclerite lunate (Fig. 18E).

**Measurements**

**Male** (n=1) and **Female** (n=3) — See Table 2 for details.
Remarks

In most aspects, e.g. (1) Cx-I separated medially, suture lines of Cx-II/III incomplete and suture lines of Cx-III/IV complete, (2) P-2 with shallow anteroventral extension and (3) two long ventral setae of P-4 not lying at the same level, the specimens from this study match the description of *L. thetis*, a species known from South Korea and Japan (Pešić and Smit 2016). However, it is worth mentioning that the shallow anteroventral extension of P-2 of

<table><caption>Table 1 Measurements of *Litarachna curtipalpis*.</caption><thead><tr><th></th><th>S1 ♂</th><th>S2 ♂</th><th>S3 ♂</th><th>S4 ♂</th><th>S5 ♀</th><th>S6 ♀</th><th>S7 ♀</th><th>S8 ♀</th></tr></thead><tbody><tr><td>Idiosoma L/W</td><td>389/297</td><td>378/302</td><td>392/352</td><td>354/316</td><td>392/329</td><td>380/310</td><td>368/287</td><td>413/351</td></tr><tr><td>El<sub>1</sub></td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>16</td><td>15</td><td>17</td></tr><tr><td>El<sub>2</sub></td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>14</td><td>13</td><td>14</td></tr><tr><td>Coxal field L</td><td>196</td><td>192</td><td>198</td><td>187</td><td>202</td><td>219</td><td>191</td><td>209</td></tr><tr><td>Cx-IV Ma L</td><td>48</td><td>48</td><td>46</td><td>36</td><td>54</td><td>60</td><td>45</td><td>50</td></tr><tr><td>Sclerotized ring L/W</td><td>46/28</td><td>44/26</td><td>43/30</td><td>48/31</td><td>/</td><td>/</td><td>/</td><td>/</td></tr><tr><td>Sclerotized ring Ae L</td><td>25</td><td>25</td><td>26</td><td>25</td><td>/</td><td>/</td><td>/</td><td>/</td></tr><tr><td>Pregenital sclerite W</td><td>/</td><td>/</td><td>/</td><td>/</td><td>39</td><td>44</td><td>35</td><td>41</td></tr><tr><td>Postgenital sclerite W</td><td>/</td><td>/</td><td>/</td><td>/</td><td>37</td><td>42</td><td>36</td><td>41</td></tr><tr><td>Gonopore L</td><td>14</td><td>14</td><td>12</td><td>16</td><td>43</td><td>44</td><td>39</td><td>45</td></tr><tr><td>Gnathosoma L</td><td>/</td><td>/</td><td>135</td><td>/</td><td>/</td><td>/</td><td>/</td><td>156</td></tr><tr><td>Chelicera base L</td><td>134</td><td>133</td><td>133</td><td>/</td><td>161</td><td>161</td><td>/</td><td>156</td></tr><tr><td>Chelicera claw L</td><td>40</td><td>38</td><td>41</td><td>/</td><td>/</td><td>50</td><td>/</td><td>46</td></tr><tr><td>P-1 dL/W</td><td>14/22</td><td>15/23</td><td>15/25</td><td>15/25</td><td>15/27</td><td>20/27</td><td>13/23</td><td>16/27</td></tr><tr><td>P-2 dL/W</td><td>78/41</td><td>77/38</td><td>83/46</td><td>77/40</td><td>84/42</td><td>92/48</td><td>80/42</td><td>89/48</td></tr><tr><td>P-3 dL/W</td><td>27/35</td><td>27/34</td><td>28/37</td><td>26/34</td><td>31/38</td><td>35/41</td><td>26/36</td><td>31/40</td></tr><tr><td>P-4 dL/W</td><td>81/24</td><td>81/23</td><td>83/25</td><td>78/25</td><td>89/25</td><td>93/28</td><td>81/26</td><td>91/26</td></tr><tr><td>P-5 dL/W</td><td>26/10</td><td>25/12</td><td>30/14</td><td>27/13</td><td>29/13</td><td>29/14</td><td>29/14</td><td>28/13</td></tr><tr><td>P-2 Pr</td><td>8</td><td>10</td><td>11</td><td>9</td><td>11</td><td>9</td><td>11</td><td>13</td></tr><tr><td>I-L-1-6 dL</td><td>38/49/39/45/66/76</td><td>38/45/40/46/61/76</td><td>40/52/42/48/66/78</td><td>39/50/41/44/60/75</td><td>38/52/42/48/62/76</td><td>40/56/42/50/67/82</td><td>39/48/40/44/58/79</td><td>39/59/43/48/70/80</td></tr><tr><td>II-L-1-6 dL</td><td>39/51/41/47/67/85</td><td>39/51/40/47/66/81</td><td>39/53/40/49/63/88</td><td>39/50/42/42/64/81</td><td>39/54/42/46/71/83</td><td>41/55/46/53/75/86</td><td>39/49/40/45/62/80</td><td>44/54/48/51/72/85</td></tr><tr><td>III-L-1-6 dL</td><td>41/51/39/52/76/96</td><td>42/49/38/51/74/92</td><td>41/57/46/52/76/100</td><td>41/49/41/48/73/92</td><td>44/58/43/50/74/97</td><td>46/54/49/51/81/105</td><td>41/50/40/48/73/86</td><td>41/56/39/54/76/99</td></tr><tr><td>IV-L-1-6 dL</td><td>68/59/56/94/98/112</td><td>65/65/55/93/97/101</td><td>71/64/55/96/97/106</td><td>64/61/56/85/94/104</td><td>65/64/57/92/101/113/70/69/59/98/104/118</td><td>65/59/57/95/94/104</td><td>67/68/60/98/106/120</td><td></td></tr></tbody></table>

<table><caption>Table 2 Measurements of *Litarachna thetis* (L-S1–L-S4) and *Pontarachna australis* (P-S1–P-S2).</caption><thead><tr><th></th><th>L-S1 ♂</th><th>L-S2 ♀</th><th>L-S3 ♀</th><th>L-S4 ♀</th><th>P-S1 ♂</th><th>P-S2 ♀</th></tr></thead><tbody><tr><td>Idiosoma L/W</td><td>424/385</td><td>533/458</td><td>/</td><td>448/394</td><td>347/284</td><td>453/376</td></tr><tr><td>Coxal field L</td><td>264</td><td>295</td><td>285</td><td>259</td><td>214</td><td>228</td></tr><tr><td>Cx-IV Ma L</td><td>57</td><td>63</td><td>57</td><td>46</td><td>63</td><td>67</td></tr><tr><td>Sclerotized ring L/W</td><td>59/36</td><td>/</td><td>/</td><td>/</td><td>46/45</td><td>/</td></tr><tr><td>Sclerotized ring Ae L</td><td>19</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td></tr><tr><td>Pregenital sclerite W</td><td>/</td><td>54</td><td>53</td><td>46</td><td>/</td><td>43</td></tr><tr><td>Postgenital sclerite W</td><td>/</td><td>49</td><td>51</td><td>45</td><td>/</td><td>44</td></tr><tr><td>Gonopore L</td><td>28</td><td>49</td><td>52</td><td>42</td><td>27</td><td>56</td></tr><tr><td>Gnathosoma L</td><td>/</td><td>/</td><td>152</td><td>/</td><td>/</td><td>/</td></tr><tr><td>Chelicera base L</td><td>136</td><td>174</td><td>167</td><td>148</td><td>131</td><td>152</td></tr><tr><td>Chelicera claw L</td><td>34</td><td>47</td><td>48</td><td>42</td><td>134</td><td>156</td></tr><tr><td>P-1 dL/W</td><td>17/31</td><td>18/33</td><td>19/38</td><td>16/31</td><td>15/19</td><td>20/20</td></tr><tr><td>P-2 dL/W</td><td>85/51</td><td>101/60</td><td>106/60</td><td>94/52</td><td>42/24</td><td>50/27</td></tr><tr><td>P-3 dL/W</td><td>45/41</td><td>45/50</td><td>43/52</td><td>43/44</td><td>39/21</td><td>48/26</td></tr><tr><td>P-4 dL/W</td><td>110/22</td><td>137/25</td><td>128/24</td><td>111/21</td><td>56/17</td><td>60/17</td></tr><tr><td>P-5 dL/W</td><td>46/12</td><td>51/17</td><td>50/17</td><td>44/17</td><td>19/8</td><td>22/10</td></tr><tr><td>I-L-1-6 dL</td><td>48/61/54/65/94/104</td><td>54/72/65/73/100/112</td><td>53/72/59/68/99/105</td><td>48/64/55/63/89/101</td><td>34/49/39/39/56/74</td><td>42/53/45/44/60/79</td></tr><tr><td>II-L-1-6 dL</td><td>53/63/57/71/98/117</td><td>56/74/64/78/112/122</td><td>48/71/63/73/109/116</td><td>51/61/55/67/87/111</td><td>38/54/36/45/66/81</td><td>41/52/48/46/73/83</td></tr><tr><td>III-L-1-6 dL</td><td>58/66/55/76/112/126</td><td>60/66/67/86/124/135</td><td>61/70/66/83/119/131</td><td>55/64/55/72/104/122</td><td>43/53/46/55/86/95</td><td>48/58/49/56/91/99</td></tr><tr><td>IV-L-1-6 dL</td><td>92/79/63/106/123/123</td><td>108/98/77/120/139/140</td><td>103/91/73/113/133/132</td><td>95/81/61/101/124/125</td><td>68/57/52/87/97/98</td><td>67/72/56/98/102/106</td></tr></tbody></table>
<figure><img src="image_13.png" /><figcaption>**Figure 11** Micrographs of *Litarachna thetis* Pešić & Smit, 2016 habitus: (A) ♂ dorsal view; (B) ♂ ventral view; (C) ♀ dorsal view; (D) ♀ ventral view. Scale bars = 200 µm.</figcaption></figure>

our specimens is more obvious than in the original descriptions. Different geographical populations may be a reasonable explanation for this phenomenon. For the time being we assign our specimens to this species, but more research is needed, especially with molecular techniques.

**Genus Pontarachna Philippi 1840**

**Pontarachna australis** Smit, 2003 (Figs 20-23)

**Material examined**

1♂, 1♀, Lingshui Li Autonomous County, Hainan Province, P. R. China (18.41°N, 110.06°E, 2.8 m a.s.l.) (Fig. 1A), leg. Hai-Tao Li & Lu-Ping Zhao, 17-II-2025, Slides No. HN-PO-2025021713-2025021714.
<figure><img src="image_14.png" /><figcaption>**Figure 12** *Litarachna thetis* ♂ (HN-PO-2025021709). Optical microscope photographs: (A) Dorsal view of idiosoma; (B) Ventral view of idiosoma; (C) Lateral view of idiosoma; (D) Eye lenses; (E) Genital field; (F) Lateral view of palp; (G) Lateral view of chelicera. Scale bar A–C = 200 µm; scale bars D, E, F–G = 50 µm.</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>**Figure 13** *Litarachna thetis* ♂, characters of palps, SEM photographs, captions as shown in each photo.</figcaption></figure>

**Habitat**

Same as *L. curtipalpis*.

**Diagnosis**

$L_4$ close to $D_3$: Cx-I separated medially; two pairs of small wheel-like acetabula located posteriorly to the genital field; cheliceral claw stylet-like; P-2 without sclerotized ventral
<figure><img src="image_16.png" /><figcaption>**Figure 14** *Litarachna thetis*, characters of I-L, (A–F) ♂, (G–L) ♀, SEM photographs, captions as shown in each photos.</figcaption></figure>

extension; P-4 ventrally straight, without setal tubercles.

**Male** — Genital field consisting of a sclerotized ring, without an anterior extension, with 12–16 setae.

**Female** — Genital field partially located between medial posterior apodemes of Cx-IV, postgenital sclerite with one pair of small wheel-like acetabula.
<figure><img src="image_17.png" /><figcaption>**Figure 15** *Litarachna thetis*, characters of II-L, (A–F) ♂, (G–L) ♀, SEM photographs, captions as shown in each photos.</figcaption></figure>

**Description**

**Female** (n=1) — In dorsal view: El₁ slightly larger than El₂ (Fig. 20D), lying beneath the integument; L₄ close to D₃; idiosoma without sclerites (Fig. 20A). In ventral view: Cx-I separated medially; suture lines of Cx-II/III incomplete; suture lines of Cx-III/IV posteriorly ending in long apodemes; medial apodeme of Cx-IV longer than lateral apodeme, C₄ located postlaterally the lateral apodeme; V₃ larger than other glandularia, almost at the same level
<figure><img src="image_18.png" /><figcaption>**Figure 16** *Litarachna thetis*, characters of III-L, (A–F) ♂, (G–L) ♀, SEM photographs, captions as shown in each photos.</figcaption></figure>

as postgenital sclerite; genital field partially located between medial posterior apodemes of Cx-IV, postgenital sclerite with one pair of small wheel-like acetabula (Figs 20E); two pairs of small wheel-like acetabula (sensu Cook 1996) or specialized glandularia (sensu Tuzovskij 1978) located posteriorly to the genital field (Fig. 20B).

Gnathosoma not fused with ACG, with a short rostrum and bearing two pairs of setae (Fig. 4H). Chelicera consisting of two segments (Fig. 20G); cheliceral claw stylet-like, having a groove medially and some teeth laterally (Fig. 4I). Palp five-segmented (Fig. 20F); P-1 with
<figure><img src="image_19.png" /><figcaption>**Figure 17** *Litarachna thetis*, characters of IV-L, (A–C, J, K) ♂, (D–I, L) ♀, SEM photographs, captions as shown in each photos.</figcaption></figure>

one dorsal seta; P-2 with four dorsal setae, without sclerotized extension ventrally (Fig. 21B, F); P-3 with a fine dorsal seta; P-4 ventrally straight, without setal tubercles, and with two long subterminal setae (Fig. 21C, G); P-5 tapering (Fig. 21D, H).

All legs simple, without modifications; claws well-developed, four-branched (Fig. 22I).
“Swimming setae” (but it’s not sure if these are strictly speaking swimming setae, as they are
noticeably thinner than the swimming setae of III–IV-L) occurring terminally of I–II-L-4–5
(Fig. 22A–D); III–IV-L-4–5 with one and two terminal swimming setae respectively (Fig.
<figure><img src="image_20.png" /><figcaption>**Figure 18** *Litarachna thetis* ♀ (HN-PO-2025021710). Optical microscope photographs: (A) Dorsal view of idiosoma; (B) Ventral view of idiosoma; (C) Lateral view of idiosoma; (D) Eye lenses; (E) Genital field; (F) Lateral view of palp; (G) Lateral view of chelicera; (H) Lateral view of gnathosoma; (I) Ventral view of gnathosoma. Scale bar A–C = 200 µm; scale bars D, E, F–I = 50 µm.</figcaption></figure>
<figure><img src="image_21.png" /><figcaption>**Figure 19** *Litarachna thetis* ♀, characters of palps, SEM photographs, captions as shown in each photo.</figcaption></figure>

22E-L).

**Male** (n=1) — In most aspects similar to female (Fig. 23). Genital field consisting of a sclerotized ring, without anterior extension, and with 12 setae on the left side and 16 setae on the right side. (Fig. 23E).

**Measurements**

**Male** (n=1) and **Female** (n=1) — See Table 2 for details.
<figure><img src="image_22.png" /><figcaption>**Figure 20** *Pontarachna australis* ♀ (HN-PO-2025021714). Optical microscope photographs: (A) Dorsal view of idiosoma; (B) Ventral view of idiosoma; (C) Lateral view of idiosoma; (D) Eye lenses; (E) Genital field; (F) Lateral view of palp; (G) Lateral view of chelicera. Scale bar A–C = 200 µm; scale bars D, E, F–G = 50 µm.</figcaption></figure>
<figure><img src="image_23.png" /><figcaption>**Figure 21** *Pontarachna australis* ♀, characters of palps, SEM photographs, captions as shown in each photo.</figcaption></figure>

**Remarks**

*Pontarachna australis* was described from a single female from Western Australia (Smit 2003). Pešić *et al.* (2008) collected this species from Taiwan and added the description of the male. Due to our specimens have following characters: (1) two pairs of small wheel-like acetabula or specialized glandularia located posteriorly of the genital field; (2) the male genital field consisting of a sclerotized ring, without an anterior extension; (3) the female genital field partially located between the medial posterior apodemes; (4) the postgenital sclerite with one
<figure><img src="image_24.png" /><figcaption>**Figure 22** *Pontarachna australis* ♀, characters of I–IV-L, SEM photographs, captions as shown in each photos.</figcaption></figure>

pair of small wheel-like acetabula; and (5) a similarly shaped palp (Fig. 24C), we assign our
specimens to *P. australis*.
<figure><img src="image_25.png" /><figcaption>**Figure 23** *Pontarachna australis* ♂ (HN-PO-2025021713). Optical microscope photographs: (A) Dorsal view of idiosoma; (B) Ventral view of idiosoma; (C) Lateral view of idiosoma; (D) Eye lenses; (E) Genital field; (F) Lateral view of palp; (G) Lateral view of chelicera; (H) Ejaculatory complex. Scale bar A–C = 200 µm; scale bars D, E, F–H = 50 µm.</figcaption></figure>
<figure><img src="image_26.png" /><figcaption>**Figure 24** Paratypes from Naturalis Biodiversity Center, (A–B) *Litarachna curtipalpis* ♀, (C–D) *Pontarachna australis* ♀, optical microscope photographs: (A) Lateral view of palp; (B) Lateral view of I-L; (C) Lateral view of palps and gnathosoma; (D) Lateral view of I-L-6. Scale bar A = 50 µm; scale bar B = 100 µm; scale bar C = 20 µm; scale bar D = 50 µm.</figcaption></figure>

**Discussion**

We used camera, optical microscope and SEM to make a comprehensive description of three species from Hainan. Except *P. australis* these species have been reported from Taiwan by Pešić *et al.* (2008). The remaining two, *i.e.* *L. curtipalpis* Smit, 2003 and *L. thetis* Pešić & Smit, 2016, are recorded new for Chinese fauna.

Cook (1974) divided *Litarachna* into two subgenera based on the fusion between Cx-I, but as more species were recorded later on, this system was abandoned (Cook 1986). We found that the characters of the currently known species in this genus can be divided into two groups: (1) incomplete suture lines of Cx-III/IV + gnathosoma as a trapezoid in the ventral view + P-4 with a setal tubercle, (2) complete suture lines of Cx-III/IV + gnathosoma as a rectangle in the ventral view + P-4 without a setal tubercle. Therefore, the taxonomy of this genus needs further research involving molecular techniques.

In addition, we examined the cheliceral claw of three species using SEM. They are different in shape and medial surface, *i.e.* *P. australis* is stylet-like and without seta-like projections, *L. curtipalpis* is “normal” and with dense seta-like projections, *L. thetis* is “normal” and without seta-like projections. These very strong differences in the structure of the mouth parts of these three species investigated are strongly indicating completely different dietary habits of
these cohabiting species. Unfortunately, respective detailed descriptions of the mouth parts are lacking for other species of the family. Nevertheless, our results show the great potential of these characters for revisional studies. Moreover, further research should include as well molecular studies in order to provide data for phylogenetic studies.

## Acknowledgements

We are indebted to Dr. Tom Goldschmidt (Germany) for providing suggestions on text and figures. Moreover, Thanks for Guang-Hui Li, Li-Ping Wang, Ai-Guo Zhao and Gui-Hua Wang (P. R. China), to help in specimen collection. This research was supported by Guizhou Provincial Science and Technology Projects (Qiankehe Pingtai Rencai-GCC [2022]029-1).

## ORCID

Hai-Tao Li https://orcid.org/0009-0002-4639-7843

Harry Smit https://orcid.org/0000-0002-0376-6808

Bao-Xiang Zhan https://orcid.org/0009-0006-3428-6125

Dao-Chao Jin https://orcid.org/0000-0003-2727-5621

Jian-Jun Guo https://orcid.org/0000-0002-0523-6704

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