Pseudoleiobunum lutulentum Tan, 2025

Tan, Desmond Kai Teck, Tsurusaki, Nobuo, Fong, Jonathan J. & Zhang, Chao, 2025, Reinstatement of the genus Pseudoleiobunum Müller, 1914 with the inclusion of a new species from Hong Kong and reallocation of the Leiobunum maximum species complex (Arachnida: Opiliones: Eupnoi: Sclerosomatidae), Zootaxa 5646 (3), pp. 301-343 : 306-310

Pseudoleiobunum lutulentum Tan sp. nov.

Type material examined. Holotype ♂ ( LINGU-INV154 ), CHINA: Hong Kong Special Administrative Region, New Territories , Tai Mo Shan [N22°24.5867' E114°7.9283'], 22 October 2024, Tan ; paratype 1 ( LINGU-INV72 ), CHINA: Hong Kong Special Administrative Region, Lantau Island , Tei Tong Zai [N22°15.1707' E113°56.3469'], 19 April 2023, Tan ; paratype 2 ( LINGU-INV59 ), CHINA: Hong Kong, New Territories, Tai Mo Shan [N22°24.49' E114°7.37'], 12 August 2021 ; Paratype 3 ( LINGU-INV55 ), CHINA: Hong Kong Special Administrative Region, New Territories , Shing Mun Reservoir [N22°23.70', E114°8.83'] ; Paratype 4 ( LINGU-INV60 ) , same data as Paratype 3 ; Paratype 5 ( LINGU-INV106 ), CHINA: Hong Kong Special Administrative Region, New Territories , Ma On Shan, Mui Tsz Lam [N22°22.803' E114°14.357'] and Paratype 6 ( LINGU-INV107 ), same as Paratype 5; Paratype 7 ( LINGU-INV118 ) and Paratype 8 ( LINGU-INV115 ), CHINA: Hong Kong Special Administrative Region, New Territories , Ma On Shan [N22°24.012' E114°14.972'] ; Paratype 9 ♀ ( LINGU-INV116 ) , Paratype 10 ♀ ( LINGU-INV117 ) and Paratype 11 ♀ ( LINGU-INV119 ), all three same as Paratype 6 and 7; Paratype 12 ♂ ( LINGU-INV132 ) , Paratype 13 ♀ ( LINGU-INV134 ) , Paratype 14 ♀ ( LINGU-INV145 ) and Paratype 15 ♀ ( LINGU-INV146 ), CHINA: Hong Kong Special Administrative Region, New Territories , Shing Mun Reservoir [N22°23.9267', E114°9.164'] .

Diagnosis. This species can be distinguished from other congeneric species by its smaller body size (male body 3 mm long, female body 5 mm long; meanwhile the body sizes of other species range from 6.3–9.8 mm in males and 9.2–13.7 mm in females). Additionally, the male genitalia of this species possess a fairly developed alate winging that is confined to the distal section of the shaft, similar to that found in Gagrellinae species ( Figs 6A–C , 7 ) (Martens 1987) while other proposed Pseudoleiobunum species possess tapered alate sections ( Suzuki 1976, Tsurusaki 1991).

Etymology. The species name “ lutulentum ” is derived from the Latin adjective for muddy and dirty, “ lutulentus ”, referring to the overall mud-yellow colored and roughly granulated dorsal surface that is unique amongst Hong Kong harvestmen.

Distribution. Found throughout Hong Kong, although it occurs more commonly in areas with high humidity, lower temperature, high elevation and close to water sources, such as Tai Mo Shan and Mui Tsz Lam ( Figs 1 , 12).

Dorsum ( Figs 2C–E , 3 ). Scutum parvum. Scutum widest at the prosoma; scutum weak and leathery, surface covered with tiny, coarse granules. The lateral margins of the scute elevated with two apparent lateral-posterior protuberances by the IV scutal area. Meanwhile the free tergites extend below the elevated scute, sometimes compressed and extending downwards from the angled dorsal scute ( Figs 2C–E , 3 ). This is especially prominent in males or underfed individuals. Each scutal area with two small median protuberances, those on area I and II being the most apparent. Ocularium short and unarmed, shallowly canaliculate, its width longer than height. Supracheliceral lamina dorsally toothed with irregular and minute sub-quadratic tubercles ( Figs 3A , 6G ). Labrum smooth, short and unarmed, the terminal end curves downwards ventrally ( Fig. 6D–F ). Coxa I dorso-anteriorly and coxa IV dorso-posteriorly sometimes armed with visible small sub-quadratic tubercles.

Both scutal area and coxae dorsally muddy, yellowish brown, with small dark-brown and light-yellow spots scattered unevenly throughout; central figure borders slightly highlighted in light-yellow pattern. The IV area, including the two latero-posteriorly protuberances, is highlighted with a bright yellow or light brown horizontal band.

Ventral ( Fig. 3B ). Smooth and unarmed except for a scattering of short hairs; coxae scattered with tiny coarse granules similar to that of the dorsal. Lateral margins of both the genital operculum and coxae lined with sub-quadratic tubercles. Venter of trochanters unarmed.

Ventral surface light yellow. Coxae greyish brown. Free tergites brown. Posteriorly margins of free tergites and anal operculum dark brown.

Chelicera ( Figs 2F–G , 4C–D ). Short and slender, mostly unarmed. 1 st segment armed with a ventral spur while 2 nd segment scattered with dorsal hairs. Tiny granules are also found disto-laterally, more apparent in a small cluster behind the fingers. In some specimens a small dorso-lateral granule can be found, right behind the movable finger. Fingers toothed and curved.

The entire chelicerae are pale yellow with dark brown fingers and granules.

Pedipalpus ( Fig. 4A–B ) Slender and short; trochanters ventrally toothed.Femora also ventrally and retrolaterally armed with a row of sharp tubercles. A laterodistal apophysis can be found on both pedipalpal patella and a smaller (size varies among individuals) apophysis can be seen extending out of the sides of the tibia ( Fig. 4 ). Both patella and tibia densely armed with dorsal and retrolateral, small, sharp tubercles. Tibiae and tarsi both armed with long hairs, with tarsi being the most densely armed. Pedipalps armed with a single terminal pectinate claw.

Trochanters, femora, patellae and tibiae brownish yellow, tarsi translucent yellow, similar to venter.

Legs ( Fig. 5 ). All legs long and slender. Leg I femur generally longer than body. There are no pseudoarticulations on all legs. The surface of the leg filled with tiny granules that, at first glance, may resemble dirty soil particles stuck to it ( Fig. 5C–D ). Leg tarsi without scopulae and armed with a single simple claw.

Penis ( Figs 6A–C , 7 ). Overall structure dorso-ventrally flattened. Truncus slender, long and unarmed. Glans short, with 1–2 lateral bristles (Sinnesborst from Martens 1987). Alate with larger ventral lamella and smaller dorsal mantle (Lamelle and Ummantelung from Martens 1987); the former curves dorsally at the edges and fuses with only the posterior section of the mantle, enveloping it. A large ‘pocket’ opening (Tasche from Marten 1987) is formed that extends to 2/3 of the lateral alate. The structure curves ventromedially, lamellae swollen. The mantle extends only slightly down 1/3 of the truncus. The ventral tendon (Sehne from Martens 1987) elongates and attaches to the posterior end of the truncus. Overall structure of the genital resembles a curved partisan spear with a pair of rounded lateral protrusions.

Female ( Fig. 2C–D, F ). Overall similar to its male counterpart but generally larger in overall size. Female abdominal free tergites longer than males’, the latter shorter and compressed, slightly extending downward. Both pedipalps and chelicerae slightly larger in females than males ( Fig. 2F ).

Ovipositor Overall structure similarly flattened as penis. Shape of the seminal receptacle as shown in Fig. 6H .

Measurements ( Tables 1–2). Male Holotype (Female paratype): body 3.61 (5.19) long, 2.67 (3.25) wide at the widest portion; ocularium 0.54 (0.56) wide, 0.46 (0.48) long; chelicera segment I 0.73 (1.82), segment II 1.10 (2.59). Measurements for the pedipalps and legs as in Table 1.

Variation. The shape of the dorsal scutum can vary between individuals from being overall oval to the abdominal scutum being triangular with the lateral-posterior edges being elevated, flat to a swollen, oval shape typical in Gagrellinae harvestmen (but still with an elevated, angled dorsal scutum). Overall coloring of individuals may vary from pale brown to overall dark, muddy yellow (See Fig. 11A–D ). As mentioned in the Etymology section, all these colors are perfect to camouflage with their habitats along streams and muddy ground near water bodies (See Fig. 11E ). When threatened, the harvestman flattens its body to the surface with all eight legs fully extended. Despite being a delimiting feature, the length of leg I femora is highly variable amongst individuals (See Table 1). For females, body is generally longer than femora while it is the opposite for most male individuals or even smaller female individuals (See Appendices 7–8).

Figures

FIGURE 1. Altitudinal map of Hong Kong, China and the locations of the specimens used in this study. Pseudoleiobunum lutulentum sp. nov. were found in places with higher altitudes and higher humidity, preferably streams.

FIGURE 2. Comparisons between Pseudoleiobunum specimens. A–C Comparison of female dorsal bodies between three Pseudoleiobunum species, highlighting features of the genus, yellow rectangle highlighting the small central, dorsal hump on the dorsal scutum; yellow circles highlighting the elevated lateral-posterior edges of the dorsal scute, resembling a pair of tubercles. D–E Comparison of general body size between male and female. F–G Comparison of male and female cheliceral size. A P. maximum distinctum, female. B P. japanense japonicus, female. C P. lutulentum sp. nov, LINGU-INV117, female. D Dorsal view of the female body, LINGU-INV117. E Dorsal view of the male body, LINGU-INV118. F Full lateral view of male chelicera, LINGU-INV72. G Full lateral view of female chelicera, LINGU-INV146. Scale bars: 1 mm.

FIGURE 3. Pseudoleiobunum lutulentum sp. nov., male (LINGU-INV154), body. A Dorsal view. B Ventral view. Scale bars: 1 mm.

FIGURE 4. A–B Pseudoleiobunum lutulentum sp. nov., close-ups of pedipalpal tibia and tarsus apophyses. A (Left) Close-up of male pedipalpal patella and tibia, LINGU-INV154. A (Right) Close-up of female pedipalpal patella and tibia, LINGU- INV146. Red rectangles for patella apophyses, blue rectangles for tibia apophyses. Scale bar: 2 mm. B Full lateral view of left pedipalp; C–D Pseudoleiobunum lutulentum sp. nov. C Full lateral view of left chelicera. D Close-up of left chelicerae distal structure. Scale bars: 0.5 mm.

FIGURE 5. Pseudoleiobunum lutulentum sp. nov., close-up comparisons of femora II under light microscope and scanning electron microscope of leg surface, revealing the granules that are present in the legs of P. lutulentum sp. nov. A Light microscopy of leg II femur, LINGU-INV72. B Light microscopy of leg II femur, LINGU-INV106. C Scanning electron microscopy of the surface of leg II femur, LINGU-INV115. D Close-up of the granules on leg surface, LINGU-INV116. Scale bars: 100 μm for C; 20 μm for D.

FIGURE 6. Pseudoleiobunum lutulentum sp. nov., different views of male, female genitals, labrum, supracheliceral lamina and a close-up of the female seminal receptacle. A Ventral view of male genital, LINGU-INV47. B Dorsal view of male genital, LINGU-INV46. C Lateral view of male genital, LINGU-INV154. D Dorsal view of labrum, LINGU-INV154.. E Lateral view of labrum, LINGU-INV154. F Ventral view of labrum, LINGU-INV154. G Dorsal view of the supracheliceral lamina, LINGU- INV154. H Seminal receptacle, LINGU-INV145. Scale bars: 200 μm for A & B; 500 μm for C; 0.2 mm for D, E & F; 0.5 mm for G; 20 μm for H.

FIGURE 7. Pseudoleiobunum lutulentum sp. nov. Male genital under electron microscopy. A Dorsal view, LINGU-INV46. B Ventral view, LINGU-INV47. Scale bars: 100 μm for A; 200 μm for B.

FIGURE 11. Pseudoleiobunum lutulentum sp. nov., in-situ. A Resting on a leaf litter surface besides a stream, New Territories, Tai Mo Shan. B Resting on a rocky surface, New Territories, Tai Mo Shan. C Station besides water body in a rocky stream, Ma On Shan. D Full view of the individual on a rock. E Overview of the habitat, Ma On Shan.