Pseudoleiobunum Müller, 1914

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 : 304-306

Pseudoleiobunum Müller, 1914

Pseudoliobunum Müller, 1914: 95 ; Roewer, 1923: 923–924; Crawford, 1992: 41.

Metaliobunum Suzuki, 1940: 276 ; Crawford, 1992: 30.

Metaleiobunum Suzuki, 1965: 353.

Pseudoleiobunum Suzuki & Ohrui, 1972: 47 ; Suzuki, 1965: 193; 1976: 199–202.

Leiobunum (in part) Suzuki, 1973; 1953; 1976: 191, 204; Crawford, 1992: 26.

Type species: Pseudoleiobunum japanense Müller, 1914: 95 .

Diagnosis. Pseudoleiobunum shares many of Leiobunum ’s characteristics, but can be distinguished by having medium to large brown leathery or heavily granulated body, generally dorsoventrally flattened. The abdomen is usually truncated (more apparent in males or underfed individuals). Scutal tergite areas I–III often with one small, inconspicuous central hump (size of the hump varies greatly even amongst individuals of the same species) ( Figure 2 ). In many individuals, the two lateral-posterior tips of the scutum elevate slightly, resembling a pair of small angled posterior armaments (such characteristic is also more apparent in underfed/male individuals, degree of scutal tip formation is highly variable between species and individuals) ( Figs 2–3 ). Labrum generally slender and unarmed. Pseudoleiobunum also possesses relatively shorter legs compared to Leiobunum , femur I often (but not always) shorter than body (ratio of the length of femur I to body ranges from 0.66–1.6, with a mean of 1.06; for other species of East Asian Leiobunum and Nelima , the ratio ranges from 0.97–3.52, with a mean of 1.69) ( Table 1 & Figure 12). The pedipalp of Pseudoleiobunum also possesses distomesal patellar and tibial apophysis in both males and females. In some species (e.g., P. lutulentum sp. nov. and P. maximum distinctum ), the pedipalpal tibial apophysis may be less apparent than the patella apophysis.

of Pseudoleiobunum lutulentum sp. nov. All measurements are in millimeters (mm).

Etymology. Latin designation is derived from the combination of the prefix ‘pseudes’ (false) with the genus name Leiobunum ( Crawford 1992) .

Distribution. Southeastern China, Hong Kong, Taiwan and southern Japan, including Ryukyu Islands ( Figure 12).

Notes. The genus was established for Pseudoleiobunum japanense Müller, 1914 from Hakone, Kanagawa Prefecture, Japan. Suzuki & Ohrui (1972) amended the genus name Pseudoliobunum to Pseudoleiobunum to accommodate reinstatement of Leiobunum from Liobunum that was erroneously amended by Agassiz (1846) ( Roewer 1957, Crawford 1992). The spelling was deemed unjustified following ICZN code (International Code of Zoological Nomenclature, Articles 33.1 & 33.2, Fowler 1984). The same rationale is applied to changing Metaliobunum to Metaleiobunum ( Suzuki 1965).

The Suzuki(1976) revision showed that Metaleiobunum Suzuki,1940 and Pseudoleiobunum are indistinguishable from other East Asian Leiobunum species. However, a monophyletic group was inferred in molecular phylogeny comprised of L. japanense ( maximum -group), L. rubrum ( rubrum -group) and all Japanese Nelima species ( Hedin et al. 2012). Furthermore, the maximum -group can be distinguished from other species of Leiobunum by a combination of several characters ( Table 1 in Tsurusaki 1985). The resurrection of Pseudoleiobunum accommodates all the above groups and resolves a part of the polyphyletic issue (i.e., Asian clades) within the large genus of Leiobunum .

In the following we show the superspecies name in parentheses after the genus name following ICZN article 6.2

(International Code of Zoological Nomenclature 1999).

Figures

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.