Magnacrus Hoang, Yu, Wendt, West & Wirth, 2025, gen. nov.

Genus Magnacrus gen. nov. Hoang, Yu, Wendt, West, von Wirth Type species: Magnacrus taynguyenensis gen. nov. sp. nov. Etymology. The generic name is a combination of Latin words “magna” (feminine adjective, meaning “large”) and “crus” (gender neutral noun meaning “leg”), reflecting the significantly thicker leg IV of the species females currently included. The gender is masculine. Diagnosis. Magnacrus gen. nov. and Citharognathus both exhibit modified (enlarged to some extent) posterior legs in females (Figs 4A, 8A, 12A). However, Magnacrus gen. nov. can be distinguished from all other genera of Ornithoctoninae, including Citharognathus, based on the following features in females: (1) the presence of spinules on the carapace on the posterior edge (Figs 13C–D); (2) the presence of a setal brush on the retrolateral side of leg IV, formed by conspicuously elongated setae of the patella to metatarsus (Figs 1C, 4A, 7C, 8A). These features are absent in both sexes of any other ornithoctonine genera (including Citharognathus), and are therefore considered putatively synapomorphic for Magnacrus. In females of Magnacrus, the patellae, tibiae, and metatarsi of legs III and IV are all relatively thicker and more robust than those in the legs I and II (Figs 4A, 8A), which is distinct from females of Citharognathus, where only the middle part of tibia IV is slightly enlarged (Fig. 9C). Magnacrus lacks spinules above the suture of the palpal coxa (Figs 1E, 2E, 5E, 7E), a feature that aligns it with Cyriopagopus and distinguishes them from all remaining genera (Fig. 10E). However, aside from the putative synapomorphies mentioned above, Magnacrus can be further distinguished from Cyriopagopus by the following: Magnacrus lacks a dense fringe of long white hairs above the retrolateral cheliceral scopulae and has a reduced number of spines on metatarsus IV (no more than 5 spines). In contrast, species of Cyriopagopus either possess such a fringe on the cheliceral scopulae (C. schmidti group) or always have more than 6 spines on metatarsus IV (C. minax group). The LRF of female Magnacrus is below 90, whereas females of other ornithoctonine genera are consistently above 90, with the exception of Cyriopagopus longipes (von Wirth & Striffler, 2005) (LRF~ 85). Description. Medium to large spiders (34–55 mm) with remarkably thickened rear legs in females, which have a more or less dense brush of longer hairs on the tibiae retrolaterally. Carapace elongated oval, with small spines in the marginal dorsal-basal area. Caput raised in females. Eye group elongated oval or roundish oval, wider than long, ocular tubercle well defined. Clypeus distinct. Labium wider than long. Labiosternal groove with two distinct mounds. Cuspules 67–106 in the sub-apical region of the labium. Maxillae longer than wide, overall setose, prolateral anterior angle distinctly produced, serrula absent. Chelicerae retrolateral with a large field of feathered setae. In the basal-dorsal region, the setae are more pronounced. In the basal-ventral region, some of these setae are feathered and sword-shaped. Prolateral face of maxilla consists of diffusely arranged spines. Sternum longer than wide. Legs moderately stout, hirsute, spines present on tibiae and metatarsi I–IV. Abdomen roundish oval, with very weak pattern. Spermathecae undivided with distinct dent in middle. Tibial apophysis of males apically numerous bristled. Distribution. China (?); Vietnam (Fig. 17). Biogeography. Based on the first author’s field observations, all specimens of M. tongmianensis from Vietnam were collected or observed at elevations below 600 m above sea level. In contrast, the new species M. taynguyenensis was collected at elevations higher than 1000 m above sea level, suggesting a distinct altitudinal distribution pattern among members of the genus Magnacrus. Remark. Based on the examination of nearly all type species of ornithoctonine genera by Volker von Wirth, the presence of spines above the prolateral palp coxa suture are recognized as a synapomorphy. This character may be useful for dividing the subfamily Ornithoctoninae into two major clades. However, the result will be published in a separate study. Although, Magnacrus tongmianensis (Zhu, Li & Song, 2002) gen. nov. comb. nov., was original described under the genus Citharognathus, the new genus Magnacrus is separated from Citharognathus by: both male and female specimens of new genus without spines above the prolateral palp coxa suture (Figs 1E, 2E, 5E, 7E) vs. present in Citharognathus (Figs 9E, 10E); in females, there is a unique dense setal brush on the metatarsus of leg IV retrolaterally (Figs 4A, 8A) while absent in Citharognathus (Fig. 12A); there are no spinules on the carapace in Citharognathus (Fig. 9A); the strongly incrassate patella, tibia and metatarsus of legs III and IV compared to legs I and II (Figs 4A, 8A) while in Citharognathus only the tibia of leg IV is incrassate (Fig. 12A); there are numerous short, stout black spinules on patellae, tibiae and metatarsi of leg III & IV in C. hosei (Figs 9C, 12A, 13B), but absent in the new genus Magnacrus. Additionally, male Citharognathus possess distinct long dense setae on all legs and abdomen (Fig. 12B) while this feature is less distinct in male Magnacrus (Figs 4B, 8B). Thus, we propose the new ornithortonine genus Magnacrus gen. nov., to accommodate the new combination M. tongmianensis (Zhu, Li & Song, 2002) gen. nov. comb. nov., and the new species M. taynguyenensis gen. nov. sp. nov., both from Vietnam. Additionally, the two genera show differences in both distribution and lifestyle species as Magnacrus are currently known only from the Central Highlands of Vietnam and are typical ground-dwelling spiders (Figs 14A–D, 15A–B), whereas the type species of Citharognathus, C. hosei, is an arboreal species distributed in northern Borneo (Fig. 16 A–B). Although both genera show an incrassate tibia of leg IV, the thickened posterior legs are not rare for Theraphosids, and this trait is usually of multiple independent origins, such as those genera of the theraphosinae, Eupalaestrus Pocock, 1901, Crassicrus Reichling & West, 1996 (Reichling & West 1996; Borges et al. 2021). At first glance, this feature seems to closely link Magnacrus and Citharognathus. However, the presence of spinules above the maxillary suture and the presence of numerous short, stout black spinules on patella, tibia and metatarsus of leg III & IV in Citharognathus (Figs 9C, 12A, 13B) as well as their geographical distribution and lifestyle, suggest that their phylogenetic positions are actually quite distant from each other (Wendt et al. in prep.)

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