Magnacrus

Magnacrus Hoang, Yu, Wendt, West & von Wirth, 2025 is a small, recently erected genus of terrestrial fossorial theraphosids in the subfamily Ornithoctoninae, currently endemic to the Central Highlands of Vietnam. The genus was established in Zootaxa 5701(3): 351–381 (October 2025) to accommodate two species: M. tongmianensis (Zhu, Li & Song, 2002), originally described in Citharognathus Pocock, 1895 and transferred to Magnacrus on the basis of new Vietnamese material, and M. taynguyenensis Hoang et al., 2025, described concurrently from Lâm Đồng Province with both sexes. The generic name combines Latin magna ("large") and crus ("leg") in reference to the conspicuously thickened fourth leg of adult females, which is the most readily visible morphological signature of the group. The same paper redescribed the type species of Citharognathus (C. hosei Pocock, 1895) from fresh Sarawak material, clarifying the boundary between the two genera and confirming that the longstanding placement of tongmianensis in Citharognathus had been a misplacement of convenience rather than a phylogenetic match.

The genus's geographic story is a small but instructive correction. M. tongmianensis was originally described from material attributed to Tongmian, Guangxi (China), and circulated in both the academic and pet-trade literature for two decades as a Chinese species — the trade name "Chinese Stout-Leg Earth Tiger" still follows it. Hoang et al. (2025) found the original locality data unreliable and, on the basis of fresh collections, place the species firmly in Vietnam alongside its sister M. taynguyenensis. The current hypothesis is that Magnacrus is a Vietnamese Central Highland endemic, and that the historical Chinese record reflects either mislabeled material or commercial movement of specimens prior to formal description.

Members of the genus are obligate ground-dwellers and active burrowers in lowland-to-lower-montane secondary forest. Wild animals excavate deep silk-lined retreats in compactable forest soil, typically with a silk apron at the entrance, and are reliably nocturnal: surface activity outside of feeding and male wandering is uncommon. Adult females are stoutly built relative to the more gracile arboreal Ornithoctoninae of the same region (Cyriopagopus, Phormingochilus, Omothymus), with the diagnostic thickening of leg IV giving a conspicuously robust hindquarter when viewed dorsally. Coloration in M. tongmianensis is fawn brown overall with longer pale brown setae and a darker venter; pale longitudinal banding is sometimes visible across the chelicerae and femora. As with all Ornithoctoninae, the genus lacks urticating setae — defense is behavioral (rapid retreat, threat display) and chemical (bite). No species-level toxinology has yet been published for either Magnacrus species, but documented envenomations from related ornithoctonines have produced severe localized pain, prolonged muscle cramping, and systemic effects, and the genus should be assumed medically significant by inheritance from the subfamily.

No Magnacrus species is currently listed on CITES, and neither has a published IUCN Red List assessment, but both occupy fragmented secondary-forest habitat in a region under sustained agricultural and infrastructure pressure; both have, at the time of this writing, been known to formal science only through the 2025 redescription. In captivity, the genus expects a deep substrate column (commonly 6–8 in) of compactable mix, a cork retreat anchored to a clear dig-start, mid-to-high 70s °F with a modest seasonal cool dip, and moderate-to-high humidity with steady cross-ventilation; arboreal protocols and very dry setups are both inappropriate. Magnacrus is an advanced-keeper genus on temperament grounds — the animals are fast, defensive, and reliably out of sight — and an unusually current one to follow scientifically: the genus is fewer than a year old at time of writing, and meaningful additions to its species list, range, and natural history can be expected as the Central Highland fauna receives further survey work.