Lagynochthonius fragilis n. sp. is described from a limestone cave in the Hong Chong karst of Kien Giang Province, southern Vietnam, which is currently threatened by quarrying activities. This is the first record of a troglomorphic species of Lagynochthonius Beier, 1951 from continental Asia. The presence of chemosensory setae on the dorsum of the chelal palm is interpreted as a synapomorphy of the tribe Tyrannochthoniini Chamberlin, 1962. The New Zealand genus Maorichthonius Chamberlin, 1925 is transferred from the Chthoniini Daday, 1888 to the Tyrannochthoniini. The genus Tyrannochthoniella Beier, 1966, also endemic to New Zealand, is assigned to the tribe Chthoniini Daday, 1888. The genus Stygiochthonius Carabajal Márquez, García Carrillo & Rodríguez Fernández, 2001, from southern Spain, is synonymized with Paraliochthonius Beier, 1956 (n. subj. syn.). Five new combinations are proposed: Lagynochthonius ovatus Vitali-di Castri, 1984 (ex Tyrannochthonius); Paraliochthonius barrancoi (Carabajal Márquez, García Carrillo & Rodríguez Fernández, 2001) (ex Stygiochthonius); P. curvidigitatus (Mahnert, 1997) (ex Lagynochthonius); P. setiger (Mahnert, 1997) (ex Tyrannochthonius); and P. superstes (Mahnert, 1986) (ex Tyrannochthonius). A key is given to the genera of the Tyrannochthoniini. The parallel evolution in several groups of pseudoscorpions of a characteristic chelal morphology, here termed lagyniform, is discussed. New designations are proposed for the spot-sensilla of the chelal fingers. The so-called ‘sensorium’ near the tip of the fixed chelal finger of Lagynochthonius species is shown to be a modified tooth that has migrated dorsally from the dental margin. The new term rallum is introduced as a replacement for the inappropriate term ‘flagellum’, as applied to the cheliceral blades of pseudoscorpions. The term bothridial vestibulum is introduced for the internal cuticular sheath at the base of the bothridia of the trichobothria.Lagynochthonius fragilis n. sp. est décrit d’une grotte calcaire de la province de Kien Giang, au sud du Vietnam, actuellement menacée par une exploitation de carrière. Elle est la première espèce troglomorphe du genre Lagynochthonius Beier, 1951 connue de l’Asie continentale. La présence des soies chemosensorielles sur la main de la pince est interprétée comme une synapomorphie de la tribu des Tyrannochthoniini Chamberlin, 1962. Le genre néo-zélandais Maorichthonius Chamberlin, 1925 est transféré des Chthoniini Daday à la tribu des Tyrannochthoniini. Le genre Tyrannochthoniella Beier, 1966, également endémique de la Nouvelle Zélande, est attribué à la tribu des Chthoniini Daday, 1888. Le genre Stygiochthonius Carabajal Márquez, García Carrillo & Rodríguez Fernández, 2001, du sud de l’Espagne, est mis en synonymie avec Paraliochthonius Beier, 1956 (n. syn. subj.). Cinq combinaisons nouvelles sont proposées : Lagynochthonius ovatus Vitali-di Castri, 1984 (ex Tyrannochthonius) ; Paraliochthonius barrancoi (Carabajal Márquez, García Carrillo & Rodríguez Fernández, 2001) (ex Stygiochthonius) ; P. curvidigitatus (Mahnert, 1997) (ex Lagynochthonius) ; P. setiger (Mahnert, 1997) (ex Tyrannochthonius) ; et P. superstes (Mahnert, 1986) (ex Tyrannochthonius). Une clé de détermination des genres de Tyrannochthoniini est fournite. L’évolution parallèle des facies caractéristiques de la pince, ici qualifié de “ lagyniforme ”, est évoquée chez plusieurs groupes de pseudoscorpions. Desnouveaux sigles sont proposés pour les sensilles punctiformes des doigts de la pince. Il est démontré que le “ sensorium ” à l’extrémité du doigt fixe de la pince des espèces de Lagynochthonius est une dent modifiée qui a migré dorsalement dès la marge dentale. Le terme inapproprié de “ flagelle ”, dans le sens de son application aux lames chélicèriennes des pseudoscorpions, est remplacé par rallum. Le terme nouveau vestibule trichobothriale est introduit pour la gaine cuticulaire à la base des bothridies des trichobothries.

Here we study the evolution of nucleotide composition in third codon-positions of CO1 sequences of Chelicerata, using a phylogenetic framework, based on 180 taxa and three markers (CO1, 18S, and 28S rRNA; 5,218 nt). The analyses of nucleotide composition were also extended to all CO1 sequences of Chelicerata found in GenBank (1,701 taxa). The results show that most species of Chelicerata have a positive strand bias in CO1, i.e., in favor of C nucleotides, including all Amblypygi, Palpigradi, Ricinulei, Solifugae, Uropygi, and Xiphosura. However, several taxa show a negative strand bias, i.e., in favor of G nucleotides: all Scorpiones, Opisthothelae spiders and several taxa within Acari, Opiliones, Pseudoscorpiones, and Pycnogonida. Several reversals of strand-specific bias can be attributed to either a rearrangement of the control region or an inversion of a fragment containing the CO1 gene. Key taxa for which sequencing of complete mitochondrial genomes will be necessary to determine the origin and nature of mtDNA rearrangements involved in the reversals are identified. Acari, Opiliones, Pseudoscorpiones, and Pycnogonida were found to show a strong variability in nucleotide composition. In addition, both mitochondrial and nuclear genomes have been affected by higher substitution rates in Acari and Pseudoscorpiones. The results therefore indicate that these two orders are more liable to fix mutations of all types, including base substitutions, indels, and genomic rearrangements.

The first extant representatives of the pseudoscorpion family Feaellidae from Southeast Asia are described. Cybella n. gen. is proposed for Cybella deharvengi n. sp. (type species), collected from an isolated limestone hill in Hon Chong Province, Vietnam, and C. bedosae n. sp., found in a limestone cave in Kampuchea, Cambodia. Cybella species seem to be restricted to karst formations and are probably troglophilic. The type localities of the two known species are threatened by quarrying activities, these being particularly pressing in the case of C. deharvengi n. sp. Cybella shows important differences from other Feaellidae that require a modification of the familial diagnosis and justify the erection of a new subfamily, Cybellinae. The discovery of this group provides insights into the evolution of the unusual morphology of the family, notably concerning the pleural plates of Feaellinae, which are lacking in Cybellinae. The smaller sclerites of the pleura of Pseudogarypidae and Feaellidae are shown to be muscle apodemes, which provide an additional synapomorphy for Feaelloidea. Two types of coxal spines, termed primary and secondary, are distinguished in Feaelloidea, based on the presence of a lumen within the primary spines and its absence in secondary spines. The new morphological term atrial plate is proposed for a sclerotized plate of the male genitalia, extending between the lateral rods and the lateral apodemes. Claims that the internal genital setae of males of non-chthonioid pseudoscorpions are secretory are reviewed and found to lack support.        Additional information concerning the fossil genus Protofeaella Henderickx, 2016 is provided, based on an adult male in amber from the Cretaceous (lowermost Cenomanian) of Myanmar. Protofeaella shares with Cybella the absence of pleural plates and the antiaxial position of the chemosensory setae of the movable chelal finger. However, it differs from both Cybellinae and Feaellinae in having relatively long chelal fingers that lack a tuberculate basal tooth, both of which are interpreted as symplesiomorphic states within Feaellidae. Protofeaella is therefore provisionally treated as a stem-group feaellid and not assigned to a subfamily.        The existence of a Cretaceous member of the Pseudogarypidae is noted in the mid-Cretaceous (late Albian‒early Cenomanian) of Germany, representing the oldest record of this family.