Nucleotide composition of CO1 sequences in Chelicerata (Arthropoda): detecting new mitogenomic rearrangements.

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.

A new subfamily of Feaellidae (Arachnida, Chelonethi, Feaelloidea) from Southeast Asia.

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.