Redescription of the Argasidae subfamilies, Argasinae and Ornithodorinae: Reflections on the genera Alveonasus and Otobius

The Argasidae (soft tick) family has historically been classified into two subfamilies, the Argasinae and Ornithodorinae. The classic morphological definition of the subfamilies is based on a flattened body margin with a sutural line demarcated by cells or striations in the Argasinae, and a rounded body margin with no sutural line in the Ornithodorinae. Cladistic and molecular analysis also indicate two clades corresponding to two subfamilies, but the definitions of the subfamilies became invalid due to placement of Alveonasus and Proknekalia in the Argasinae and Carios and Chiropterargas in the Ornithodorinae. As such, no morphological definition to differentiate these new subfamilies exists. The current study updated descriptions congruent with cladistic and molecular analysis for the subfamilies based on the presence of a tracheal system, seta pd1 present on the palp femur, at least 4 setae on the proximal two-thirds of the palpal tibiotarsus and setae dm absent on tarsi II-III in Argasinae larvae. These characters are, respectively, absent, present or different in the Ornithodorinae. However, the grouping of Otobius lagophilus (for which a tracheal system is absent) in the Argasinae by molecular analysis invalidates this new definition of the subfamilies. We recognized that this may be a means to test the new classification hypothesis by predicting that the mitochondrial genome sequences belonging to O. lagophilus (ON756085, ON800860, ON800861) were erroneously assigned to this species. Sequencing of a 16S rRNA fragment from a O. lagophilus museum specimen showed grouping as sister to Otobius megnini within the Ornithodorinae, with no sister relationship to ON756085, ON800860, ON800861. We therefore conclude that these latter sequences were erroneously assigned to O. lagophilus. We additionally report mitochondrial genome sequences for Alveonasus cooleyi and Alveonasus eboris and data analysis suggests that the specimens misidentified as O. lagophilus probably represent a new Alveonasus species from Texas. The data supports the new definitions of the subfamilies, providing stable morphological characters allowing placement of species in subfamilies without the need for exclusive use of molecular data to differentiate the subfamilies. It also suggests that the subfamilies and their respective genera are indeed separate monophyletic natural lineages.