A revised setal nomenclature based on ontogenetic and phylogenetic characters and universally applicable to the idiosoma of Gamasina (Acari, Parasitiformes)

Abstract

The configuration of body setation in a given species is essentially constant and therefore important for diagnosis and determination keys. Previous concepts of setal nomenclature are critically analysed. The majority of these efforts were mostly restricted to a limited taxonomic group and therefore limited in use, although most concepts aimed towards general application. For the revised setal nomenclature, embryonic development was analysed. A decisive process is the formation of the gnathosoma with a separation from the subsequent idiosoma segments. In the anterior part of the idiosoma, the segements of legs I, II, III and IV develop, furthermore those of the genital segment consisting of the fused segments 7 and 8. The posterior part of the idiosoma comprises the segments 9, 10, 11, 12 and 13. The parts of the dorsal shield should be named prodorsum and postdorsum, the parts of the ventral idiosoma sternum and venter. Transverse rows of setae and gland pores allow residues of the ancestral body segmentation to be recognised. On the dorsum of basal derivative Gamasina groups, 10 transverse rows of setae are clearly differentiated. On the dorsum we refer to four pairs of longitudinal rows with a tranverse division in five rows on the prodorsum and five rows on the postdorsum. We define a corresponding setal nomenclature separately for the prodorsum: i1 to i5, z1 to z5, s1 to s5, r1 to r5 and for the postdorsum: I1 to I5, Z1 to Z5, S1 to S5, R1 to R5. This pattern is generally maintained in all superfamilies of Gamasina. However, in single groups certain setae are suppressed or additional setae developed. Also, sometimes setae have changed their positions. The superfamilies of the Gamasina show specialisations concerning habitats and nutrition. According to their evolution, each superfamily has also developed characteristic trends in dorsal setation. This facilitates categorising unknown species. The findings are explained by 27 figures of species grouped into 6 superfamilies.