Idiosomal lyrifissures, Setae, and small glands as taxonomic characters and potential indicators of ancestral segmentation patterns in larval ixodidae (Acari: Ixodida)

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Abstract
Variability in idiosomal chaetotaxy, lyrifissure, and gland patterns among ixodid larvae is assessed based on a comparative analysis of these structures in 53 species of ixodid ticks. A revised system of nomenclature is proposed for all of these structures within a framework of probable ancestral segmentation. The system is based on the modified Hirschman system of setal nomenclature used for other groups of Parasitiformes, and allows identification of individual structures in nearly all larval ixodids examined. In addition it allows preliminary comparisons between larval Ixodidae and Mesostigmata. Intraspecific variability varies considerably between structures. Setae, which are already commonly used in systematic analyses, were confirmed as quite consistent. The proposed nomenclature system adds to their utility by providing specific hypotheses of homology. Lyrifissure patterns were found to be very conserved, precluding their use at lower taxonomic levels, but suggesting great utility for phylogenetic analysis at higher taxonomic levels. With few exceptions, small glands patterns are too variable to be useful as characters at higher taxonomic levels. However, they may be very useful in differentiating closely related taxa, in particular in groups that have limited overall numbers of glands (some Ixodes subgenera, derived metastriates).