Post-embryonic development in the mite suborder Opilioacarida, with notes on segmental homology in Parasitiformes (Arachnida)

Abstract

In order to study homology among the major lineages of the mite (super)order Parasitiformes, developmental patterns in Opilioacarida are documented, emphasizing morphology of the earliest, post-embryonic instars. Developmental patterns are summarized for all external body structures, based on examination of material in four different genera. Development includes an egg, a 6-legged prelarva and larva, three 8-legged nymphal instars, and the adults, for the most complete ontogenetic sequence in Parasitiformes. The prelarva and larva appear to be non-feeding. Examination of cuticular structures over ontogeny allows development of an updated model for body segmentation and sensillar distribution patterns in Opilioacarida. This model includes a body made up of a well-developed ocular segment plus at most 17 additional segments. In the larvae and protonymphs each segment may carry up to six pairs of sensilla (setae or lyrifissures) arranged is distinct series (J, Z, S, Sv, Zv, Jv). The post-protonymphal instars add two more series (R and Rv) but no extra segments. This basic model is compatible with sensillar patterns in other Parasitiformes, leading to the hypothesis that all taxa in that (super)order may have the same segmental ground plan. The substantial segmental distortion implied in the model can be explained using a single process involving differential growth in the coxal regions of all appendage-bearing segments.

Neocarus spelaion sp. n. (Parasitiformes, Opilioacaridae), a new species of cave dwelling Neocarus from Minas Gerais state, Brazil

“…Dorsal shield with 130-172 ribbed setae and two pairs of eyes. One pair of lyrifissures present (same position and shape as observed by Klompen et al 2015). Rostrum rounded.…”

“…A female was placed on an aluminium support stub covered with a film of aluminium foil with carbon tape, sputter-covered with gold (Baltec SCD 050), and observed in a LO EVO 40 XVP scanning electron microscope. The nomenclature of setae and other morphological characters follows Grandjean (1936), van der Hammen (1969van der Hammen ( , 1976van der Hammen ( , 1977, Vázquez and Klompen (2002), Bernardi et al (2014, and Klompen et al (2015).…”

Ancestral reconstruction of tick lineages

“…In the Acari, the mouthparts are beared by the capitulum, while the prosoma and opisthosoma are fused into a non-segmented idiosoma . However, segmentation in embryos, body pattern of setae, fissures, folds and festoons, support a more ancient arthropod segmentation plan in ticks (Klompen et al 2015(Klompen et al , 1996bSantos et al 2013). Further, opisthosomal segmentation during the germ band stage is observed in ticks (and other Parasitiformes?…”

“…Relationships between these groups have indicated a relative consensus of morphological and molecular data, with Opilioacarida being the most basal lineage, Holothyrida sharing a sister group relationship with the Ixodida and the Mesostigmata as their sister group (Klompen, 2010;Klompen et al 2015Klompen et al , 2007Lehtinen, 1991). Even so, a study has indicated a closer relationship between Ixodida and Mesostigmata (Burger et al 2014a).…”

Segmentation and tagmosis in Chelicerata

“…Reconstructing segmentation for opilioacarids, mesostigmatids and ticks has also proven problematic. Here, we orientate ourselves on Klompen et al (2015) who inferred 17 somites as the Parasitiformes groundplan (Fig. 4).…”