A morphological comparison of two closely related ptychoid oribatid mite species: Phthiracarus longulus and P. globosus (Acari: Oribatida: Phthiracaroidea)

Abstract

We studied exoskeletal and muscular adaptations to ptychoidy in the oribatid mite Phthiracarus globosus (Phthiracaridae, Phthiracaroidea) using synchrotron X-ray microtomography, and compared the results to Phthiracarus longulus, a closely related mite that we investigated earlier. As expected, both species show high similarity in most of the characters investigated, but there were also clear differences: the sensillus groove is more prominent and the bothridial scale is more angular in P. globosus than in P. longulus. The coxisternal retractor first found in P. longulus was also found in P. globosus and therefore could be a synapomorphy for the genus. The number of muscle fibres of the anterior dorsal endosternal muscle (ade), inferior prodorsal retractor (ipr), ventral plate adductor (vpa) and the notogaster lateral compressor (nlc) found in P. globosus is double or even triple that found in P. longulus. Our results suggest that muscle morphology might provide a phylogenetically informative set of characters for oribatid mite systematics, when more data are available.

Keywords

• Synchrotron X-ray microtomography
• SR-µCT
• Ptychoidy
• Phthiracaridae
• Box mite
• Predator defence