Ultrastructure and functional morphology of the mouthparts in Pterygosoma pseudotrapelus (Bochkov, Melnikov et Nazarov, 2009) (Acariformes, Pterygosomatidae)

The mouthparts of the pterygosomatid mite, Pterygosoma pseudotrapelus (Bochkov, Melnikov et Nazarov, 2009) (Acariformes, Pterygosomatidae), were studied with light microscopy, scanning (SEM) and transmission (TEM) electron microscopy. The mouthparts are located within the (pseudo)tagma gnathosoma. The gnathosoma is formed of the two frontal body segments with their appendages – chelicerae and pedipalps (palps). The two-segmented chelicerae occupy a dorsal position, whereas the infracapitulum – a derivative of the fused palp coxae – occupies a ventral position. The basal cheliceral segments are widen basally, and contain protractors and retractors of the movable digits and nerve fibres. The distal cheliceral segments, the movable digits, are small and stout, bear a lateral spur, and are provided with tips looking aside. The fixed digits are long and branched. The frontal projection of the infracapitulum, the hypostome, partly envelopes laterally the distal cheliceral portions. The dorsal wall, or the roof of the infracapitulum, consists of the long labrum anteriorly possessing its own muscles and the complexly organized epistome posteriorly. The epistome and its posterior projections – the epistomal apodemes serve for origin of the pharyngeal dilators. The wide cap-shaped pharynx goes along the bottom of the infracapitulum and attaches to it. The two sigmoid pieces articulate posteriorly to the epistome and serve for origin of different sets of muscles performing retraction and protraction of the chelicerae and retraction of the gnathosoma. The peritremes are exceedingly long and protrude freely above the chelicerae. The general architecture of the mouthparts of P. pseudotrapelus corresponds more to the anystid than eleutherengonid ground pattern.