Comparative morphology and ultrastructure of the mouthparts in unfed larvae of Platytrombidium fasciatum and Camerotrombidium pexatum (Acariformes: Microtrombidiidae).

The mouthparts of unfed larvae of Platytrombidium fasciatum (C. L. Koch, 1836) and Camerotrombidium pexatum (C. L. Koch, 1837) (Acariformes: Microtrombidiidae) were studied using both light optical (whole-mounted specimens, toluidine blue stained semi-thin sections) and electron microscope (TEM, SEM) methods. The mouth apparatus incorporated within the gnathosoma occupies an axial position and is covered from above by the arched dorsal shield, or scutum. The chelicerae are comparatively long and separated, and the lateral lips form a permanent apomorphic sucker provided with an internal cuticular sclerite. The pharynx is extremely wide and totally fused with the bottom of the infracapitulum. The pharyngeal dilators originate on the posterior portions of the cervix (epistome) and on the capitular apodemes and run nearly parallel to the cervix to the dorsal pharyngeal wall. Comparatively short sigmoid pieces serve as origin of the muscles--cheliceral levators inserting on the posterior wall of the basal cheliceral segments. There are two sets of the extrinsic gnathosomal muscles originating on the posterior portion of the scutum: retractors of chelicerae inserting on the posterior portions of the basal cheliceral segments, and retractors of the gnathosoma inserting on the very posterior parts of the capitular apodemes. The labrum and the cervix delimit the pharynx and the subcheliceral space. The labrum and the cervix for the most part are weakly sclerotized cuticular plates and do not have own muscles. The larval mouth apparatus, in comparison with that of adult microtrombidiid mites, is simply organized and more specialized for ingestion of large masses of liquid food.