DESCRIPTION OF MOUTHPARTS IN ADULT MITES OF PLATYTROMBIDIUM FASCIATUM (C.L. KOCH, 1836) (ACARIFORMES: MICROTROMBIDIIDAE) WITH A COMPARISON OF THOSE OF THE LARVAE

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Acknowledgments:

This study is supported by a grant N 03 - 04 - 49081 from the Russian Foundation for Fundamen-tal Research and by a grant N Scientific School-1664.2003.4 from the president of the Russian Federation. I gratefully thank the engineers of the Department of Electron Microscopy of the Zoolog-ical Institute, A.E. Tenison, Т.К. Zogoev, and P.I. Genkin, for their qualified assistance with the elec-tron microscopy.

Annotation:

The mouthparts of adult mites of Platytrom-bidiumfasciatum (C.L. Koch, 1836) (Acariformes: Microtrombidiidae) were examined using both light optical (mounted mites, toluidine blue stained semi-thin sections) and electron microscope (ТЕМ, SEM) methods. The gnathosoma is formed ventrally by the wide gnathocoxal plate, extending forward as the cone-shaped hypostome without a conspicuous sucker, and dorsally by two-segmented chelicerae, each with a blade-like cheliceral claw (movable digit). The proximal portion of the gnathosoma is inserted into a camerostomal fold formed of the body wall. The voluminous subcheliceral space terminates posteriorly by the proximal chamber with characteristic sclerotization of its walls. Mem-branous bottom of the subcheliceral space bears the labrum anteriorly and the weakly expressed episto-me posteriorly. The proximal chamber serves as a saliva reservoir. The labrum and the inner walls of the hypostome form the mouth leading to a crescent pharynx. The latter possesses dorsal dilators origi-nating on the floor of the subcheliceral space and mostly on the lateral walls of the gnathocoxal plate and constrictors. The ventral pharyngeal wall is conspicuously separated from the gnathosomal bottom and has no ventral dilators. The main tra-cheal trunks are S-shaped in longitudinal sections and are connected with the proximal chamber through narrow channels. Posterior portions of the tracheal trunks have sclerotized walls and serve for origination of the extrinsic cheliceral muscles. The cheliceral apodemes are therefore expressed twice as the sclerotized elements behind the inner walls of the basal cheliceral segments and as the particular sclerotization of the tracheal trunks. Laterally, the gnathosoma bears large 5-segmented palps. On the dorsal aspect of the tibia, there are two sclerotized claws. Such an organization of the mouthparts of adult microtrombidiid mites seems to be closely responded to the actinedid prototype and appears to be more generalized than the specialized mouth-parts of the larvae.

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