Morphology and structural organization of spiracles in female Argas (Persicargas) walkerae (Acari: Argasidae).

Scanning electron microscopical investigations of fractures and corrosion casts of the spiracles from female A. walkerae ticks revealed a four-part structure, consisting of spiracular plate, ostium and macula forming the external closure, followed by the subostial space and the vestibulum of regulable volume, as well as the atrial chamber as the innermost part from which the main tracheal trunks originate. On the average, the spiracular plate was 158 microns long and 188 microns at the broadest width. It consisted of a thin, highly perforated external and a thick internal layer, which enclosed the interpedicellar space with numerous stout pedicels. In its posterior region, the spiracular plate was covered by the macula, which was up to 80 microns in length and 110 microns in width. The interpedicellar cavity opened into the subostial space measuring 95.5 microns in length and 159.6 microns in width, which proceeded into the 112-microns long vestibulum. The roof of the vestibulum was flexible and could be everted and inverted. Inverted, the roof formed a quadratic bulge with numerous deep cuticular folds, which confined the lumen of the vestibulum either partially or completely. In corrosion casts, the roof was everted to a length of up to 89.3 microns. In the posterior part of the vestibulum, as well as in the initial fourth of the atrial chamber, numerous anvil-, cone- or drop-like cuticular projections were arranged in wedge-like fashion. The atrial chamber was almost spherical with a diameter of 138.4 microns. Five main tracheal trunks of different luminal diameter as well as numerous channels opened into the atrial chamber.