Desmonomata
An example of Desmonomata, Camisia segnis (HERM.) (Camisiidae) adult, in dorsal view, with the legs (in blue) partially shown. Only the trochanter, femur, and proximal part of the patella are seen in legs I and II whereas, in legs III and IV, only the trochanter and proximal part of the femur are represented. The cuticular, negative reticulation (i.e. made up of concave meshes; cf. Grandjean, 1962a, p. 410) which covers the whole notogaster is shown only in one place. The positive reticulation (i.e. made up of convex meshes) which covers the prodorsum is not shown.
– Comments. The anterior part of the prodorsum (or rostrum) is a large-sized cuticular fold (a border tectum sensu Grandjean, 1934b, called ‘rostral tectum’ or ‘rostral hood’) that protects the chelicerae at rest (‘stegasimous’ oribatid mite). A narrow, roof-like structure bearing the rostral setae ro overhangs axially the rostral region.
The lamellar setae la are inserted on the tip of a large, triangular apophysis a bit curved forwards (in yellow). This construction carries a pellet of debris (not shown) to which the interlamellar setae in are attached. A pair of carinae arise from the base tubercles of the setae in, and converge forwards.
The sensilli bo (or bothridic or pseudostigmatic setae) are club-shaped and covered with small papillae. The cavities into the bottom of which the sensilli are inserted (or bothridia; in green) are prominent. Their opening is relatively large and accentuated by a circular ridge. Whereas the trichobothria (i.e. sensilli + bothridia) are of normal size in adults as well as in tritonymphs and deutonymphs, they are clearly reduced in size in protonymphs and larvae.
In fact, in the series Desmonomata except in the family Hermanniidae (Grandjean, 1953a, p. 431), a shortening of the trichobothia and even a complete suppression of these organs may affect immature instars (only larvae or larvae and nymphal stages) or all the instars. This regression (or ‘trichobothridic regression of the Camisia type’ sensu Grandjean, 1939d, p. 304; also labelled BoRasc) is likewise detected in some families among the Mixonomata and Circumdehiscentiae series (cf. Grandjean, 1953a). It is apparently correlated with a particular mode of life (i.e. aquatic, semi-aquatic or cryptic like e.g. borers of wood and needles). Yet its precise causes are unknown (see Grandjean, 1939d, p. 305, Travé et al., 1996, and Alberti et al., 1994, for a discussion).
A transverse carina forms the limit between the prodorsum and the dorsosejugal zone dsj (or das). Both dorsosejugal dsj and ventrosejugal vsj (not shown) zones are sclerified. Accordingly, in this species just as in the other Desmonomata and in the series Circumdehiscentiae (i.e. in the Holosomata sensu Grandjean, 1969b, p. 135), the proterosoma, namely the prodorsum together with the gnathosoma and the anterior parts of the podosoma, and the hysterosoma, namely the opisthosoma and the posterior parts of the podosoma, are not movably connected by a sejugal articular cuticle (i.e. no protero-hysterosomatic articulation is developed).
The notogaster is remarkable for both the existence of two prominent, parallel and medio-longitudinal carinae and the thickness of the base tubercles of the setae h2. Posteriorly, the medio-longitudinal carinae are interrupted transversely by an elongated and twisted carina. Behind this carina, the notogasteral surface on which the setae h1 are inserted is inclined. While posteriorly the apparent outline of the notogaster is clearly concave between the setae h2, its lateral, ridge-shaped borders are convex and undulating. Small carinae obliquely directed are found here and there in the vicinity of the lateral borders.
Some dorsal, differentiated setae may be ciliated, such as setae ro and in, or equipped with cylindrical, finger-like processes, such as setae la, h2 and h3. Other differentiated setae bear small, more or less distinct lobes, such as notogasteral setae c1-c3, cp, d1, d2, e1, e2, and f2.
– Abbreviation. gla, opening of the exocrine, latero-abdominal gland (or ‘lateral opisthosomal gland’ or ‘opisthonotal gland’ or ‘oil gland’; in red). (modified from Grandjean, 1936a).
