Functional anatomy of oil glands in Collohmannia gigantea (Acari, Oribatida)

Abstract

Chemical and behavioural studies indicated that the oil glands of the Oribatida represented a central organ for protection and semiochemical communication. The hitherto unknown mode of action of these glands and their microscopic anatomy have been investigated in Collohmannia gigantea by histological and SEM techniques. The paired oil glands are located dorsolaterally in the hysterosoma and mainly comprise large intima-lined and sac-like reservoirs which are surrounded by glandular tissue. The reservoirs consist of a single-layered flat epithelium and probably serve for storage of the oil gland secretion only, but not for its production. Each reservoir opens to the body outside via a single pore. Externally, the pores appear as oval-shaped rings of smooth cuticle, moderately projecting from the surface of the notogaster. The pore orifices are supplied with trapdoor-like closing mechanisms, consisting of cuticular flaps which permit reservoir opening by muscles attaching to the posterior part of the reservoir and the inner side of the notogaster. These morphological data, especially the large intima-lined reservoirs along with closing mechanisms under muscular control, are consistent with supposed biological roles of oil glands as defensive or alarm pheromonal organs.