Fine structure of the idiosomatic protuberances in the gamasid mite Epicrius mollis (Acari, Gamasida, Epicriidae).

Adult Epicriidae are characterized by stigmata placed on lateral protuberances and the lack of an obvious peritreme. Mites of the genusEpicriusadditionally show a pair of further prominent protuberances, which bear glandular pores. Both structures, glandular and stigmata protuberances, are occasionally called “pustules”, and both are investigated here for the first time using scanning and transmission electron microscopy. It is suggested to restrict the term “pustule” only to the glands-bearing structures. Three glands of similar morphology are present in each pustule ofEpicrius mollis.A single gland consists of a proximal vesicle formed by a secretory cell, a duct with corresponding duct cell and a calyx with calyx cell. The calyx likely functions as a valve connecting to the evacuation canal, which starts with flat lateral extensions forming an infundibulum. The secretion produced in the gland is delivered through a simple glandular pore, or solenostome, and contributes to the cerotegument. The calyx in particular has a very distinctive structure consisting of an inner and outer calyx. The stigma-bearing protuberance includes a depression, the stigmatic atrium representing a reduced peritreme and provided with many micropapillae. The stigma is located at its bottom and leads into a tracheal atrium, from which the main tracheae provided with typical taenidia start. Two glands of a similar structure to those described for the pustules open into the stigmatic atrium. Dermal glands exhibiting the peculiar calices are found also in other anactinotrichid mites, but never in actinotrichids. [ABSTRACT FROM PUBLISHER]