Structural Organization of the Chelicerae and Venom Gland of Vitalius dubius (Araneae, Theraphosidae)

Rocha-e-Silva, T.A.A.¹; Cruz-Höfling, M.A.²; Hyslop, S.¹

1 Department of Pharmacology, Faculty of Medical Sciences; 2 Department of Histology and Embryology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, SP, Brazil.

The spider family Theraphosidae (tarantulas) contains approximately 900 species. Studies of the venoms of a few of these species have shown that they contain a variety of toxins, including ion channel antagonists. There have been few reports of the morphology and histology of theraphosid venom glands. In this work, we used light microscopy to examine the histology of the venom apparatus of the Brazilian theraphosid Vitaliusdubius. Spiders collected in the region of Campinas (São Paulo state) and Poços de Caldas (Minas Gerais state) were sacrificed with chloroform and the chelicerae containing the venom glands were removed and fixed in Bouin fixative overnight or in Karnovsky solution for one week and then embedded in historesin (Leica) and processed for histological analysis.  Sections 2-5 mm thick were stained with toluidine blue O or hematoxylin-eosin (HE).  The chelicerae consisted of a variety of striated muscles, some of which were attached to the base of the fangs. The inner surface of the chitin coat was covered with a thin layer of epithelial cells that were sparse at the sites of muscle adhesion. Caliciform hair cells were observed crossing from the epithelium to the surface of the chelicerae. The venom gland was surrounded by circular striated muscle fibers that were unattached to other chelicera muscles. Between this muscle layer and the gland there was a layer of connective tissue that served as a support for the network of venom secretory cells. The secretory cells had a large nucleus and numerous granules that were clearly visible with HE and toluidine blue O staining, respectively. These cells were closely packed in the posterior region of the gland, but the density of the cellular network decreased  progressively towards the base of the fang. No well-defined lumen was seen in the gland. Rather, the network of cells appeared to form a series of canals that channeled the venom towards the fangs. The venom gland eventually narrowed into a single canal that entered the fangs at their base, the inner surface of which was coated with a layer of  epithelial cells.

Finanacial support: FAPESP.

Correspondence to: t027546@dac.unicamp.br