The mollusks of the family Thaididae are predators of others mollusks drilling their shell using alternately secretions from the accessory boring organ (ABO) and scraping movements of the radula. In this family the ABO is located in the median-anterior ventral part of the foot. The animals examined in the study were collected in the "Praia do Futuro", Fortaleza, Ceará, Brazil. The glandular part of ABO in Thais haemastoma (Linnaeus, 1758) is located in a cavity inside the foot, surrounded by foot muscle, and shows an excretory duct connecting that glandular portion to the outside. The analysis of microscopic sections stained by eosin-hematoxylin showed an epithelial tissue lining the cavity, and separating the glandular portion of ABO from the foot muscle. This ephitelial tissue is continuous with the excretory duct ephitelium. Under this tissue was observed a loose connective tissue. The ABO gland of T. haemastoma has a discoidal format and an irregular surface due to the presence of reentrances heading to the central part of the gland. The pseudoestratificated glandular epithelium with cylindrical and ciliated cells reacted negatively to the histochemical tests. Under the epithelium a connective loose tissue of support was observed.
Thaididae; ABO; histology; Brazil