Odontophoroma in a captive red abalone Haliotis rufescens

Red abalone Haliotis rufescens is a gastropod species that has historically been used for purposes including food, currency, and curio trade. Research into gastropod diseases often focuses on their potential as intermediate hosts of bacteria, viruses, or parasites due to their consumption by humans; neoplasms are rarely reported. The red abalone presented in the present case had multiple masses that were diagnosed histologically as mesenchymal neoplasms composed of spindle cells within lacunae embedded in abundant basophilic matrix resembling the cartilage of vertebrates. Some histochemical staining properties of the matrix were also similar to the chondroid matrix of vertebrate cartilage. In abalones, the sole cartilaginous or 'cartilage-like' structure is the odontophore, a mass of tissue that surrounds the radula, a structure used to prehend food. This paper categorizes the histochemical staining characteristics of the abalone odontophore and compares it to the neoplasm in this animal. The similarities in morphology and histochemical staining between the neoplasm and the odontophore, and the lack of other cartilaginous structures in this species, support that this tumor arose from the odontophore, consistent with a diagnosis of an odontophoroma. The odontophore is an anatomic structure unique to the phylum Mollusca, and this mesenchymal neoplasm has not been previously reported in any species within this phylum.