Orthohalarachne attenuata (family: Halarachnidae) is a species of mite normally found in the nasal passages of fur seals, sea lions, and walruses. In seals, the mites can be both prevalent (almost every single seal has them) and abundant (more than 1000 mites per seal). Although clinical observations and gross examination indicate that O. attenuata parasitization alone is not serious, some erosion and inflammation of the nasal turbinates and nasopharynx in seals has been observed in histological sections. If concomitant parasitization with O. attenuata and O. diminuta occurs, alveolar emphysema and more serious ailments can threaten the life of the mammal.