Thyroid of the Coelacanth, Latimeria chalumnae Smith

Abstract

THE thyroid of bony fishes is composed usually of thyroid follicles more or less scattered in the ventral pharyngeal area, although two additional variations in thyroid structure have been found in teleosts. Earlier reports have described the aggregation of thyroid follicles to form a discrete thyroid mass lacking a fibrous capsule, so that additional follicles located elsewhere are not uncommon. It was later revealed that functional thyroid follicles may be scattered not only in the pharyngeal region but also heterotopically in areas such as the lymphoidal pronephric rudiment (head kidney). With the capture in the Comoros of a small (85 cm) living Latimeria chalumnae on March 22, 1972¹, it became feasible for the first time to define the thyroidal structure and the relationship of this gland in terms of osteichthyean or tetrapod characteristics.