Abstract:The accessory nidamental gland (ANG) is a type of accessory gland found in Sepioidea species. It is an important part of the female reproductive system and plays an important role in the formation of the egg membrane, disease control, and buoyancy adjustment. Here, the ultrastructure of the ANG from adult Sepia esculenta was studied using light and electron microscopy. The results showed that the ANG forms an ear-like shape; its bottom forms an ‘M’ shape, which is closely attached to the nidamental gland; and the color is white and orange. ANG is composed of a gland wall, tubules, and connective tissue. The inside layer is muscular, whereas the outer layer is composed of simple columnar epithelium cells. A number of tubules were observed with an average diameter of 70 μm; the lumen surface has a microvilli layer, and a large number of substances are secreted inside the lumen. The connective tissue contains concentrated distributions of blood vessels and muscle fibers. The cytoplasm of the epithelial cells contains many concentrated distributed vesicles, and some contain secretion globules. The microvilli are widely distributed; while the cilia are discontinuous, with some concentrated and others arranged in a single line. The tubule lumens contained a large number of symbiotic bacteria, most of which were coccoid-shaped bacteria, containing many secretion globules. Consequently, the ANG of S. esculenta possesses secretory function; the existence of symbiotic bacteria in the ANG might play an important role in disease resistance during embryonic development. We show the ultrastructure of the ANG in adult S. esculenta and discuss its function and role in reproduction. The aim is to reveal the breeding strategies of S. esculenta and to enrich knowledge of the reproductive biology of cephalopods, thus, providing a reference for optimization of S. esculenta breeding technology.
