Glands associated with the anterior adhesive areas of the monogeneans, Entobdella sp. and Entobdella australis (Capsalidae) from the skin of Himantura fai and Taeniura lymma (Dasyatididae)

Abstract

Using scanning and transmission electron microscopy, investigations were carried out on the anterior adhesive areas of Entobdella sp. from the skin of Himantura fai and Entobdella australis from the skin of Taeniura lymma at Heron Island, Australia. All studies were of parasites detached from either host tissue or a substrate. Both species of monogeneans have two characteristic anteroventral adhesive pads, one on either side of the head, subdivided to form a “diadem”. Two types of gland cells are associated with the anterior adhesive areas in both species and each cell type produces a different secretion: a rod-shaped secretion and a smaller, roughly spherical secretion. Each secretion type differs in electrondensity, with those putatively in the process of formation being less electron-dense. Both types of secretory bodies are membrane-bound. Microtubules are evident around forming rod-shaped bodies. The bounding membranes of the rods of both species show a periodic banding of approximately 12 nm. Both types of secretion are present at the surface of the adhesive pads in specimens of Entobdella sp. fixed when detached from the host. The secretory bodies observed in Entobdella sp. and E. australis from rays show some differences to those reported from Entobdella soleae, a parasite of a flatfish teleost. Other ultrastructural differences also exist. We conclude that the types of adhesive secretory bodies may remain constant within genera providing the hosts are similar.