Observations of the organ of bellonci of the shrimp Paratya rasmaniensis Riek (Crustacea : Decapoda : Atyidae) with particular reference to the structure of the onion body cells

Abstract

The organ of Bellonci of P. tasmaniensis is near the posterior ventral surface of the eyestalk and adjacent to the medulla externa. It is surrounded by a connective tissue sheath and contains lightly staining cells and onion bodies. There is a lumen with colloidal material. Histochemical observations reveal that the onion bodies are proteinaceous, with some lipid and carbohydrate also present. Glycoprotein appears to exist in the cells, while the colloidal material contains carbohydrates and acid mucopolysaccharides. The onion body cells may each be divided into three regions, the basal region, the terminal region, and the onion body. The basal region contains the nucleus, microbodies, golgi complexes, phaosomes, and 4004 electron-dense granules. The terminal region is notable for its high concentration of mitochondria and for its folded outer plasma membrane. From the terminal region, a ciliary process with a poorly defined 9+2 fibril arrangement arises. This structure expands into a bulbous process which then gives rise to lamellae. The lamellae are folded into an oval structure which constitute the onion body. The lamellae may contain mitochondria, lipid droplets, and lysosome-like bodies. The lamellate form of the onion bodies may be transformed into a vesiculated form, cyclically. It is suggested that the organ of Bellonci of P. tasmaniensis is a photoreceptor organ. It also appears to be an active secretory organ.