ИСТИНА

Gonads of the articulate brachiopods are located in the mantle. Chuang (1983) identified four main types of such gonads: unbranched, arborescent, reticulate and ovoid. The reticulate gonad is formed by a network of the outgrowing blood vessels, pierced by the connective tissue pillars. They are the most enigmatic structures of such gonads, and some authors have interpreted them as short muscles that participate in releasing gametes (Hancock, 1859). James et al. (1991) proposed that these pillars are supporting columns and not contractile. We studied the microscopical anatomy of the ovary of Hemithyris psittacea by light and transmission electron microscopy with special reference to the connective tissue pillars. The gonads lie in the broad proximal mantle coelomic sinuses. Its walls are formed by the mantle epithelium: the inner mantle wall covers the mantle cavity, the outer mantle wall underlies the valve. The inner mantle wall consists of the epidermis covering the inner side of the mantle cavity, and the coelomic epithelium covering the inner side of the coelomic sinus. The connective tissue matrix lies between the basal laminae of both epidermis and coelomic epithelium. The amoebocytes and the globular cells occur among the connective tissue fibers. The globular cells are oval. Their cytoplasm is filled with numerous electron-dense membrane-free globules and large membrane-bound homogenous inclusions of moderate electron density. The globular cells perhaps take part in the storage of nutrients. The coelomic sinus is lined by the myoepithelial cells. The connective tissue pillars have a wine-glass form and consist of two parts: a column, attached to the inner mantle wall, and a broader part attached to the outer mantle wall. The coelomic epithelium, which is a continuation of the coelomic epithelium of the inner mantle wall, covers the connective tissue pillars. The connective tissue matrix is enclosed within the columns. The coelomic epithelium of the columns contains myofilaments forming the smooth muscles, that are orientated across the gonad cavity. The broad part of the connective tissue pillars contains the parenchymal tissue of oval or polygonal cells. Numerous profiles of rough endoplasmic reticulum, which accompany the nucleus and enmesh with irregular-shaped membrane-bound inclusions of different dimension, are characteristic of these cells. The inclusions (from 1 to 8 μm diameter) contain homogenous material of moderate electron density, bearing ribosomes in its membrane. Probably, these inclusions are expanded profiles of rough endopalsmic reticulum. The unique parenchymal tissue has not been described before for the brachiopod gonads. It is possible that this tissue plays a role in the nutrition of the developing gametes. Thus the connective tissue pillars contain both connective tissue, and muscle fibers in the myoepithelial coelomic cells. Therefore, these pillars could perform a dual function: supporting and contractile. The pillars may prevent the collapse of the gonad during gametogenesis but contract to facilitate spawning. References: Chuang, S.H., 1983. Brachiopoda. 517–530 in Adiyodi, K.G. and Adiyodi, R.G. (eds.), Reproductive Biology of Invertebrates. Spermatogenesis and Sperm Function. V. 2. Wiley, New York. Hancock, A., 1859. On the organization of the Brachiopodes. Philosophical Transactions of the Royal Society 148, 791–869. James, M.A., Ansell, A.D. and Curry, G.B., 1991. Functional morphology of the gonads of the articulate brachiopod Terebratulina retusa. Marine Biology 111, 401–410.