Structure of the ovary and mode of oogenesis in a freshwater crab Potamon dehaani

Abstract

Structure of the adult ovary and oogenetic mode were examined in the freshwater crab Potamon dehaani. An H-shaped ovary consisting of a pair of long ovarian sacs connected by a narrow bridge tube is located in the cephalothorax on the dorsal side of the stomach. A short oviduct with a seminal receptacle is connected with the posterior end of each ovarian sac, and a genital pore opens on the sternum of the sixth thoracic segment. The ovarian wall consists of a layer of ovarian epithelium that infolds to form a number of oogenetic pouches of various sizes. These are present mainly in the anterior regions of the ovarian sacs, are scarce in the posterior regions of the ovarian sacs, and are absent from the bridge tube. Each oogenetic pouch contains an egg or a relative large oocyte in its lumen. Germaria containing oogonia, very early previtellogenic oocytes, and somatic interstitial cells are located in the ovarian epithelium near the necks of the oogenetic pouches in the anterior regions of the ovarian sacs and are randomly scattered throughout the ovarian epithelium in the posterior regions of the ovarian sacs. In cross section, the germaria appear to be concentrated into a central germarial cluster in the ovarian sac. In the posterior regions of the ovarian sacs, however, the germaria are randomly scattered throughout the ovarian epithelium. An early previtellogenic oocyte leaves its germarium and raises the ovarian epithelium infolds to form a new oogenetic pouch in which it grows to maturity. Mature eggs are ovulated from the oogenetic pouches into the ovarian lumen, transferred from the ovarian lumen into the oviducts, fertilized there by sperm stored in the seminal receptacles, and then oviposited through the genital pores. The female reproductive system is surrounded wholly and tightly by a thin, cellular, membranous sheath, which has often been mistaken as the ovarian epithelium in some decapod crustaceans. J. Morphol. 239:107-114, 1999. © 1999 Wiley-Liss, Inc.

Keywords: basic structure; crab; ovary.