Structure of the adult female reproductive system and oogenetic mode in the sea spider, Endeis nodosa (Pycnogonida; Endeidae)

Abstract As in other pycnogonids, the adult female reproductive system of Endeis nodosa is limited to the trunk and walking legs of the cephalothorax. The U‐shaped trunk ovary extends eight blind branches separately into the corresponding walking legs up to each femoral segment. In both the trunk and pedal region, the ovary lies dorsally above the gut, sandwiched between the dorsal and the ventral layer of the horizontal septum. Oogonia and very young oocytes occur throughout the ovary. They fill the trunk ovary and, in the tubular pedal ovary, are aggregated into several cord‐shaped longitudinally arranged germ zones. More advanced oocytes occur only in the pedal ovary. None lie in the germ zones. but instead they protrude individually from the wall of the pedal ovary into the hemocoel on cellular stalks. Vitellogenesis occurs in the larger stalked oocytes. An oval genital pore with a cuticular lid lies on the ventral surface of the second coxa of each walking leg. The pedal ovarian lumen is directly connected to the genital pore by a short oviduct in the second coxa. The ovarian structure and oogenetic modes in this pycnogonid species show some common characteristics with those of most chelicerates.