ИСТИНА

Sea spiders (Pycnogonida) are a sister group of Euchelicerata. In this work, the female reproductive system of Phoxichilidium femoratum is described using histological sections, TEM, and SEM. As it is typical of pycnogonids, the ovary of Ph. femoratum consists of a U-shaped trunk part and leg outgrowths, reaching the end of the fourth leg segment; gonopores open on all walking legs, in the distal part of the second segment. The trunk part and leg outgrowths until the middle of the second segment function as a germarium. Distal portions of leg outgrowths function as vitellarium. The germarium lays dorsolaterally to the midgut between two sheets of the horizontal septum. Its wall consists of a thin epithelium, contains no muscle fibers, and is separated from the horizontal septum by a double basal membrane. The cavity of the germarium is filled with previtellogenic oocytes. The vitellarium lays dorsally to the midgut. The vitellarium has two cavities: one is the cavity of the gonad, another is a hemocoel compartment between the gonad and the midgut fenced by the horizontal septum. The gonad cavity is narrow and functions as an oviduct. Here, the dorsal wall of the ovary is not divided from the horizontal septum, consists of a thin epithelium, and contains muscle fibers. Through the ventral wall, vitellogenic oocytes protrude into the hemocoel’s compartment. Each oocyte attaches to the gonad’s wall with a stalk, formed by cells of the ventral wall of the ovary. Cells of the stalks form outgrowths extending into the vitelline envelope. The wall, the stalks, and the oocytes are surrounded by a basal membrane. A short oviduct connects with the cavity of the ovary. Its wall consists of internal epithelial and external muscular layers. Two types of glands with different granules size and structure open near the gonopore.