Reproductive System of Hutchinsoniella macracantha (Cephalocarida)

Abstract

Hutchinsoniella macracantha is a simultaneous hermaphrodite. The small, paired ovaries are cephalic. From each, a long oviduct runs posteriorly to the eighteenth trunk segment, where it loops forward and runs toward the sixth trunk segment. The paired, sausage-shaped testes are dorsal to the midgut in the anterior end of the abdomen. A vas deferens runs down from the anterior end of each testis to join the oviduct. A common gonoduct exits on the posterior face of the sixth thoracopod. The ovaries contain no nurse or follicle cells, although projections from the epithelial cells and oocytes intertwine in the core of the ovary. The mechanism for translocating oocytes along the oviduct is problematical; a conveyor belt hypothesis is offered. Vitellogenesis does not begin until the posterior loops of the oviduct. Only 1 pair of oocytes matures at a time. Spermatogonia are scattered over the length of the testes. Each multiplies to form a small cluster of simultaneously developing spermatocytes; there are no cytoplasmic bridges or nurse cells. Within the testes, sperm formation is asynchronous and continuous. In addition to the acrosome, nucleus, and aflagellar central rod, each sperm cell forms voluminous vacuoles in the remaining cytoplasm; the associated volume increase probably causes mature sperm to enter and move through the testicular central lumen into the vas deferens. There is no obvious morphological obstacle to self fertilization. Each huge (approximately 0.4 mm long) ovum is attached to the ninth thoracopod with cement secreted by glands located midventrally in the ninth thoracic segment (Less)