The Dynamics of Oogenesis and the Annual Ovarian Cycle of Stichopus californicus (Echinodermata: Holothuroidea)

¹ Friday Harbor Laboratories and Department of Zoology, University of Washington, Seattle, Washington 98195

The major cytological stages of oogenesis in the holothurian Stichopus californicus are morphologically separated in distinct classes of tubules, the discrete anatomical units comprising the ovary. Primordial germ cells are in the connective tissue compartment of the gonad basis. Mitotic oogonia are in the smallest and most anterior set of primary ovarian tubules. Oocytes in the early prophase stages of meiosis I are in secondary tubules located more posteriorly. Diplotene oocytes occur in larger, more posterior secondary tubules. The most advanced oocytes are in the most posterior fecund tubules. S. californicus oocytes bear nuage, a subcellular marker common to many germ line cells. The striking axial polarization of these oocytes, evident as the egg axis, is indistinguishable from the apical basal axial polarization in epithelial germ line cells. These axes are congruent throughout the developmental history of the oocyte. I present a model for the annual cycle of the S. californicus ovary and assess its application to other holothurians. I infer function from the structure of oogenesis presented here; and contrast this information with what is known about oogenesis in the other echinoderm classes.