Ultrastructure of the Ovary and Oogenesis in the Ovoviviparous Ophiuroid Ophiolepis paucispina (Echinodermata)

¹ Harbor Branch Oceanographic Institution Inc., R.R. 1, Box 196, Ft. Pierce, Florida 33450

Ophiolepis paucispina (Say) produces large yolky oocytes and has ovoviviparous reproduction. The ultrastructure of the somatic tissue layers of the ovarian wall and the germinal epithelium of O. paucispina is described. Oogenesis is continuous with oocytes at different stages of development interspersed in the ovary. Proliferation of oogonia and initial growth of the primary oocytes occur within a follicle. Thereafter, the oocytes are largely independent of the germinal layer, and oogenesis is solitary. The oocytes bulge outwards as they grow, forming a sac-like depression in the ovarian connective tissue, and are connected to the germinal layer by a short stalk. Subsequently, haemal fluid accumulates in the connective tissue adjacent to each vitellogenic oocyte. Although each oocyte is enveloped by haemal fluid, it is separated from the fluid by the inner basal lamina. Vitellogenesis involves an accumulation of yolk bodies that appear to be formed jointly by the endoplasmic reticulum and the Golgi complex. Endocytotic activity is prevalent throughout vitellogenesis, indicating incorporation of exogenous material by the oocytes. It is suggested that the genital haemal sinus serves as an intragonadal nutrient store and that yolk precursors, potentially a component of haemal fluid, may be sequestered by the oocytes. O. paucispina appears to have heterosynthetic yolk formation and the evidence for this mechanism of vitellogenesis in the Echinodermata is discussed.

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