Ultrastructural evidence for both autosynthetic andheterosynthetic yolk formation in the oocytes of an annelid (Phragmatopoma Lapidosa: Polychaeta)

The ovaries of the reef-building polychaete Phragmatopoma lapidosa are
attached to the genital blood vessels on the caudal surface of the intersegmental septa
of the abdominal segments. Oogenesis is not synchronized and vitellogenesis occurs
before the oocytes are released from the ovary into the coelomic cavity. A portion of
each developing oocyte rests on the basal lamina of the genital blood vessel while the
remaining surface of the oocyte is covered by follicle cells. Two morphologically
distinct types of yolk are formed during vitellogenesis: Type I, which may be formed
autosynthetically by thc conjoined efforts of the rough ER and Golgi systems; and
Type II, which is pesumably formed heterosynthetically from endocytosis of yolk
precursors from the genital blood vessel. Heterosynthetic production of yolk in an annelid has not been reported previously.