ULTRASTRUCTURE OF THE GENITAL ORGANS IN THE INTERSTITIAL SYLLID PETITIA-AMPHOPHTHALMA (ANNELIDA, POLYCHAETA)

The gonochoristic syllid Petitia amphophthalma is one of the truly int erstitial polychaetes. P. amphophthalma does not show any epitokous mo difications at maturity such as those that usually occur in syllids. T he reproductive structures are unique: the male genital organs consist of a seminal vesicle in chaetigers 6-10, subdivided into a dorsal par t tightly filled with spermatozoa and a ventral part with contents in different stages of spermatogenesis, one pair of sperm ducts and consp icuous gland cells situated in chaetigers 10 and 11. Their glandular s ecretions are discharged into the sperm duct together with those of ot her types of gland cells that form the duct. The oocytes develop freel y within the body cavity of the females. Each of the fertile segments possesses a paired oviduct ending in a large ciliated funnel. Sperm du cts and oviducts are probably modifications of excretory organs; nephr idia are absent in segments where gonoducts occur. A direct sperm tran sfer by lyric opening of the integument of the female and internal fer tilization are inferred. Copyright (C) 1996 Published by Elsevier Scie nce Ltd on behalf of the Royal Swedish Academy of Sciences