SINOHESIONE-GENITALIPHORA GEN ET SP-N (POLYCHAETA, HESIONIDAE), AN INTERSTITIAL ANNELID WITH UNIQUE DIMORPHOUS EXTERNAL GENITAL ORGANS

A new hesionid, Sinohesione genitaliphora gen. et sp. n., is described from intertidal sandy sediments of Hainan Island, China. It differs f rom hitherto known hesionids by the presence of external genital organ s in both sexes. In the males there is one pair of sac-like appendages , each bearing a tube-shaped penis, on chaetiger 10. In the females th e paired sac-shaped organs are situated on chaetiger 12. Reconstructio ns of semi- and ultrathin sections show that a long, heavily coiled sp erm duct opens at the tip of each penis. The duct opens with a ciliate d funnel into a seminal vesicle in chaetiger 9. Prominent gland cells surround the sperm duct for the most part. The female genital organs e ach have two openings; one of which leads to a blind ending seminal re ceptacle. The other is the external pore of a ciliated oviduct that or iginates as an open funnel in the coelom of chaetiger 10. The function al and phylogenetic significance of these structures is discussed.