Morphology of Gametes and Insemination in the Vestimentiferan Riftia pachyptila

A. L. Drozdov, S. V. Galkin

A.V. Zhirmunsky Institute of Marine Biology FEB RAS, ul. Palchevskogo, Vladivostok, Russia.
P.P. Shirshov Institute of Oceanology RAS, Nakhimovsky pr., Moscow, Russia.

DOI: 10.4236/ojms.2012.23013                

Abstract

Ultrastructure of gametes (sperm and eggs) of vestimentiferan tubeworms and external-internal insemination by means of spermatozeugmata in Riftia pachyptila were described. The spermatozoa of Riftia are threadlike, about 130 μm long, and have a diameter of about 0.7 μm, narrowing to 0.2 μm in the apical portion of the macrodome, and pointed at the end of the tail. Oocytes are produced by the ovaries at the first meiotic prophase stage. The early oocytes are small, hardly exceeding 10 μm in diameter, spherical cells with a poorly differentiated cytoplasm and large nuclei with a nucleolus. Completely formed oocytes reaching up to 130 μm in diameter leave the ovary, their germinal vesicle is unresorbed and has a nucleolus. They are coated by a yolk membrane of 1.2 μm. The eggs enter the oviduct, move along, and accumulate in its expanded anterior portion, the ovisack. The sperm is released in seawater as sperm packages, each having the shape of a torch. Then sperm moves to females and sperm packages at the posterior end of the oviduct surrounding of eggs. Inside the female tube, spermatozoa and, possibly, yet unsplit sperm packages, invade the oviducts through genital openings, where the unfertilized eggs are already present in the terminal portion of the eggsack.

Keywords

Riftia; Sperm; Eggs; Insemination; Spermatozeugmata

Conflicts of Interest

The authors declare no conflicts of interest.

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