Ultrastructure of the spermatophores of Siboglinum ekmani Jägersten (Pogonophora)

Abstract

THE marine invertebrate phylum Pogonophora has attracted much attention since its discovery in 1914 because of its uncertain phylogenetic position and its unusual biological features, such as the lack of a digestive tract^1,2. Little is known of the spermatophores and the mechanism of fertilisation^1,3, although it has been suggested that the long filament of the spermatophore serves as a flotation device⁴. Because the expulsion of spermatophores into the sea would involve great wastage of sperm, however, some form of copulation has been said to be likely⁵. Expulsion of spermatophores by the tentacles of the male has been observed in one species³, but even in dense populations of 200 animals per m², which have been reported¹, the tentacles are too short to transfer the spermatophores to the females. Electron microscopy has now revealed that the spermatophoral filament is equipped with numerous electron dense ‘threads’, composed of tubular elements with a central electron dense core. Apparently the ‘threads’ which receive their strength from the tubular elements, play an important part as a flotating or adhesive apparatus of the released spermatophores.