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The ejaculatory ducts of the two paired copulatory organs in the interstitial polychaeteHesionides arenaria are ciliated tubes, which open into simple, partly groove-like, non-stiffened penis papillae. The larger part of the ducts within the dorsal body wall is surrounded by circular muscle cells. Voluminous gland cell bodies lie between the pharynx-gut system and the body wall in the anterior part of the body; they extend anteriorly like long, thin necks, of which severl are always united in prominent strands. Their distal ends are expanded and penetrate the ducts. Six different types of glands can be distinguished according to the ultrastructure of their secretory granules. They produce the sheath of the double spermatophore or probably contain lytic enzymes that provide for the penetration of sperm into the body of the female. Differences in ultrastructure of the male organs in the interstitial generaHesionides andMicrophthalmus do not support the recent erection of the subfamily “Microphthalminae”.

Ultrastructure of the genital organs in interstitial polychaetes. III. Penes and ejaculatory ducts inHesionides arenaria (Hesionidae)