An ultrastructural study of the spermatozoa ofEulalia sp. (Phyllodocidae),Lepidonotus sp. (Polynoidae),Lumbrineris sp. (Lumbrineridae) andOwenia fusiformis (Oweniidae)

The ultrastructure of the mature spermatozoa of four polychaetes is described:Eulalia sp. (Phyllodocidae),Lepidonotus sp. (Polynoidae),Lumbrineris sp. (Lumbrineridae) andOwenia fusiformis (Oweniidae). All the sperm show features typical of externally fertilizing sperm in having a rounded nucleus, a short unmodified midpiece, and a simple flagellum with a 9+2 axoneme.Owenia fusiformis andLepidonotus sp. have a nuclear cone extending into the subacrosomal space that may act to present the inner acrosomal membrane to the egg during fertilization. The acrosome ofLumbrineris sp. is flattened and crenulated. The sperm ofEulalia sp. is unusual in having the four mitochondria of the midpiece ensheathed by a membrane. Comparisons are made with other polychaete sperm, and the use of sperm ultrastructure as a taxonomic tool within the Polychaeta is discussed.