title: Ultrastructure and evolution of a sperm: phylogenetic implications of altered motile machinery in Ophryotrocha puerilis spermatozoon.
abstract: Modifications to the mitochondria and flagellum of the Ophryotrocha spermatozoon render it immotile. The sperm may represent an evolutionary unstable intermediate between flagellate and aflagellate sperm types.
mesh_terms: D000177:Acrosome / Q000648:ultrastructure; D000818:Animals; D005075:Biological Evolution; D002502:Centrioles / Q000648:ultrastructure; D008297:Male; D008928:Mitochondria / Q000648:ultrastructure; D011077:Polychaeta / Q000502:physiology*; D013082:Sperm Tail / Q000648:ultrastructure; D013094:Spermatozoa / Q000648:ultrastructure*