sentences:  In many species, an elongate cytoplasmic collar binds the flagellum to the elongate nucleus at some stage of spermiogenesis.In almost all species, the sperm cell bodies are elongate.In the tribe Diapomini, the genus "Planaltina" expresses only round sperm (like that of externally fertilizing characins) and the genera "Diapoma" and "Acrobrycon" only express slightly elongated sperm; this may indicate a possible plesiomorphy.