 Male sharks and rays can pass sperm along a duct into a seminal vesicle, where they store it for a while before it is expelled, while teleosts usually employ separate sperm ducts.Externally, many marine animals, even when spawning, show little sexual dimorphism (difference in body shape or size) or little difference in colouration.Where species are dimorphic, such as sharks or guppies, the males often have penis-like intromittent organs in the form of a modified fin.