Mostly hermaphroditic, barnacles are famous for their genitalia — the longest in the animal kingdom, relative to size — which can change shape and size to fertilize neighboring barnacles. For the times when accessing a potential mate is too difficult, most barnacles rely on self-fertilization to spread their seed.
The exception to this behavior is the Pacific gooseneck barnacle. Never observed self-fertilizing, gooseneck barnacles confounded researchers, who wondered how they reproduce when other barnacles are outside their "penis range," according to National Geographic magazine. The answer: sperm-casting. Gooseneck barnacles spray out "sticky sperm masses" that are picked up by other barnacles. According to the article, this discovery "overturns a century of beliefs about what barnacles can, or cannot, do."