Reproduction
Animals in phylum Nemertea show sexual dimorphism, although freshwater species may be hermaphroditic. Eggs and sperm are released into the water; fertilization occurs externally. The zygote develops into a special kind of nemertean larvae called a planuliform larva. In some nemertine species, another larva specific to the nemertinis, a pilidium, may develop inside the young worm from a series of imaginal discs. This larval form, characteristically shaped like a deerstalker cap, devours tissues from the young worm for survival before metamorphosing into the adult-like morphology.