Gonochorism

In biology, gonochorism is a sexual system where there are two sexes and each individual organism is either male or female.

[2]: 213 Gonochorism is thought to be the ancestral state in polychaetes,[9]: 126  Hexacorallia,[12]: 74  nematodes,[13]: 62  and hermaphroditic fishes.

[14] Two papers from 2008 have suggested that transitions between hermaphroditism and gonochorism or vice versa have occurred in animals between 10 and 20 times.

[15] In a 2017 study involving 165 taxon groups, more evolutionary transitions from gonochorism to hermaphroditism were found than the reverse.

Plant species can thus be hermaphrodite, monoecious, dioecious, trioecious, polygamomonoecious, polygamodioecious, andromonoecious, or gynomonoecious.

Examples of species with gonochoric or dioecious pollination include hollies and kiwifruit.

[30] The sex of an individual may also change during its lifetime – this sequential hermaphroditism can, for example, be found in parrotfish[31][32] and cockles.

Unlike most flatworms , schistosomes are gonochoric. The narrow female can be seen emerging from the thicker male's gynecophoral canal below his ventral sucker.