Humans are the only species with sex. Gender is a psychological perception of sexual identity, which can be different from a person's gender. Sex is determined by chromosomes; Gender is how you feel about your sexual orientation. Most of us are either men or women, but many of us are either men or women, and vice versa. This topic is much deeper, but I don't want to go any further. )

Other species can be asexual or sexual, and sexual species can be hermaphrodite, male or female. But these are not gender.

that is to say, except for many examples of fish mentioned by others, every oyster and shrimp you eat is female, and they were male at first. Males are too small to be of commercial value. There are several examples of animals changing sex in their lifetime. This is called continuous hermaphroditism (as opposed to simultaneous hermaphroditism).

if an animal starts from male reproduction and later becomes female, it is called male reproduction (from proto = first, andro = male)-oysters and shrimps are examples. If it begins to reproduce as a female and later becomes a male, it is called protogyous (gyn = female). About three-quarters of hermaphroditic fish are females. Many examples of these two situations can be found here: continuous hermaphroditism-Wikipedia.

When I was a teenager, as a zoologist, my favorite animal was Hydra. They reproduce asexually through germination, especially in spring and summer; Sexual reproduction, usually in autumn. In the sexual stage, some hydra species are only male, some are female, and some are hermaphroditic, showing testicles and ovaries at the same time, and sometimes both of them are branches of the body column. I think this is very interesting. As an imaginative young boy, hydra's testicles often look like human female breasts-a pile of tissues with nipples at the top. However, this is not just a childish imagination; The most famous hydra biologist is libie Henrietta Hyman, who instructed me a little in the 196s. She described Hydra in her own publications. In the brief language of the classification paper, she described this feature of a species as "testicular mammal".

This is a picture of three reproduction modes of Hydra, one is asexual bud, the other is ovary and the other is testis. Chlorohydra ("Green Hydra") has one bud and three mammalian testes (two with apical papillae). Green comes from Chlorella, a unicellular algae living in its epidermal cells.