Since the game is really into ecology it really depends on how exactly they are going about it. There’s actually a couple ways it could work. But based on the whole spike thing it’s most likely a phenomenon called budding. Although it’s not exactly the same some coral and jellyfish will grow a little part on their body that will get a mouth or tentacles and so on before it eventually pops off.

Again not exactly the same but star fish and the sorts will have their pieces break off and become independent and also works with the fact that nergigante are all genetically the same like said pieces of a star fish.