Well after about an hour of reading I found plenty of examples of gender reversal examples and some cool behaviors but nothing regarding chromosomes seems easily accessible or even mentioned. Reproductive behavior seems to be one of the main criteria used to establish evolutionary relationships (aka the cladogram) but that's as far as the layman can find online. I didn't search in Scholar though.
really all it should take is just the word "seahorse", most people have at some point heard about how the males carry the children there. Can't really dismiss that.