In the English dub of the third episode, Pleakley mentions that his species is genderless. But in the original series, he is shown to have both a mom and a dad, and is even betrothed to a female of his species, and his mother asks him to start wearing men's clothing. If the species was genderless, then why would they have a culture with males and females, and why would his mother by bothered by her son wearing female's clothing when, if they were genderless, he could just as easily decide one day that he preferred to identify as female, or just continue to ride the line like he does now.
I've never seen the show, but I've got some ideas for answers. One: They Just Didn't Care. Two: Simple mistake caused by not having time to check. Three: Maybe things were changed between series to make that possible (I don't know what, though). Four: I don't know if it actually exists in this universe, and, depending on interprtation, could overlap with three, but...It's magic, I don't have to explain it.