Any partial transformation we've seen in natural zoans were still hybrids in the sense that Marco's human legs turned into bird claws, Pekoms's back turned into a shell, Onigumo's lower body turned into an abdomen... No matter the degree, their original limbs turned into or merged with those of the animal, but here is different because Black Maria is literally growing with no actual hybridation the head that should be combined with or replacing her human one. That's the kind of transformation that occurs among gifters, but never natural fruits.
To be honest, I think the guy just wanted Black Maria to be a spider but he didn't want her to be a common model because it would feel lesser than her coleagues nor mythical because it would feel higher, so made a quick search and found pretty much the only ancient spider that more or less fit what he needed. I'm sure the man had a good ride in some Prehistoric Animals Wiki.
It's possible, but Black Maria's hybrid didn't really need to be much uglier than Ulti's or the Boa sisters. It was really easy to add some more eyes to her human face and keep the centaur-like anatomy if he wanted to play safe, but this thing with a completely human upper-body yet the spider face also there (and way too cartoonish) is weird as hell.
People still want to go this route huh. He's not even fighting her in this chapter
Seriously, these guys will never learn.
