Sure, go for it.
So like this?
Snappers are ill-tempered and territorial, apt to viciously attack at the least provocation. They usually open combat by shooting crossbow bolts, and switch to claws and bite in close combat. Snappers often throw nets at fast-moving opponents to try to remove their speed advantage.
Looks good!
Anything about their relation to standard tortles?
Creature Catalogue said:When the time comes for them to mate, snappers may travel hundreds of miles to congregate at special egg-laying grounds. These grounds often take the form of rock-walled, roofless labyrinths just above the high-tide line. The snappers defend these places fiercely, attacking all who venture near them.
Well I'm not entirely clear what there relationship to tortles is. It just says they're a "primitive marine relative" of tortles.
The AC9 Creature Catalog (1986) mentions they lay their eggs in beachfront labyrinths, which we should certainly include in the background text:
I'd imagine they'd have encountered one another by now. I suppose divergent evolution and the general bad temperament of the snappers would set them at odds with their landbound kin.
Agreed.
Well, all of that would work:
Leaders ride nik'too.
Travel long distances to defensible egg-laying grounds to breed.
Have poor relationships with land-dwelling cousins, the tortles, when they happen to meet along the shore.
But it's probably best if someone else writes it, since my text is usually pretty poor.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.