Mantis shrimp the size of eighteen-wheelers, spiders that dwarf saber-toothed tigers, worms that burrow into your eyes, trees that drink your blood... this is arguably the most horrific Lost World ever created.
Henders Isle. It's a nonstop orgy of killing and eating where you're lucky if you live for a few minutes after setting foot there unprotected (and even protection is just delaying the inevitable). Everything isn't justtrying to kill you, everything is trying to kill everything!
Also notable are the plants which nurture seabird chicks. Doesn't sound so bad, right? Except that the plants ate the chicks' parents, and nurture the chicks so they'll come back to breed and be eaten in turn.
The relatively nondangerous species (including species that can kill you, but choose not to, like Hender and the other Hendropods) in this ecosystem can be counted on one hand!
It's theorized (with good reason, as the most charismatic Henders creatures vaguely resemble them, and giant versions inhabit its rivers) by some of the characters that mantis shrimp evolved on Henders Isle (which might explain why they're so Bad Ass)