Wollyhop
Wollywog
Amphicaris albino
Wollywogs are the different species of mature amphitubers that live in the bowels of subterranean areas. They are instead gray and have red eyes. They are usually in watery cave habitats. As a general rule, this is true for the Forest Navel since it is sort of a cave. They are just like Yellow Wollywogs, just throw Pikmin on its body and call them away when the creature falls after its jump. These creatures are more aggresive than their cousin, and have changed their coloration due to its sun lacking cave environment.
In Pikmin 1, you'll see them before the Yellow Wollywog. In Pikmin 2, you will likely see them second since they are in more difficult caves.
How to kill
Pikmin
Throw Pikmin onto it, then call them back right as it jumps.
Captains
This is tough because it's hard to judge when it'll jump. Punch it a couple times, then run. If it jumps, wait until it's down, then repeat. If not, then go punch it once more.