There isn't a widely known rainforest animal that starts with the letter W. However, there are some possibilities:

* Wombat: While not typically found in rainforests, some wombat species inhabit mountainous regions that can be considered rainforests.

* Worm: Many types of worms live in rainforest soil and leaf litter.

* Wasp: Rainforests are home to a variety of wasp species.

Let me know if you'd like to explore any of these options further or if you're looking for a more specific type of animal.