My suggestion.

[MachoNacho]

Crab Spiders

Basically aquatic spiders. Their nests spawn floating in water, tied to the ocean floor via webs. In shallow water or on land, they basically behave like any other spider, but in deeper waters, they walk along the bottom so you can't see them, and to attack, they leap at your boat and latch on, which drains your boat's health until the spider is removed from the boat (they fall off after being hit enough). Their nests, instead of spawning sticky web, spawn silk nets which float on top of the water. Silk nets slow your boat and trap any small creatures that enter (which the crab spiders will then eat). If you are Webber, silk nets do not affect you, of course, and you can tame the crab spiders for companions that can actually follow you when you sail to another island (which is the main reason I suggested this in the first place). Crab spiders are rarer than regular spiders because they have more potential to be annoying.