"There it is" the pirate pointed toward a giant pinkish balloon floating just below the surface.
"It's bigger than I expected." Feris said. "How can we get it while it's under the surface?"
"Oh, there are a few tricks we can use. The thing we really need to worry about is that once we attack it, the Vethmer will try to swarm the ship."
"Which is why the city elders sent us" Feris noted.
"True, but you've never fought them before. They're slippery, the Vethmer. You don't want to go touching them, they're skin'll burn you.
"Do they spit fire or anything?"
"Naaa, nothin like that." The pirate spit over the rail before continuing. "It's just that between their shells and their rubbery flesh, they're hard to kill, is all."
"We'll do our part. You do yours and sink that hive."
Armor Class: 5
Hit Dice: 2+1* (M)
Move: 120' (30')
Swim: 150' (50')
No. Appearing: 1d6 (3d10)
Save As: F2
Treasure Type: None
XP Value: 35
Monster Type: Lowlife Humanoid
Vethmer are tailed humanoid slug-like creatures that live in water, but can breath air and walk on land. Their slimy skin is poisonous, and anyone touching it, or being touched by it must make a saving throw vs poison at a +2 bonus or take 1d4 damage. Warrior vethmers (the only type encountered out of their jellyfish like hive) grow a strong exoskeleton, and use their heavy forearms to attack with. They are single minded in advancing the will of the hive, and have not been known to communicate with any other species. They are known to leave the water to take things, sometimes seemingly random things, back to their hives. Often it's animals (including humans) that are fed to the hive mother.
Image Source: Monsters By Email