sea lice 

Extremely tiny, baby crabs usually lain offshore but washed in by storms, etc. They attach themselves via their tiny claws to the bodies of unsuspecting swimmers. Painful and annoying, especially when there are thousands of them. Even worse once they get into ones swimsuit and entangled in pubic/butt hair.

Swimmer: Mr. lifeguard, something in the water is biting my testicles
Lifeguard: sounds like sea lice
Swimmer: huh?

sea lice by giglbox May 25, 2008

sea lices

little jelly fishes that sting holly when she is wearing a wet suit

she had 17 sea lices on the one side of her ankle.

sea lices by b wid May 22, 2006