Researchers from the North Carolina Museum of Natural Sciences identified the creatures as bristle worms, or polychaete worms belonging to the family Amphinomidae. This family of creatures includes fireworms and sea mice.
The creatures are known as bristle worms because of their toxin coating spikes known as seta. These seta cover the bristle worm's body and makes it potentially dangerous to humans. The toxins in bristle worms can cause significant skin irritation.
The worms can grow on objects floating in the open ocean. In this instance, they were on a coconut which eventually made its way to the North Carolina coast.