Barnacle

Barnacles are stationary arthropods found in the Commonwealth and on the Island in 2287.

Background
It's unknown which species of barnacle this variant has evolved from, but it's much larger than the smaller crustaceans that can often be found beside it. These smaller variants are likely a younger version of the species. Barnacles can only be encountered in coastal regions of the Commonwealth and the Island. They can be easy to miss noticing due to their shell coloration making them resemble a rock and can hard to spot when traversing coastal terrain.

Biology
The barnacle is protected by an extremely hard exterior shell that protects it from predators. It's outer shell has a dark green tint and closer to the mouth is tinted red. These barnacles have developed a unique defense mechanism that causes them to release a small cloud of radiation when it senses danger.

Gameplay attributes
Upon approaching it, the barnacle releases a radioactive cloud that irradiates the Sole Survivor at a rate of +30 rads/s for a few seconds. The player can activate the barnacle and cause it to release it's radiation cloud if it hasn't been triggered yet.

Appearances
Barnacles appear in Fallout 4 and it's add-on, Far Harbor.