Barnacles are always attached to walls. They appear as a large pink cylinder surrounded by many other pink cylinders of varying sizes, with the smaller cylinders placed closer to the edges of the barnacles. Out of the middle large pink cylinder comes a constantly moving tongue like tentacle, that moves in and out.
Barnacles are found attached to walls in Aquanaut, often nearby other barnacles. Barnacles attack by moving their tongue like tentacle in and out, slowly. They stick their tongue out every two seconds, and pull them back in a single second. Barnacles, although looking a lot and acting like a usual hazard found in other Nitrome games, can be killed. The tentacle that sticks out can be damaged by bombs, three bombs to the tentacle required to kill it.
A killed tentacle will not destroy the barnacle like part of the barnacles. Tentacles do not respawn, and yield nothing upon being destroyed. Barnacles are often placed in hallways, alongside many other barnacles. This makes it highly dangerous to venture down the corridor, killing the barnacles making the hallway easier to venture down.