Just try not to think about this video the next time you clean out your fish tank.

This gigantic stowaway was discovered by YouTube user gurutek after he started noticing entire coral colonies from his aquarium were suddenly vanishing overnight.

Deciding to find out who was behind these unexplained disappearances, he started staying up during the night to try and figure out what exactly was lurking within his tank.

The suspicious aquarium owner discovered he had Eunice aphroditois hiding in his tank, also known as an Eunice Worm.

This unique underwater sea worm is usually found along the ocean floor, but has been know to surface in artificial marine environments by stowing away on pieces of coral.

Apparently, this particular worm had remained hidden within the fish tank for over two years before first being discovered, and had grown an impressive 1.2 metres in length by the time the unsuspecting owner found it.

These nocturnal worms usually prefer to remain buried in sand and hidden throughout the day, which would explain how this particular stowaway was able to remain undetected for so long.

Adding to the overall ickiness of the situation, these bristly worms also have razor sharp teeth, a super fast strike and are armed with a special toxin to help stun and kill their prey.