Seacon

The Seacons were a special team of Decepticons who were adapted for underwater combat. Under the lead of Snaptrap, they combine to form Piranacon.

Fury from the Deep
The Seacons landed at least ten years ago and something killed poor Snaptrap. Without him to control the gestalt, Piranacon became a mindless beast, sinking ships such as the Mary Jane at random and trying to use their parts to repair himself(ves).

Learning of the "monster" from Al, Miko, Raf, Jack, and Bumblebee decided to investigate and accidentally came across the Seacons' lair at Devil's Cove. The gang was dragged underwater, the kids ending up in Piranacon's lair and Bumblebee being attacked with full fury by Piranacon. Luckily, the kids were able find out the identity of the monster via the Autobot Archive, escape, and take Piranacon down with old World War II mines; the rockslide they caused smashed the monster in the face.