A fully-grown Malacoda appears as a long worm covered in tumorous growths. It has a circular maw ringed with long, thin teeth. The maw is accented by two large mandibles that hang off the head. It lacks eyes, with only smooth plates covering the top of its head. Its tail ends in another orifice ringed with similar looking teeth. It can extend to great lengths, and proved powerful enough to crush a helicopter without noticeable recoil damage.
In Revelations, a number of Malacodas inhabit what is surmised to be an infected whale. The creature's appearance is grotesquely modified from any known living whale, even sharing some physical attributes with shellfish. The Malacoda whale-host is massive, easily swallowing up most of the foredeck on the Queen Zenobia. It has a dark green color, with a large tear down its spinal column exposing several deformed vertebrae. The head tapers from the body and features a large mouth reminiscent of a carnivorous saurian, with large, irregular teeth and a strange white growth that functions as a weak point. This creature also seems to lack eyes.
The creature's body ends in what appears to be myriad, small claws that make a singular foot. These claws are used for grasping the deck of the Zenobia during the battle. It has what appears to be a flat, rounded tail that covers the front of the ship.