Silverfish

The image, silverfish.png, was added to the /mobs/ folder in minecraft.jar in the Beta 1.7 update. It is unknown whether the silverfish is a mob or not. It may be added in the 1.8 update, as Notch said that he would be adding a new "scary mob" to the game. It may be also be used as a mob for fishing, something Notch has wanted to add since the Halloween Update.