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Bilaterus is the final alien to be encountered in the game (if not counting Cyrax). They can be a more dangerous foe than Psychosquid if not handled correctly. Both heads have to be defeated in order to beat Bilaterus. They also have a large attack range being able to eat fish with any part of its body including the spine.

The heads can be each bought separately in the Virtual Tank for 10,000 shells.


Bilaterus is actually two skulls, one round and one "pointed", connected by a spine consisting of four segments. One of it's heads looks like the skull of the Pterodactyl, and the other one resembles an ancient fish skull. When both heads are defeated, Bilaterus' spine segments harmlessly scatter in all directions.


"Hardcore Bilaterus fans often argue over which head is superior. Judy K from Minnesota writes in: "Obviously the pointy head is the brains of the operation. The round head is just an overrated Christmas ornament." Bob J from Alabama counters: "No way. Roundy is the MAN! Pointy is just along for the ride." Whoa, easy there, you two. This is one controversy that won't be settled today!"



Because of its much larger attack range compared to other aliens, haste and caution are both advised when fighting this alien. Attacking the head that isn't currently in control will result in no damage being dealt. Only the currently active head will receive damage. Once the first head is defeated, the other one will take control. It must be defeated quickly, as the spine segments can kill an unlimited number of fish.

Challenge Mode

In Challenge Mode, these troublesome aliens will almost empty a player's tank if not prepared. It is highly recommended to have fully-upgraded laser gun to prevent this from happening. It may appear along with Balrog or Psychosquid.


  • Bilaterus' name appears to be a corruption of the word bilateral (having two sides).
    • Additionally, Bilaterus is a Type-II alien, referring to its two heads.
  • Bilaterus switches his attacking head occasionally.