Steel jellyfish

The steel jellyfish is a species of jellyfish that appears in the Nintendo DS version of the video game SpongeBob's Atlantis SquarePantis.

Description
They are robotic jellyfish native to Atlantis, being built by the Atlanteans, and are metallic gray with four tentacles.

These jellyfish are also part of the Atlantean defense system, and if said system is activated, they will gain invulnerability while constantly shooting electricity beneath them.

Role in game
Steel jellyfish appear in the final part of the game, Atlantis, and replace the pink, purple, and green ones that have appeared in the earlier parts of the game. Despite their metallic appearance, they take one hit to defeat, like the other species of jellyfish.

When and his friends have to escape Atlantis, they have to run down a hall chased by a laser wall. This hall is filled with steel jellyfish affected by the defense system, and are now invulnerable. SpongeBob and friends must avoid the jellyfish as they escape the lasers.

Trivia

 * They are the second kind of robotic jellyfish seen, the first being the robot Queen jellyfish in "I'm Your Biggest Fanatic."