Nemo

Nemos are aquatic enemies in Donkey Kong Land. They only appear in the level, Nautilus Chase, in which they are the main feature. Nemos are the game's successor to Croctopuses from Donkey Kong Country.

Nemos act somewhat similar to Croctopuses, but are much more aggressive, chasing Donkey Kong or Diddy Kong regardless of where they swim in relation to it, instead of following a set path. They also move in quick darting motions, unlike Croctopuses' smooth gliding through the water.

When the active Kong first encounters a Nemo, it appears to be dormant. As Donkey Kong or Diddy swims past the Nemo, it suddenly emerges from its shell and quickly follows him, including in tight spaces. If the active Kong does not swim fast enough, he gets hit by a Nemo, and therefore injured. Like the game's other aquatic enemies, Nemos cannot be defeated. At some point the Nemo quits chasing either Kong, and huddles back up in a corner within the coral.

Their name is taken from Captain Nemo, who pilots the  submarine in the science fiction novel, Twenty Thousand Leagues Under the Sea, likely as a joke regarding the enemy itself being a nautilus.

Reference
Nemo