Judging by the size of the jellyfish in the game, they seem to be Lion's Mane Jellyfish (Cyanea capillata), the largest known species of jellyfish known to exist. The actually anatomy of the jellyfish is very simple and cartoonish, similar to the "Blue Jellyfish" from the Spongebob series. These jellyfish give off a blue bio-luminescence, similar to the light of Ctenophora.
The only known location of jellyfish in the Crash games is deep in caverns on the bottom of the ocean floor, like in the level Coral Canyon. Their 'Frogger' movement indicates that their can be an infinite number of jellyfish in one undersea cavern. The cavern itself glows a light blue, similar to the bio-luminescence given off by the jellyfish, another, more practical indication that there are many more jellyfish down in the cavern.
The jellyfish enemies in Crash Bandicoot: The Wrath of Cortex mimic the classic 'Frogger Style' movement seen throughout the Crash series. (Ex. The seel line from the snow-themed levels in Crash Bandicoot 2: Cortex Strikes Back and the skunk lines from the jungle-themed levels in Crash Bandicoot (Game).) They will continuously file out of the abyss and the player is forced to either quickly maneuver the submarine over the jellyfish before they completely barricade the player or blast a hole through the jellyfish line and move through.