Flotsam and Jetsam are eels, specifically green moray eels, in The Little Mermaid.
The pair are Ursula’s sinister henchmen and function as her spies in the ocean. They approach Ariel after King Triton destroys her collection of human objects and lead her to Ursula’s lair, where the sea witch offers Ariel a dangerous bargain. Their glowing eyes and sleek bodies help make them visually distinctive among the film’s many sea creatures.
Although “fish” may sound broadly plausible, it is not the canonical answer used for these characters. Flotsam and Jetsam are identified as moray eels, while Flounder is the fish among Ariel’s closest friends. They are also not snakes or octopuses; Ursula herself has an octopus-like design and six tentacle-like limbs, which can cause confusion.
The two eels are portrayed as a paired, closely coordinated team. Their names are nautical terms associated with floating wreckage, reinforcing the film’s ocean setting and Ursula’s threatening presence.