Flotsam and Jetsam are two vicious green eels that work for Ursula. They have a rather unusual ability that allows Ursula to see what they see in her crystal ball. Unlike with most minions, Ursula seemed to be very fond of them, as she was upset when she accidentally killed them.
They are first seen spying on Ariel as she hurries home after remembering the concert. They next appear after King Triton has destroyed Ariel's grotto. Flotsam and Jetsam pretend to feel bad for Ariel, in an attempt trick Ariel into following them. But Ariel knows that Ursula is evil and forces the eels to skeedadle. Flotsam tells her that it was only a suggestion and he knocks a statue piece of Eric with his tail. Ariel looks at the statue's face and tells the eels to not leave.
Sebastian sees Ariel following them and asks Ariel where is she going and she tells him she's going to see Ursula. Sebastian tries to stop her, but Ariel is still angry at the panicking crab, because he told Triton. At Ursula's cave, Flotsam and Jetsam tell Ariel to follow them and strange looking kelp creatures grab her, cause they don't want her to do it. Later, as Ursula sings Poor Unforchunate Souls, Sebastian tries to tell Ariel not to do it, but the eels wrap Flounder and Sebastian in their slimy bodies and gag them.
They next appear at the end of Kiss the Girl, where they knock the boat over so Ariel and Eric can't kiss.
In the climax, Flotsam and Jetsam are accidentally killed by the trident when Ariel grabs Ursula's hair just as the sea witch fires a killing shot intended for Eric. Flotsam and Jetsam are notable for their efficiency (which is something not to take lightly- usually- especially in Disney movies, the henchmen, are clumsy and botch up every plan). Until they were killed, they succeeded at every task Ursula gave them, and due to that, Ursula, shocked that she killed her eels, sadly mourns for them, right before turning her attention and rage towards Ariel and Eric.