From the Super Mario Wiki, the Mario encyclopedia
The missile shells are uncommon enemies from Donkey Kong Country 3: Dixie Kong's Double Trouble!. They are only found in Barbos's Barrier, and they are shot by Barbos. The missile shells have a purple cone-shaped shell covering their tentacle-based bodies, and display two beady eyes. When they are shot by Barbos, they start chasing the player. A while afterwards, they stop in place to home into the character, then shoot straight towards him before hitting a wall or a Lurchin. Enguarde cannot attack the missile shells, as he will get hurt if he tries to do so. Enguarde the Swordfish must lure them at the Lurchins that protect Barbos, leaving the boss open to direct attacks from Enguarde.