Tentacle

Phazon Tentacles, or just Tentacles, as they are called in-game in Metroid Prime 3: Corruption, are large serpentine organisms that block Samus' path within the Leviathan Seed on the Space Pirate Homeworld. They are covered in a thick armor, that is immune to most forms of damage save for the Nova Beam, which when combined with the X-Ray Visor to target their delicate nervous system within their large head-like structures, destroying them in one hit, causing them to explode in a splash of phazon. It is unknown whether these are an organism onto themselves are merely part of a larger one;

Since these creatures replace the ULF 14 on the Space Pirates Homeworld Leviathan Seed, they may be related to them in some way, such as possible being the adult form of them or merely just a tentacle that grows off them. They may also have possible just outcompeted them for space within the seed.