All Pokémon, that to evolve into them there is evolution item required, cannot be neither caught in the wild, hatched from an egg nor be a Raid Boss in the gym and the only way to acquire them is the evolution.
Historically, in the Pokémon game core-series, the following conditions described below will take place when one of these items are given to a Pokémon to hold:
Pokémon capable of holding either a Dragon Scale, King's Rock or Metal Coat will evolve when traded.
Pokémon capable of holding either a Sun Stone or Up-Grade will evolve when leveled-up.
On the official support page for Pokémon GO, Deepsea Scale and Deepsea Tooth are mentioned.