There are some Vitalits that can only be found by doing certain tasks:

Level 1 Island of tranquility
there are a few...
Level 1 catch a fish on the fish fetch game by talking to one of the dolphins in the area and tailwalk on the surface and a vitalit appears

Level 2 perils of the deep
kill the great-white and a Vitalit is left in its wake

Level 3 Trial without error

These are just a few but there are loads more

Secret Tunnel in Gallery

Go to the room with a raised flat platform and look around for some door wheels (One is on the left as you enter The last is at the back) Sonar these and the platform rises to revel a hidden location.
But there is nothing down there that I can find just yellow glowing orbs a little way down.

Find the mothers 3 children and a vitalit appears at the back of the level