With the Fang unique necklace (+1 maximum wolf) equipped, a Primalist may have two wolves summoned at one time.
Leveling up the ‘Summon Wolf’ tree to the ‘Pack Hunters’ skill allows for ‘an additional wolf’ to be summoned (to the default maximum of two companions.)
As the Fang states that it allows ‘+1 maximum wolf’, when having the Fang equipped and ‘Pack Hunters’ learned, the ‘Summon Wolf’ icon stays in the ‘Summon’ mode when two wolves are present (as it should, I believe, allow for the summoning of a third wolf, by the combination of item and skill.) However, only two wolves are allowed still, and the skill icon remains as the ‘Summon’ version (rather than the ‘Howl.’
Removing the Fang unique reverts the skill to its ‘Howl’ state and still allows the two wolves. This is wholly repeatable once the conditions are met.