I remember hearing on Wikipedia that Hunters takes place after Metroid Prime.
But yeah, maybe it is a branch.
MZM
MP
MPH
MP2
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M4
Yes Metroid prime hunters is between prime and prime2.
When I say it’s a branch, I mean it has little/no relevance in the prime storyline involving Phazon etc…
um? Duh there is no phason in hunters so of course it has no relevance to he prime story and for anyone who thinks goria is Metrois Prime NO!!! Metroid Prime became Dark Samus in the end of Prime(See here(scroll down(note:possible Spoiler))) for those who haven’t seen the 100% ending hell hunters has no Metroid relivance 
metroid hunters is just an attempt to make a good fps for the ds, nothing more, in fact, if it wasn’t metroid, it would make little difference.