I've done a meditation to contact my spirit guide and when i asked for a name..they name 'Astennu' keep comming to my head, how can i be sure that this is my spirit guide/totem animal

I would say Astennu is your totem animal since he is a baboon.

What an interesting animal totem to have!  I didn't even know what Astennu meant....

Is it possible for your Spirit Guide to take the shape of animals?

That is the question, sin!  Many believe that animals can be spirit guides and many feel they can not.  As totems they can give us a hint as to characteristics, etc. and we can always learn from all spirit input.

Personally, I think that if one is talking about an individual, animal (or human) then that is a guide not a totem. A totem is a generic term for that breed or species of animal and their many traits and the lessons that can be learned from that particular animal. Totems come to help us and to show us how learning their way of life or their gifts, will enrich our own in some way.  7 of the 9 totems change as we grow and develop.  2 stay constant. And although guides do come and go they do not change nearly as often, and are distinctive.   So for me your hearing one of the wisest and greatest baboons of the underworld would mean that he is here to guide you through a certain phase of your life. Not as just another baboon!