Could be A. nana, A. validia, A. variabilis, A. cerealis or A. nasuta. Wont know till it "grows up"
FYI: The difference between A. nana and A. validia are; A. nana has smaller radial corallites than the A. validia. A. nana also has a smaller branch size (2.5mm-9mm, compaired to A. valida (10mm-20mm). Also on A. nana only some of the radials touch each other while A. valida mostly all radials touch each other.