Phylum Echinodermata
Echinoderms are marine animals with calcium skeletons formed into plates as a stem with a crown that houses the organs. Modern sub-classes of these organisms include sea stars (star fish). However, your fossil is part of a series of extinct echinoderms that were rooted to the seafloor with a long stem. The crown included arms to trap food, and a mouth. The whole structure is pictured right with the center of the crown pictured left.
Marine benthic sessile organisms. (Phylum also includes marine vagrant benthic organisms).