Is a star fish a crustacean?

No. Reptiles and starfish share membership in the same kingdom [Animalia]. But they immediately diverge on the specifics, and all the subgroupings. For example, reptiles are members of the phylum of Chordates, subphylum of Vertebrates, and class of Reptiles. Starfish are members of the phylum of Echinodermates, the subphylum of Asterozoa, and the class of Asteroidea.