Spirals have disks with young stars, spiral arms, gas and dust.
They also has central bulges and halos of older stars. The light from spiral galaxies is dominated by the O and B main sequence stars in the disk and bulge. Spirals are catagorized by how tightly wound the spiral is, and how big and what shape the central bulge is. S0 galaxies have a disk and a large central bulge, but no signs of spiral arms. There is no disk structure.