There is another class of galaxy called S0, which is morphologically a transitional type between true spirals and ellipticals. Its spiral arms are so tightly wound as to be indistinguishable; S0 galaxies have disks with a uniform brightness. They also have an extremely dominant bulge.
Existe outra clase de galaxia chamada S0, que é morfoloxicamente un tipo de transciión entre as espirais verdadeiras e as elípticas. Os seus brazos espirais están tan apretados que resultan indistinguíbeis; as galaxias SO teñen discos dun brillo uniforme. Teñen tamén un bulto extremamente dominante.