A Magellanic spiral galaxy is a spiral galaxy with only one spiral arm. Magellanic spiral galaxies are classified as the type Sm (with sub-categories SAm, SBm, SABm); the prototype galaxy and namesake for Magellanic spirals is the Large Magellanic Cloud, an SBm galaxy. They are usually smaller dwarf galaxies and can be considered to be intermediate between dwarf spiral galaxies and irregular galaxies. They are found in proximity to larger spiral galaxies such as the Milky Way, as is the case with the LMC and the Small Magellanic Cloud (SMC).
Magellanic spiral galaxies also have a stratified stellar structure; main sequence stars are found in their spiral arm, and supergiants are clustered in a thick rectangular bar across the middle.