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In distance-limited samples of galaxies, Magellanic spirals and irregulars are the most common types of galaxies. Encompassing a wide range of luminosities from dwarfs to giants, Magellanic spirals and irregulars are generally HI rich systems with considerable active star formation. Several examples are shown in Figure 1.20.

The Magellanic Clouds are considered to be examples of SB(s)m galaxies, i.e. extreme late-type galaxies having clear bars but very subtle spiral structure showing a characteristic asymmetry with a single main arm and weaker features (de Vaucouleurs and Freeman 1972). This asymmetry is recognizable even in the nearly edge-on view (Buta et al. 2015). The transition stage from Sd to Sm, or Sdm, is also well defined in showing two arms with one much longer than the other. As for Scd and Sd galaxies, Sdm, Sm and Im galaxies are often barred, except for low luminosity dwarfs that may lack the mass required to show such a feature. Non-barred giant late-type galaxies like NGC 5474 show a similar asymmetry to SBm galaxies and can be classified as type SA(s)m.

Figure 1.20. Magellanic irregular galaxies