The aggregate zooids of Salpa fusiformis Cuvier, 1804, S. maxima Forskål, 1775, and the group of the species S. aspera Chamisso, 1819, S. younti Van Soest, 1973, S. thompsoni Foxton, 1961, and S. gerlachei Foxton, 1961, show a difference in the arrangement of the oral musculature. Differences in the solitary zooids are less clear. Differences have also been found in the total number of muscle fibres of the oral musculature in the aggregate zooids of the genera Salpa and Weelia. The aggregate and solitary zooids of the genus Weelia can be distinguished on their oral muscles from those of the genus Salpa. The aggregate zooids of Salpa fusiformis show clinal variation in the number of muscle fibres of the oral musculature.