The anatomy of the larval muscular systems in Balanus improvisus (Darwin, 1854) was investigated by using phalloidin staining to visualize filamentous F-actin in combination with confocal laser scanning microscopy (CLSM). The larval musculature contains an anterior muscle complex associated with the feeding apparatus, a circular intestinal muscle system, and a pair of posterior lateral muscles. The musculature of the labrum consists of two pairs of lateral labral muscles and three pairs of distal labral muscles, which may be associated with the labral glands. A circular oesophageal muscle system is situated below the labrum. Close to the stomodeum lie a transversal muscle, a pair of oblique muscles, and a pair of supra-labral muscles. Nine pairs of muscles are attached along the dorsal midline of the head shield. These data show that the application of fluorescence techniques provides a wide range of opportunities to generate novel data concerning the larval myo-anatomy of crustaceans. © 2006 Balaban.