Arrangement of parietal and a part of mesogleal muscle fibres throughout the Pleurobrachia pileus body. The mesogleal muscle fibres visible on the equatorial plane are represented in green; all other muscle fibres in this drawing are parietal muscle fibres. Among them, latitudinal fibres are in blue and longitudinal fibres are in pink. The tentacle apparatus has been omitted for clarity. See the pictures of phalloidin-stained preparations supporting this drawing in Additional file 6.