Fig. 1

Body surface ridges. a Longitudinal section through the body surface transverse ridges in the cross-body area. The transverse ridges are supported by numerous multi-directional muscle fibers. b Detailed view through a ridge. The surface of each ridge is covered by a syncytial layer containing numerous vesicles. Scales are located on the external neodermis plasma membrane. Beneath the membrane, the cytoplasm is more electron-dense and fibrous, forming a terminal web. Numerous muscle fibers and mitochondria are located under the basal lamina. c Muscle fibers, attached to the basal lamina by the hemidesmosomes. Note the muscle fibers in different directions. d Detailed view of the apical part of the ridge. Note (i) the space between the muscle fibers is filled with parenchyma; (ii) the presence of numerous mitochondria with well-developed cristae; (iii) the outer syncytial layer contains different vesicle types and mitochondria; and (iv) the scale connected to the distal plasma membrane. Abbreviations: BL, basal lamina; Hd, hemidesmosomes; Mi, mitochondria; MF, muscle fibers; Neo, neodermis; Pa, parenchyma; S, scales; TR, transverse ridges; TW, terminal web; V, neodermal vesicles