Fig. 3

Ultrastructure of the body cuticle and of the scales. a The cuticle is made of two layers, a thin exocuticle (arrow) and a thicker endocuticle (asterisk). The scales are solid and homogeneous in structure (TEM). b Shape and arrangement of the dorsal scales (SEM). c Cross section of a pedunculate scale (TEM). d, e Cross and longitudinal sections of the trunk showing the arrangement of the scales. Note the sequence of scales fully adhering to the cuticle (arrow) and others linked to the cuticle through a peduncle (asterisk) (TEM). f Longitudinal section of the trunk of Musellifer delamarei. The ultrastructure of the cuticle and scales look like in Diuronotus aspetos. All the scales are fully adhering to the cuticle (TEM). g Single cilium surrounding the mouth ring (TEM). h Sensory cephalic receptor with about five short cilia (TEM). i A cilium lying under the dorsal body scales (TEM). j An epidermal multiciliated cell (TEM). k Basal ciliary structures: a single basal body and two striated fibres are present (TEM). bb Basal body, c cilium, cr cephalic receptors, ds dorsal scales, s scales, sf striated fibres. Scale bars a, c, g–k = 1 μm; b, d, e, f = 10 μm