Fig. 5

Three-dimensional (3D) tomographic reconstruction of the ciliary band (CB)-associated strand (CBAS) of the postoral arm. (a) Toluidine blue-stained thick cross-section of a larval arm of a 6-arm pluteus. Transmission electron microscopy (TEM, B–E) was applied to the region indicated by box. The larval arm was flattened during sample preparation. (b) TEM image of the first proximal section (0 μm) at the area indicated by box in (a). (c) TEM image of the last distal section 32 μm from the first section (B). (d) Stacked image of nine semi-serial cross-sections (0–32) by the Amira image processor. The CBAS (red) constitutes the initial bulbous proximal sections (0–8) to the long and thin stretch of strand towards the proximal sections (12–32). Squamous epithelium (SqE; yellow) encapsulates the major surface of the larval arm except the apical surface of the CB and the narrow strip of CBAS (red). (e) Smoothened 3D topographic reconstruction of (d). (b) and (c), proximal end indicated by (B) and distal end indicated by (c). Aboral, aboral ectoderm region; arrows, the apical protrusions; Blc, blastocoel; Oral, oral ectoderm region