Fig. 2

a Schematic drawing of the radula when feeding, b Taenioglossan radula of Spekia zonata (ZMH 150008/999-2), black line = area of nanoindentation for central, lateral, and marginal teeth, c Radula (ZMB220.143-2) embedded in epoxy resin and polished for nanoindentation (longitudinal section along the radula) with (d–f) magnification of some tested areas (e with nanoindentation mark; f crosses indicate points of indentation), g Representative results as nanoindentation measurement curves for basis, stylus, and cusps of central teeth (Young’s modulus, GPa, versus displacement into tooth material). The values for the cusps within the indentation depth of 480–520 nm were used for further calculation. Scale bars: b = 100 µm; c = 250 µm; d, e = 30 µm; f = 60 µm. CT central tooth, FP food particle, FZ formation zone, IMT inner marginal tooth, IRT immature radular teeth, LT lateral tooth, MRT mature radular teeth, O odontophore, OMT outer marginal tooth, RM radular muscles, RT radular teeth, WZ working zone