A typical XANES spectrum is shown in fig. 1a. The
spectrum was acquired over the black spot encircled in the image in fig. 1b (which is an X-ray fluorescence map of the
sea urchin larva, recorded at 3.56 keV). The XANES spectra
show that the black spots are associated with the presence of
agglomerated AgNPs in the sea urchin larvae. The presence of
a peak at 3.359 keV in the XANES spectrum, assigned to the
2p to 5s transition of silver (Miyamoto et al., 2010) indicates
that the black features are agglomerated AgNPs.