Iron-containing precipitates, present within the organic matrix of the poriferan Ircinia oros were identified as crystalline lepidocrocite (γ-FeOOH) by electron diffraction and57Fe Mössbauer spectroscopy. The crystals were located specifically within the spongin filaments, suggesting that the binding and subsequent accumulation of iron by macromolecules present in these filaments were responsible for mineralization. Iron biomineralization did not appear to serve any specific structural role, but may be involved in biological processes such as detoxification.
It is well recognized that Porifera are active in the biomineralization of calcium carbonate and silica, producing beautiful and intricate skeletons (Simpson, 1984). However, the formation of other biominerals is less well documented. Iron biomineralization has been reported in a few species of keratose sponges (Töwe & Riitzler, 1968; Vacelet et al., 1988), and the mineral has been identified as lepidocrocite (γ-FeOOH). Lepidocrocite is a relatively uncommon biomineral, having previously been identified as only a minor phase in chiton teeth (Webb et al., 1989; Lowenstam & Weiner, 1989).