engleski

XRD Study of Biomineralized Structures in Sea Urchins

Two different species of sea urchin, Paracentrotus lividis and Spaerechinus granularis, were collected by scuba divers from the shallow rocky shore in the northern Adriatic Sea, Croatia. Primary spines and the small area of the skeleton under the spines were analyzed by X-ray diffraction. Magnesium calcite was found to be the dominant component and quartz and magnesite were present in small amounts in all samples. However, for an individual organism, a shift of diffraction lines toward higher Bragg angles was noticed, that shift being bigger for the skeletons than for the spines. That is consistent with a contraction in lattice parameters ascribed to a varying fraction of magnesium being included in the crystal structure. The comparison between the two species showed that the skeletons appeared to have the same composition, on the contrary, the needles showed different composition. That analysis opens interesting questions as to why the primary skeleton under the spines of different species is the same yet the needles are different, and what is the biological control mechanism for that contrast.

X-ray Diffraction; Urchin; Crystallographic Phase

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