engleski

Biominerals in embryos, pluteus and adult Antarctic sea urchins Sterechinus neumayeri

The skeletons of adult sea urchins are generally built of mineral magnesium calcite. According to recent literature data contents of Mg in magnesium calcite is depending to the environmental factors, temperature, sea water composition, pollution etc. Also, different parts of adults sea urchin skeletons, i.e. plates, contained more Mg than spines. The adult sea urchins Sterechinus neumayeri was sampled by scuba divers from the bottom of McMurdo Sound, Ross Island, Antarctica during January 1999. After two weeks adaptation periods in the laboratory, sea urchins specimens were induced to spawning using standard 0.5M, KCl solution as stimulating compound. The fertilized eggs were reared under controlled condition during embryonal development to the pluteus larvae up to 500 hours after fertilization (a. f.). Samples of embryos, larval and adult sea urchins were prepared for X-ray diffraction using standard methods. Result of X-ray diffraction shows that gonads and unfertilized eggs of S.neumayeri contained only amorphous - organic components. Fertilized eggs (1 h, a. f.) between dominant amorphous component contained traces of mineral sylvite (KCl). The embryos in four cell stages (19 h, a. f.) are built mostly of organic tissue with small amounts of calcite, and traces of magnesite, dolomite, feldspars and amphiboles. Diffraction patterns for all samples from an early blastula (32 h, a. f.) to the first pluteus larvae (475 h, a. f.) are rather similar to each other, with small changes in fractions of particular phases. A substantial increase of the fraction of calcite is observed in developed pluteus larvae (500 h, a.f.). Such a combination of different minerals in invertebrate embryos or larvae was not registered in the recent literature. The magnesium calcite is dominant component of the skeleton and spines of adult S.neumayeri. Similarly like embryos and larvae adult sea urchins contained in their calcified structures between magnesium calcite traces of feldspars and amphiboles. The fraction of magnesium in magnesium calcite was measured from the angular shifts of diffraction lines 3,0,0 and 0,0,12 in relation to the angular positions of the same diffraction lines of CaCO3 p.a. It was estimated that the fraction of Mg is lower in primary spines 0.08"0.01, and reach values of 0.13"0.02 in the skeleton.

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