Development of Sea Urchin Embryos in Artificial Sea Water Containing Br−in Place of Cl−

In artificial sea water in which the Cl^?concentration was reduced to less than 10% of that in normal sea water by its replacement with Br^?, sea urchin eggs were fertilized and developed into abnormal plutei following almost the same time schedule as in natural sea water. These embryos had poorly developed spicules, short pluteus arms, somewhat jagged embryo-walls and quasi-normal archenterons. Similar embryos were obtained in another artificial sea water in which 90% of the Cl^?concentration in normal sea water was reduced by Br^?and 10% by acetate. In artificial sea water, in which either 90% of the Cl^?was replaced by Br^?or 10% was replaced by acetate, embryos developed into plutei with quasi-normal spicules, pluteus arms and archenterons. These findings indicate that deficiency of Cl^?results in somewhat abnormal sea urchin embryos. When cells derived from isolated micromeres, were cultured in these Cl^?-deficient artificial sea waters, containing Br^?in place of more than 70% of the normal Cl^?concentration in sea water, spicule formation was strongly inhibited, but pseudopodial cables were well developed. Thus, external Cl^?seems to be necessary for at least normal formation of spicule rods.