By exposure to 12 x 10 3 mol/dm3 K+ for 24 h, more than 90% of planktonic larvae of Babylonia formosae and B. areolata were effectively induced to metamorphose completely. 15 x 10 - 3 mol/dm3 K+ exerted toxic effect on larval B. areolata over a 24-h period, but produced better results of induction by 12 h exposure. Metamorphosed juveniles induced by increased by K’ could move and feed normally. Percent metamorphosis increased with average shell height for K + -induced larvae. L-DOPA, epinephrine and norepinephrine ranging from 5. 5 x 10 -- 6 to 5. 5 x 10 - 5 mol/dm3 had no inductive activity to metamorphosis in larval B. areolata, whereas the rate of metamorphosis induced by dopamine at a concentration of 10--4 mol/dm3 was approximately half less than that by 12 x 10 3 mol/dm3 K+. TEA (a K+ -channel blocker) did not inhibit metamorphosis in the two Babylonia larvae by induction of K+. Based on the results of K+ -induced experiments, it is preliminarily suggested that shell height of larvae achieving metamorphic competence was in the range of 860. 2 - 1 009. 8μm for B. formosae, and 849. 6- 956. 0 um for B. areolata. In addition, planktonic larvae of the two Babylonia had delayed metamorphosis.
