Enzymatic activity of total esterase (TE) and carbonic anhydrase (CA) activities was measured by a modification of the method early described by Pocker and Stone on whole tissue homogenate of sea hare A. punctata (Cuvier, 1803). This method first determines the enzymatic activity of total esterases, and from these activities the CA activity obtained using a specific inhibitor of CA, Acetazolamide (AZM) are subtracted to calculate specific CA activities. Initially, the CA activity of standard CAII isoform and the acetazolamide inhibitory effect on CAII was determined. Range of AZM used concentration was tested in triplicate and it was proved that 0.5 mM AZM inhibited CAII activity completely. In following measurements of TE and CA activities, 0.5 mM AZM concentration was used. Analysis of TE and CA activities during embryonal development of sea hare in general indicated increase of both activities during larval development (0-26 days). The CA activities significant increased at 7th and 15th day. The percentage of CA activities in comparison to total esterase activity was the highest at 16th and 23th day of development. In general, during development time the percentage of CA activity was reduced comparing to total esterase activities. The emergence of the first biominerals was determined by the analysis of mineral composition (XRD analysis) on the 9th day of development of sea hare embryos, and this work demonstrated that the appearance of biominerals preceded the increase of UA activity on the 7th day.