Variations in structure and color of the shell of freshwater Ostracoda crustacean genus Cypris were used as a biomarker to detect the impact of heavy metals, i.e. cadmium in the form of CdCl2 as a case of study. Concentrations of element used in experimental were submitted with their levels that were detected in Iraqi aquatic environment and the expected ranges resulting from the accumulation of these metals in aquatic systems. Therefore, salts of CdCl2 were used to prepare the required concentrations (0.1, 0.1.5, 0.2, and 0.3) mg/L, respectively. Individuals of crustacean were taken at the rate of 10 adults (A) and 10 juveniles (J) at three replicates and the exposure time was recorded, at 6,12,24,48 hours, and the tests were conducted under controlled laboratory conditions of light, pH, and temperature. The results showed that all individuals, A and J, were affected after 12 hours of treatment with CdCl2, and observed slight differences in the level of impact, the activity and resistance of Cypris individuals to the impact of element that began with exchanged of color and density of shell, level of the flexibility of shell legator flap muscle within 24 hours, followed by opening and cracking all the shell over 48 hours and exposed the internal structures of the crustacean to direct impact of Cd. When following up on the survival and mortality rate at the level of individuals and comparing the speed of vulnerability of adults and juveniles, differences between both categories of individuals can be noticed, as death rates were recorded after 12 and 24 hours of treatment, amounting to 60 and 70%, respectively, at a concentration of 0.1 mg/L, while with concentrations 0.1.5 and 0.2 mg /L, the percentage increased in J to 80%, but at concentration 0.3, the percentage of mortality rate was equal and became 90% after 24 hours in A and J. The death rate of 100% was recorded with all concentrations used in the experiments after passage 48 hours of treatment with cadmium.