The species present in solution when ${\mathrm{CO}}_2$ is dissolved in water are :

Carbon dioxide dissolves in water to form carbonic acid.

${\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{H}}_2{\mathrm{CO}}_3$

Carbonic acid is a weak acid. It dissociates to form carbonate and bicarbonate ions.

${\mathrm{H}}_2{\mathrm{CO}}_3+{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{HCO}}_3^{-}+{\mathrm{H}}_3{\mathrm{O}}^{+}$

The bicarbonate ion dissociates to form a carbonate ion.

${\mathrm{HCO}}_3^{-}+{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{CO}}_3^{2-}+{\mathrm{H}}_3{\mathrm{O}}^{+}$

Hence, the species present in the solution are ${\mathrm{CO}}_2, {\mathrm{H}}_2{\mathrm{CO}}_3, {\mathrm{HCO}}_3^{-}, {\mathrm{CO}}_3^{2-}$