The causative agent of hydatidious is . . . . . . . .

The causative agent of hydatidious is Echinococcus granulosa.
Hydatid disease (also known as hydatidosis or echinococcosis) is a potentially serious, sometimes fatal, condition caused by cysts containing the larval stages of the Echinococcus granulosus (E. granulosus) tapeworm (Dog Tapeworm).
Human echinococcosis is caused by the larval stages of cestodes (tapeworms) of the genus Echinococcus.