The correct option is A Hydrozoa
Hydrozoa is a class of individually very small, predatory animals, some solitary and some colonial, most living in salt water. A few genera within this class live in freshwater.
Scyphozoa is true jellyfishes. They are found throughout the world's oceans, from the surface to great depths, no Scyphozoa occur in freshwater.
Anthozoa is a class within the phylum Cnidaria and they are present in marine environments.
Therefore, the correct answer is option A.