While comparing invertebrate groups, hydra and Obelia are commonly placed together in the same cnidarian class in practical zoology. The feature being tested is:

Hydra and Obelia are representatives of class Hydrozoa. Hydrozoans often include polyp-dominant forms and colonial species with varied life cycles. This MCQ belongs to the Cnidaria topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.