The correct answer is e) triploblastic development.
Cnidarians, which include jellyfish, sea anemones, and hydras, are characterized by having a simple body structure with two tissue layers: the ectoderm and the endoderm, making them diploblastic. This is in contrast to triploblastic organisms that possess a third layer known as the mesoderm.
The other options listed represent key features of cnidarians:
- a) A gastrovascular cavity: This is the central cavity where digestion occurs.
- b) A polyp stage and/or a medusa stage: Cnidarians can exist in both forms during their life cycle.
- c) Tentacles: These are used for capturing prey and defense.
- d) Cnidocytes containing stingers: These specialized cells are responsible for the stinging ability of cnidarians.
Therefore, triploblastic development is not a characteristic of cnidarians, making option e the correct choice.