Bladder is definitely the word
The complete statement is this: CNIDARIA exhibit two radial body forms, the polyp and the medusa, and use stinging cells to capture prey.
Cnidaria is categorized under the Animalia kingdom. It is made up of more that eleven thousand species, which all live in aquatic habitats; either fresh or salt water environments. There are four basic classes of cnidarians, these are: Anthozoa, Cubozoa, Scyphozoan and Hydrozoa. Their common feature is the cnidocytes, which are specialized cells that they use to capture their preys.
Cnidaria have two radial body types, which are called polyp and medusa. They used cnidocytes (stinging cells) to capture the foods they feed on.
What this student is doing is collecting data. So, he wants to check how many life forms there are in the waters nearby. In order to do so, he has to take a sample, and look at it through a microscope so as to determine the number. So, he collected a sample which is his data. He is not drawing conclusions yet, but rather counting these organisms. He is not making a peer review - his peers aren't even mentioned here. He is not forming a hypothesis because he is just counting at this point.
