However, we can break down the concept and see what possibilities there are:
* Primary as in "most important": This could imply animals that are fundamental to the aquatic ecosystem, such as:
* Phytoplankton: Microscopic algae that form the base of the food chain, producing oxygen and serving as food for zooplankton.
* Zooplankton: Small animals that feed on phytoplankton and serve as prey for larger animals.
* Filter feeders: Animals like clams, mussels, and baleen whales that consume vast amounts of microscopic organisms, filtering them from the water.
* Primary as in "first to evolve": This would refer to the earliest aquatic animals, such as:
* Sponges: Simple, multicellular animals that were among the first to evolve.
* Cnidarians: Animals like jellyfish and corals that are characterized by stinging cells.
* Annelids: Segmented worms that are found in both marine and freshwater environments.
* Primary as in "living primarily in the water": This could refer to animals that spend most of their life cycle in aquatic environments, including:
* Fish: Vertebrates with gills, fins, and scales that live in the water.
* Whales: Marine mammals that have evolved to live in the ocean.
* Crustaceans: Arthropods like crabs, lobsters, and shrimp that live in water.
To clarify the meaning of "primary aquatic animals," it would be helpful to consider the context in which the term was used.
If you have more information about the context, I can help you understand the specific meaning.