1. Shell: The presence of a hard, calcareous shell is a key characteristic of clams. Clams use their shells for protection and support. While there are some terrestrial animals that have shells, most aquatic animals have them.
2. Gills: Clams are aquatic animals and as such, they breathe through gills. Gills are specialized structures that extract oxygen from water. If you can observe the clam has gills, it is likely an aquatic animal.
3. Habitat: Consider where you found the clam. If it was found in or near water, such as a beach, river, or pond, it is more likely to be aquatic. Terrestrial animals are typically found on land.
4. Locomotion: Observe how the clam moves. Aquatic animals often have specialized structures for movement in water. Clams have a muscular "foot" that they use for burrowing and moving along the bottom of a body of water.
5. Feeding: Clams are filter feeders and primarily feed on microscopic organisms in the water. If the clam is in an environment where there is an abundance of food in the water, it suggests it is an aquatic animal.
It's important to note that these are just some observations that may indicate the clam is aquatic. Additional information and observations may be necessary to make a definitive conclusion.