1. Eukaryotic Cells: Animals are made up of eukaryotic cells, meaning they have a nucleus and other membrane-bound organelles.
2. Multicellularity: Animals are multicellular organisms, meaning they are composed of many cells that work together to form tissues, organs, and organ systems.
3. Heterotrophy: Animals cannot produce their own food. They obtain nutrients by consuming other organisms (plants, animals, or decomposing matter).
4. Movement: Animals exhibit movement, whether it's through locomotion (walking, swimming, flying) or internal movements within their bodies.
5. Sexual Reproduction: While some animals can reproduce asexually, most animals reproduce sexually, involving the fusion of gametes (sperm and egg) to create offspring.
6. Blastula Formation: In their early development, animals undergo a stage called the blastula, a hollow ball of cells. This stage is a key characteristic of animal development.
It's important to note that there are exceptions to these characteristics. For example, some animals are sessile (do not move) and some reproduce asexually. However, these characteristics are generally true for the vast majority of animals.