Introduction to Animals

Animals are multicellular, heterotrophic organisms that belong to the kingdom Animalia. They are characterized by their ability to move, reproduce sexually, and obtain nutrients by ingesting other organisms.

Characteristics of Animals

• Cellular Structure: Animals are made up of eukaryotic cells, which are complex cells containing membrane-bound organelles.
• Multicellularity: Most animals are multicellular, with specialized cells organized into tissues, organs, and organ systems.
• Heterotrophy: Animals obtain their nutrients by consuming other organisms or organic matter.
• Movement: Most animals have the ability to move, either actively or in response to stimuli.
• Reproduction: Animals reproduce sexually, with the majority exhibiting separate male and female individuals.

Classification of Animals

Animals are classified into various phyla based on their body structures, developmental patterns, and evolutionary relationships. The major phyla include:

1. Porifera: Sponges
2. Cnidaria: Jellyfish, corals, sea anemones
3. Platyhelminthes: Flatworms
4. Nematoda: Roundworms
5. Arthropoda: Insects, arachnids, crustaceans
6. Mollusca: Snails, clams, octopuses
7. Chordata: Fish, amphibians, reptiles, birds, mammals

Animal Diversity

Animals exhibit a wide range of diversity in terms of body plans, habitats, behaviors, and adaptations. This diversity allows them to inhabit virtually every environment on Earth, from deep ocean trenches to polar ice caps.

Study Questions

1. What are the defining characteristics of animals?
2. How are animals classified into different phyla?
3. Discuss the diversity of animal life on Earth.

Conclusion

Understanding the characteristics and classification of animals provides a foundation for exploring the rich diversity of the animal kingdom. As you study further, consider the unique adaptations and ecological roles of different animal species.