animal

Animals are a diverse group of multicellular, eukaryotic organisms within the kingdom Animalia. They are characterized by heterotrophy, obtaining energy by consuming other organisms, and by the presence of specialized tissues and, in many species, muscles and nerves that enable movement. Most animals reproduce sexually, though some also use asexual or parthenogenetic modes of reproduction.

Diversity and classification: Animals range from simple sponges to complex mammals. They are grouped into invertebrates, which lack backbones, and vertebrates, which have a spine. Invertebrates include arthropods, mollusks, annelids, and echinoderms; vertebrates include fishes, amphibians, reptiles, birds, and mammals. The animal lineage shows extensive evolutionary diversification across hundreds of millions of years.

Anatomy, physiology, and life cycles: Most animals develop from a zygote through embryonic stages that form tissues and organs. They exhibit a wide range of body plans and levels of organization, from radial to bilaterally symmetric forms. Many possess nervous systems and specialized senses, enabling feeding, defense, and reproduction. Development patterns vary, including direct development and metamorphosis.

Ecology: Animals inhabit nearly every habitat and play key roles in ecosystems as consumers, predators, prey, pollinators, and decomposers. They influence community structure and nutrient cycling, often forming intricate relationships with plants, fungi, and microorganisms through symbiosis and predation.

Human relevance and conservation: Animals are central to science, agriculture, and culture. They provide food, labor, companionship, and biomedical models. Many species face threats from habitat loss, climate change, pollution, and overexploitation, leading to conservation efforts and ethical considerations in research and management.