Animal

An animal is a multicellular eukaryote that obtains energy by consuming organic matter and typically develops from an embryo. Animals lack rigid cell walls and include lineages ranging from sponges to mammals.

Eukaryote: An organism whose cells contain a nucleus and membrane-bound organelles. Animals belong to this broad group of organisms with complex cells.
Fertilization: The fusion of gametes that forms a zygote. In most animals, fertilization initiates development of a new individual.
Sponge: A simple aquatic animal that filters particles from water and lacks true tissues. Sponges show that animals need not have nerves, muscles, or conventional organs.
Ediacaran biota: A diverse assemblage of mostly soft-bodied organisms preserved from the Ediacaran Period. Some Ediacaran fossils may represent early animals, though their affinities remain debated.
Food web: A network of feeding relationships among organisms in an ecosystem. Animals occupy consumer roles that link producers, prey, and predators.
Multicellularity: The condition of an organism consisting of multiple cells that coordinate their activities. Animals develop as multicellular bodies whose cells acquire specialized roles.
Cleavage (embryology): Rapid mitotic divisions of an early embryo that increase cell number without substantial growth. These early divisions partition the animal zygote into smaller cells.
Jellyfish: A free-swimming cnidarian with a gelatinous body and tentacles bearing stinging cells. Jellyfish exemplify an early-branching animal lineage with organized tissues and nerve nets.
Cambrian explosion: A geologically brief interval when animal diversity and fossil visibility increased markedly. The event records the early diversification of many animal body plans.
Pollination: The transfer of pollen to a plant's reproductive structures, enabling fertilization. Many animals, especially insects, transfer pollen while feeding on flowers.

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