Animals with three germ layers, called triploblasts, are further characterized by the presence or absence of an internal body cavity called a coelom. Most animals reproduce sexually, leading to a developmental sequence that is relatively similar across the animal kingdom

Animals are eukaryotic, multicellular, heterotrophic organisms that ingest their food and usually develop into motile creatures with a fixed body plan. Most members of the animal kingdom have differentiated tissues of four main classes—nervous, muscular, connective, and epithelial—that are specialized to perform different functions.

bilateral symmetry — a type of symmetry in which there is only one plane of symmetry that creates two mirror-image sides. germ layer — a collection of cells formed during embryogenesis that will give rise to future body tissues. coelom — a lined body cavity derived from mesodermal embryonic tissue. animal kingdom — classified based on their body morphology and development.