Pronunciation: [ba͡ɪlɐtˈi͡əɹɪə] (IPA) 
The word "bilateria" refers to a group of animals that have bilateral symmetry. In terms of spelling, "bila-" is pronounced as /baɪlə/, with the "i" being a long vowel sound, while "teria" is pronounced as /tɪrɪə/, with the "e" being a schwa sound. The stress falls on the second syllable. The correct spelling is important when communicating about this group of organisms and understanding their characteristics.
Bilateria is a term used in biology to define a major group of animals that possess bilateral symmetry, which means their bodies can be divided into two similar halves along a midline. This group comprises the vast majority of animal species on Earth, including humans.
The main characteristic of bilaterians is their bilateral symmetry, which allows for efficient movement in a directed manner. This symmetry is achieved through the arrangement of body parts in pairs on either side of a central axis, resulting in a distinct head and tail region. Unlike other groups of animals, bilaterians also have specialized sensory organs, including a well-differentiated brain and complex nervous system. This enables them to process and respond to environmental stimuli in a more sophisticated manner.
Furthermore, bilaterians have three embryonic layers: the ectoderm, mesoderm, and endoderm. These layers differentiate during development to give rise to various tissues and organs, providing structural support, muscular movement, and digestive functions. This trilaminar organization is a defining feature of bilaterians and distinguishes them from simpler animals that lack this complexity.
Within the bilaterian group, there is remarkable diversity in terms of size, shape, and habitat. From tiny worms and insects to elephants and whales, bilaterians have successfully colonized almost every environment on Earth. Many important phyla belong to this group, such as arthropods (insects, spiders), mollusks (snails, squids), and chordates (vertebrates, including humans).
In sum, bilateria refers to a wide array of animal species that share the characteristics of bilateral symmetry, specialized sensory organs, trilaminar embryonic development, and an incredible variety of forms, sizes, and adaptations.
The word "bilateria" is derived from Latin and Greek roots.
The Latin root "bi-" means "two", while "latus" means "side" or "flank". These elements together imply "two-sided", referring to the bilateral symmetry exhibited by members of the Bilateria group.
The term "bilateria" was coined by German zoologist Ernst Haeckel in the late 19th century to describe a large group of animals that display bilateral symmetry, meaning their bodies can be divided into two roughly mirror-image halves. This group includes the majority of animal species, from insects and fish to mammals and humans.
