Dentist specialties are recognized in those areas where advanced knowledge and skills are essential to maintain or restore oral health. The list of recognized dental specialties differs from country to country.
In contrast, radially symmetrical animals like jellyfish have a topside and a downside, but no identifiable front or back. The bilateria are a major group of animals, including the majority of phyla but not sponges, cnidarians, placozoans and ctenophores. For the most part, bilateral embryos are triploblastic, having three germ layers: endoderm, mesoderm, and ectoderm.
The phylum Echinodermata, which includes starfish, sea urchins and sand dollars, is unique among animals in having bilateral symmetry at the larval stage, but fivefold symmetry (pentamerism, a special type of radial symmetry) as adults.owever, in the Cnidaria, different symmetries exist, and bilateral symmetry is not necessarily aligned with the direction of locomotion, so another mechanism such as internal transport may be needed to explain the origin of bilateral symmetry in animals.