Illustration of the different types of symmetry of Life Forms On Earth. Display at the Field Museum, Chicago, Illinois. The forms with bilateral symmetry can have heads. Life Forms with other types of symmetry have corresponding organs, if not a head.

The Bilateria, having bilateral symmetry, are a subregnum (a major group) of animals, including the majority of phyla; the most notable exceptions are the sponges and cnidarians. For the most part, Bilateria have bodies that develop from three different germ layers, called the endoderm, mesoderm, and ectoderm. From this they are called triploblastic. Nearly all are bilaterally symmetrical, or approximately so. The most notable exception is the echinoderms, which are radially symmetrical as adults, but are bilaterally symmetrical as larvae. Image File history File links Download high resolution version (2304x1728, 802 KB)Illustation of the different types of symmetry of LifeForms On Earth. ... Image File history File links Download high resolution version (2304x1728, 802 KB)Illustation of the different types of symmetry of LifeForms On Earth. ... Square with symmetry group D₄ Symmetry is a characteristic of geometrical shapes, equations, and other objects; we say that such an object is symmetric with respect to a given operation if this operation, when applied to the object, does not appear to change it. ... Earth, also known as Terra, and (mostly in the 19th century) Tellus, is the third-closest planet to the Sun. ... Field Museum of Natural History, Chicago The Field Museum of Natural History, in Chicago, Illinois, USA, sits on Lake Shore Drive next to Lake Michigan, part of a scenic complex called known as the Museum Campus which includes Soldier Field, the football stadium that is the home of the Chicago... ... A human head In anatomy, the head of an animal is the anterior part (from anatomical position) that comprises the mouth, the brain and various sensory organs (e. ... In biology, bilateral symmetry is a characteristic of multicellular organisms, particularly animals. ... A subregnum or subkingdom is a taxon below the regnum and above the superphylum. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anenomes) Placozoa (trichoplax) Subregnum Bilateria (bilateral symmetry) Acoelomorpha (basal) Orthonectida (flatworms, echinoderms, etc. ... Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... It has been suggested that Porifera/Temp be merged into this article or section. ... Classes Anthozoa - Corals and sea anemones Cubozoa - Sea wasps or box jellyfish Hydrozoa - Hydroids, hydra-like animals Scyphozoa - Jellyfish Cnidaria (from New Latin cnida nematocyst, fr. ... The endoderm, sometimes refered to as entoderm, is one of the three germ layers of the developing embryo, the other two being the ectoderm and the mesoderm. ... The mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. ... The ectoderm is outermost of the three germ layers of the developing embryo, the other two being the mesoderm and the endoderm. ... Classes Asteroidea Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Echinoderms (Echinodermata) is a phylum of marine animals found in the ocean at all depths. ...

Except for a few primitive forms, the Bilateria have complete digestive tracts with separate mouth and anus. Most Bilateria also have an internal body cavity, called a coelom when it lies within the mesoderm, and a pseudocoelom otherwise. It was previously thought that acoelomates gave rise to the other group, but it now appears that in the main acoelomate phyla (flatworms and gastrotrichs) the absence is secondary. Even the oldest known bilaterian animal, Vernanimalcula had a coelom. For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... Sagittal section of nose mouth, pharynx, and larynx. ... Male Anatomy In anatomy, the anus (from Latin ānus ring, anus) is the external opening of the rectum. ... A body cavity is an aspect of a number of basic animal body plans (phyla) that incorporate a central body cavity, known as a coelom. ... A pseudocoelom is a body cavity that surrounds the tissue of the endoderm layer of the cell. ... Classes Monogenea Trematoda Cestoda Turbellaria The flatworms (Platyhelminthes, Greek platy: flat; helminth: worm) are a phylum of relatively simple soft-bodied invertebrate animals. ... The gastrotrichs (from Greek gaster stomach and thrix hair) are a phylum of microscopic animals, found in fresh water and marine environments. ... The oldest known examples of a bilaterian, bilateral animals. ...

There are two superphyla (main lineages) of Bilateria. The deuterostomes include the echinoderms, hemichordates, chordates, and possibly a few smaller phyla. The protostomes include most of the rest, such as arthropods, annelids, mollusks, flatworms, and so forth. There are a number of differences, most notably in how the embryo develops. In particular, the first opening of the embryo becomes the mouth in protostomes, and the anus in deuterostomes. Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Phyla Echinodermata Hemichordata Chordata Chaetognatha Deuterostomes (taxonomic term: Deuterostomia; from the Greek: other mouth) are a superphylum of animals. ... Classes Asteroidea Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Echinoderms (Echinodermata) is a phylum of marine animals found in the ocean at all depths. ... Classes Enterepneusta Pterobranchia Planctosphaeroidea Hemichordata is a phylum of deuterostome animals, generally considered the sister group of our own, the chordates. ... Typical Classes Subphylum Urochordata - Tunicatas Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with... Protostomes (from the Greek: first the mouth) are a taxon of animals. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - Trilobites (extinct) Subphylum Chelicerata Arachnida - Spiders, Scorpions, etc. ... Classes and subclasses Class Polychaeta (paraphyletic?) Class Clitellata    Oligochaeta - Earthworms and others    Acanthobdellida    Branchiobdellida    Hirudinea - Leeches Class Myzostomida Class Archiannelida (polyphyletic) Class Echiura *Some authors consider the subclasses under Clitellata to be classes The annelids, collectively called Annelida (from Latin annellus little ring), are a large phylum of animals, comprising... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... Classes Monogenea Trematoda Cestoda Turbellaria The flatworms (Platyhelminthes, Greek platy: flat; helminth: worm) are a phylum of relatively simple soft-bodied invertebrate animals. ... Embryos (and one tadpole) of the wrinkled frog (Rana rugosa). ...