Animals Fossil range: Ediacaran - Recent
Clockwise from top-left: Loligo vulgaris (a mollusk), Chrysaora quinquecirrha (a cnidarian), Aphthona flava (an arthropod), Eunereis longissima (an annelid), and Panthera tigris (a chordate). The Ediacaran Period (ˌiːdiˈækərən named after the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic The European Squid ( Loligo vulgaris) is a large Squid belonging to the family Loliginidae. Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 The stinging sea nettle ( Chrysaora quinquecirrha) is a Species of Jellyfish occurring particularly in Atlantic estuaries Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments Arthropods are Animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, " Joint " Nereis is a Genus of Polychaete Worms in the family Nereidae. The annelids, collectively called Annelida (from Latin anellus "little ring" are a large phylum of Animals comprising The tiger ( Panthera tigris) is a member of the Felidae family the largest and the most powerful of the four " Big cats quot in the Genus Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates
Scientific classification
Domain: Eukaryota (unranked) Opisthokonta Kingdom: Animalia Linnaeus, 1758
Phyla
Subkingdom Parazoa Porifera Subkingdom Eumetazoa Placozoa Radiata (unranked) Ctenophora Cnidaria Bilateria (unranked) Orthonectida Rhombozoa Acoelomorpha Chaetognatha Superphylum Deuterostomia Chordata Hemichordata Echinodermata Xenoturbellida Vetulicolia † Protostomia (unranked) Superphylum Ecdysozoa Kinorhyncha Loricifera Priapulida Nematoda Nematomorpha Lobopodia † Onychophora Tardigrada Arthropoda Superphylum Platyzoa Platyhelminthes Gastrotricha Rotifera Acanthocephala Gnathostomulida Micrognathozoa Cycliophora Superphylum Lophotrochozoa Sipuncula Hyolitha † Nemertea Phoronida Bryozoa Entoprocta Brachiopoda Mollusca Annelida Echiura

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex The opisthokonts ( Greek: (opisthō- = "rear posterior" + (kontos = "pole" i Carl Linnaeus (Latinized as Carolus Linnaeus, also known after his ennoblement as, May 23 new style (13 May old style 1707 who laid the foundations for The book Systema Naturae was one of the major works of the Swedish doctor of medicine Carolus Linnaeus. A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class. The Parazoa are an ancestral subkingdom of Animals literally translated as "beside the animals" The sponges or poriferans (from Latin porus "pore" and ferre "to bear" are Animals Eumetazoa is a Clade comprising all major Animal groups except sponges Characteristics of eumetazoans include true tissues organized into Trichoplax adhaerens is a simple balloon-like marine Animal with a body cavity filled with pressurized fluid The Radiata are the radially symmetric animals of the Eumetazoa subregnum The phylum Ctenophora (tɨˈnɒfərə commonly known as comb jellies, is a phylum that includes the Sea gooseberry ( Pleurobrachia pileus) and Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments The Bilateria (ˌbaɪləˈtɪəriə are all animals having a bilateral symmetry, i Orthonectida is a small phylum of poorly-known Parasites of marine invertebrates that are among the simplest of multi-cellular organisms Rhombozoa, or Dicyemida, is a phylum of tiny Parasites that live in the renal appendages of Cephalopods Although the name Dicyemida The Acoelomorpha are a Phylum of animals with planula-like features and formerly considered to be in Platyhelmintha, but recently classified by Jaume Chaetognatha is a phylum of predatory marine worms that are a major component of Plankton worldwide Deuterostomes (taxonomic term Deuterostomia; from the Greek "second mouth" are a superphylum of Animals They are a subtaxon of the Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates Hemichordata is a phylum of worm-shaped marine Deuterostome Animals generally considered the sister group of the Echinoderms They date Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars) Xenoturbella is a Genus of Bilaterian animals it contains two marine Worm -like species Vetulicolia is an extinct Phylum erected by Shu et al (2001 encompassing several early- Cambrian Fossil forms In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. Protostomia (from the Greek: mouth first) are a Taxon of Animals Together with the Deuterostomes and a few smaller phyla The Ecdysozoa (ˌɛkdɪsəˈzoʊə are a grouping of Protostome animals including the Arthropoda ( Insects, Chelicerata, Crustaceans Kinorhyncha (Gr κίνηω kīneō 'move' + ρυνχος rhynchos 'snout' is a phylum of small (1 mm or less marine pseudocoelomate Loricifera (from Latin, lorica, Corselet + Greek, φορη phora, bearing is a small Phylum of marine sediment-dwelling Priapulida ( priapulid worms or penis worms, from Gr πριάπος priāpos ' Priapus ' + Lat The nematodes or roundworms ( Phylum Nematoda from Greek (nema "thread" + -ode "like" are one of the most common Nematomorpha (sometimes called Gordiacea, and commonly known as Horsehair worms or Gordian worms) are a Phylum of Parasitic Lobopodia is a group of poorly understood animals which mostly fall as a Stem group of Arthropods. In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. The velvet worms ( Onychophora — literally "claw bearers" form a Clade within the Ecdysozoa and can be simply described as " Worms Tardigrades (commonly known as water bears) form the Phylum Tardigrada, part of the superphylum Ecdysozoa. Arthropods are Animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, " Joint " The Platyzoa (ˌplætɨˈzoʊə are a group of Protostome animals proposed by Thomas Cavalier-Smith in 1998 The flatworms (Phylum Platyhelminthes from the Greek πλατύ platy, meaning "flat" and ἕλμινς (root ἑλμινθ- helminth- The gastrotrichs (from Greek γαστερ gaster "stomach" and θριξ thrix "hair" are a phylum of microscopic (0 The rotifers make up a Phylum of microscopic and near-microscopic pseudocoelomate Animals They were first described by Rev The Acanthocephala ( Greek ακανθος akanthos, thorn + κεφαλη kephale, head is a phylum of Parasitic worms known as Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine Animals Most measure between 0 Limnognathia maerski is a microscopic animal discovered living in homothermic springs on Disko Island, Greenland in 1994 that was given Symbion is the name of a Genus of aquatic animals less than ½ mm wide found living attached to the bodies of cold-water lobsters The Lophotrochozoa (ləˌfɒtroʊkəˈzoʊə "crest-bearing animals" are one of three major groupings of Protostome animals The Sipuncula or Sipunculida, sipunculid worms or peanut worms, are a phylum containing 144-320 Species (estimates vary of bilaterally Hyolitha are enigmatic Animals with small conical shells known from the Palaeozoic Era In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. Nemertea is a Phylum of Invertebrate Animals also known as ribbon worms or proboscis worms   Phoronids (' Phoronida') commonly known as horseshoe worms, are a relatively small animal Phylum: twenty species are known in two genera Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some Entoprocta (Gr εντος entos inside + προκτος proktos anus is a phylum of small aquatic Animals ranging in size from 0 Brachiopods (from Latin brachium, arm + New Latin -poda, foot are a small phylum of Benthic Invertebrates Also Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 The annelids, collectively called Annelida (from Latin anellus "little ring" are a large phylum of Animals comprising The Echiura, or spoon worms are a small group of marine Animals They are often considered to be a group of Annelids although they lack the segmented Multicellular organisms are Organisms consisting of more than one cell, and having Differentiated cells that perform specialized functions Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex In biological Taxonomy, a kingdom or regnum is a Taxonomic rank in either (historically the highest rank or (in the new three-domain system Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. A body plan, or bauplan, is essentially the blueprint for the way the body of an organism is laid out Metamorphosis is a Biological process by which an Animal physically develops after Birth or hatching involving a conspicuous and relatively Most animals are motile - they can move spontaneously and independently. Motility is a biological term which refers to the ability to move spontaneously and actively consuming energy in the process Animals are heterotrophs - they are dependent on other organisms (e. A heterotrophs, or chemoorganotrophy ( Greek heterone = (another and trophe = nutrition is an Organism that requires g. plants) for sustenance. Plants are living Organisms belonging to the kingdom Plantae.

Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. The Cambrian explosion or Cambrian radiation was the seemingly rapid appearance of most major groups of complex Animals around, as evidenced by the

Etymology

The word "animal" comes from the Latin word animale, neuter of animalis, and is derived from anima, meaning vital breath or soul. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. In Linguistics, grammatical genders, sometimes also called Noun classes are classes of nouns reflected in the behavior of associated words every noun must belong In everyday colloquial usage, the word usually refers to non-human animals. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus The biological definition of the word refers to all members of the Kingdom Animalia. Therefore, when the word "animal" is used in a biological context, humans are included. ^[1]

Characteristics

Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and usually multicellular^[2] (although see Myxozoa), which separates them from bacteria and most protists. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Multicellular organisms are Organisms consisting of more than one cell, and having Differentiated cells that perform specialized functions The Myxozoa ( Etymology: Greek: myx- "slime" or "mucus" + zoa "animals" are a group of parasitic The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this They are heterotrophic,^[3] generally digesting food in an internal chamber, which separates them from plants and algae. A heterotrophs, or chemoorganotrophy ( Greek heterone = (another and trophe = nutrition is an Organism that requires Plants are living Organisms belonging to the kingdom Plantae. Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms They are also distinguished from plants, algae, and fungi by lacking cell walls. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ A cell wall is a tough flexible and sometimes fairly rigid layer surrounding a cell, located external to the Cell membrane, which provides the cell with structural ^[4] All animals are motile,^[5] if only at certain life stages. In most animals, embryos pass through a blastula stage, which is a characteristic exclusive to animals. An embryo (from Greek:, plural, lit "that which grows" from en- "in" + bryein "to swell be full" is a multicellular The blastula is an early stage of Embryonic development in Animals It is also called blastosphere

Structure

With a few exceptions, most notably the sponges (Phylum Porifera), animals have bodies differentiated into separate tissues. The sponges or poriferans (from Latin porus "pore" and ferre "to bear" are Animals Tissue is a cellular organizational level intermediate between cells and a complete organism These include muscles, which are able to contract and control locomotion, and nerve tissue, which sends and processes signals. Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the The nervous system is a Network of specialized cells that communicate information about an animal's surroundings and itself There is also typically an internal digestive chamber, with one or two openings. Digestion is the breaking down of chemicals in the body into a form that can be absorbed Animals with this sort of organization are called metazoans, or eumetazoans when the former is used for animals in general. Eumetazoa is a Clade comprising all major Animal groups except sponges Characteristics of eumetazoans include true tissues organized into

All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Collagen is the main Protein of Connective tissue in Animals and the most abundant protein in Mammals making up about 50% of the whole-body protein Not to be confused with Peptidoglycan. Glycoproteins are proteins that contain Oligosaccharide chains ( Glycans) covalently attached This may be calcified to form structures like shells, bones, and spicules. Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce This article is about the skeletal structure See also Spicule (solar physics and Spicule (glass manufacture. During development it forms a relatively flexible framework upon which cells can move about and be reorganized, making complex structures possible. In contrast, other multicellular organisms like plants and fungi have cells held in place by cell walls, and so develop by progressive growth. Also, unique to animal cells are the following intercellular junctions: tight junctions, gap junctions, and desmosomes. Tight junctions, or zonula occludens, are the closely associated areas of two cells whose membranes join together forming a virtual impermeable barrier A gap junction or nexus is a specialized Intercellular connection between certain animal cell -types A desmosome, also known as macula adherens or macula adherentes ( Latin: adhering spot) is a cell structure specialized for cell-to-cell

Reproduction and development

Nearly all animals undergo some form of sexual reproduction. Adults are diploid or polyploid. "Haplo" redirects here For the fictional character see The Death Gate Cycle. Polyploidy occurs in cells and Organisms when there are more than two homologous sets of Chromosomes. They have a few specialized reproductive cells, which undergo meiosis to produce smaller motile spermatozoa or larger non-motile ova. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half A spermatozoon or spermatozoan ( pl spermatozoa) from the Ancient Greek σπέρμα (seed and ζῷον (living being and more commonly known An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. These fuse to form zygotes, which develop into new individuals. For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked"

A newt lung cell stained with fluorescent dyes undergoing mitosis, specifically early anaphase. A newt is an Amphibian of the Salamandridae family order Urodela or Caudata, found in North America, Europe, and lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Staining is an auxiliary Technique used in Microscopy to enhance contrast in the microscopic image Fluorescence is a Luminescence that is mostly found as an A dye can generally be described as a Colored substance that has an affinity to the substrate to which it is being applied Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei Anaphase, from the Ancient Greek ἀνά (up and φάσις (stage is the stage of Mitosis when Chromosomes

Many animals are also capable of asexual reproduction. Asexual reproduction is a form of reproduction which does not involve Meiosis, Ploidy reduction or Fertilization. This may take place through parthenogenesis, where fertile eggs are produced without mating, or in some cases through fragmentation. Parthenogenesis (from the Greek παρθένος parthenos, "virgin" + γένεσις genesis, "creation" is an asexual form

A zygote initially develops into a hollow sphere, called a blastula, which undergoes rearrangement and differentiation. For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" The blastula is an early stage of Embryonic development in Animals It is also called blastosphere In sponges, blastula larvae swim to a new location and develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form a gastrula with a digestive chamber, and two separate germ layers - an external ectoderm and an internal endoderm. Invagination means to fold inward or to sheath In Biology, this can refer to a number of processes Gastrulation is a phase early in the development of animal Embryos during which the morphology of the embryo is dramatically restructured by Cell migration. A germ layer is a collection of cells formed during animal Embryogenesis. The ectoderm is the start of a tissue that covers the body surfaces Endoderm, (sometimes called Entoderm) is one of the Germ layers formed during animal Embryogenesis. In most cases, a mesoderm also develops between them. One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. These germ layers then differentiate to form tissues and organs.

Most animals grow by indirectly using the energy of sunlight. Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. Plants use this energy to convert sunlight into simple sugars using a process known as photosynthesis. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Starting with the molecules carbon dioxide (CO₂) and water (H₂O), photosynthesis converts the energy of sunlight into chemical energy stored in the bonds of glucose (C₆H₁₂O₆) and releases oxygen (O₂). Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Water is a common Chemical substance that is essential for the survival of all known forms of Life. Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the These sugars are then used as the building blocks which allow the plant to grow. When animals eat these plants (or eat other animals which have eaten plants), the sugars produced by the plant are used by the animal. They are either used directly to help the animal grow, or broken down, releasing stored solar energy, and giving the animal the energy required for motion. This process is known as glycolysis. See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized

Animals who live close to hydrothermal vents and cold seeps on the ocean floor are not dependent on the energy of sunlight. A hydrothermal vent is a Fissure in a planet's surface from which geothermally heated Water issues A cold seep (sometimes called a cold vent) is an area of the Ocean floor where Hydrogen sulfide, Methane and other Hydrocarbon -rich Instead, chemosynthetic archaea and eubacteria form the base of the food chain. Chemosynthesis is the biological conversion of one or more carbon molecules (usually Carbon dioxide or Methane) and nutrients into organic matter using the Oxidation The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have

Origin and fossil record

Animals are generally considered to have evolved from a flagellated eukaryote. eVolution is the third Album by eLDee, it was due to be released in 2008 Flagellates are cells with one or more whip-like organelles called flagella. Their closest known living relatives are the choanoflagellates, collared flagellates that have a morphology similar to the choanocytes of certain sponges. The choanoflagellates are a group of free-living unicellular and colonial Flagellate Eukaryotes considered to be the closest living relatives of the Animals Molecular studies place animals in a supergroup called the opisthokonts, which also include the choanoflagellates, fungi and a few small parasitic protists. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by The opisthokonts ( Greek: (opisthō- = "rear posterior" + (kontos = "pole" i A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The name comes from the posterior location of the flagellum in motile cells, such as most animal spermatozoa, whereas other eukaryotes tend to have anterior flagella. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex

The first fossils that might represent animals appear towards the end of the Precambrian, around 610 million years ago, and are known as the Ediacaran or Vendian biota. The Precambrian ( Pre-Cambrian) is an informal name for the supereon comprising the eons of the Geologic timescale that came before the current The Ediacara (ˌiːdɪˈækərə formerly Vendian) biota are ancient lifeforms of the Ediacaran Period which represent the earliest known complex These are difficult to relate to later fossils, however. Some may represent precursors of modern phyla, but they may be separate groups, and it is possible they are not really animals at all. Aside from them, most known animal phyla make a more or less simultaneous appearance during the Cambrian period, about 542 million years ago. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with It is still disputed whether this event, called the Cambrian explosion, represents a rapid divergence between different groups or a change in conditions that made fossilization possible. The Cambrian explosion or Cambrian radiation was the seemingly rapid appearance of most major groups of complex Animals around, as evidenced by the However some paleontologists and geologists would suggest that animals appeared much earlier than previously thought, possibly even as early as 1 billion years ago. Trace fossils such as tracks and burrows found in Tonian era strata in India indicate the presence of triploblastic worm like metazoans roughly as large (about 5mm wide) and complex as earthworms. The Tonian (from Greek tonas, "stretch" is the first Geologic period in the Neoproterozoic Era and lasted from Triploblasty is a condition of the Blastula in which there are three primary Germ layers the Ectoderm, Mesoderm, and Endoderm. Earthworm is the usual name for the largest members of Oligochaeta (which is either a class or subclass depending on the author in the phylum Annelida In classical ^[6] In addition during the beginning of the Tonian period around 1 billion years ago (roughly the same time that the trace fossils previously discussed in this article date back to) there was a decrease in Stromatolite diversity which may indicate the appearance of grazing animals during this time as Stromatolites also increased in diversity shortly after the end-Ordovician and end-Permian rendered large amounts of grazing marine animals extinct and decreased shortly after their populations recovered. Stromatolites (from Greek στρώμα strōma, mattress bed stratum and λιθος lithos, rock are layered accretionary Structures formed in However some other scientists doubt that these fossils are authentic and have suggested these trace fossils are just the result of natural processes such as erosion.

Groups of animals

Orange elephant ear sponge, Agelas clathrodes, in foreground. Agelas clathrodes, also known as the elephant ear sponge, is a species of Sponge that lives in Reefs more than 10 meters below the surface Two corals in the background: a sea fan, Iciligorgia schrammi, and a sea rod, Plexaurella nutans.

The sponges (Porifera) were long thought to have diverged from other animals early. The sponges or poriferans (from Latin porus "pore" and ferre "to bear" are Animals As mentioned above, they lack the complex organization found in most other phyla. Their cells are differentiated, but in most cases not organized into distinct tissues. Sponges are sessile and typically feed by drawing in water through pores. Sessile is a term in Biology with two distinct meanings In botany and medicine In Botany, sessile means "without a stalk Archaeocyatha, which have fused skeletons, may represent sponges or a separate phylum. The Archaeocyatha or archaeocyathids ("ancient cups" were Sessile However, a phylogenomic study in 2008 of 150 genes in 21 genera^[7] revealed that it is the Ctenophora or comb jellies which are the basal lineage of animals, at least among those 21 phyla. The phylum Ctenophora (tɨˈnɒfərə commonly known as comb jellies, is a phylum that includes the Sea gooseberry ( Pleurobrachia pileus) and The authors speculate that sponges—or at least those lines of sponges they investigated—are not so primitive, but may instead be secondarily simplified.

Among the other phyla, the Ctenophora and the Cnidaria, which includes sea anemones, corals, and jellyfish, are radially symmetric and have digestive chambers with a single opening, which serves as both the mouth and the anus. Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments Sea anemones are a group of water dwelling predatory animals of the order Actiniaria; they are named after the Anemone, a terrestrial Flower Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the Both have distinct tissues, but they are not organized into organs. In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument There are only two main germ layers, the ectoderm and endoderm, with only scattered cells between them. As such, these animals are sometimes called diploblastic. Diploblasty is a condition of the ovum in which there are two primary Germ layers the Ectoderm and Endoderm. The tiny Placozoans are similar, but they do not have a permanent digestive chamber. Trichoplax adhaerens is a simple balloon-like marine Animal with a body cavity filled with pressurized fluid

The remaining animals form a monophyletic group called the Bilateria. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor The Bilateria (ˌbaɪləˈtɪəriə are all animals having a bilateral symmetry, i For the most part, they are bilaterally symmetric, and often have a specialized head with feeding and sensory organs. The body is triploblastic, i. Triploblasty is a condition of the Blastula in which there are three primary Germ layers the Ectoderm, Mesoderm, and Endoderm. e. all three germ layers are well-developed, and tissues form distinct organs. The digestive chamber has two openings, a mouth and an anus, and there is also an internal body cavity called a coelom or pseudocoelom. The coelom (pronounced "seal-um" is a fluid filled cavity formed within the Mesoderm. There are exceptions to each of these characteristics, however - for instance adult echinoderms are radially symmetric, and certain parasitic worms have extremely simplified body structures. Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars)

Genetic studies have considerably changed our understanding of the relationships within the Bilateria. Most appear to belong to two major lineages: the Deuterostomes and Protostomes, which includes the Ecdysozoa, Platyzoa, and Lophotrochozoa. Deuterostomes (taxonomic term Deuterostomia; from the Greek "second mouth" are a superphylum of Animals They are a subtaxon of the Protostomia (from the Greek: mouth first) are a Taxon of Animals Together with the Deuterostomes and a few smaller phyla The Ecdysozoa (ˌɛkdɪsəˈzoʊə are a grouping of Protostome animals including the Arthropoda ( Insects, Chelicerata, Crustaceans The Platyzoa (ˌplætɨˈzoʊə are a group of Protostome animals proposed by Thomas Cavalier-Smith in 1998 The Lophotrochozoa (ləˌfɒtroʊkəˈzoʊə "crest-bearing animals" are one of three major groupings of Protostome animals In addition, there are a few small groups of bilaterians with relatively similar structure that appear to have diverged before these major groups. These include the Acoelomorpha, Rhombozoa, and Orthonectida. The Acoelomorpha are a Phylum of animals with planula-like features and formerly considered to be in Platyhelmintha, but recently classified by Jaume Rhombozoa, or Dicyemida, is a phylum of tiny Parasites that live in the renal appendages of Cephalopods Although the name Dicyemida Orthonectida is a small phylum of poorly-known Parasites of marine invertebrates that are among the simplest of multi-cellular organisms The Myxozoa, single-celled parasites that were originally considered Protozoa, are now believed to have developed from the Bilateria as well. The Myxozoa ( Etymology: Greek: myx- "slime" or "mucus" + zoa "animals" are a group of parasitic

Deuterostomes

Superb Fairy-wren, Malurus cyaneus

Deuterostomes differ from the other Bilateria, called protostomes, in several ways. The Superb Fairy-wren ( Malurus cyaneus) also known as Superb Blue-wren or colloquially as Blue wren, is a common and familiar Passerine bird Deuterostomes (taxonomic term Deuterostomia; from the Greek "second mouth" are a superphylum of Animals They are a subtaxon of the Protostomia (from the Greek: mouth first) are a Taxon of Animals Together with the Deuterostomes and a few smaller phyla In both cases there is a complete digestive tract. However, in protostomes the initial opening (the archenteron) develops into the mouth, and an anus forms separately. The primitive gut that forms during Gastrulation in the developing Blastula is known as the archenteron. In deuterostomes this is reversed. In most protostomes, cells simply fill in the interior of the gastrula to form the mesoderm, called schizocoelous development, but in deuterostomes it forms through invagination of the endoderm, called enterocoelic pouching. Invagination means to fold inward or to sheath In Biology, this can refer to a number of processes Deuterostomes also have a dorsal, rather than a ventral, nerve chord and their embryos undergo different cleavage.

All this suggests the deuterostomes and protostomes are separate, monophyletic lineages. The main phyla of deuterostomes are the Echinodermata and Chordata. Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars) Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates The former are radially symmetric and exclusively marine, such as starfish, sea urchins, and sea cucumbers. Starfish (also called sea stars) are any Echinoderms belonging to the class Asteroidea. Sea urchins are small globular spiny sea cat animals composing most of class Echinoidea. The sea cucumber (also known as trepang, bêche-de-mer, or ambiguously Sea slug) is an Echinoderm of the class Holothuroidea The latter are dominated by the vertebrates, animals with backbones. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes These include fish, amphibians, reptiles, birds, and mammals. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands

In addition to these, the deuterostomes also include the Hemichordata or acorn worms. Hemichordata is a phylum of worm-shaped marine Deuterostome Animals generally considered the sister group of the Echinoderms They date Although they are not especially prominent today, the important fossil graptolites may belong to this group. Graptolites (Graptolithina are Fossil colonial Animals known chiefly from the Upper Cambrian through the Lower Carboniferous ( Mississippian

The Chaetognatha or arrow worms may also be deuterostomes, but more recent studies suggest protostome affinities. Chaetognatha is a phylum of predatory marine worms that are a major component of Plankton worldwide

Ecdysozoa

Yellow-winged Darter, Sympetrum flaveolum

The Ecdysozoa are protostomes, named after the common trait of growth by moulting or ecdysis. The Yellow-winged Darter, Sympetrum flaveolum, is a Dragonfly found in Europe and mid and Northern Asia. The Ecdysozoa (ˌɛkdɪsəˈzoʊə are a grouping of Protostome animals including the Arthropoda ( Insects, Chelicerata, Crustaceans Ecdysis is the Molting of the Cuticula in Arthropods and related groups ( Ecdysozoa) The largest animal phylum belongs here, the Arthropoda, including insects, spiders, crabs, and their kin. Arthropods are Animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, " Joint " Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Spiders are Predatory Invertebrate Animals that have two body segments, eight legs no chewing mouth parts and no wings Crabs are decapod Crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (βραχύ / brachy All these organisms have a body divided into repeating segments, typically with paired appendages. Two smaller phyla, the Onychophora and Tardigrada, are close relatives of the arthropods and share these traits. The velvet worms ( Onychophora — literally "claw bearers" form a Clade within the Ecdysozoa and can be simply described as " Worms Tardigrades (commonly known as water bears) form the Phylum Tardigrada, part of the superphylum Ecdysozoa.

The ecdysozoans also include the Nematoda or roundworms, the second largest animal phylum. The nematodes or roundworms ( Phylum Nematoda from Greek (nema "thread" + -ode "like" are one of the most common Roundworms are typically microscopic, and occur in nearly every environment where there is water. A number are important parasites. Smaller phyla related to them are the Nematomorpha or horsehair worms, and the Kinorhyncha, Priapulida, and Loricifera. Nematomorpha (sometimes called Gordiacea, and commonly known as Horsehair worms or Gordian worms) are a Phylum of Parasitic Kinorhyncha (Gr κίνηω kīneō 'move' + ρυνχος rhynchos 'snout' is a phylum of small (1 mm or less marine pseudocoelomate Priapulida ( priapulid worms or penis worms, from Gr πριάπος priāpos ' Priapus ' + Lat Loricifera (from Latin, lorica, Corselet + Greek, φορη phora, bearing is a small Phylum of marine sediment-dwelling These groups have a reduced coelom, called a pseudocoelom.

The remaining two groups of protostomes are sometimes grouped together as the Spiralia, since in both embryos develop with spiral cleavage.

Platyzoa

Bedford's flatworm, Pseudobiceros bedfordi

The Platyzoa include the phylum Platyhelminthes, the flatworms. The Platyzoa (ˌplætɨˈzoʊə are a group of Protostome animals proposed by Thomas Cavalier-Smith in 1998 The flatworms (Phylum Platyhelminthes from the Greek πλατύ platy, meaning "flat" and ἕλμινς (root ἑλμινθ- helminth- These were originally considered some of the most primitive Bilateria, but it now appears they developed from more complex ancestors. ^[8]

A number of parasites are included in this group, such as the flukes and tapeworms. Parasitism is a type of symbiotic relationship between Organisms of different Species. Tapeworm is also an older name for a type of Computer virus. Cestoda is a class of Parasitic Flatworms commonly called Flatworms are acoelomates, lacking a body cavity, as are their closest relatives, the microscopic Gastrotricha. By the broadest definition a body cavity is any fluid filled space in a Multicellular organism. The gastrotrichs (from Greek γαστερ gaster "stomach" and θριξ thrix "hair" are a phylum of microscopic (0 ^[9]

The other platyzoan phyla are mostly microscopic and pseudocoelomate. By the broadest definition a body cavity is any fluid filled space in a Multicellular organism. The most prominent are the Rotifera or rotifers, which are common in aqueous environments. The rotifers make up a Phylum of microscopic and near-microscopic pseudocoelomate Animals They were first described by Rev They also include the Acanthocephala or spiny-headed worms, the Gnathostomulida, Micrognathozoa, and possibly the Cycliophora. The Acanthocephala ( Greek ακανθος akanthos, thorn + κεφαλη kephale, head is a phylum of Parasitic worms known as Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine Animals Most measure between 0 Limnognathia maerski is a microscopic animal discovered living in homothermic springs on Disko Island, Greenland in 1994 that was given Symbion is the name of a Genus of aquatic animals less than ½ mm wide found living attached to the bodies of cold-water lobsters ^[10] These groups share the presence of complex jaws, from which they are called the Gnathifera.

Lophotrochozoa

Roman snail, Helix pomatia

The Lophotrochozoa include two of the most successful animal phyla, the Mollusca and Annelida. Helix pomatia, Common names the Burgundy snail or Roman snail or edible snail, is a Species of large edible air-breathing The Lophotrochozoa (ləˌfɒtroʊkəˈzoʊə "crest-bearing animals" are one of three major groupings of Protostome animals Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 The annelids, collectively called Annelida (from Latin anellus "little ring" are a large phylum of Animals comprising ^[11][12] The former includes animals such as snails, clams, and squids, and the latter comprises the segmented worms, such as earthworms and leeches. The word snail is a Common name that can be used for almost all members of the Molluscan class Gastropoda which have coiled shells in the Clam is a word which can be used for all some or only a few Species of Bivalve Mollusks the word is a Common name which has Squid are marine Cephalopods of the order Teuthida, which comprises around 300 species Earthworm is the usual name for the largest members of Oligochaeta (which is either a class or subclass depending on the author in the phylum Annelida In classical Leeches are Annelids comprising the Subclass Hirudinea. There are freshwater terrestrial and marine leeches These two groups have long been considered close relatives because of the common presence of trochophore larvae, but the annelids were considered closer to the arthropods,^[13] because they are both segmented. A trochophore (ˈtrɒkəfɔər also spelled trocophore) is a type of marine Larva with several bands of Cilia. Now this is generally considered convergent evolution, owing to many morphological and genetic differences between the two phyla. Convergent evolution describes the acquisition of the same biological trait in unrelated lineages ^[14]

The Lophotrochozoa also include the Nemertea or ribbon worms, the Sipuncula, and several phyla that have a fan of cilia around the mouth, called a lophophore. Nemertea is a Phylum of Invertebrate Animals also known as ribbon worms or proboscis worms   The Sipuncula or Sipunculida, sipunculid worms or peanut worms, are a phylum containing 144-320 Species (estimates vary of bilaterally The lophophore (ˈlɒfəfɔər is a characteristic feeding organ possessed by three major groups of animals the Brachiopoda, Bryozoa, and Phoronida. ^[15] These were traditionally grouped together as the lophophorates. ^[16] but it now appears they are paraphyletic,^[17] some closer to the Nemertea and some to the Mollusca and Annelida. In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all ^[18][19] They include the Brachiopoda or lamp shells, which are prominent in the fossil record, the Entoprocta, the Phoronida, and possibly the Bryozoa or moss animals. Brachiopods (from Latin brachium, arm + New Latin -poda, foot are a small phylum of Benthic Invertebrates Also Entoprocta (Gr εντος entos inside + προκτος proktos anus is a phylum of small aquatic Animals ranging in size from 0 Phoronids (' Phoronida') commonly known as horseshoe worms, are a relatively small animal Phylum: twenty species are known in two genera Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some ^[20]

Model organisms

Main articles: Model organism and Animal testing

Because of the great diversity found in animals, it is more economical for scientists to study a small number of chosen species so that connections can be drawn from their work and conclusions extrapolated about how animals function in general. A model organism is a Species that is extensively studied to understand particular biological Phenomena, with the expectation that discoveries made Animal testing or animal research is the use of non-human Animals in scientific experimentation. Because they are easy to keep and breed, the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans have long been the most intensively studied metazoan model organisms, and were among the first lifeforms to be genetically sequenced. Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a two-winged insect that belongs to the Diptera, the order Caenorhabditis elegans (ˌsiːnoʊræbˈdaɪtɪs ˈɛlɪgænz is a free-living Nematode (roundworm about 1  mm in length which A model organism is a Species that is extensively studied to understand particular biological Phenomena, with the expectation that discoveries made This was facilitated by the severely reduced state of their genomes, but the double-edged sword here is that with many genes, introns and linkages lost, these ecdysozoans can teach us little about the origins of animals in general. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Introns, derived from the term "intragenic regions" and also called intervening sequence (IVS are DNA regions in a Gene that are not translated into Genetic linkage occurs when particular genetic loci or Alleles for genes are inherited jointly The extent of this type of evolution within the superphylum will be revealed by the crustacean, annelid, and molluscan genome projects currently in progress. Genome projects are Scientific endeavours that ultimately aim to determine the complete Genome sequence of an Organism (be it an Animal, a Analysis of the starlet sea anemone genome has emphasised the importance of sponges, placozoans, and choanoflagellates, also being sequenced, in explaining the arrival of 1500 ancestral genes unique to the Eumetazoa. The starlet sea anemone ( Nematostella vectensis) is a Species of Sea anemone native to the east coast of the United States with introduced populations The choanoflagellates are a group of free-living unicellular and colonial Flagellate Eukaryotes considered to be the closest living relatives of the Animals ^[21]

An analysis of the homoscleromorph sponge Oscarella carmela also suggests that the last common ancestor of sponges and the eumetazoan animals was more complex than previously assumed. ^[22]

Other model organisms belonging to the animal kingdom include the mouse (Mus musculus) and zebrafish (Danio rerio}. The House Mouse ( Mus musculus) is one of the most numerous species of the genus Mus commonly termed a Mouse. The zebrafish or zebra danio, Danio rerio, a Tropical Freshwater Fish belonging to the minnow family ( Cyprinidae)

History of classification

Carolus Linnaeus known as the father of modern taxonomy

Aristotle divided the living world between animals and plants, and this was followed by Carolus Linnaeus (Carl von Linné), in the first hierarchical classification. Carl Linnaeus (Latinized as Carolus Linnaeus, also known after his ennoblement as, May 23 new style (13 May old style 1707 who laid the foundations for Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. Plants are living Organisms belonging to the kingdom Plantae. Carl Linnaeus (Latinized as Carolus Linnaeus, also known after his ennoblement as, May 23 new style (13 May old style 1707 who laid the foundations for Since then biologists have begun emphasizing evolutionary relationships, and so these groups have been restricted somewhat. For instance, microscopic protozoa were originally considered animals because they move, but are now treated separately. Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular

In Linnaeus's original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Carl Linnaeus (Latinized as Carolus Linnaeus, also known after his ennoblement as, May 23 new style (13 May old style 1707 who laid the foundations for Vermes (" Worms quot is an obsolete Taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non- Arthropod Invertebrate Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Since then the last four have all been subsumed into a single phylum, the Chordata, whereas the various other forms have been separated out. Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates The above lists represent our current understanding of the group, though there is some variation from source to source.

See also

• Fauna
• List of animal names
• Animal behavior
• Animal rights
• List of animals by number of neurons
• Holocene extinction event

Notes

References

• Klaus Nielsen. Animal Evolution: Interrelationships of the Living Phyla (2nd edition). Oxford Univ. Press, 2001.
• Knut Schmidt-Nielsen. Animal Physiology: Adaptation and Environment. (5th edition). Cambridge Univ. Press, 1997.

External links

• Tree of Life Project
• Animal Diversity Web - University of Michigan's database of animals, showing taxonomic classification, images, and other information. The University of Michigan Ann Arbor ( U of M, U-M, UM or simply Michigan) is a top-ranked Coeducational public research
• ARKive - multimedia database of worldwide endangered/protected species and common species of UK.
• Scientific American Magazine (December 2005 Issue) - Getting a Leg Up on Land About the evolution of four-limbed animals from fish.