Overview
Animals are a major group of mostly multicellular, organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. Most animals are also heterotrophs, meaning they must ingest other organisms for sustenance.
Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago.
Etymology
The word "animal" comes from the Latin word animale, neuter of animalis, and is derived from anima, meaning vital breath or soul. In everyday colloquial usage, the word usually refers to non-human animals[citation needed]. The biological definition of the word refers to all members of the Kingdom Animalia including humans.[1]
Characteristics
Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and are multicellular[2] (although see Myxozoa), which separates them from bacteria and most protists. They are heterotrophic,[3] generally digesting food in an internal chamb er, which separates them from plants and algae (some sponges are capable of photosynthesis and nitrogen fixation though).[4] They are also distinguished from plants, algae, and fungi by lacking rigid cell walls.[5] All animals are motile,[6] if only at certain life stages. In most animals, embryos pass through a blastula stage, which is a characteristic exclusive to animals.
Structure
With a few exceptions, most notably the sponges (Phylum Porifera) and Placozoa, animals have bodies differentiated into separate tissues. These include muscles, which are able to contract and control locomotion, and ne rve tissue, which sends and processes signals. There is also typically an internal digestive chamber, with one or two openings. Animals with this sort of organization are called metazoans, or eumetazoans when the former is used for animals in general.
All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells, bones, and spicules. 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.
Reprod uction and Development
Nearly all animals undergo some form of sexual reproduction. They have a few specialized reproductive cells, which undergo meiosis to produce smaller motile spermatozoa or larger non-motile ova. These fuse to form zygotes, which develop into new individuals.
Many animals are also capable of asexual reproduction. This may take place through parthenogenesis, where fertile eggs are produced without mating, or in some cases through fragmentation.
A zygote initially develops into a hollow sphere, called a blastula, which undergoe s rearrangement and differentiation. 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. In most cases, a mesoderm also develops between them. These germ layers then differentiate to form tissues and organs.
Food and Energy Sourcing
Predation is a biological interaction where a predator (a heterotroph that i s hunting) feeds on its prey (the organism that is attacked). Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of the prey. The other main category of consumption is detritivory, the consumption of dead organic matter. It can at times be difficult to separate the two feeding behaviours, for example where parasitic species prey on a host organism and then lay their eggs on it for their offspring to feed on its decaying corpse. Selective pressures imposed on one another has led to an evolutionary arms race between prey and predator, resulting in various antipredator adaptations.
Most animals feed indirectly from the energy of sunlight. Plants use this energy to convert sunlight into simple sugars using a process known as photosynthesis. Starting with the molecules carbon dioxide (CO2) and water (H2O), photosynthesis converts the energy of sunlight into chemical energ y stored in the bonds of glucose (C6H12O6) and releases oxygen (O2). 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.
Animals who live close to hydrothermal vents and cold seeps on the ocean floor are not dependent on the energy of sunlight. Instead chemosynthetic archaea and bacteria form the base of the food chain.
Origin and Fossil Record
Animals are generally considered to have evolved from a flagellated eukaryote. Their closest known living relatives are the choanoflagellates, collared flagellates that hav e a morphology similar to the choanocytes of certain sponges. Molecular studies place animals in a supergroup called the opisthokonts, which also include the choanoflagellates, fungi and a few small parasitic protists. 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.
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. 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. It is still disputed whether this event, called the Cambrian explosion, represents a rapi d divergence between different groups or a change in conditions that made fossilization possible. 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 indicate the presence of triploblastic worm like metazoans roughly as large (about 5 mm wide) and complex as earthworms.[8] 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. The discovery that tracks very similar to these early trace fossils are produced today by the giant single-celled protist Gromia sphaerica casts further doubt on their interpretation as evidence of early animal evolution.[9][10]
Groups of Animals
Porifera
The sponges (Porifera) were long thought to have diverged from other animals early. 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. Archaeocyatha, which have fused skeletons, may represent sponges or a separate phylum. However, a phylogenomic study in 2008 of 150 genes in 21 genera[11] revealed that it is the Ctenophora or comb jellies which are the basal lineage of animals, at least among those 21 phyla. The authors speculate that sponges—or at least those lines of sponges they investigated—are not so primitive, b ut 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. Both have distinct tissues, but they are not organized into organs. 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. The tiny Placozoans are similar, but they do not have a permanent digestive chamber.
The remaining animals form a monophyletic group called the Bilateria. For the most part, they are bilaterally symmetric, and often have a specialized head with feeding and sensory organs. The body is triploblastic, i.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 b ody cavity called a coelom or pseudocoelom. 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.
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. 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 Myxozoa, single-celled parasites that were originally considered Protozoa, are now believed to have developed from the Bilateria as well.
Deuterostomes
Deuterostomes differ from the other Bilateria, called protostomes, in several ways. 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. 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. 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 lin eages. The main phyla of deuterostomes are the Echinodermata and Chordata. The former are radially symmetric and exclusively marine, such as starfish, sea urchins, and sea cucumbers. The latter are dominated by the vertebrates, animals with backbones. These include fish, amphibians, reptiles, birds, and mammals.
In addition to these, the deuterostomes also include the Hemichordata or acorn worms. Although they are not especially prominent today, the important fossil graptolites may belong to this group.
The Chaetognatha or arrow worms may also be deuterostomes, but more recent studies suggest protostome affinities.
Ecdysozoa
The Ecdysozoa are protostomes, named after the common trait of growth by moulting or ecdysis. The largest animal phylum belongs here, the Arthropoda, including insects, spiders, crabs, and their kin. 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 ecdysozoans also include the Nematoda or roundworms, the second largest animal phylum. 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. These groups have a reduced coelom, called a pseudocoelom.
The remaining two groups of proto stomes are sometimes grouped together as the Spiralia, since in both embryos develop with spiral cleavage.
Platyzoa
The Platyzoa include the phylum Platyhelminthes, the flatworms. These were originally considered some of the most primitive Bilateria, but it now appears they developed from more complex ancestors.[12]
A number of parasites are included in this group, such as the flukes and tapeworms. Flatworms are acoelomates, lacking a body cavity, as are their closest relatives, the microscopic G astrotricha.[13]
The other platyzoan phyla are mostly microscopic and pseudocoelomate. The most prominent are the Rotifera or rotifers, which are common in aqueous environments. They also include the Acanthocephala or spiny-headed worms, the Gnathostomulida, Micrognathozoa, and possibly the Cycliophora.[14] These groups share the presence of complex jaws, from which they are called the Gnathifera.
Lophotrochozoa
The Lophotrochozoa include two of the most successful animal phyla, the Mollusca and Annelida.[15][16] The former, which is the second-largest animal phylum, includes animals such as snails, clams, and squids, and the latter comprises the segmented worms, such as earthworms and 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,[17] because they are both segmented. Now this is generally considered convergent evolution, owing to many morphological and genetic differences between the two phyla.[18]
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.[19] These were traditionally grouped together as the lophophorates.[20] but it now appears they are paraphyletic,[21] some closer to the Nemertea and some to the Mollusca and Annelida.[22][23] 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.[24]
Model Organisms
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. 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 life-forms to be genetically sequenced. This was facilitated by the severely reduced state of their genomes, but the double-edged sword here is that with many genes, introns and linka ges lost, these ecdysozoans can teach us little about the origins of animals in general. The extent of this type of evolution within the superphylum will be revealed by the crustacean, annelid, and molluscan genome projects currently in progress. 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.[25]
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.[26]
Other model organisms belonging to the animal kingdom include the mouse (Mus musculus) and zebrafish (Danio rerio).
History of Classification
Aristotle divided the living world between animals and plants, and this was followed by Carolus Linnaeus (Carl von Linné), in the first hierarchical classification. 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.
In Linnaeus's original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, the Chordata, whereas the various other forms have been separated out. The above lists represent our current understanding of the group, though there is some variation from source to source.
Photos
Taxonomy
The Kingdom Animalia is a member of the Domain Eukaryota. Here is the complete "parentage" of Animalia:
The Kingdom Animalia is further organized into finer groupings including:
- Subkingdom (3): Bilateria · Chromobiota · Radiata
- Branch (2): Deuterostomia · Protostomia
- Infrakingdom (8): Chordonia · Coelenterata · Coelomopora · Ecdysozoa · Lophotrochozoa · Placozoa · Platyzoa · Spongiaria
- Phylum (49): Acanthocephala · Acoelomorpha · Annelida · Arthropoda · Brachiopoda · Bryozoa · Cephalorhyncha · Chaetognatha · Chordata · Cnidaria · Coelenterata · Ctenophora · Cycliophora · Dicyemida · Echinodermata · Echiura · Ectoprocta · Entoprocta · Euglenophycota · Gastrotricha · Gnathostomulida · Haptophyta · Hemichordata · Kinorhyncha · Loricifera · Mandibulata · Mollusca · Myxozoa · Nemata · Nematoda · Nematomorpha · Nemertea · Onychophora · Orthonectida · Phoronida · Placozoa · Platyhelminthes · Porifera · Prasinophyta · Priapulida · Protozoa · Rotifera · Sarcomastigophora · Sipuncula · Tardigrada · Tentaculata · Trilobozoa · Vendobionta · Vetulicolia
- Species: ZipcodeZoo has pages for 1,296,932 species and subspecies in the Kingdom Animalia.
Phyla
Acanthocephala
The Acanthocephala ( a?a????, akanthos, thorn + ?efa??, kephale, head) is a phylum of parasitic worms known as acanthocephales, thorny-headed worms, or spiny-headed worms, characterised by the presence of an evertable proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host. Acanthocephalans typically have complex life cycles, involving a number of hosts, including invertebrates, fishes, amphibians, birds, and mammals. About 1150 species have been described. [more]
Acoelomorpha
Annelida
The annelids, collectively called Annelida (from annelés "ringed ones", ultimately from Latin anellus "little ring"), are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches. They are found in marine environments from tidal zones to hydrothermal vents, in freshwater, and in moist terrestrial environments. Although most textbooks still use the traditional division into polychaetes (almost all marine), oligochaetes (which include earthworms) and leech-like species, research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes. In addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-groups of polychaetes. Annelids are considered members of the Lophotrochozoa, a "super-phylum" of protostomes that also includes molluscs, brachiopods, flatworms and nemerteans. [more]
Arthropoda
An arthropod is an that has an exoskeleton (external skeleton), a segmented body, and jointed attachments called appendages. Arthropods are animals belonging to the Phylum Arthropoda (from Greek ?????? arthron, "joint", and p?d?? podos "foot", which together mean "jointed feet"), and include the insects, arachnids, crustaceans, and others. Arthropods are characterized by their jointed limbs and cuticles, which are mainly made of a-chitin; the cuticles of crustaceans are also biomineralized with calcium carbonate. The rigid cuticle inhibits growth, so arthropods replace it periodically by molting. The arthropod body plan consists of repeated segments, each with a pair of appendages. It is so versatile that they have been compared to Swiss Army knives, and it has enabled them to become the most species-rich members of all ecological guilds in most environments. They have over a million described species, making up more than 80% of all described living species, and are one of only two animal groups that are really successful in dry environments – the other being the amniotes. They range in size from microscopic plankton up to forms a few meters long. [more]
Brachiopoda
Brachiopods (from brachium, arm + New Latin -poda, foot) are a small phylum of benthic invertebrates. Also known as lamp shells (or lampshells), "brachs" or Brachiopoda, they are sessile, two-valved, marine animals with an external morphology superficially resembling bivalves to which they are not closely related. Paleobiologists estimate that 99 percent of all documented brachiopod species are both fossils and extinct. [more]
Bryozoa
Bryozoans, also known as ectoprocts, are tiny colonial that generally build stony skeletons of calcium carbonate, superficially similar to coral (although some species lack any calcification in the colony and instead have a mucilaginous structure). Members of the phylum Bryozoa are known as "moss animals" or "moss animacules" (which is the literal translation of the Greek term ß?????a, "bryózoa") or as "sea mats". They generally prefer warm, tropical waters, but are known to occur worldwide. There are about 8,000 living species, with several times that number of fossil forms known. [more]
Cephalorhyncha
Scalidophora is a group of marine invertebrates, consisting of the three phyla Kinorhyncha, Priapulida, and Loricifera. The members of the group share a number of characteristics, including introvert larvae and moulting of the cuticle (ecdysis). Their closest relatives are thought to be the Panarthropoda, Nematoda and Nematomorpha; they are thus placed in the group Ecdysozoa. [more]
Chaetognatha
Chaetognatha, meaning hair-jaws, is a of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic and can attach to algae or rocks. They are found in all marine waters from surface tropical waters and shallow tide pools to the deep sea and polar regions. Most chaetognaths are transparent and are torpedo shaped. Some deep-sea species are orange. They range in size from 2 mm to 12 cm. The common term for the phylum is Arrow Worms. There are more than 120 modern species assigned to over 20 genera. Despite the limited diversity of species, the number of individuals is staggering. [more]
Chordata
Chordates ( Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates. They are united by having, at some time in their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. The phylum Chordata consists of three subphyla: Urochordata, represented by tunicates; Cephalochordata, represented by lancelets; and Craniata, which includes Vertebrata. The Hemichordata have been presented as a fourth chordate subphylum, but they are now usually treated as a separate phylum. Urochordate larvae have a notochord and a nerve cord but these are lost in adulthood. Cephalochordates have a notochord and a nerve cord but no brain or specialist sense organs, and a very simple circulatory system. Craniates are the only sub-phylum whose members have skulls. In all craniates except for Hagfish, the dorsal hollow nerve cord has been surrounded with cartilaginous or bony vertebrae and the notochord generally reduced; hence hagfish are not regarded as vertebrates. The chordates and three sister phyla, the Hemichordata, the Echinodermata and the Xenoturbellida, make up the deuterostomes, one of the two superphyla that encompass all fairly complex animals. [more]
Cnidaria
Cnidaria is a containing over 9,000 species of animals found exclusively in aquatic, mostly marine, environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. They have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both. Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Several free-swimming Cubozoa and Scyphozoa possess balance-sensing statocysts, and some have simple ey es. All cnidarians reproduce sexually. Many have complex lifecycles with asexual polyp stages and sexual medusae, but some omit either the polyp or the medusa stage. [more]
Coelenterata
Coelenterata is an obsolete long term encompassing two animal , the Ctenophora (comb jellies) and the Cnidaria (coral animals, true jellies, sea anemones, sea pens, and their allies). The name comes from the Greek "koilos" ("full bellied"), referring to the hollow body cavity common to these two phyla. They have very simple tissue organization, with only two layers of cells, external and internal. [more]
Ctenophora
The Ctenophora , commonly known as comb jellies, are a of animals that live in marine waters worldwide. Their most distinctive feature is the "combs", groups of cilia that they use for swimming, and they are the largest animals that swim by means of cilia — adults of various species range from a few millimeters to 1.5 meters (59 in) in size. Like cnidarians, their bodies consist of a mass of jelly with one layer of cells on the outside and another lining the internal cavity. In ctenophores these layers are two cells deep while those in cnidarians are only one cell deep. Ctenophores also resemble cnidarians in having a decentralized nerve net rather than a brain. Some authors combined ctenophores and cnidarians in one phylum, Coelenterata, as both groups rely on water flow though the body cavity for both digestion and respiration. Increasing awareness of the differences persuaded more recent authors to classify them in separate phyla. [more]
Cycliophora
Symbion is the name of a of aquatic animals, less than ½ mm wide, found living attached to the bodies of cold-water lobsters. They have sac-like bodies, and three distinctly different forms in different parts of their two-stage life-cycle. They appear so different from other animals that they were assigned their own, new phylum Cycliophora shortly after they were discovered in 1995. This was the first new phylum of multicelled organism to be discovered since the Loricifera in 1983. [more]
Dicyemida
Echinodermata
Echinoderms (Phylum Echinodermata) are a of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. Aside from the problematic Arkarua, the first definitive members of the phylum appeared near the start of the Cambrian period [more]
Echiura
The Echiura, or spoon worms, are a small group of animals. They are often considered to be a group of annelids, although they lack the segmented structure found in other members of that group, and so may also be treated as a separate phylum. However, phylogenetic analyses of DNA sequences place echiurans and pogonophorans within the Annelida. The Echiura fossilise poorly and the earliest known specimen is from the Upper Carboniferous (called the Pennsylvanian in North America). However, U-shaped fossil burrows that could be Echiuran have been found dating back to the Cambrian. [more]
Ectoprocta
Bryozoans, also known as ectoprocts, are tiny colonial that generally build stony skeletons of calcium carbonate, superficially similar to coral (although some species lack any calcification in the colony and instead have a mucilaginous structure). Members of the phylum Bryozoa are known as "moss animals" or "moss animacules" (which is the literal translation of the Greek term ß?????a, "bryózoa") or as "sea mats". They generally prefer warm, tropical waters, but are known to occur worldwide. There are about 8,000 living species, with several times that number of fossil forms known. [more]
Entoprocta
Entoprocta (Gr. e?t??, entos inside + p???t??, proktos anus) is a of small aquatic animals, ranging in size from 0.5 mm to 5.0 mm. They have a lophophore, and as their name suggests, are distinguished from other lophophorates by the position of the anus inside the ring of cilia rather than outside. Other names include goblet worm and kamptozoan. [more]
Euglenophycota
Gastrotricha
The gastrotrichs (from ?aste?, gaster "stomach" and ????, thrix "hair") are a phylum of microscopic (0.06-3.0 mm) animals abundant in fresh water and marine environments. Most fresh water species are part of the periphyton and benthos. Marine species are found mostly interstitially in between sediment particles. The Gastrotrich has the shortest life span of all animals, living for just 3 days. [more]
Gnathostomulida
Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine . Most measure between 0.5 and 1 mm long. Like flatworms they have a ciliated epidermis, but are unique in having but one cilium per cell. They have no body cavity, and no circulatory or respiratory system. Each gnathostomulid is simultaneously hermaphrodite, possessing an ovary and a testis. They are characterized by a specialized, muscular jaw, which they use to scrape smaller organisms off of the grains of sand that make up their anoxic seabed mud habitat. This bilaterally symmetrical pharynx with its complex cuticular mouth parts make them appear closely related to rotifers and their allies, together making up the Gnathifera. [more]
Haptophyta
The haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a of algae. [more]
Hemichordata
Hemichordata is a of worm-shaped marine deuterostome animals, generally considered the sister group of the echinoderms. They date back to the Lower or Middle Cambrian and include an important class of fossils called graptolites, most of which became extinct in the Carboniferous. They seem to have a primitive form of notochord, formed from a diverticulum of the foregut called a stomochord, but this is most likely the result of convergent evolution rather than homology with the vertebrate notochord. A hollow neural tube exists among some species (at least in early life), probably a primitive trait they share with the common ancestor of chordata and the rest of the deuterostomes. [more]
Kinorhyncha
Kinorhyncha (Gr. ?????, kineo 'move' + ??????, rhynchos 'snout') is a of small (1 mm or less) marine pseudocoelomate invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos. They are also called mud dragons. [more]
Loricifera
Mandibulata
In arthropods, the mandible is either of a pair of mouthparts used for biting, cutting and holding food. Mandibles are often simply referred to as jaws. The arthropods with mandibles form the clade Mandibulata, comprising the extant subphyla Myriapoda, Crustacea and Hexapoda. Mandibulata is currently believed to be the sister group to the rest of arthropods, the clade Arachnomorpha (Chelicerata+Trilobita). The mandibulates constitute the largest and most varied arthropod group. [more]
Mollusca
Molluscs are animals belonging to the Mollusca. There are around 93,000 recognized extant species, making it the largest marine phylum with about 23% of all named marine organisms. Representatives of the phylum live in a huge range of habitats including marine, freshwater, and terrestrial environments. Molluscs are a highly diverse group, in size, in anatomical structure, in behaviour and in habitat. [more]
Myxozoa
The Myxozoa (: Greek: myx- "slime" or "mucus" + zoa "animals") are a group of parasitic animals of aquatic environments. Over 1300 species have been described and many have a two-host lifecycle, involving a fish and an annelid worm or bryozoan. The average size of a Myxosporea spore usually ranges from 10µm to 20µm and Malacosporea up to 2mm. Infection occurs through valved spores. These contain one or two sporoblast cells and one or more polar capsules that contain filaments which anchor the spore to its host. The sporoblasts are then released as a motile form, called an amoebula, which penetrates the host tissues and develops into one or more multinucleate plasmodia. Certain nuclei later pair up, one engulfing another, to form new spores. [more]
Nemata
The "roundworms" or "nematodes" ( Nematoda) are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 80,000 have been described, of which over 15,000 are parasitic. It has been estimated that the total number of described and undescribed roundworms might be more than 500,000. Unlike cnidarians or flatworms, roundworms have a digestive system that is like a tube at both ends. [more]
Nematoda
The "roundworms" or "nematodes" ( Nematoda) are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 80,000 have been described, of which over 15,000 are parasitic. It has been estimated that the total number of described and undescribed roundworms might be more than 500,000. Unlike cnidarians or flatworms, roundworms have a digestive system that is like a tube at both ends. [more]
Nematomorpha
Nematomorpha (sometimes called Gordiacea, and commonly known as Horsehair worms or Gordian worms) are a of parasitic animals that are morphologically and ecologically similar to nematode worms, hence the name. They range in size from 1cm to 1 meter long, and 1 to 3 millimetres in diameter. Horsehair worms can be discovered in damp areas such as watering troughs, streams, puddles, and cisterns. The adult worms are free living, but the larvae are parasitic on beetles, cockroaches, Orthoptera and crustaceans. About 326 species are known and a conservative estimate suggests that there may be about 2000 species worldwide. The name "Gordian" stems from the legendary Gordian knot. This relates to the fact that nematomorpha often tie themselves in knots. [more]
Nemertea
Nemertea is a of invertebrate animals also known as ribbon worms or proboscis worms. Most of the 1,400 or so species are marine, with a few living in fresh water and a small number of terrestrial forms; they are found in all marine habits, and throughout the world's oceans. Nemerteans are named for Nemertes, one of the Nereids of Greek mythology, and alternative spellings for the phylum have included Nemertini and Nemertinea. Libbie Hyman named them Rhynchocoela, a name used primarily in North America but gradually abandoned since the 1980s. [more]
Onychophora
The velvet worms (Onychophora — literally "claw bearers") form a within the Ecdysozoa and can be simply described as "worms with legs". Most common in the Southern Hemisphere, they prey on smaller animals such as insects, which they catch by squirting a sticky slime. In modern zoology they are particularly renowned for their curious mating behaviour and for bearing live young. They are becoming increasingly popular in the 'exotic pets' trade, due to their bizarre appearance and eating habits. The Lobopodia, possible ancestors of velvet worms from the Cambrian period, are of great interest in paleontology. [more]
Orthonectida
Phoronida
Phoronids ('Phoronida'), commonly known as horseshoe worms, are a relatively small animal : twenty species are known, in two genera, Phoronis and Phoronopsis. Phoronids are worm-shaped, but with a gut that loops and exits the body near the mouth, instead of running the length of the animal, as in annelids (and many vertebrates). They are found in all oceans and seas (except the polar seas) and all species have wide geographical ranges and most are cosmopolitan. They occur at depths ranging to about 400 metres, but mainly between 0 to 70 metres. The life span is thought to be about one year. The adults secrete chitinous tubes in which to live. These tubes can be buried in the mud or sand that makes up the sea bed or can be resting on the surface of a rocky substrate, in this case they tend to live in colonies and their tubes become twisted around each other for support to form a large impenetrable mass. Some species can dissolve away holes in rocks such as limestone, calcareous seashells or even cement piers, they then live in these holes which they line with their secreted tubes. [more]
Placozoa
The Placozoa are a primitive form of . They are the simplest in structure of all non-parasitic multicellular animals (Metazoa). They are generally classified as a single species, Trichoplax adhaerens, although there is enough genetic diversity that it is likely that there are multiple, morphologically similar species. A common name does not yet exist for the taxon; the scientific name literally means "flat animals". [more]
Platyhelminthes
The flatworms, known in scientific literature as Platyhelminthes (from the p?at?, platy, meaning "flat" and ??µ??? (root: ??µ???-), helminth-, meaning worm) are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals. Unlike other bilaterians they have no body cavity, and no specialized circulatory and respiratory organs, which restricts them to flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. [more]
Porifera
Sponges are of the phylum Porifera . Their bodies consist of jelly-like mesohyl sandwiched between two thin layers of cells. While all animals have unspecialized cells that can transform into specialized cells, sponges are unique in having some specialized cells that can transform into other types, often migrating between the main cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems. Instead most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, and the shapes of their bodies are adapted to maximize the efficiency of the water flow. All are sessile aquatic animals and, although there are freshwater species, the great majority are marine (salt water) species, ranging from tidal zones to depths exceeding 8,800 metres (5.5 mi). While most of the approximately 9,000 known species feed on bacteria and other food particles in the water, some host photosynthesizing micro-organisms as endosymbionts and these alliances often produce more food and oxygen than they consume. A few species of sponge that live in food-poor environments have become carnivores that prey mainly on small crustaceans. [more]
Prasinophyta
Priapulida
Priapulida (priapulid worms or penis worms, from Gr. p???p??, priapos '' + Lat. -ul-, diminutive) are a phylum of marine worms with an extensible spiny proboscis. Priapulid fossils are known at least as far back as the Middle Cambrian. Their nearest relatives are probably Kinorhyncha and Loricifera with which they constitute the taxon Scalidophora. Besides arthropods and velvet worms, it is only among Priapulida that we can find members of the Ecdysozoa which are relatively large in size. They were likely major predators of the Cambrian period. There are 16 known species of Priapulid worms. [more]
Protozoa
Protozoa or protozoans (from p??t?? proton "first" and ??a zoa "animals"; singular protozoon; the word "protozoan" is originally an adjective, used as a noun) are microorganisms classified as unicellular eukaryotes. [more]
Rotifera
The rotifers make up a of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John Harris in 1696, and other forms were described by Anton van Leeuwenhoek in 1703. Most rotifers are around 0.1–0.5 mm long (although their size can range from 50µm to over 2 millimeters), and are common in freshwater environments throughout the world with a few saltwater species. Some rotifers are free swimming and truly planktonic, others move by inchworming along the substrate, and some are sessile, living inside tubes or gelatinous holdfasts that are attached to a substrate. About 25 species are colonial (e.g., Sinantherina semibullata), either sessile or planktonic. Rotifers play an important part of the freshwater zooplankton, being a major foodsource and with many species also contributing to the decomposition of soil. [more]
Sarcomastigophora
The Sarcomastigophora belongs to the Protist kingdom and it includes many unicellular or colonial, autotrophic, or heterotrophic organisms. The two main subphyla are Mastigophora and Sarcodina. A third is Opalinata. [more]
Sipuncula
The Sipuncula or Sipunculida, sipunculid worms or peanut worms, are a containing 144-320 species (estimates vary) of bilaterally symmetrical, unsegmented marine worms. Sipunculid worm jelly (???) is a delicacy in the town of Xiamen in Fujian province of China. [more]
Tardigrada
Tardigrades (commonly known as water bears) form the Tardigrada, part of the superphylum Ecdysozoa. They are microscopic, water-dwelling, segmented animals with eight legs. Tardigrades were first described by Johann August Ephraim Goeze in 1773 (kleiner Wasserbär = little water bear). The name Tardigrada means "slow walker" and was given by Lazzaro Spallanzani in 1777. The name water bear comes from the way they walk, reminiscent of a bear's gait. The biggest adults may reach a body length of 1.5 mm, the smallest below 0.1 mm. Freshly hatched larvae may be smaller than 0.05 mm. [more]
Tentaculata
Tentaculata is a class of . The common feature of this class is a pair of long, feathery, contractile tentacles, which can be retracted into specialised ciliated sheaths. In some species, the primary tentacles are reduced and they have smaller, secondary tentacles. The tentacles have colloblasts, which are sticky-tipped cells that trap small prey. [more]
Trilobozoa
Vendobionta
Vetulicolia
At least 3 species and subspecies belong to the Phylum Vetulicolia.
More info about the Phylum Vetulicolia may be found here.
References
- ^ "Animal". The American Heritage Dictionary (Forth ed.). Houghton Mifflin Company. 2006.
- ^ National Zoo. "Panda Classroom" (in English). http://nationalzoo.si.edu/Animals/GiantPandas/PandasForKids/classification/classification.htm. Retrieved on September 30 2007.
- ^ Jennifer Bergman. "Heterotrophs" (in English). http://www.windows.u car.edu/tour/link=/earth/Life/heterotrophs.html&edu=high. Retrieved on September 30 2007.
- ^ Douglas AE, Raven JA (January 2003). "Genomes at the interface between bacteria and organelles". Philosophical transactions of the Royal Society of London. Series B, Biological sciences 358 (1429): 5–17; discussion 517–8. doi:
- ^ Davidson, Michael W.. "Animal Cell Structure" (in English). http://micro.magnet.fsu.edu/cells/animalcell.html. Retrieved on September 20 2007.
- ^ Saupe, S.G. "Concepts of Biology" (in English). http://employees.csbsju.edu/SSAUPE/biol116/Zoology/digestion.htm. Retrieved on September 30 2007.
- ^ Monster fish crushed opposition with strongest bite ever, smh.com.au
- ^ Seilacher, A., Bose, P.K. and Pflüger, F. (1998). "Animals More Than 1 Billion Years Ago: Trace Fossil Evidence from India". Science 282 (5386): 80–83. doi:
- ^ Matz, Mikhail V.; Tamara M. Frank, N. Justin Marshall, Edith A. Widder and Sonke Johnsen (2008-12-09). "Giant Deep-Sea Protist Produces Bilaterian-like Traces". Current Biology (Elsevier Ltd) 18 (18): 1–6. doi:
- ^ Reilly, Michael (2008-11-20). "Single-celled giant upends early evolution". MSNBC. http://www.msnbc.msn.com/id/27827279/. Retrieved on 2008-12-05.
- ^ Dunn et al. 2008. "Broad phylogenomic sampling improves resolution of the animal tree of life". Nature 06614.
- ^ Ruiz-Trillo, I.; Ruiz-Trillo, Iñaki; Riutort, Marta; Littlewood, D. Timothy J.; Herniou, Elisabeth A.; Baguñà, Jaume (March 1999). "Acoel Flatworms: Earliest Extant Bilaterian Metazoans, Not Members of Platyhelminthes". Science 283 (5409): 1919–1923. doi:
- ^ Todaro, Antonio. "Gastrotricha: Overview". Gastrotricha: World Portal. University of Modena & Reggio Emilia. http://www.gastrotricha.unimore.it/overview.htm. Retrieved on 2008-01-26.
- ^ Kristensen, Reinhardt Møbjerg (July 2002). "An Introduction to Loricifera, Cycliophora, and Micrognathozoa". Integrative and Comparative Biology (Oxford Journals) 42 (3): 641–651. doi:
- ^ "Biodiversity: Mollusca". The Scottish Association for Marine Science. http://www.lophelia.org/lophelia/biodiv_6.htm. Retrieved on 2007-11-19.
- ^ Russell, Bruce J. (Writer), Denning, David (Writer). (2000). Branches on the Tree of Life: Annelids. [VHS]. BioMEDIA ASSOCIATES.
- ^ Eernisse, Douglas J.; Eernisse, Douglas J.; Albert, James S.; Ander son , Frank E. (1992). "Annelida and Arthropoda are not sister taxa: A phylogenetic analysis of spiralean metazoan morphology". Systematic Biology 41 (3): 305–330. doi:
- ^ Eernisse, Douglas J.; Kim, Chang Bae; Moon, Seung Yeo; Gelder, Stuart R.; Kim, Won (September 1996). "Phylogenetic Relationships of Annelids, Molluscs, and Arthropods Evidenced from Molecules and Morphology" ([dead link]–Scholar search). Journal of Molecular Evolution (New York: Springer) 43 (3): 207–215. doi:
- ^ [|Collins, Allen G.] (1995), The Lophophore, University of California Museum of Paleontology, http://www.ucmp.berkeley.edu/glossary/gloss7/lophophore.html
- ^ Adoutte, A.; Adoutte, André; Balavoine, Guillaume; Lartillot, Nicolas; Lespinet, Olivier; Prud'homme, Benjamin; de Rosa, Renaud (April, 25 2000). "The new animal phylogeny: Reliability and implications". Proceedings of the National Academy of Sciences 97 (9): 4453–4456. doi:
- ^ Passamaneck, Yale J. (2003), "Woods Hole Oceanographic Institution" (PDF), Molecular Phylogenetics of the Metazoan Clade Lophotrochozoa, pp. 124, http:/ /handle.dtic.mil/100.2/ADA417356
- ^ Adoutte, A.; Sundberg, Per; Turbevilleb, J. M.; Lindha, Susanne (September 2001). "Phylogenetic relationships among higher nemertean (Nemertea) taxa inferred from 18S rDNA sequences". Molecular Phylogenetics and Evolution 20 (3): 327–334. doi:
- ^ "The mitochondrial genome of the Sipunculid Phascolopsis gouldii supports its association with Annelida rather than Mollusca" (PDF). Molecular Biology and Evolution 19 (2): 127–137. February 2002. ISSN 0022-2844. PMID 11801741. http://mbe.oxfordjournals.org/cgi/reprint/19/2/127.pdf. Retrieved on 2007-11-19.
- ^ Nielsen, Claus (April 20 01). "Bryozoa (Ectoprocta: ‘Moss’ Animals)". Encyclopedia of Life Sciences (John Wiley & Sons, Ltd). doi:
- ^ N.H. Putnam, et al. (July 2007). "Sea anemone genome reveals ancestral eumetazoan gene repertoire and genomic organization". Science 317 (5834): 86–94. doi:
- ^ Wang, X.; Wang, Xiujuan; Lavrov Dennis V. (2006-10-27). "Mitochondrial Genome of the Homoscleromorph Oscarella carmela (Porifera, Demospongiae) Reveals Unexpected Complexity in the Common Ancestor of Sponges and Other Animals". Molecular Biology and Evolution (Oxford Journals) 24 (2): 363–373. doi:
Footnotes
- ^ "Animal". The American Heritage Dictionary (Forth ed.). Houghton Mifflin Company. 2006.
- ^ National Zoo. "Panda Classroom" (in English). http://nationalzoo.si.edu/Animals/GiantPandas/PandasForKids/classification/classification.htm. Retrieved on September 30 2007.
- ^ Jennifer Bergman. "Heterotrophs" (in English). http://www.windows.u car.edu/tour/link=/earth/Life/heterotrophs.html&edu=high. Retrieved on September 30 2007.
- ^ Douglas AE, Raven JA (January 2003). "Genomes at the interface between bacteria and organelles". Philosophical transactions of the Royal Society of London. Series B, Biological sciences 358 (1429): 5–17; discussion 517–8. doi:
- ^ Davidson, Michael W.. "Animal Cell Structure" (in English). http://micro.magnet.fsu.edu/cells/animalcell.html. Retrieved on September 20 2007.
- ^ Saupe, S.G. "Concepts of Biology" (in English). http://employees.csbsju.edu/SSAUPE/biol116/Zoology/digestion.htm. Retrieved on September 30 2007.
- ^ Monster fish crushed opposition with strongest bite ever, smh.com.au
- ^ Seilacher, A., Bose, P.K. and Pflüger, F. (1998). "Animals More Than 1 Billion Years Ago: Trace Fossil Evidence from India". Science 282 (5386): 80–83. doi:
- ^ Matz, Mikhail V.; Tamara M. Frank, N. Justin Marshall, Edith A. Widder and Sonke Johnsen (2008-12-09). "Giant Deep-Sea Protist Produces Bilaterian-like Traces". Current Biology (Elsevier Ltd) 18 (18): 1–6. doi:
- ^ Reilly, Michael (2008-11-20). "Single-celled giant upends early evolution". MSNBC. http://www.msnbc.msn.com/id/27827279/. Retrieved on 2008-12-05.
- ^ Dunn et al. 2008. "Broad phylogenomic sampling improves resolution of the animal tree of life". Nature 06614.
- ^ Ruiz-Trillo, I.; Ruiz-Trillo, Iñaki; Riutort, Marta; Littlewood, D. Timothy J.; Herniou, Elisabeth A.; Baguñà, Jaume (March 1999). "Acoel Flatworms: Earliest Extant Bilaterian Metazoans, Not Members of Platyhelminthes". Science 283 (5409): 1919–1923. doi:
- ^ Todaro, Antonio. "Gastrotricha: Overview". Gastrotricha: World Portal. University of Modena & Reggio Emilia. http://www.gastrotricha.unimore.it/overview.htm. Retrieved on 2008-01-26.
- ^ Kristensen, Reinhardt Møbjerg (July 2002). "An Introduction to Loricifera, Cycliophora, and Micrognathozoa". Integrative and Comparative Biology (Oxford Journals) 42 (3): 641–651. doi:
- ^ "Biodiversity: Mollusca". The Scottish Association for Marine Science. http://www.lophelia.org/lophelia/biodiv_6.htm. Retrieved on 2007-11-19.
- ^ Russell, Bruce J. (Writer), Denning, David (Writer). (2000). Branches on the Tree of Life: Annelids. [VHS]. BioMEDIA ASSOCIATES.
- ^ Eernisse, Douglas J.; Eernisse, Douglas J.; Albert, James S.; Ander son , Frank E. (1992). "Annelida and Arthropoda are not sister taxa: A phylogenetic analysis of spiralean metazoan morphology". Systematic Biology 41 (3): 305–330. doi:
- ^ Eernisse, Douglas J.; Kim, Chang Bae; Moon, Seung Yeo; Gelder, Stuart R.; Kim, Won (September 1996). "Phylogenetic Relationships of Annelids, Molluscs, and Arthropods Evidenced from Molecules and Morphology" ([dead link]–Scholar search). Journal of Molecular Evolution (New York: Springer) 43 (3): 207–215. doi:
- ^ [|Collins, Allen G.] (1995), The Lophophore, University of California Museum of Paleontology, http://www.ucmp.berkeley.edu/glossary/gloss7/lophophore.html
- ^ Adoutte, A.; Adoutte, André; Balavoine, Guillaume; Lartillot, Nicolas; Lespinet, Olivier; Prud'homme, Benjamin; de Rosa, Renaud (April, 25 2000). "The new animal phylogeny: Reliability and implications". Proceedings of the National Academy of Sciences 97 (9): 4453–4456. doi:
- ^ Passamaneck, Yale J. (2003), "Woods Hole Oceanographic Institution" (PDF), Molecular Phylogenetics of the Metazoan Clade Lophotrochozoa, pp. 124, http:/ /handle.dtic.mil/100.2/ADA417356
- ^ Adoutte, A.; Sundberg, Per; Turbevilleb, J. M.; Lindha, Susanne (September 2001). "Phylogenetic relationships among higher nemertean (Nemertea) taxa inferred from 18S rDNA sequences". Molecular Phylogenetics and Evolution 20 (3): 327–334. doi:
- ^ "The mitochondrial genome of the Sipunculid Phascolopsis gouldii supports its association with Annelida rather than Mollusca" (PDF). Molecular Biology and Evolution 19 (2): 127–137. February 2002. ISSN 0022-2844. PMID 11801741. http://mbe.oxfordjournals.org/cgi/reprint/19/2/127.pdf. Retrieved on 2007-11-19.
- ^ Nielsen, Claus (April 20 01). "Bryozoa (Ectoprocta: ‘Moss’ Animals)". Encyclopedia of Life Sciences (John Wiley & Sons, Ltd). doi:
- ^ N.H. Putnam, et al. (July 2007). "Sea anemone genome reveals ancestral eumetazoan gene repertoire and genomic organization". Science 317 (5834): 86–94. doi:
- ^ Wang, X.; Wang, Xiujuan; Lavrov Dennis V. (2006-10-27). "Mitochondrial Genome of the Homoscleromorph Oscarella carmela (Porifera, Demospongiae) Reveals Unexpected Complexity in the Common Ancestor of Sponges and Other Animals". Molecular Biology and Evolution (Oxford Journals) 24 (2): 363–373. doi:
Further Reading
- Klaus Nielsen. Animal Evolution: Interrelationships of the Living Phyla (2nd edition). Oxford University Press, 2001.
- Knut Schmidt-Nielsen. Animal Physiology: Adaptation and Environment. (5th edition). Cambridge University Press, 1997.
Sources
- The text on this page is licensed under the GNU Free Documentation License. It includes material from Wikipedia retrieved Thursday, August 13, 2009.
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