Thursday, February 21, 2008

taken from Wikipedia 21Feb2008

Neomura is a speculative clade composed of the two domains of Archaea and Eukarya. The group was first proposed by Thomas Cavalier-Smith and its name means "new walls"; so called because it is thought to have evolved from Bacteria, and one of the major changes of this evolution was the replacement of peptidoglycan cell walls with other glycoproteins. The adjectival form is Neomuran, and a single individual from the group is called a Neomuran.

Animals, plants, fungi, and protists are eukaryotes (IPA: /ju?'kær??t/), organisms whose cells are organized into complex structures by internal membranes. The most characteristic membrane-bound structure is the nucleus. The presence of a nucleus gives these organisms their name: which comes from the Greek e?, meaning good/true, and ??????, meaning nut, referring to the nucleus. Many eukaryotic cells contain other membrane-bound organelles such as mitochondria, chloroplasts and Golgi bodies. Eukaryotes often have unique flagella made of microtubules in a 9+2 arrangement.
Cell division in eukaryotes is also different from organisms without a nucleus. This process involves separating the duplicated chromosomes, through movements directed by microtubules. There are two types of these division processes. In mitosis, one cell divides to produce two genetically-identical cells. In meiosis, which is required in sexual reproduction, one diploid cell (having two copies of each chromosome, one from each parent) undergoes a process of recombination between each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes), each of which has only a single complement of chromosomes, each one being a unique mix and match of the corresponding pair of parental chromosomes.
Eukaryotes appear to be monophyletic, and thus make up one of the three domains of life. The two other domains, bacteria and archaea (prokaryotes (without a nucleus)), share none of the previously-described features, though the eukaryotes do share some aspects of their biochemistry with the archaea, and, as such, are grouped with the archaea in the clade Neomura.

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan becomes fixed as they develop, usually early on in their development as embryos, although some undergo a process of metamorphosis later on in their life. Most animals are motile - they can move spontaneously and independently. Animals are heterotrophs - they are dependent on other organisms (e.g. plants) for sustenance.
Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago.
Eumetazoa is a clade comprising all major animal groups except sponges. Characteristics of eumetazoans include true tissues organized into germ layers, and an embryo that goes through a gastrula stage. The clade is usually held to contain at least Ctenophora, Cnidaria, and Bilateria. Whether mesozoans and placozoans belong is in dispute.

The Bilateria are all animals having a bilateral symmetry, i.e. they have a front and a back end, as well as an upside and downside. Radially symmetrical animals like jellyfish have a topside and downside, but no front and back. The bilateralians are a subregnum (a major group) of animals, including the majority of phyla; the most notable exceptions are the sponges and cnidarians. For the most part, Bilateria have bodies that develop from three different germ layers, called the endoderm, mesoderm, and ectoderm. From this they are called triploblastic. Nearly all are bilaterally symmetrical, or approximately so. The most notable exception is the echinoderms, which are radially symmetrical as adults, but are bilaterally symmetrical as larvae.
Except for a few primitive forms, the Bilateria have complete digestive tracts with separate mouth and anus. Most Bilateria also have a type of internal body cavity, called a coelom. It was previously thought that acoelomates gave rise to the other group, but there is some evidence now that in the main acoelomate phyla (flatworms and gastrotrichs) the absence could be secondary. The indirect evidence for the primitivity of the coelom is that the oldest known bilaterian animal, Vernanimalcula, had a structure that could be interpreted as a body cavity.

Kingdom: Animalia
Subkingdom: Eumetazoa (unranked)
Bilateria Hatschek, 1888
Phyla Orthonectida Rhombozoa Acoelomorpha Chaetognatha
Superphylum Deuterostomia Chordata Hemichordata Echinodermata Xenoturbellida Vetulicolia †
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

Deuterostomes (taxonomic term: Deuterostomia; from the Greek: "second mouth") are a superphylum of animals. They are a subtaxon of the Bilateria branch of the subregnum Eumetazoa, and are opposed to the protostomes. Deuterostomes are distinguished by their embryonic development; in deuterostomes, the first opening (the blastopore) becomes the anus, while in protostomes it becomes the mouth.
There are four living phyla of deuterostomes:
Phylum Chordata (vertebrates and their kin) Phylum Echinodermata (starfishes, sea urchins, sea cucumbers, etc.) Phylum Hemichordata (acorn worms and possibly graptolites) Phylum Xenoturbellida (2 species of worm-like animals)

Protostomes (from the Greek: mouth first) are a taxon of animals. Together with the deuterostomes and a few smaller phyla, they make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers. The major distinctions between deuterostomes and protostomes are found in embryonic development. In protostome development, the first opening in development, the blastopore, becomes the animal's mouth. In deuterostome development, the blastopore becomes the animal's anus. Protostomes have what is known as spiral cleavage which is determinate, meaning that the fate of the cells is determined as they are formed. This is in contrast to deuterostomes which have radial cleavage that is indeterminate.
Another contrast resides in the formation of the coelom. Protostomes are schizocoelomates, meaning a solid mass of the embryonic mesoderm splits to form a coelom. Deuterostomes are enterocoelous, meaning the folds of the archenteron form the coelom.
Current molecular data suggest that protostome animals can be divided into three major groups as follows: [ ?Ecdysozoa, Lophotrochozoa, Platyzoa?]
Nematoda, e.g. nematodes roundworms Mollusca, e.g. molluscs, snails, slugs, clams, octopus, squid Platyhelminthes, e.g. flatworms Arthropoda, e.g. spiders, insects, crustaceans Annelida, e.g. segmented worms, earthworms, leeches Of these, the latter two make up the Spiralia, including most animals where the embryo undergoes spiral cleavage.

The Ecdysozoa are a group of protostome animals, including the Arthropoda (insects, arachnids, crustaceans, et cetera), Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on trees constructed using 18S ribosomal RNA genes.[1] The group is also supported by morphological characters, and can be considered as including all animals that shed their exoskeleton (see ecdysis). Groups corresponding roughly to the Ecdysozoa had been proposed previously by Perrier in 1897 and Seurat in 1920 based on morphology alone.

The Lophotrochozoa ("crest-bearing animals") are one of two or three major groups of protostome animals. The taxon was introduced in the 1990s as a result of studies of the evolution of small-subunit ribosomal RNA (rRNA) supporting the monophyly of the phyla listed in the infobox shown at right.[1]
Trochozoans produce trochophore larvae, which have two bands of cilia around their middle. Previously these were treated together as the Trochozoa, together with the arthropods, which do not produce trochophore larvae but were considered close relatives of the annelids because they are both segmented. However, they show a number of important differences, and the arthropods are now placed separately among the Ecdysozoa.
The Lophophorata are united by the presence of a lophophore, a fan of ciliated tentacles surrounding the mouth, and so were treated together as the lophophorates. They are unusual in showing radial cleavage, and some authors considered them deuterostomes, before RNA trees placed them together with the trochozoans. The exact relationships between the different phyla are not entirely certain. However, it appears that neither the lophophorates nor the Trochozoa are monophyletic groups by themselves, but are mixed together.
Other phyla are included on the basis of molecular data.

The Platyzoa are a group of protostome animals proposed by Thomas Cavalier-Smith in 1998. Cavalier-Smith included in Platyzoa the Phylum Platyhelminthes or flatworms, and a new phylum, Acanthognatha, into which he gathered several previously described phyla of microscopic animals. Subsequent studies have supported Platyzoa as a clade, a monophyletic group of organisms with a common ancestor, while differing on the phyla included and on relationships within Platyzoa.
One current scheme places the following traditional phyla in Platyzoa:
Platyhelminthes Gastrotricha Gnathifera Rotifera Acanthocephala Gnathostomulida Micrognathozoa Cycliophora The Platyhelminthes and Gastrotricha are acoelomate. The other phyla have a pseudocoel, and share characteristics such as the structure of their jaws and pharynx, although these have been secondarily lost in the parasitic Acanthocephala. They form a monophyletic subgroup called the Gnathifera.
The Platyzoa are close relatives of the Lophotrochozoa, and are sometimes included in that group. Together the two make up the Spiralia.


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