Salinella salve is a dubious species of simple animal that may not exist, but which some have named as the sole member of the phylum Monoblastozoa. It was discovered in 1892 by Johannes Frenzel in the salt pans of Argentina and cultivated in a laboratory by him; this animal has not been found since and its real existence is considered as doubtful. More organized than Protozoa, but still primitive multicellular organisms, they are characterised by their distinct anterior/posterior parts and being densely ciliated around the "mouth" and "anus", they have only one layer of cells. They reproduce asexually by transverse fission of their bodies. Although sexual reproduction was suspected, no evidence exists of it. Michael Schrödl from the Zoological State Collection in Munich is involved in a project to search for Salinella in Argentina. Monoblastozoa was granted the title of phylum after the recognition that Mesozoa was too diverse to be a phylum into itself
Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying the genetic instructions used in the growth, development and reproduction of all known organisms and many viruses. DNA and ribonucleic acid are nucleic acids; the two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases, a sugar called deoxyribose, a phosphate group; the nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules, with hydrogen bonds to make double-stranded DNA; the complementary nitrogenous bases are divided into two groups and purines. In DNA, the pyrimidines are cytosine. Both strands of double-stranded DNA store the same biological information.
This information is replicated as and when the two strands separate. A large part of DNA is non-coding, meaning that these sections do not serve as patterns for protein sequences; the two strands of DNA are thus antiparallel. Attached to each sugar is one of four types of nucleobases, it is the sequence of these four nucleobases along the backbone. RNA strands are created using DNA strands as a template in a process called transcription. Under the genetic code, these RNA strands specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells, DNA is organized into long structures called chromosomes. Before typical cell division, these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms store most of their DNA inside the cell nucleus as nuclear DNA, some in the mitochondria as mitochondrial DNA, or in chloroplasts as chloroplast DNA. In contrast, prokaryotes store their DNA only in circular chromosomes.
Within eukaryotic chromosomes, chromatin proteins, such as histones and organize DNA. These compacting structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA was first isolated by Friedrich Miescher in 1869, its molecular structure was first identified by Francis Crick and James Watson at the Cavendish Laboratory within the University of Cambridge in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Raymond Gosling, a post-graduate student of Rosalind Franklin. DNA is used by researchers as a molecular tool to explore physical laws and theories, such as the ergodic theorem and the theory of elasticity; the unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro- and nano-fabrication. Among notable advances in this field are DNA origami and DNA-based hybrid materials. DNA is a long polymer made from repeating units called nucleotides.
The structure of DNA is dynamic along its length, being capable of coiling into tight loops and other shapes. In all species it is composed of two helical chains, bound to each other by hydrogen bonds. Both chains are coiled around the same axis, have the same pitch of 34 angstroms; the pair of chains has a radius of 10 angstroms. According to another study, when measured in a different solution, the DNA chain measured 22 to 26 angstroms wide, one nucleotide unit measured 3.3 Å long. Although each individual nucleotide is small, a DNA polymer can be large and contain hundreds of millions, such as in chromosome 1. Chromosome 1 is the largest human chromosome with 220 million base pairs, would be 85 mm long if straightened. DNA does not exist as a single strand, but instead as a pair of strands that are held together; these two long strands coil in the shape of a double helix. The nucleotide contains both a segment of the backbone of a nucleobase. A nucleobase linked to a sugar is called a nucleoside, a base linked to a sugar and to one or more phosphate groups is called a nucleotide.
A biopolymer comprising multiple linked nucleotides is called a polynucleotide. The backbone of the DNA strand is made from alternating sugar residues; the sugar in DNA is 2-deoxyribose, a pentose sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings; these are known as the 3′-end, 5′-end carbons, the prime symbol being used to distinguish these carbon atoms from those of the base to which the deoxyribose forms a glycosidic bond. When imagining DNA, each phosphoryl is considered to "belong" to the nucleotide whose 5′ carbon forms a bond therewith. Any DNA strand therefore has one end at which there is a phosphoryl attached to the 5′ carbon of a ribose and another end a
Thomas Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow, is a Professor of Evolutionary Biology in the Department of Zoology, at the University of Oxford. His research has led to discovery of a number of unicellular organisms and definition of taxonomic positions, such as introduction of the kingdom Chromista, other groups including Chromalveolata, Opisthokonta and Excavata, he is well known for his system of classification of all organisms. Cavalier-Smith was born on 21 October 1942 in London, his parents were Mary Maude Cavalier-Smith. He was educated at Norwich School and Caius College and King's College London, he was under the supervision of Sir John Randall for his PhD thesis between 1964 and 1967. From 1967 to 1969, he was a guest investigator at Rockefeller University, he became Lecturer of biophysics at King's College London in 1969. He was promoted to Reader in 1982. In 1989 he was appointed Professor of botany at the University of British Columbia. In 1999, he joined the University of Oxford, becoming Professor of evolutionary biology in 2000.
Cavalier-Smith was elected Fellow of the Linnean Society of London in 1980, the Institute of Biology in 1983, the Royal Society of Arts in 1987, the Canadian Institute for Advanced Research in 1988, the Royal Society of Canada in 1997, the Royal Society of London in 1998. He received the International Prize for Biology from the Emperor of Japan in 2004, the Linnean Medal for Zoology in 2007, he was appointed Fellow of the Canadian Institute for Advanced Research between 1998 and 2007, Advisor of the Integrated Microbial Biodiversity of CIFAR. He won the 2007 Frink Medal of the Zoological Society of London. Cavalier-Smith has written extensively on the classification of protists. One of his major contributions to biology was his proposal of a new kingdom of life: the Chromista, he introduced a new group for primitive eukaryotes called the Chromalveolata, as well as Opisthokonta and Excavata. Though well known, many of his claims have been controversial and have not gained widespread acceptance in the scientific community to date.
His taxonomic revisions lead to changes in the overall classification of all life forms. Cavalier-Smith's first major classification system was the division of all organisms into eight kingdoms. In 1981, he proposed that by revising Robert Whittaker's Five Kingdom system, there could be eight kingdoms: Bacteria, Ciliofungi, Biliphyta, Viridiplantae and Euglenozoa. In 1993, he revised his system in the light of the general acceptance of Archaebacteria as separate group from Bacteria. In addition, some protists lacking mitochondria were discovered; as mitochondria were known to be the result of the endosymbiosis of a proteobacterium, it was thought that these amitochondriate eukaryotes were primitively so, marking an important step in eukaryogenesis. As a result, these amitochondriate protists were separated from the protist kingdom, giving rise to the, at the same time and kingdom Archezoa; this was known as the Archezoa hypothesis. The eight kingdoms became: Eubacteria, Archezoa, Chromista, Plantae and Animalia.
However, kingdom Archezoa is now defunct. He now assigns former members of the kingdom Archezoa to the phylum Amoebozoa. By 1998, Cavalier-Smith had reduced the total number of kingdoms from eight to six: Animalia, Fungi, Plantae and Bacteria, he had presented this simplified scheme for the first time on his 1981 paper and endorsed it in 1983. Five of Cavalier-Smith's kingdoms are classified as eukaryotes as shown in the following scheme: Eubacteria Neomura Archaebacteria Eukaryotes Kingdom Protozoa Unikonts Kingdom Animalia Kingdom Fungi Bikonts Kingdom Plantae Kingdom ChromistaThe kingdom Animalia was divided into four subkingdoms: Radiata, Myxozoa and Bilateria, he created three new animal phyla: Acanthognatha and Lobopoda and recognised a total of 23 animal phyla. Cavalier-Smith's 2003 classification scheme: Unikonts protozoan phylum Amoebozoa opisthokonts uniciliate protozoan phylum Choanozoa kingdom Fungi kingdom Animalia Bikonts protozoan infrakingdom Rhizaria phylum Cercozoa phylum Retaria protozoan infrakingdom Excavata phylum Loukozoa phylum Metamonada phylum Euglenozoa phylum Percolozoa protozoan phylum Apusozoa the chromalveolate clade kingdom Chromista protozoan infrakingdom Alveolata phylum Ciliophora phylum Miozoa kingdom Plantae Cavalier-Smith and his collaborators revised the classification in 2015, published it in PLOS ONE.
In this scheme they reintroduced the division of prokaryotes into two kingdoms and Archaea. This is based on the consensus in the Taxonomic Outline of Bacteria and Archaea and the Catalogue of Life. In 2006, Cavalier-Smith proposed that the last universal common ancestor to all life was a non-flagellate negibacterium with two membranes. University of Oxford Faculty Web Page for T. Cavalier-Smith T. Cavalier-Smith on
Molecular Biology and Evolution
Molecular Biology and Evolution is a monthly peer-reviewed scientific journal published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. It publishes work in the intersection of evolutionary biology; the founding editors-in-chief were Masatoshi Nei. According to the Journal Citation Reports, the journal has a 2017 Impact Factor of 10.217. Official website
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, 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 third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
A protist is any eukaryotic organism, not an animal, plant or fungus. The protists do not form clade, since they exclude certain eukaryotes. In some systems of biological classification, such as the popular five-kingdom scheme proposed by Robert Whittaker in 1969, the protists make up a kingdom called Protista, composed of "organisms which are unicellular or unicellular-colonial and which form no tissues". Besides their simple levels of organization, protists do not have much in common; when used, the term "protists" is now considered to mean a paraphyletic assemblage of similar-appearing but diverse taxa. In the classification system of Lynn Margulis, the term protist is reserved for microscopic organisms, while the more inclusive term Protoctista is applied to a biological kingdom that includes certain large multicellular eukaryotes, such as kelp, red algae and slime molds. Others use the term protist more broadly, to encompass both microbial eukaryotes and macroscopic organisms that do not fit into the other traditional kingdoms.
In cladistic systems, there are no equivalents to the taxa Protista or Protoctista, both terms referring to a paraphyletic group that spans the entire eukaryotic tree of life. In cladistic classification, the contents of Protista are distributed among various supergroups. "Protista","Protoctista" and "Protozoa" are considered obsolete. However, the term "protist" continues to be used informally as a catch-all term for unicellular eukaryotic microorganisms. For example, the word "protist pathogen" may be used to denote any disease-causing microbe, not bacteria, viroid, prion, or metazoa; the term protista was first used by Ernst Haeckel in 1866. Protists were traditionally subdivided into several groups based on similarities to the "higher" kingdoms such as: Protozoa These unicellular "animal-like" organisms are further sub-divided based on characteristics such as motility, such as the Flagellata, the Ciliophora, the amoeba, the Sporozoa. Protophyta These "plant-like" organisms are composed of unicellular algae.
Molds Slime molds and water molds are "fungus-like" organisms. Some protists, sometimes called ambiregnal protists, have been considered to be both protozoa and algae or fungi, names for these have been published under either or both of the ICN and the ICZN. Conflicts, such as these – for example the dual-classification of Euglenids and Dinobryons, which are mixotrophic – is an example of why the kingdom Protista was adopted; these traditional subdivisions based on superficial commonalities, have been replaced by classifications based on phylogenetics. Molecular analyses in modern taxonomy have been used to redistribute former members of this group into diverse and sometimes distantly related phyla. For instance, the water molds are now considered to be related to photosynthetic organisms such as Brown algae and Diatoms, the slime molds are grouped under Amoebozoa, the Amoebozoa itself includes only a subset of "Amoeba" group, significant number of erstwhile "Amoeboid" genera are distributed among Rhizarians and other Phyla.
However, the older terms are still used as informal names to describe the morphology and ecology of various protists. For example, the term protozoa is used to refer to heterotrophic species of protists that do not form filaments. Among the pioneers in the study of the protists, which were ignored by Linnaeus except for some genera were Leeuwenhoek, O. F. Müller, C. G. Ehrenberg and Félix Dujardin; the first groups used to classify microscopic organism were the Infusoria. In 1818, the German naturalist Georg August Goldfuss introduced the word Protozoa to refer to organisms such as ciliates and corals. After the cell theory of Schwann and Schleiden, this group was modified in 1848 by Carl von Siebold to include only animal-like unicellular organisms, such as foraminifera and amoebae; the formal taxonomic category Protoctista was first proposed in the early 1860s by John Hogg, who argued that the protists should include what he saw as primitive unicellular forms of both plants and animals. He defined the Protoctista as a "fourth kingdom of nature", in addition to the then-traditional kingdoms of plants and minerals.
The kingdom of minerals was removed from taxonomy in 1866 by Ernst Haeckel, leaving plants and the protists, defined as a “kingdom of primitive forms”. In 1938, Herbert Copeland resurrected Hogg's label, arguing that Haeckel's term Protista included anucleated microbes such as bacteria, which the term "Protoctista" did not. In contrast, Copeland's term included nucleated eukaryotes such as green algae and fungi; this classification was the basis for Whittaker's definition of Fungi, Animalia and Protista as the four kingdoms of life. The kingdom Protista was modified to separate prokaryotes into the separate kingdom of Monera, leaving
Orthonectida is a small phylum of poorly known parasites of marine invertebrates that are among the simplest of multi-cellular organisms. Members of this phylum are known as orthonectids; the adults are microscopic wormlike animals, consisting of a single layer of ciliated outer cells surrounding a mass of sex cells. They swim within the bodies of their hosts, which include flatworms, polychaete worms, bivalve molluscs, echinoderms, they are gonochoristic, with separate male and female individuals. When they are ready to reproduce, the adults leave the host, sperm from the males penetrate the bodies of the females to achieve internal fertilisation; the resulting zygote develops into a ciliated larva that escapes from the mother to seek out new hosts. Once it finds a host, the larva develops into a syncytial plasmodium larva. This, in turn, breaks up into numerous individual cells; the phylum consists of about 20 known species. The phylum is not divided into classes or orders, contains just two families.
Although described in 1877 as a class, sometimes characterized as an order of the phylum Mesozoa, recent study shows that orthonectids are quite different from the rhombozoans, the other group in Mesozoa. The genome of one species, Intoshia linei, has been sequenced; these animals are simplified spiralians. Their position in the phylogenetic tree has yet to be determined; the genome data confirms the earlier proposal that these organisms are spiralians based on their morphology. They appear to be related to the Annelida. Phylum Orthonectida Family Rhopaluridae Stunkard, 1937 Ciliocincta akkeshiensis Tajika, 1979 – Hokkaido, Japan.