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Donald I. Williamson
Donald Irving Williamson (8 January 1922, in Alnham, England – 29 January 2016, in Port Erin, Isle of Man) was a British planktologist and carcinologist. Education Williamson gained his first degree from the Newcastle division of Durham University in 1942. He earned his PhD from the same university in 1948, and a DSc from Newcastle University in 1972. He worked at the Port Erin Marine Laboratory of the University of Liverpool from 1948 to 1997, and published on Irish Sea plankton, crustacean behaviour and taxonomy, and crustacean larvae. Works He also published speculative works on hybridisation in evolution: ''Larvae and Evolution'' (1992, a book foreworded by Lynn Margulis and Alfred I. Tauber), ''The Origins of Larvae'' (2003, a revised and extended edition of ''Larvae and Evolution'', not to be confounded with his 2007 article of same title published in the magazine American Scientist), and some articles on the same subject. In ''Larvae and Evolution'' Williamson deve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alnham
Alnham is a hamlet and civil parish in Northumberland, England. It is about west of Alnwick, about from Scotland and is located on the south of a small tributary of the River Aln. The village stands on uneven ground, sloping from south to north, at the foot of the southern outliers of the Cheviot Hills. The River Aln flows eastward through the village from its source in the Cheviot Hills down to the coast. The layout of the village appears to have been dictated by the river. The estimated population taken at the 2011 Census was around 245. There is evidence of human occupation in Alnham and the surrounding areas dating from prehistoric times. The remains of a Medieval settlement, hillforts, and other historic buildings can still be found in the village today. Located near the border between England and Scotland, Alnham often suffered at the hands of Anglo-Scottish border conflict during its history. The economy of Alnham has been focussed on agriculture throughout its exi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Holometabolism
Holometabolism, also called complete metamorphosis, is a form of insect development which includes four life stages: egg, larva, pupa, and imago (or adult). Holometabolism is a synapomorphic trait of all insects in the superorder Endopterygota. Immature stages of holometabolous insects are very different from the mature stage. In some species the holometabolous life cycle prevents larvae from competing with adults because they inhabit different ecological niches. The morphology and behavior of each stage are adapted for different activities. For example, larval traits maximize feeding, growth, and development, while adult traits enable dispersal, mating, and egg laying. Some species of holometabolous insects protect and feed their offspring. Other insect developmental strategies include ametabolism and hemimetabolism. Developmental stages There are four general developmental stages, each with its own morphology and function. Egg The first stage of the insect life cycle is t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
National Academy Of Sciences
The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the National Academy of Medicine (NAM). As a national academy, new members of the organization are elected annually by current members, based on their distinguished and continuing achievements in original research. Election to the National Academy is one of the highest honors in the scientific field. Members of the National Academy of Sciences serve '' pro bono'' as "advisers to the nation" on science, engineering, and medicine. The group holds a congressional charter under Title 36 of the United States Code. Founded in 1863 as a result of an Act of Congress that was approved by Abraham Lincoln, the NAS is charged with "providing independent, objective advice to the nation on matters related to science and technology. ... to provide scien ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Body Plan
A body plan, ( ), or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many. This term, usually applied to animals, envisages a "blueprint" encompassing aspects such as symmetry, layers, segmentation, nerve, limb, and gut disposition. Evolutionary developmental biology seeks to explain the origins of diverse body plans. Body plans have historically been considered to have evolved in a flash in the Ediacaran biota; filling the Cambrian explosion with the results, and a more nuanced understanding of animal evolution suggests gradual development of body plans throughout the early Palaeozoic. Recent studies in animals and plants started to investigate whether evolutionary constraints on body plan structures can explain the presence of developmental constraints during embryogenesis such as the phenomenon referred to as phylotypic stage. History Among the pioneering zoologist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proceedings Of The National Academy Of Sciences
''Proceedings of the National Academy of Sciences of the United States of America'' (often abbreviated ''PNAS'' or ''PNAS USA'') is a peer-reviewed multidisciplinary scientific journal. It is the official journal of the National Academy of Sciences, published since 1915, and publishes original research, scientific reviews, commentaries, and letters. According to ''Journal Citation Reports'', the journal has a 2021 impact factor of 12.779. ''PNAS'' is the second most cited scientific journal, with more than 1.9 million cumulative citations from 2008 to 2018. In the mass media, ''PNAS'' has been described variously as "prestigious", "sedate", "renowned" and "high impact". ''PNAS'' is a delayed open access journal, with an embargo period of six months that can be bypassed for an author fee ( hybrid open access). Since September 2017, open access articles are published under a Creative Commons license. Since January 2019, ''PNAS'' has been online-only, although print issues are a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature for algae, fungi, and plants accepts the terms as equivalent. Depending on definitions, the animal kingdom Animalia contains about 31 phyla, the plant kingdom Plantae contains about 14 phyla, and the fungus kingdom Fungi contains about 8 phyla. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta. General description The term phylum was coined in 1866 by Ernst Haeckel from the Greek (, "race, stock"), related to (, "tribe, clan"). Haeckel noted that species constantly evolved into new species that seemed to retain few consistent features among themselves and therefore few features that distinguished them as a group ("a self-contained unity" ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echinus Esculentus
''Echinus esculentus'', the European edible sea urchin or common sea urchin, is a species of marine invertebrate in the Echinidae family. It is found in coastal areas of western Europe down to a depth of . It is considered "Near threatened" in the IUCN Red List of Threatened Species. Description ''E. esculentus'' is approximately spherical but slightly flattened at both poles. It is reddish or purplish with white tubercles and grows to about ten centimetres in diameter. The brittle, limy test is rigid and divided into five ambulacral areas separated by five inter-ambulacral areas. There are two rows of plates in each of these areas, making twenty rows of plates in total. The test is covered in spines each articulating with a tubercle. There is a dense covering of secondary spines and a smaller number of longer, primary spines, carried on each second or third ambulacral plate. The spines are blunt ended and usually white with purplish tips. There is a radially symmetrical patter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ascidia Mentula
''Ascidia mentula'' is a species of solitary tunicate. It is found in the north east Atlantic Ocean, the Mediterranean Sea and Black Sea. It occurs round the coasts of Britain but is seldom seen on the east coast of England or Scotland. Description ''Ascidia mentula'' has a tough leathery envelope or tunic composed partly of cellulose. The translucent tunic encloses a fluid-filled body with irregular bulges and two inconspicuous siphons. It is tall, bottle or flask-shaped with the oral (inlet) siphon at the tip and the six-lobed atrial siphon half to two thirds of the way down. The oral siphon has six to eight, often white-tipped, lobes and is surrounded by up to 100 branchial tentacles. It is usually red, pink or sometimes olive green in colour, and may be grey in deep water. It normally adheres to the substrate by the side opposite the atrial siphon. Distribution and habitat ''Ascidia mentula'' is native to the north eastern Atlantic Ocean, its range extending from Norway s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cambrian Explosion
The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil record. It lasted for about 13 – 25 million years and resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversification in other groups of organisms as well. Before early Cambrian diversification, most organisms were relatively simple, composed of individual cells, or small multicellular organisms, occasionally organized into colonies. As the rate of diversification subsequently accelerated, the variety of life became much more complex, and began to resemble that of today. Almost all present-day animal phyla appeared during this period, including the earliest chordates. A 2019 paper suggests that the timing should be expanded back to include the late Ediacaran, rather than just the n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Species (biology)
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. The most recent rigorous estimate for the total number of species of eukaryotes is between 8 and 8.7 million. However, only about 14% of these had been described by 2011. All species (except viruses) are given a two-part name, a "binomial". The first part of a binomial is the genus to which the species belongs. The second part is called the specific name or the specific epithet (in botanical nomenclature, also sometimes in zool ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chimera (genetics)
A genetic chimerism or chimera ( ) is a single organism composed of cells with more than one distinct genotype. In animals, this means an individual derived from two or more zygotes, which can include possessing blood cells of different blood types, subtle variations in form (phenotype) and, if the zygotes were of differing sexes, then even the possession of both female and male sex organs. Animal chimeras are produced by the merger of two (or more) embryos. In plant chimeras, however, the distinct types of tissue may originate from the same zygote, and the difference is often due to mutation during ordinary cell division. Normally, genetic chimerism is not visible on casual inspection; however, it has been detected in the course of proving parentage. Another way that chimerism can occur in animals is by organ transplantation, giving one individual tissues that developed from a different genome. For example, transplantation of bone marrow often determines the recipient's en ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature for algae, fungi, and plants accepts the terms as equivalent. Depending on definitions, the animal kingdom Animalia contains about 31 phyla, the plant kingdom Plantae contains about 14 phyla, and the fungus kingdom Fungi contains about 8 phyla. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta. General description The term phylum was coined in 1866 by Ernst Haeckel from the Greek (, "race, stock"), related to (, "tribe, clan"). Haeckel noted that species constantly evolved into new species that seemed to retain few consistent features among themselves and therefore few features that distinguished them as a group ("a self-contained unity" ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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