In ecology, a habitat is the type of natural environment in which a particular species of organism lives. It is characterized by both biological features. A species' habitat is those places where it can find food, shelter and mates for reproduction; the physical factors are for example soil, range of temperature, light intensity as well as biotic factors such as the availability of food and the presence or absence of predators. Every organism has certain habitat needs for the conditions in which it will thrive, but some are tolerant of wide variations while others are specific in their requirements. A habitat is not a geographical area, it can be the interior of a stem, a rotten log, a rock or a clump of moss, for a parasitic organism it is the body of its host, part of the host's body such as the digestive tract, or a single cell within the host's body. Habitat types include polar, temperate and tropical; the terrestrial vegetation type may be forest, grassland, semi-arid or desert. Fresh water habitats include marshes, rivers and ponds, marine habitats include salt marshes, the coast, the intertidal zone, reefs, the open sea, the sea bed, deep water and submarine vents.
Habitats change over time. This may be due to a violent event such as the eruption of a volcano, an earthquake, a tsunami, a wildfire or a change in oceanic currents. Other changes come as a direct result of human activities; the introduction of alien species can have a devastating effect on native wildlife, through increased predation, through competition for resources or through the introduction of pests and diseases to which the native species have no immunity. The word "habitat" has been in use since about 1755 and derives from the Latin habitāre, to inhabit, from habēre, to have or to hold. Habitat can be defined as the natural environment of an organism, the type of place in which it is natural for it to live and grow, it is similar in meaning to a biotope. The chief environmental factors affecting the distribution of living organisms are temperature, climate, soil type and light intensity, the presence or absence of all the requirements that the organism needs to sustain it. Speaking, animal communities are reliant on specific types of plant communities.
Some plants and animals are generalists, their habitat requirements are met in a wide range of locations. The small white butterfly for example is found on all the continents of the world apart from Antarctica, its larvae feed on a wide range of Brassicas and various other plant species, it thrives in any open location with diverse plant associations. The large blue butterfly is much more specific in its requirements. Disturbance is important in the creation of biodiverse habitats. In the absence of disturbance, a climax vegetation cover develops that prevents the establishment of other species. Wildflower meadows are sometimes created by conservationists but most of the flowering plants used are either annuals or biennials and disappear after a few years in the absence of patches of bare ground on which their seedlings can grow. Lightning strikes and toppled trees in tropical forests allow species richness to be maintained as pioneering species move in to fill the gaps created. Coastal habitats can become dominated by kelp until the seabed is disturbed by a storm and the algae swept away, or shifting sediment exposes new areas for colonisation.
Another cause of disturbance is when an area may be overwhelmed by an invasive introduced species, not kept under control by natural enemies in its new habitat. Terrestrial habitat types include forests, grasslands and deserts. Within these broad biomes are more specific habitats with varying climate types, temperature regimes, soils and vegetation types. Many of these habitats grade into each other and each one has its own typical communities of plants and animals. A habitat may suit a particular species well, but its presence or absence at any particular location depends to some extent on chance, on its dispersal abilities and its efficiency as a coloniser. Freshwater habitats include rivers, lakes, ponds and bogs. Although some organisms are found across most of these habitats, the majority have more specific requirements; the water velocity, its temperature and oxygen saturation are important factors, but in river systems, there are fast and slow sections, pools and backwaters which provide a range of habitats.
Aquatic plants can be floating, semi-submerged, submerged or grow in permanently or temporarily saturated soils besides bodies of water. Marginal plants provide important habitat for both invertebrates and vertebrates, submerged plants provide oxygenation of the water, absorb nutrients and play a part in the reduction of pollution. Marine habitats include brackish water, bays, the open sea, the intertidal zone, the sea bed and deep / shallow water zones. Further variations include rock pools, sand banks, brackish lagoons and pebbly beaches, seagrass beds, all supporting their own flora and fauna; the benth
The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean in the south and is bounded by Asia and Australia in the west and the Americas in the east. At 165,250,000 square kilometers in area, this largest division of the World Ocean—and, in turn, the hydrosphere—covers about 46% of Earth's water surface and about one-third of its total surface area, making it larger than all of Earth's land area combined; the centers of both the Water Hemisphere and the Western Hemisphere are in the Pacific Ocean. The equator subdivides it into the North Pacific Ocean and South Pacific Ocean, with two exceptions: the Galápagos and Gilbert Islands, while straddling the equator, are deemed wholly within the South Pacific, its mean depth is 4,000 meters. The Mariana Trench in the western North Pacific is the deepest point in the world, reaching a depth of 10,911 meters; the western Pacific has many peripheral seas. Though the peoples of Asia and Oceania have traveled the Pacific Ocean since prehistoric times, the eastern Pacific was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and discovered the great "southern sea" which he named Mar del Sur.
The ocean's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favorable winds on reaching the ocean. He called it Mar Pacífico, which in both Portuguese and Spanish means "peaceful sea". Important human migrations occurred in the Pacific in prehistoric times. About 3000 BC, the Austronesian peoples on the island of Taiwan mastered the art of long-distance canoe travel and spread themselves and their languages south to the Philippines and maritime Southeast Asia. Long-distance trade developed all along the coast from Mozambique to Japan. Trade, therefore knowledge, extended to the Indonesian islands but not Australia. By at least 878 when there was a significant Islamic settlement in Canton much of this trade was controlled by Arabs or Muslims. In 219 BC Xu Fu sailed out into the Pacific searching for the elixir of immortality. From 1404 to 1433 Zheng He led expeditions into the Indian Ocean; the first contact of European navigators with the western edge of the Pacific Ocean was made by the Portuguese expeditions of António de Abreu and Francisco Serrão, via the Lesser Sunda Islands, to the Maluku Islands, in 1512, with Jorge Álvares's expedition to southern China in 1513, both ordered by Afonso de Albuquerque from Malacca.
The east side of the ocean was discovered by Spanish explorer Vasco Núñez de Balboa in 1513 after his expedition crossed the Isthmus of Panama and reached a new ocean. He named it Mar del Sur because the ocean was to the south of the coast of the isthmus where he first observed the Pacific. In 1519, Portuguese explorer Ferdinand Magellan sailed the Pacific East to West on a Spanish expedition to the Spice Islands that would result in the first world circumnavigation. Magellan called the ocean Pacífico because, after sailing through the stormy seas off Cape Horn, the expedition found calm waters; the ocean was called the Sea of Magellan in his honor until the eighteenth century. Although Magellan himself died in the Philippines in 1521, Spanish Basque navigator Juan Sebastián Elcano led the remains of the expedition back to Spain across the Indian Ocean and round the Cape of Good Hope, completing the first world circumnavigation in a single expedition in 1522. Sailing around and east of the Moluccas, between 1525 and 1527, Portuguese expeditions discovered the Caroline Islands, the Aru Islands, Papua New Guinea.
In 1542–43 the Portuguese reached Japan. In 1564, five Spanish ships carrying 379 explorers crossed the ocean from Mexico led by Miguel López de Legazpi, sailed to the Philippines and Mariana Islands. For the remainder of the 16th century, Spanish influence was paramount, with ships sailing from Mexico and Peru across the Pacific Ocean to the Philippines via Guam, establishing the Spanish East Indies; the Manila galleons operated for two and a half centuries, linking Manila and Acapulco, in one of the longest trade routes in history. Spanish expeditions discovered Tuvalu, the Marquesas, the Cook Islands, the Solomon Islands, the Admiralty Islands in the South Pacific. In the quest for Terra Australis, Spanish explorations in the 17th century, such as the expedition led by the Portuguese navigator Pedro Fernandes de Queirós, discovered the Pitcairn and Vanuatu archipelagos, sailed the Torres Strait between Australia and New Guinea, named after navigator Luís Vaz de Torres. Dutch explorers, sailing around southern Africa engaged in discovery and trade.
In the 16th and 17th centuries Spain considered the Pacific Ocean a mare clausum—a sea closed to other naval powers. As the only known entrance from the Atlantic, the Strait of Magellan was at times patrolled by fleets sent to prevent entrance of non-Spanish ships. On the western side of the Pacific Ocean the Dutch threatened the Spanish Philippines; the 18th cen
Santa Clara County, California
Santa Clara County the County of Santa Clara, is California's 6th most populous county, with a population of 1,781,642, as of the 2010 census. The county seat and largest city is San Jose, the 10th most populous city in the United States and California's 3rd most populous city. Home to Silicon Valley, Santa Clara County is an economic center for high technology and has the third highest GDP per capita in the world, according to the Brookings Institution; the county's concentration of wealth due to the tech industry, has made it the most affluent county on the West Coast of the United States and one of the most affluent places in America. Santa Clara County is part of the San Jose-Sunnyvale-Santa Clara, CA Metropolitan Statistical Area as well as the San Jose-San Francisco-Oakland, CA Combined Statistical Area. Located at the southern end of the San Francisco Bay, the urbanized Santa Clara Valley within Santa Clara County is known as Silicon Valley. Santa Clara is the most populous county in the San Francisco Bay Area and in Northern California, is one of the most affluent counties in the United States.
Santa Clara County is named for Mission Santa Clara, established in 1777 and was in turn named for Saint Clare of Assisi. Santa Clara County was one of the original counties of California, formed in 1850 at the time of statehood; the original inhabitants included the Ohlone, residing on Calaveras Creek. Part of the county's territory was given to Alameda County in 1853. In 1882, Santa Clara County tried to levy taxes upon property of the Southern Pacific Railroad within county boundaries; the result was the U. S. Supreme Court case of Santa Clara County v. Southern Pacific Railroad, 118 U. S. 394, in which the Court extended Due Process rights to artificial legal entities. In the early 20th Century, the area was promoted as the "Valley of the Heart's Delight" due to its natural beauty, including a significant number of orchards; the first major technology company to be based in the area was Hewlett-Packard, founded in a garage in Palo Alto in 1939. IBM selected San Jose as its West Coast headquarters in 1943.
Varian Associates, Fairchild Semiconductor, other early innovators were located in the county by the late 1940s and 1950s. The U. S. Navy had a large presence in the area and began giving large contracts to Silicon Valley electronics companies; the term "Silicon Valley" was coined in 1971. The trend accelerated in the 1980s and 1990s, agriculture has since been nearly eliminated from the northern part of the county. Today, Santa Clara County is the headquarters for 6500 high technology companies, including many of the largest tech companies in the world, among them hardware manufacturers AMD, Cisco Systems and Intel and consumer electronics companies Apple Inc. and Hewlett-Packard, internet companies eBay and Yahoo!. Most of what is considered to be Silicon Valley is located within the county, although some adjoining tech regions in San Mateo and Santa Cruz counties are considered a part of Silicon Valley. According to the U. S. Census Bureau, the county has a total area of 1,304 square miles, of which 1,290 square miles is land and 14 square miles is water.
Counties which border with Santa Clara County are, Santa Cruz County, San Mateo County, San Joaquin, Stanislaus and San Benito. Santa Clara County shared borders with Contra Costa, Monterey, Turlock counties until 1853, 1874, 1854 respectively; the San Andreas Fault runs along the Santa Cruz Mountains in the west of the county. Don Edwards San Francisco Bay National Wildlife Refuge In 1978, California Department of Fish and Game warden Henry Coletto urged the department to choose the Mount Hamilton area as one of California's relocation sites under a new statewide effort to restore tule elk. While other ranchers refused, tech pioneers Bill Hewlett and David Packard allowed Coletto and state biologists to translocate 32 tule elk from the Owens Valley in the eastern Sierra onto the 28,000-acre San Felipe Ranch, which the families jointly own, in the hills east of Morgan Hill. From the three original 1978–1981 translocations to the Mount Hamilton region of the Diablo Range, there are multiple herds in different locations including the Isabel Valley, San Antonio Valley, Livermore area, San Felipe Ranch, Metcalf Canyon, Coyote Ridge, Anderson Lake, surrounding areas.
As of 2012, an estimated 400 tule elk roam 1,875 square kilometres in northeastern Santa Clara County and southeastern Alameda County. As of 2017 there are four herds in the Coyote Ridge area visible from U. S. Highway 101, according to Craige Edgerton retired executive director of the Silicon Valley Land Conservancy and local naturalist Michael Hundt; the Nature Conservancy "Mount Hamilton Project" has acquired or put under conservation easement 100,000 acres of land towards its 500,000 acres goal for habitat conservation within a 1,200,000 acres area encompassing much of eastern Santa Clara County as well as portions of southern Alameda County, western Merced and Stanislaus Counties, northern San Benito County. Acquisitions to date include the 1,756-acre Rancho Cañada de Pala, straddling the Alameda Creek and Coyote Creek watersheds for California tiger salamander habitat.
Garter snake is a common name for the nearly harmless, small to medium-sized snakes belonging to the genus Thamnophis. Endemic to North America, species in the genus Thamnophis can be found from the subarctic plains of Canada to Central America; the common garter snake, Thamnophis sirtalis, is the state reptile of Massachusetts. With no real consensus on the classification of species of Thamnophis, disagreement between taxonomists and sources, such as field guides, over whether two types of snakes are separate species or subspecies of the same species is common. Garter snakes are related to the genus Nerodia, with some species having been moved back and forth between genera. Garter snakes are present throughout most of North America, they have a wide distribution due to their varied diets and adaptability to different habitats, with varying proximity to water. Garter snakes populate a variety of habitats, including forests, fields and lawns, but never far away from some form of water an adjacent wetland, stream, or pond.
This reflects the fact. Garter snakes have complex systems of pheromonal communication, they can find other snakes by following their pheromone-scented trails. Male and female skin pheromones are so different as to be distinguishable. However, male garter snakes sometimes produce both female pheromones. During the mating season, this ability fools other males into attempting to mate with them; this causes the transfer of heat to them in kleptothermy, an advantage after hibernation, allowing them to become more active. Male snakes giving off both male and female pheromones have been shown to garner more copulations than normal males in the mating balls that form at the den when females enter the mating melee. Garter snakes use the vomeronasal organ to communicate via pheromones through the tongue flicking behavior which gathers chemical cues in the environment. Upon entering the lumen of the organ, the chemical molecules will come into contact with the sensory cells which are attached to the neurosensory epithelium of the vomeronasal organ.
If disturbed, a garter snake may coil and strike, but it will hide its head and flail its tail. These snakes will discharge a malodorous, musky-scented secretion from a gland near the cloaca, they use these techniques to escape when ensnared by a predator. They will slither into the water to escape a predator on land. Birds of prey, egrets, cranes, raccoons and other snake species will eat garter snakes, with shrews and frogs eating the juveniles. Being heterothermic, like all reptiles, garter snakes bask in the sun to regulate their body temperature. During brumation, garter snakes occupy large, communal sites called hibernacula; these snakes will migrate large distances to brumate. Garter snakes, like all snakes, are carnivorous, their diet consists of any creature they are capable of overpowering: slugs, leeches, amphibians and rodents. When living near water, they will eat other aquatic animals; the ribbon snake in particular favors frogs eating them despite their strong chemical defenses. Food is swallowed whole.
Garter snakes adapt to eating whatever they can find, whenever, because food can be scarce or abundant. Although they feed on live animals, they will sometimes eat eggs. Garter snakes were long thought to be nonvenomous, but discoveries in the early 2000s revealed they do, in fact, produce a neurotoxic venom. Despite this, garter snakes cannot kill humans with the small amounts of comparatively mild venom they produce, they lack an effective means of delivering it, they do have enlarged teeth in the back of their mouths, but their gums are larger, the secretions of their Duvernoy's gland are only mildly toxic. Evidence suggests that garter snake and newt populations share an evolutionary link in their levels of tetrodotoxin resistance, implying coevolution between predator and prey. Garter snakes feeding upon toxic newts can retain those toxins in their liver for weeks, making those snakes poisonous as well as venomous. Garter snakes go into brumation, they stop eating for about two weeks beforehand to clear their stomachs of any food that would rot there otherwise.
Garter snakes begin mating as soon. During the mating season, the males mate with several females. In chillier parts of their range, male common garter snakes awaken from brumation first, giving themselves enough time to prepare to mate with females when they appear. Males come out of their dens and, as soon, surround them. Female garter snakes produce a specific pheromone that attracts male snakes in droves, sometimes leading to intense male to male competition and the formation of mating balls of up to 25 males per female. After copulation, a female leaves the den/mating area to find a place to give birth. Female garter snakes are able to store the male's sperm for years before fertilization; the young are incubated in the lower abdomen, at about the midpoint of the length of the female's body. Garter snakes are ovoviviparous. However, this is different from being viviparous, seen in mammals. Gestation is two to three months in most species; as few as three or as many as 80
Robert C. Stebbins
Robert Cyril Stebbins was an American herpetologist and illustrator known for his field guides and popular books as well as his studies of reptiles and amphibians. His Field Guide to Western Reptiles and Amphibians, first published in 1966, is still considered the definitive reference of its kind, owing to both the quality of the illustrations and the comprehensiveness of the text. A professor of zoology at the University of California, for over 30 years, he was the first curator of herpetology at the Museum of Vertebrate Zoology, a 1949 Guggenheim fellow, author of over 70 scientific articles, his discovery of the ring species phenomenon in Ensatina salamanders is now a textbook example of speciation, he performed extensive research on the parietal eye of reptiles. He produced nature films, supported science education in primary grades, organized conservation efforts that aided in the passing of the 1994 California Desert Protection Act. After retirement he continued to paint, collect field notes, write books.
Stebbins is commemorated in the scientific names of three species: Batrachoseps stebbinsi, the Tehachapi slender salamander. Robert Stebbins was born on March 31, 1915, in Chico, California, to parents Cyril Adelbert and Louise Stebbins, his father, born in Wisconsin of English descent, was an instructor at Chico State Normal School who had published on birds and agriculture, stressing the importance of gardening in education. The oldest of seven children, young Robert grew up learning about local birds and exploring the wildlife of Northern California, his mother, born in Switzerland and educated at the Normal School, instilled a sense of artistry in Robert, painting pictures for Robert and his siblings in her spare time. When Stebbins was seven, his family moved to the San Francisco Bay Area, where his father worked on agricultural curriculum for children and taught at the University of California, Berkeley. Around the age of nine, his family moved to Southern California, living first in Pomona in Sherman Oaks, Los Angeles.
Stebbins spent time hiking in the nearby Santa Monica Mountains, exploring the wildlife and amassing a collection of bird and mammal specimens which he prepared and mounted himself. Stebbins attended North Hollywood High School, where his father taught agriculture. Robert graduated in 1933, he discovered his artistic talents around sixteen years old. His early work consisted of cartoons: he drew illustrations on classmates' clothing and contributed cartoons to youth magazines, winning several awards. Shortly after graduating high school, Stebbins enrolled in the University of California, Los Angeles, he majored in civil engineering, thinking it a better career option than biology, but became unhappy with the program. Struggling with poor performance and health issues related to congenital heart problems, he took a leave for year and a half. During his time in recuperation, he turned his attention back to natural history, was persuaded to return to UCLA by Raymond Cowles, a biology professor there.
Stebbins returned with enthusiasm despite the perceived lack of job security, remarking in 1985: "I was cautious because of the Great Depression, but I was determined to pursue biology if it meant standing on a corner with a tin cup." He graduated in 1940 with highest honors. After graduating, Stebbins split his time between a summer job as a naturalist at Lassen Volcanic National Park and pursuing graduate school at UCLA. Over the next few years he obtained teaching credentials in junior college, high school, elementary education. Stebbins planned to study birds, with an eye towards roadrunners, but felt the field of ornithology was too crowded, while herpetology, the study of reptiles and amphibians, offered more opportunities for new research. Cowles became his graduate advisor; the main focus of Stebbins' graduate research was the biology of fringe-toed lizards, a group of sand-dwelling lizards of the American Southwest. For his master's degree he studied the anatomical structure of the nasal passages of the lizards, documenting in detail the looped, horseshoe-shaped structure of the nasal passages that functions as a u-trap, preventing sand grains from being inhaled while the lizards lay buried at the sand's surface.
His Ph. D dissertation further explored the anatomical and physiological adaptations of the lizards. During this time he published on the behavior of the sidewinder rattlesnake, with his father, produced two field guides to birds, providing illustrations to his father's text, their first book, What Bird is That?, was pressed in the family garage. Stebbins considered his father "a pioneer of sorts in the extensive use of drawings in teaching natural history," a tradition he strove to continue in his own works. On June 8, 1941, Stebbins married Anna-rose Cooper, who would type the text of all of Stebbins' field guides. Part of their honeymoon was spent camping in the Owens Valley of southeastern California. In 1945 Stebbins was hired an assistant professor of zoology at the University of California and became the first curator of herpetology at the Museum of Vertebrate Zoology, where he would remain throughout his career; the first faculty member to teach herpetology at Berkeley, he wrote new lab manuals, created the herpetology teaching collection, co-taught a popular course on vertebrate natural history.
Stebbins soon became interested in Ensatina salamanders, which occur from British Columbia to Baja California and are present in both the Sierra Nevada and Coast Ranges of
A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma
Algae is an informal term for a large, diverse group of photosynthetic eukaryotic organisms that are not closely related, is thus polyphyletic. Including organisms ranging from unicellular microalgae genera, such as Chlorella and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 m in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types, such as stomata and phloem, which are found in land plants; the largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example and the stoneworts. No definition of algae is accepted. One definition is that algae "have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells". Although cyanobacteria are referred to as "blue-green algae", most authorities exclude all prokaryotes from the definition of algae.
Algae constitute a polyphyletic group since they do not include a common ancestor, although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, the roots and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy; some unicellular species of green algae, many golden algae, euglenids and other algae have become heterotrophs, sometimes parasitic, relying on external energy sources and have limited or no photosynthetic apparatus.
Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery derived from cyanobacteria that produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago. The singular alga retains that meaning in English; the etymology is obscure. Although some speculate that it is related to Latin algēre, "be cold", no reason is known to associate seaweed with temperature. A more source is alliga, "binding, entwining"; the Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it. The Latinization, fūcus, meant the cosmetic rouge; the etymology is uncertain, but a strong candidate has long been some word related to the Biblical פוך, "paint", a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean.
It could be any color: black, green, or blue. Accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used; the name Fucus appears in a number of taxa. The algae contain chloroplasts. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events; the table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members; some retain plastids, but not chloroplasts. Phylogeny based on plastid not nucleocytoplasmic genealogy: Linnaeus, in Species Plantarum, the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are considered among algae.
In Systema Naturae, Linnaeus described the genera Volvox and Corallina, a species of Acetabularia, among the animals. In 1768, Samuel Gottlieb Gmelin published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the new binomial nomenclature of Linnaeus, it included elaborate illustrations of seaweed and marine algae on folded leaves. W. H. Harvey and Lamouroux were the first to divide macroscopic algae into four divisions based on their pigmentation; this is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae, brown algae, green algae, Diatomaceae. At this time, microscopic algae were discovered and reported by a different group of workers studying the Infusoria. Unlike macroalgae, which were viewed as plants, microalgae were considered animals because they are motile; the nonmotile microalgae were sometimes seen as stages of the lifecycle of plants, macroalgae, or animals. Although used as a taxonomic category in some pre-D