California is a state in the Pacific Region of the United States. With 39.6 million residents, California is the most populous U. S. the third-largest by area. The state capital is Sacramento; the Greater Los Angeles Area and the San Francisco Bay Area are the nation's second and fifth most populous urban regions, with 18.7 million and 9.7 million residents respectively. Los Angeles is California's most populous city, the country's second most populous, after New York City. California has the nation's most populous county, Los Angeles County, its largest county by area, San Bernardino County; the City and County of San Francisco is both the country's second-most densely populated major city after New York City and the fifth-most densely populated county, behind only four of the five New York City boroughs. California's $3.0 trillion economy is larger than that of any other state, larger than those of Texas and Florida combined, the largest sub-national economy in the world. If it were a country, California would be the 5th largest economy in the world, the 36th most populous as of 2017.
The Greater Los Angeles Area and the San Francisco Bay Area are the nation's second- and third-largest urban economies, after the New York metropolitan area. The San Francisco Bay Area PSA had the nation's highest GDP per capita in 2017 among large PSAs, is home to three of the world's ten largest companies by market capitalization and four of the world's ten richest people. California is considered a global trendsetter in popular culture, innovation and politics, it is considered the origin of the American film industry, the hippie counterculture, fast food, the Internet, the personal computer, among others. The San Francisco Bay Area and the Greater Los Angeles Area are seen as global centers of the technology and entertainment industries, respectively. California has a diverse economy: 58% of the state's economy is centered on finance, real estate services and professional, scientific and technical business services. Although it accounts for only 1.5% of the state's economy, California's agriculture industry has the highest output of any U.
S. state. California is bordered by Oregon to the north and Arizona to the east, the Mexican state of Baja California to the south; the state's diverse geography ranges from the Pacific Coast in the west to the Sierra Nevada mountain range in the east, from the redwood–Douglas fir forests in the northwest to the Mojave Desert in the southeast. The Central Valley, a major agricultural area, dominates the state's center. Although California is well-known for its warm Mediterranean climate, the large size of the state results in climates that vary from moist temperate rainforest in the north to arid desert in the interior, as well as snowy alpine in the mountains. Over time and wildfires have become more pervasive features. What is now California was first settled by various Native Californian tribes before being explored by a number of European expeditions during the 16th and 17th centuries; the Spanish Empire claimed it as part of Alta California in their New Spain colony. The area became a part of Mexico in 1821 following its successful war for independence but was ceded to the United States in 1848 after the Mexican–American War.
The western portion of Alta California was organized and admitted as the 31st state on September 9, 1850. The California Gold Rush starting in 1848 led to dramatic social and demographic changes, with large-scale emigration from the east and abroad with an accompanying economic boom; the word California referred to the Baja California Peninsula of Mexico. The name derived from the mythical island California in the fictional story of Queen Calafia, as recorded in a 1510 work The Adventures of Esplandián by Garci Rodríguez de Montalvo; this work was the fifth in a popular Spanish chivalric romance series that began with Amadis de Gaula. Queen Calafia's kingdom was said to be a remote land rich in gold and pearls, inhabited by beautiful black women who wore gold armor and lived like Amazons, as well as griffins and other strange beasts. In the fictional paradise, the ruler Queen Calafia fought alongside Muslims and her name may have been chosen to echo the title of a Muslim leader, the Caliph. It's possible.
Know ye that at the right hand of the Indies there is an island called California close to that part of the Terrestrial Paradise, inhabited by black women without a single man among them, they lived in the manner of Amazons. They were robust of body with great virtue; the island itself is one of the wildest in the world on account of the craggy rocks. Shortened forms of the state's name include CA, Cal. Calif. and US-CA. Settled by successive waves of arrivals during the last 10,000 years, California was one of the most culturally and linguistically diverse areas in pre-Columbian North America. Various estimates of the native population range from 100,000 to 300,000; the Indigenous peoples of California included more than 70 distinct groups of Native Americans, ranging from large, settled populations living on the coast to groups in the interior. California groups were diverse in their political organization with bands, villages, on the resource-rich coasts, large chiefdoms, such as the Chumash and Salinan.
Trade, intermarriage a
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals have mouthparts adapted to rasping or grinding. Horses and other herbivores have wide flat teeth that are adapted to grinding grass, tree bark, other tough plant material. A large percentage of herbivores have mutualistic gut flora that help them digest plant matter, more difficult to digest than animal prey; this flora is made up of cellulose-digesting bacteria. Herbivore is the anglicized form of a modern Latin coinage, cited in Charles Lyell's 1830 Principles of Geology. Richard Owen employed the anglicized term in an 1854 work on fossil skeletons. Herbivora is derived from the Latin herba meaning a small plant or herb, vora, from vorare, to eat or devour. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants and photosynthesizing bacteria.
More organisms that feed on autotrophs in general are known as primary consumers. Herbivory is limited to animals that eat plants. Fungi and protists that feed on living plants are termed plant pathogens, while fungi and microbes that feed on dead plants are described as saprotrophs. Flowering plants that obtain nutrition from other living plants are termed parasitic plants. There is, however, no single exclusive and definitive ecological classification of consumption patterns. In zoology, an herbivore is an animal, adapted to eat plant matter. Our understanding of herbivory in geological time comes from three sources: fossilized plants, which may preserve evidence of defence, or herbivory-related damage. Although herbivory was long thought to be a Mesozoic phenomenon, fossils have shown that within less than 20 million years after the first land plants evolved, plants were being consumed by arthropods. Insects fed on the spores of early Devonian plants, the Rhynie chert provides evidence that organisms fed on plants using a "pierce and suck" technique.
During the next 75 million years, plants evolved a range of more complex organs, such as roots and seeds. There is no evidence of any organism being fed upon until the middle-late Mississippian, 330.9 million years ago. There was a gap of 50 to 100 million years between the time each organ evolved and the time organisms evolved to feed upon them. Further than their arthropod status, the identity of these early herbivores is uncertain. Hole feeding and skeletonisation are recorded in the early Permian, with surface fluid feeding evolving by the end of that period. Herbivory among four-limbed terrestrial vertebrates, the tetrapods developed in the Late Carboniferous. Early tetrapods were large amphibious piscivores. While amphibians continued to feed on fish and insects, some reptiles began exploring two new food types and plants; the entire dinosaur order ornithischia was composed with herbivores dinosaurs. Carnivory was a natural transition from insectivory for medium and large tetrapods, requiring minimal adaptation.
In contrast, a complex set of adaptations was necessary for feeding on fibrous plant materials. Arthropods evolved herbivory in four phases, changing their approach to it in response to changing plant communities. Tetrapod herbivores made their first appearance in the fossil record of their jaws near the Permio-Carboniferous boundary 300 million years ago; the earliest evidence of their herbivory has been attributed to dental occlusion, the process in which teeth from the upper jaw come in contact with teeth in the lower jaw is present. The evolution of dental occlusion led to a drastic increase in plant food processing and provides evidence about feeding strategies based on tooth wear patterns. Examination of phylogenetic frameworks of tooth and jaw morphologes has revealed that dental occlusion developed independently in several lineages tetrapod herbivores; this suggests that evolution and spread occurred within various lineages. Herbivores form an important link in the food chain because they consume plants in order to digest the carbohydrates photosynthetically produced by a plant.
Carnivores in turn consume herbivores for the same reason, while omnivores can obtain their nutrients from either plants or animals. Due to a herbivore's ability to survive on tough and fibrous plant matter, they are termed the primary consumers in the food cycle. Herbivory and omnivory can be regarded as special cases of Consumer-Resource Systems. Herbivores come in all sizes in the animal kingdom, they include aquatic and non-aquatic vertebrates. They can be large, like an elephant. Many herbivores found living in close proximity to humans, such as rodents, cows and camels. Two herbivore feeding strategies are browsing. For a terrestrial mammal to be called a grazer, at least 90% of the forage has to be grass, for a browser at least 90% tree leaves and/or twigs. An intermediate feeding strategy is called "mixed-feeding". In their daily need to take up energy from forage, herbivores of different body mass may be selective in choosing their food. "Selective" means that herbivores may choose their forage source depending on, e.g. season or food avail
In biology, a hermaphrodite is an organism that has complete or partial reproductive organs and produces gametes associated with both male and female sexes. Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the "female" or "male." For example, the great majority of tunicates, pulmonate snails, opisthobranch snails and slugs are hermaphrodites. Hermaphroditism is found in some fish species and to a lesser degree in other vertebrates. Most plants are hermaphrodites; the term hermaphrodite has been used to describe ambiguous genitalia and gonadal mosaicism in individuals of gonochoristic species human beings. The word intersex has come into preferred usage for humans, since the word hermaphrodite is considered to be misleading and stigmatizing, as well as "scientifically specious and clinically problematic."A rough estimate of the number of hermaphroditic animal species is 65,000.
The percentage of animal species that are hermaphroditic is about 5%.. Most hermaphroditic species exhibit some degree of self-fertilization; the distribution of self-fertilization rates among animals is similar to that of plants, suggesting that similar processes are operating to direct the evolution of selfing in animals and plants. The term derives from the Latin: hermaphroditus, from Ancient Greek: ἑρμαφρόδιτος, translit. Hermaphroditos, which derives from Hermaphroditus, the son of Hermes and Aphrodite in Greek mythology. According to Ovid, he fused with the nymph Salmacis resulting in one individual possessing physical traits of male and female sexes; the word hermaphrodite entered the English lexicon as early as the late fourteenth century. Alexander ab Alexandro stated, using the term hermaphrodite, that the people who bore the sexes of both man and woman were regarded by the Athenians and the Romans as monsters, thrown into the sea at Athens and into the Tiber at Rome. Sequential hermaphrodites occur in species in which the individual is born as one sex, but can change into the opposite sex.
This contrasts simultaneous hermaphrodites, in which an individual may possess functional male and female genitalia. Sequential hermaphroditism is common in fish and many gastropods, some flowering plants. Sequential hermaphrodites can only change sex once. Sequential hermaphroditism can best be understood in terms of behavioral ecology and evolutionary life history theory, as described in the size-advantage mode first proposed by Michael T. Ghiselin which states that if an individual of a certain sex could increase its reproductive success after reaching a certain size, it would be to their advantage to switch to that sex. Sequential hermaphrodites can be divided into three broad categories: Protandry: Where an organism is born as a male, changes sex to a female. Example: The clownfish are colorful reef fish found living in symbiosis with sea anemones. One anemone contains a'harem', consisting of a large female, a smaller reproductive male, smaller non-reproductive males. If the female is removed, the reproductive male will change sex and the largest of the non-reproductive males will mature and become reproductive.
It has been shown that fishing pressure can change when the switch from male to female occurs, since fishermen prefer to catch the larger fish. The populations are changing sex at a smaller size, due to natural selection. Protogyny: Where the organism is born as a female, changes sex to a male. Example: wrasses are a group of reef fish in which protogyny is common. Wrasses have an uncommon life history strategy, termed diandry. In these species, two male morphs exists: a terminal phase male. Initial phase males do not spawn in groups with other females, they are not territorial. They are female mimics. Terminal phase males have a distinctively bright coloration. Individuals are born as males or females, but if they are born males, they are not born as terminal phase males. Females and initial phase males can become terminal phase males; the most dominant female or initial phase male replaces any terminal phase male when those males die or abandon the group. Bidirectional Sex Changers: where an organism has female and male reproductive organs, but act as either female or male during different stages in life.
Example: Lythrypnus dalli are a group of coral reef fish in which bidirectional sex change occurs. Once a social hierarchy is established a fish changes sex according to its social status, regardless of the initial sex, based on a simple principle: if the fish expresses subordinate behavior it changes its sex to female, if the fish expresses dominant or not subordinate behavior the fish changes its sex to male. Dichogamy can have both conservation-related implications for humans, as mentioned above, as well as economic implications. For instance, groupers are favoured fish for eating in many Asian countries and are aquacultured. Since the adults take several
The red algae, or Rhodophyta, are one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest phyla of algae, containing over 7,000 recognized species with taxonomic revisions ongoing; the majority of species are found in the Florideophyceae, consist of multicellular, marine algae, including many notable seaweeds. 5% of the red algae occur in freshwater environments with greater concentrations found in the warmer area. There are no terrestrial species, assumed to be traced back to an evolutionary bottleneck where the last common ancestor lost about 25% of its core genes and much of its evolutionary plasticity; the red algae form a distinct group characterized by having eukaryotic cells without flagella and centrioles, chloroplasts that lack external endoplasmic reticulum and contain unstacked thylakoids, use phycobiliproteins as accessory pigments, which give them their red color. Red algae store sugars as floridean starch, a type of starch that consists of branched amylopectin without amylose, as food reserves outside their plastids.
Most red algae are multicellular, macroscopic and reproduce sexually. The red algal life history is an alternation of generations that may have three generations rather than two. Chloroplasts evolved following an endosymbiotic event between an ancestral, photosynthetic cyanobacterium and an early eukarytoic phagotroph; this event resulted in the origin of the red and green algae, the glaucophytes, which make up the oldest evolutionary lineages of photosynthetic eukaryotes. A secondary endosymbiosis event involving an ancestral red alga and a heterotrophic eukaryote resulted in the evolution and diversification of several other photosynthetic lineages such as Cryptophyta, Stramenopiles, Centrohelids and Telonemi; the coralline algae, which secrete calcium carbonate and play a major role in building coral reefs, belong here. Red algae such as dulse and laver are a traditional part of European and Asian cuisines and are used to make other products such as agar and other food additives. Unicellular members of the Cyanidiophyceae are thermoacidophiles and are found in sulphuric hot springs and other acidic environments.
The remaining taxa are found in freshwater environments. Most rhodophytes are marine with a worldwide distribution, are found at greater depths compared to other seaweeds because of dominance in certain pigments within their chloroplasts; some marine species are found on sandy shores, while most others can be found attached to rocky substrata. Freshwater species account for 5% of red algal diversity, but they have a worldwide distribution in various habitats. A few freshwater species are found in black waters with sandy bottoms and fewer are found in more lentic waters. Both marine and freshwater taxa are represented by free-living macroalgal forms and smaller endo/epiphytic/zoic forms, meaning they live in or on other algae and animals. In addition, some marine species have adopted a parasitic lifestyle and may be found on or more distantly related red algal hosts. In the system of Adl et al. 2005, the red algae are classified in the Archaeplastida, along with the glaucophytes and green algae plus land plants.
The authors use a hierarchical arrangement. No subdivisions are given. However, other studies have suggested; as of January 2011, the situation appears unresolved. Below are other published taxonomies of the red algae using molecular and traditional alpha taxonomic data. If one defines the kingdom Plantae to mean the Archaeplastida, the red algae will be part of that kingdom If Plantae are defined more narrowly, to be the Viridiplantae the red algae might be considered their own kingdom, or part of the kingdom Protista. A major research initiative to reconstruct the Red Algal Tree of Life using phylogenetic and genomic approaches is funded by the National Science Foundation as part of the Assembling the Tree of Life Program; some sources place all red algae into the class "Rhodophyceae". A subphylum - Proteorhodophytina - has been proposed to encompass the existing classes Compsopogonophyceae, Porphyridiophyceae and Stylonematophyceae; this proposal was made on the basis of the analysis of the plastid genomes.
Over 7,000 species are described for the red algae, but the taxonomy is in constant flux with new species described each year. The vast majority of these are marine with about 200; some examples of species and genera of red algae are: Cyanidioschyzon merolae, a primitive red alga Atractophora hypnoides Gelidiella calcicola Lemanea, a freshwater genus Palmaria palmata, dulse Schmitzia
Spiny lobsters known as langustas, langouste, or rock lobsters, are a family of about 60 species of achelate crustaceans, in the Decapoda Reptantia. Spiny lobsters are especially in Australia, New Zealand, South Africa, the Bahamas, called crayfish, sea crayfish, or crawfish, terms which elsewhere are reserved for freshwater crayfish; the furry lobsters were separated into a family of their own, the Synaxidae, but are considered members of the Palinuridae. The slipper lobsters are their next-closest relatives, these two or three families make up the Achelata. Genera of spiny lobsters include Palinurus and a number of anagrams thereof: Panulirus, etc. In total, 12 extant genera are recognised, containing around 60 living species: Although they superficially resemble true lobsters in terms of overall shape and having a hard carapace and exoskeleton, the two groups are not related. Spiny lobsters can be distinguished from true lobsters by their long, spiny antennae, by the lack of chelae on the first four pairs of walking legs, although the females of most species have a small claw on the fifth pair, by a specialized larval phase called phyllosoma.
True lobsters have much smaller antennae and claws on the first three pairs of legs, with the first being enlarged. Spiny lobsters have a compressed carapace, lacking any lateral ridges, their antennae lack the flattened exopod of the antenna. This is fused to the epistome; the flagellum, at the top of the antenna, is stout and long. The ambulatory legs end in claws; the fossil record of spiny lobsters has been extended by the discovery in 1995 of a 110-million-year-old fossil near El Espiñal in Chiapas, Mexico. Workers from the National Autonomous University of Mexico have named the fossil Palinurus palaecosi, report that it is closest to members of the genus Palinurus living off the coasts of Africa. Spiny lobsters are found in all warm seas, including the Caribbean and the Mediterranean Sea, but are common in Australasia, where they are referred to as crayfish or sea crayfish, in South Africa. Spiny lobsters tend to live in crevices of rocks and coral reefs, only venturing out at night to seek snails, sea-hares, crabs, or sea urchins to eat.
Sometimes, they migrate in large groups in long files of lobsters across the sea floor. These lines may be more than 50 lobsters long. Spiny lobsters navigate using the smell and taste of natural substances in the water that change in different parts of the ocean, it was discovered that spiny lobsters can navigate by detecting the Earth's magnetic field. They keep together by contact. Potential predators may be deterred from eating spiny lobsters by a loud screech made by the antennae of the spiny lobsters rubbing against a smooth part of the exoskeleton. Spiny lobsters exhibit the social habit of being together; however recent studies indicate that healthy lobsters move away from infected ones, leaving the diseased lobsters to fend for themselves. Like true lobsters, spiny lobsters are an economically significant food source. Many spiny lobsters produce rasping sounds to repel predators by rubbing the "plectrum" at the base of the spiny lobster's antennae against a "file"; the noise is produced by frictional vibrations - sticking and slipping, similar to rubber materials sliding against hard surfaces.
While a number of insects use frictional vibration mechanisms to generate sound, this particular acoustic mechanism is unique in the animal kingdom. The system does not rely on the hardness of the exoskeleton, as many other arthropod sounds do, meaning that the spiny lobsters can continue to produce the deterrent noises in the period following a moult when they are most vulnerable; the stridulating organ is present in all but three genera in the family, its form can distinguish different species. Spiny lobster culture in Vietnam "Spiny Lobster Factsheet". Waitt Institute. Retrieved 2015-06-08. An audio recording of the rasp of a spiny lobster
Aplysia is a genus of medium-sized to large sea slugs sea hares, which are one clade of large sea slugs, marine gastropod mollusks. These benthic herbivorous creatures can become rather large compared with most other mollusks, they graze in tidal and subtidal zones of tropical waters in the Indo-Pacific Ocean. Aplysia species, when threatened release clouds of ink, it is believed in order to blind the attacker. Following the lead of Eric R. Kandel, the genus has been studied as a model organism by neurobiologists, because its gill and siphon withdrawal reflex, as studied in Aplysia californica, is mediated by electrical synapses, which allow several neurons to fire synchronously; this quick neural response is necessary for a speedy reaction to danger by the animal. Aplysia has only about 20,000 neurons, making it a favorite subject for investigation by neuroscientists. The'tongue' on the underside is controlled by only two neurons, which allowed complete mapping of the innervation network to be carried out.
In neurons that mediate several forms of long-term memory in Aplysia, the DNA repair enzyme poly ADP ribose polymerase 1 is activated. In all eukaryotic cells tested, the addition of polyADP-ribosyl groups to proteins occurs as a response to DNA damage, thus the finding of activation of PARP-1 during learning and its requirement for long-term memory was surprising. Cohen-Aromon et al. suggested that fast and transient decondensation of chromatin structure by polyADP-ribosylation enables the transcription needed to form long-term memory without strand-breaks in DNA. Subsequent to these findings in Aplysia, further research was done with mice and it was found that polyADP-ribosylation is required for long-term memory formation in mammals. In 2018, scientists from the University of California, Los Angeles, have shown that the behavioral modifications characteristic of a form of nonassociative long-term memory in Aplysia can be transferred by RNA. Operant conditioning is considered a form of associative learning.
Because operant conditioning involves intricate interaction between an action and a stimulus it is associated with the acquisition of compulsive behavior. The Aplysia species serve as an ideal model system for the physical studying of food-reward learning, due to “the neuronal components of parts of its ganglionic nervous system that are responsible for the generation of feeding movements.” As a result, Aplysia has been used in associative learning studies to derive certain aspects of feeding and operant conditioning in the context of compulsive behavior. In Aplysia, the primary reflex studied by scientists while studying operant conditioning is the gill and siphon withdrawal reflex; the gill and siphon withdrawal reflex allows the Aplysia to pull back its siphon and gill for protection. The links between the synapses during the gill and siphon withdrawal reflex are directly correlated with many behavioral traits in the Aplysia such as its habits and conditioning. Scientists have studied the conditioning of the Aplysia to identify correlations with conditioning in mammals regarding behavioral responses such as addiction.
Through experiments on the conditioning of the Aplysia, links have been discovered with the synaptic plasticity for reward functions involved in the trait of addiction within mammals. Synaptic plasticity is the idea that the synapses will become stronger or weaker depending on how much those specific synapses are used. Conditioning of these synapses can lead them to become stronger or weaker by causing the neurons to fire or not fire when influenced by a stimulus; the conditioning of behavioral traits is based on the idea of a reward function. A reward function is; the neurons will adapt to that stimulus, fire those neurons more even if the stimulus has a negative effect on the subject. In mammals, the reward function is controlled by ventral tegmental area dopamine neurons. During conditioning, the VTA dopamine neurons have an increased effect on the stimuli being conditioned, a decreased effect on the stimuli not being conditioned; this induces the synapses to form an expectation for reward for the stimuli being conditioned.
The properties of the synapses displayed in the tests on conditioning involving the Aplysia are proposed to be directly comparable to behavioral responses such as addiction in mammals. The California sea hare, Aplysia californica, is a simultaneous hermaphrodite. A. californica has the ability to store and digest allosperm and mates with multiple partners. Studies of multiple matings in A. californica have provided insights on how conflicts between the sexes are resolved. A potent sex pheromone, the water-borne protein attractin, is employed in promoting and maintaining mating in Aplysia. Attractin interacts with three other Aplysia protein pheromones in a binary fashion to stimulate mate attraction. Aplysia species were once thought to use ink to escape from predators, much like the octopus. Instead, recent research has made it clear that these sea slugs are able to produce and secrete multiple compounds within their ink, including the chemodeterrant Aplysioviolin and toxic substances such as ammonia for self-defense.
The ability of the Aplysia species to hold toxins within their bodies without poisoning itself is a result of the unique way
Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails that over evolutionary time have either lost their shells, or have lost their shells due to having a reduced or internal shell. The name "sea slug" is most applied to nudibranchs, as well as to a paraphyletic set of other marine gastropods without obvious shells. True sea slugs have enormous variation in body shape and size. Most are translucent; the bright colors of reef-dwelling species implies that these are under constant threat of predators, but the color can serve as a warning to other animals of the sea slug's toxic stinging cells or offensive taste. Like all gastropods, they have small razor-sharp teeth, called radulas. Most sea slugs have two pairs of tentacles on their head used for sense of smell, with a small eye at the base of each tentacle. Many have feathery structures on the back in a contrasting color, which act as gills.
All species of genuine sea slugs have a selected prey animal on which they specialize for food, including certain jellyfish, sea anemones, plankton as well as other species of sea slugs. The name "sea slug" is applied to numerous different evolutionary lineages of marine gastropod molluscs or sea snails those gastropods that are either not conchiferous or appear not to be. In evolutionary terms, losing the shell altogether, having a small internal shell, or having a shell so small that the soft parts of the animal cannot retract into it, are all features that have evolved many times independently within the class Gastropoda, on land and in the sea. Nudibranchs are a large group of marine gastropods; these may be the most familiar sort of sea slug, at least to scuba divers. In addition to nudibranchs, a number of other taxa of marine gastropods are often called "sea slugs". Within the various groups of gastropods that are called "sea slugs" numerous families are within the informal taxonomic group Opisthobranchia: The phrase "sea slug" is most applied to nudibranchs, many of which are brightly patterned and conspicuously ornate.
For two examples see the images of Nembrotha aurea and Glossodoris atromarginata within this article. The name "sea slug" is often applied to the sacoglossans, the so-called sap-sucking or solar-powered sea slugs. Another group of main gastropods that are labeled as "sea slugs" are the various families of headshield slugs and bubble snails within the clade Cephalaspidea; the sea hares, clade Aplysiomorpha, have a small, proteinaceous internal shell. The clades Thecosomata and Gymnosomata are small pelagic gastropods known as "sea butterflies" and "sea angels". Many species of sea butterflies retain their shells; these are known as "pteropods" but are sometimes called sea slugs. There is one group of "sea slugs" within the informal group Pulmonata: One unusual group of marine gastropods that are shell-less are the pulmonate species in the family Onchidiidae, within the clade Systellommatophora. Like many nudibranchs, Glaucus atlanticus can store and use stinging cells from its prey in its finger-like cerata.
Other species like the Pyjama slug Chromodoris quadricolor may use their striking colors to advertise their foul chemical taste. The lettuce sea slug has lettuce-like ruffles; this slug, like other Sacoglossa uses kleptoplasty, a process in which the slug absorbs chloroplasts from the algae it eats, uses "stolen" cells to photosynthesize sugars. The ruffles of the lettuce sea slug increase the slug's surface area, allowing the cells to absorb more light. Headshield slugs like the Chelidonura varians use their shovel-shaped heads to dig into the sand, where they spend most of their time; the shield protects sand from entering the mantle during burrowing. The largest species of sea hare, the California black sea hare, Aplysia vaccaria can reach a length of 75 centimetres and a weight of 14 kilograms. Most sea hares have several defenses.