1.
Taxonomy (biology)
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Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate
2.
Animal
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Animals are multicellular, eukaryotic organisms of the kingdom Animalia. The animal kingdom emerged as a clade within Apoikozoa as the group to the choanoflagellates. Animals are motile, meaning they can move spontaneously and independently at some point in their lives and their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later in their lives. All animals are heterotrophs, they must ingest other organisms or their products for sustenance, most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals can be divided broadly into vertebrates and invertebrates, vertebrates have a backbone or spine, and amount to less than five percent of all described animal species. They include fish, amphibians, reptiles, birds and mammals, the remaining animals are the invertebrates, which lack a backbone. These include molluscs, arthropods, annelids, nematodes, flatworms, cnidarians, ctenophores, the study of animals is called zoology. The word animal comes from the Latin animalis, meaning having breath, the biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish, insects, and humans. Aristotle divided the world between animals and plants, and this was followed by Carl Linnaeus, in the first hierarchical classification. In Linnaeuss original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, in 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms, Metazoa and Protozoa. The protozoa were later moved to the kingdom Protista, leaving only the metazoa, thus Metazoa is now considered a synonym of Animalia. Animals have several characteristics that set apart from other living things. Animals are eukaryotic and multicellular, which separates them from bacteria and they are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at life stages. In most animals, embryos pass through a stage, which is a characteristic exclusive to animals. With a few exceptions, most notably the sponges and Placozoa and these include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals
3.
Chordate
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Chordates are deuterostomes, as during the embryo development stage the anus forms before the mouth. They are also bilaterally symmetric coelomates, in the case of vertebrate chordates, the notochord is usually replaced by a vertebral column during development, and they may have body plans organized via segmentation. There are also additional extinct taxa, the Vertebrata are sometimes considered as a subgroup of the clade Craniata, consisting of chordates with a skull, the Craniata and Tunicata compose the clade Olfactores. Of the more than 65,000 living species of chordates, the worlds largest and fastest animals, the blue whale and peregrine falcon respectively, are chordates, as are humans. Fossil chordates are known from at least as early as the Cambrian explosion, Hemichordata, which includes the acorn worms, has been presented as a fourth chordate subphylum, but it now is usually treated as a separate phylum. The Hemichordata, along with the Echinodermata, form the Ambulacraria, the Chordata and Ambulacraria form the superphylum Deuterostomia, composed of the deuterostomes. Attempts to work out the relationships of the chordates have produced several hypotheses. All of the earliest chordate fossils have found in the Early Cambrian Chengjiang fauna. Because the fossil record of early chordates is poor, only molecular phylogenetics offers a prospect of dating their emergence. However, the use of molecular phylogenetics for dating evolutionary transitions is controversial and it has also proved difficult to produce a detailed classification within the living chordates. Attempts to produce family trees shows that many of the traditional classes are paraphyletic. While this has been known since the 19th century, an insistence on only monophyletic taxa has resulted in vertebrate classification being in a state of flux. Although the name Chordata is attributed to William Bateson, it was already in prevalent use by 1880, ernst Haeckel described a taxon comprising tunicates, cephalochordates, and vertebrates in 1866. Though he used the German vernacular form, it is allowed under the ICZN code because of its subsequent latinization, among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail. In fish and other vertebrates, this develops into the spinal cord, the pharynx is the part of the throat immediately behind the mouth. In fish, the slits are modified to form gills, a muscular tail that extends backwards behind the anus. This is a groove in the wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus and it also stores iodine, and may be a precursor of the vertebrate thyroid gland
4.
Mammal
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Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles by the possession of a neocortex, hair, three middle ear bones and mammary glands. All female mammals nurse their young with milk, secreted from the mammary glands, Mammals include the largest animals on the planet, the great whales. The basic body type is a quadruped, but some mammals are adapted for life at sea, in the air, in trees. The largest group of mammals, the placentals, have a placenta, Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale. With the exception of the five species of monotreme, all modern mammals give birth to live young, most mammals, including the six most species-rich orders, belong to the placental group. The largest orders are the rodents, bats and Soricomorpha, the next three biggest orders, depending on the biological classification scheme used, are the Primates, the Cetartiodactyla, and the Carnivora. Living mammals are divided into the Yinotheria and Theriiformes There are around 5450 species of mammal, in some classifications, extant mammals are divided into two subclasses, the Prototheria, that is, the order Monotremata, and the Theria, or the infraclasses Metatheria and Eutheria. The marsupials constitute the group of the Metatheria, and include all living metatherians as well as many extinct ones. Much of the changes reflect the advances of cladistic analysis and molecular genetics, findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora. The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade, the early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the line that led to todays reptiles. Some mammals are intelligent, with some possessing large brains, self-awareness, Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation. Mammals can organize themselves into fission-fusion societies, harems, and hierarchies, most mammals are polygynous, but some can be monogamous or polyandrous. They provided, and continue to provide, power for transport and agriculture, as well as commodities such as meat, dairy products, wool. Mammals are hunted or raced for sport, and are used as model organisms in science, Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion. Defaunation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is accepted, McKenna & Bell and Wilson & Reader provide useful recent compendiums. Though field work gradually made Simpsons classification outdated, it remains the closest thing to a classification of mammals
5.
Even-toed ungulate
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The even-toed ungulates are ungulates whose weight is borne equally by the third and fourth toes. By contrast, odd-toed ungulates, such as horses, bear their weight primarily on their third toe, the aquatic cetaceans evolved from within even-toed ungulates, and therefore modern taxonomic classification sometimes combines Artiodactyla and Cetacea into Cetartiodactyla. The oldest fossils of even-toed ungulates date back to the early Eocene, since these findings almost simultaneously appeared in Europe, Asia, and North America, it is very difficult to accurately determine the origin of artiodactyls. The fossils are classified as belonging to the family Dichobunidae, their best-known and these were small animals, some as small as a hare, with a slim build, lanky legs, and a long tail. The hind legs were longer than the front legs. The early to middle Eocene saw the emergence of the ancestors of most of todays mammals, two formerly widespread, but now extinct, families of even-toed ungulates were Enteledontidae and Anthracotheriidae. Entelodonts existed from the middle Eocene to the early Miocene in Eurasia and they had a stocky body with short legs and a massive head, which was characterized by two humps on the lower jaw bone. Anthracotheres had a large, porcine build, with short legs and this group appeared in the middle Eocene up until the Pliocene, and spread throughout Eurasia, Africa, and North America. Anthracothereres are thought to be the ancestors of hippos, and, likewise, hippopotamuses appeared in the late Miocene and occupied Africa and Asia – they never got to the Americas. The camels were, during parts of the Cenozoic, limited to North America. Among the North American camels were groups like the stocky, short-legged Merycoidodontidae and they first appeared in the late Eocene and developed a great diversity of species in North America. Only in the late Miocene or early Pliocene did they migrate from North America into Eurasia, the North American varieties became extinct around 10,000 years ago. Suina have been around since the Eocene, in the late Eocene or the Oligocene, two families stayed in Eurasia and Africa, the peccaries, which became extinct in the Old World, exist today only in the Americas. South America was settled by even-toed ungulates only in the Pliocene, with only the peccaries, lamoids, and various species of capreoline deer, South America has comparatively fewer artiodactyl families than other continents. The classification of artiodactyls was hotly debated because the ocean-dwelling cetaceans evolved from the land-dwelling even-toed ungulates, some semiaquatic even-toed ungulates are more closely related to the ocean-dwelling cetaceans than to the other even-toed ungulates. This makes the Artiodactyla as traditionally defined an invalid paraphyletic taxon, since it includes animals descended from a common ancestor, phylogenetic classification only recognizes monophyletic taxa, that is, groups that descend from a common ancestor and include all its descendants. To address this problem, the traditional order Artiodactyla and infraorder Cetacea are sometimes subsumed into the more inclusive Cetartiodactyla taxon, an alternative approach is to include both land-land dwelling even toed ungulates and ocean-dwelling cetaceans in a revised Artiodactyla taxon. Order Artiodactyla/Clade CetartiodactylaSuborder Tylopoda Family †Anoplotheriidae, molecular biology involves sequencing an organisms DNA and RNA and comparing the sequence with that of other living beings – the more similar they are, the more closely they are related
6.
Cetacea
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Cetacea are a widely distributed and diverse clade of aquatic mammals that today consists of the whales, dolphins, and porpoises. Most species live in the sea, some in rivers, the name is derived from the Latin cetus whale and Greek ketos huge fish. The extinct ancestors of modern whales are the Archaeoceti, while cetaceans were historically thought to have descended from mesonychids, molecular evidence supports them as a relative of Artiodactyls. Cetaceans belong to the order Cetartiodactyla and their closest living relatives are hippopotamuses and other hoofed mammals, having diverged about 50 million years ago. Cetaceans range in size from the 1 m and 50 kg Mauis dolphin to the 29.9 m and 190,000 kg blue whale and they have streamlined bodies and two limbs that are modified into flippers. Dolphins are able to very tight turns while swimming at high speeds. The hindlimbs of cetaceans are internal, and are thought to be vestigial, baleen whales have short hairs on their mouth, unlike the toothed whales. Cetaceans have well-developed senses—their eyesight and hearing are adapted for both air and water, and baleen whales have a system in their vibrissae. They have a layer of fat, or blubber, under the skin to maintain body heat in cold water, Some species are well adapted for diving to great depths. Although cetaceans are widespread, most species prefer the waters of the Northern and Southern Hemispheres. They spend their lives in the water, having to mate, give birth, molt or escape predators, like killer whales. This has drastically affected their anatomy to be able to do so and they feed largely on fish and marine invertebrates, but a few, like the killer whale, feed on large mammals and birds, such as penguins and seals. Some baleen whales are specialised for feeding on benthic creatures, male cetaceans typically mate with more than one female, although the degree of polygyny varies with the species. Cetaceans are not shown to have pair bonds, male cetacean strategies for reproductive success vary between herding females, defending potential mates from other males, or whale song which attracts mates. Calves are typically born in the fall and winter months, cetaceans produce a number of vocalizations, notably the clicks and whistles of dolphins, the moaning songs of the humpback whale. The meat, blubber and oil of cetaceans have traditionally used by indigenous peoples of the Arctic. Cetaceans have been depicted in cultures worldwide. Dolphins are commonly kept in captivity and are sometimes trained to perform tricks and tasks
7.
Oceanic dolphin
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Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. They include several big species whose common names contain whale rather than dolphin, such as the killer whale, Delphinidae is a family within the superfamily Delphinoidea, which also includes the porpoises and the Monodontidae. River dolphins are relatives of the Delphinoidea, oceanic dolphins range in size from the 5. 6-foot -long and 110-pound Mauis dolphin to the 31-foot and 11-short-ton killer whale, the largest known dolphin. Several species exhibit sexual dimorphism, the males are larger than females and they have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals, some dolphins can travel at 34.5 mph and they typically have between 100 and 200 teeth, although a few species have considerably fewer. Delphinids travel in pods, which may number a thousand individuals in some species. Each pod forages over a range of a few dozen to a few hundred square miles, some pods have a loose social structure, with individuals frequently joining or leaving, but others seem to be more permanent, perhaps dominated by a male and a harem of females. Individuals communicate by sound, producing low-frequency whistles, and also produce high-frequency broadband clicks of 80-220 kHz, gestation lasts from 10 to 18 months, and results in the birth of a single calf. Some species are adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water, although oceanic dolphins are widespread, most species prefer the warmer waters of the tropic zones, but some, like the right whale dolphin, prefer colder climates. Some have a distribution, like the killer whale. Oceanic dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer, and females bear all the responsibility for raising them, mothers of some species fast and nurse their young for relatively long times. Dolphins produce a variety of vocalizations, usually in the form of clicks, oceanic dolphins are sometimes hunted in places such as Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they face threats from bycatch, habitat loss. Dolphins have been depicted in cultures worldwide. They occasionally feature in literature and film, as in the Warner Bros film Free Willy, oceanic dolphins are kept in captivity and trained to perform tricks, but breeding success has been poor and the animals often die within a few months of capture. The most common dolphins kept are the whales and bottlenose dolphins
8.
Dolphin
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Dolphins are a widely distributed and diverse group of aquatic mammals. They are a grouping within the order Cetacea, excluding whales and porpoises. The dolphins comprise the extant families Delphinidae, Platanistidae, Iniidae, and Pontoporiidae, there are 40 extant species of dolphins. Dolphins, alongside other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates and their closest living relatives are the hippopotamuses, having diverged about 40 million years ago. Dolphins range in size from the 1.7 m long and 50 kg Mauis dolphin to the 9.5 m and 10 t killer whale, several species exhibit sexual dimorphism, in that the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers, though not quite as flexible as seals, some dolphins can travel at 55.5 km/h. Dolphins use their conical shaped teeth to capture fast moving prey and they have well-developed hearing which is adapted for both air and water and is so well developed that some can survive even if they are blind. Some species are adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water, although dolphins are widespread, most species prefer the warmer waters of the tropic zones, but some, like the right whale dolphin, prefer colder climates. Dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them, mothers of some species fast and nurse their young for a relatively long period of time. Dolphins produce a variety of vocalizations, usually in the form of clicks, Dolphins are sometimes hunted in places like Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they face threats from bycatch, habitat loss. Dolphins have been depicted in cultures worldwide. Dolphins occasionally feature in literature and film, as in the film series Free Willy, Dolphins are sometimes kept in captivity and trained to perform tricks, but breeding success has been poor and the animals often die within a few months of capture. The most common dolphins kept are killer whales and bottlenose dolphins, the name is originally from Greek δελφίς, dolphin, which was related to the Greek δελφύς, womb. The animals name can therefore be interpreted as meaning a fish with a womb, the name was transmitted via the Latin delphinus, which in Medieval Latin became dolfinus and in Old French daulphin, which reintroduced the ph into the word. The term mereswine has also historically been used, the term dolphin can be used to refer to, under the parvorder Odontoceti, all the species in the family Delphinidae and the river dolphin families Iniidae, Pontoporiidae, Lipotidae and Platanistidae
9.
Common dolphin
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The common dolphin is the name given to two species of dolphin making up the genus Delphinus. Prior to the mid-1990s, most taxonomists only recognised one species in this genus, modern cetologists usually recognise two species — the short-beaked common dolphin, which retains the systematic name Delphinus delphis, and the long-beaked common dolphin Delphinus capensis. However, this dolphin was the most frequently represented in the art and literature of ancient Greece and Rome. Both common dolphin species are medium-sized, adults range between 1.9 and 2.5 m long, and can weigh between 80–235 kg, although the range between 80–150 kg is more common, males are generally longer and heavier. The color pattern on the body is unusual, the back is dark and the belly is white, while on each side is an hourglass pattern colored light grey, yellow, or gold in front and dirty grey in back. They have long, thin rostra with up to 50–60 small, sharp, despite the historic practice of lumping the entire Delphinus genus into a single species, these widely distributed dolphins exhibit a wide variety of sizes, shapes and colors. Indeed, over the past few decades, over 20 distinct species in the genus have been proposed, scientists in California in the 1960s concluded there were two species — the long-beaked and short-beaked. This analysis was confirmed by a more in-depth genetic study in the 1990s. This study also suggested a third species, characterized by a long and thin beak and found in the Red Sea and Indian Ocean. The current standard taxonomic works recognize this as just a regional variety, D. tropicalis is a subspecies of D. capensis. Common dolphins live in both warm-temperate and tropical waters ranging from 40–60°N to 50°S, long-beaked common dolphins mostly inhabit shallow, warm coastal water. Short-beaked common dolphins are common along shelf edges and in areas with sharp bottom relief such as seamounts and escarpments, common dolphin have a varied diet consisting of many species of fish and squid. This includes both species and epipelagic schooling species. They have been recorded to make dives up to 200 metres deep, common dolphins can live in aggregations of hundreds or even thousands of dolphins. They sometimes associate with other species, such as pilot whales. They have also been observed bow riding on baleen whales, and they are fast swimmers, and breaching behavior and aerial acrobatics are common with this species. They are also known to display behaviors to support injured members. The short-beaked common dolphin has a period of 10 to 11 months
10.
Cetacean surfacing behaviour
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Cetacean surfacing behaviour is a group of behaviours demonstrated by the Cetacea infraorder when they come to the waters surface to breathe. Time intervals between surfacing can vary depending on the species, surfacing style or the purpose of the dive, in addition to respiration, cetaceans have developed and used surface behaviours for many other functions such as display, feeding and communication. All regularly observed members of the order Cetacea, including whales, dolphins and porpoises, Cetacea is usually split into two suborders, Odontoceti and Mysticeti, based on the presence of teeth or baleen plates in adults respectively. However, when considering behaviour, Cetacea can be split into whales and dolphins, although some behaviours such as spyhopping, logging and lobtailing occur in both groups, others such as bow riding or peduncle throws are exclusive to one or the other. It is these energetic behaviours that humans observe most frequently, which has resulted in an amount of scientific literature on the subject. A breach or a lunge is an out of the water. This latter lunging behaviour is often a result of feeding in rorquals, the right, humpback and sperm whales are the most widely observed jumpers. However other baleen whales such as fin, blue, minke, gray, some non-cetacean marine creatures also exhibit breaching behavior, such as several shark species and rays of the genera Manta and Mobula. Two techniques are used by cetaceans in order to breach, the first method, most common in sperm and humpback whales, is conducted by swimming vertically upwards from depth, and heading straight out of the water. The other more common method is to close to the surface and parallel to it. In all breaches the cetacean clears the water with the majority of its body at an acute angle, the whale then turns to land on its back or side, and less frequently may not turn but belly flop instead. In order to achieve 90% clearance, a humpback needs to leave the water at a speed of eight metres per second or 29 kilometres per hour, for a 36 metric tons animal, this results in a momentum of 288 thousand newton seconds. Despite its energetic cost, breaching is often carried out in series, the longest recorded sustained series was by a humpback near the West Indies totaling 130 leaps in less than 90 minutes. Repeated breaches tire the animal, so less of the body clears the water each time. Ultimately, the reasons for breaching are unknown, however, there is evidence to support a range of hypotheses, whales are more likely to breach when they are in groups, suggesting that it is a non-acoustic signal to other group members during social behaviour. Scientists have called this theory honest signalling, the immense cloud of bubbles and underwater disturbance following a breach cannot be faked, neighbours then know a breach has taken place. A single breach costs a whale only about 0. 075% of its daily energy intake. A breach is therefore a sign that the animal is physically fit enough to afford energy for this display, hence it could be used for ascertaining dominance
11.
Pelagic fish
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The marine pelagic environment is the largest aquatic habitat on Earth, occupying 1,370 million cubic kilometres, and is the habitat for 11% of known fish species. The oceans have a depth of 4000 metres. About 98% of the water volume is below 100 metres. Marine pelagic fish can be divided into pelagic coastal fish and oceanic pelagic fish, coastal fish inhabit the relatively shallow and sunlit waters above the continental shelf, while oceanic fish inhabit the vast and deep waters beyond the continental shelf. Pelagic fish range in size from small forage fish, such as herrings and sardines, to large apex predator oceanic fishes, such as bluefin tuna. They are usually agile swimmers with streamlined bodies, capable of sustained cruising on long-distance migrations, the Indo-Pacific sailfish, an oceanic pelagic fish, can sprint at over 110 kilometres per hour. Some tuna species cruise across the Pacific Ocean, many pelagic fish swim in schools weighing hundreds of tonnes. Others are solitary, like the ocean sunfish weighing over 500 kilograms. Epipelagic fish inhabit the epipelagic zone, the epipelagic zone is the water from the surface of the sea down to 200 metres. It is also referred to as the waters or the sunlit zone. The photic zone is defined as the surface waters down to the point where the sunlight has attenuated to 1% of the surface value and this depth depends on how turbid the water is, but in clear water can extend to 200 metres, coinciding with the epipelagic zone. The photic zone has sufficient light for phytoplankton to photosynthese, the epipelagic zone is vast, and is the home for most pelagic fish. The zone is well lit so visual predators can use their eyesight, is well mixed and oxygenated from wave action. However, it is an almost featureless habitat and this lack of habitat diversity results in a lack of species diversity, so the zone supports less than 2% of the worlds known fish species. Epipelagic fish can be divided into small forage fish and larger predator fish which feed on them. Forage fish school and filter feed on plankton, most epipelagic fish have streamlined bodies capable of sustained cruising on migrations. In general, predatory and forage fish share the same morphological features, predator fish are usually fusiform with large mouths, smooth bodies, and deeply forked tails. Many use vision to predate zooplankton or smaller fish, while others feed on plankton
12.
Squid
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Squid are cephalopods of the order Teuthida, which comprises around 304 species. Like all other cephalopods, squid have a head, bilateral symmetry, a mantle. Squid, like cuttlefish, have eight arms arranged in pairs, squid are strong swimmers and certain species can fly for short distances out of the water. Squid are members of the class Cephalopoda, subclass Coleoidea, order Teuthida, Teuthida is the largest cephalopod order with around 300 species classified into 29 families. The order Teuthida is a member of the superorder Decapodiformes, two other orders of decapodiform cephalopods are also called squid, although they are taxonomically distinct from Teuthida and differ recognizably in their gross anatomical features. They are the bobtail squid of order Sepiolida and the rams horn squid of the monotypic order Spirulida, the vampire squid, however, is more closely related to the octopuses than to any squid. Class Cephalopoda Subclass Nautiloidea, nautilus Subclass Coleoidea, squid, octopus, what before may have been the foot of the ancestor is modified into a complex set of tentacles and highly developed sense organs, including advanced eyes similar to those of vertebrates. The ancestral shell has been lost, with only an internal gladius, or pen, the pen is a feather-shaped internal structure that supports the squids mantle and serves as a site for muscle attachment. It is made of a chitin-like material, the main body mass is enclosed in the mantle, which has a swimming fin along each side. These fins, unlike in other organisms, are not the main source of locomotion in most species. The skin is covered in chromatophores, which enable the squid to change color to suit its surroundings, the underside is also almost always lighter than the topside, to provide camouflage from both prey and predator. Under the body are openings to the cavity, which contains the gills and openings to the excretory. At the front of the mantle cavity lies the siphon, which the squid uses for locomotion via precise jet propulsion, in this form of locomotion, water is sucked into the mantle cavity and expelled out of the siphon in a fast, strong jet. The direction of the siphon can be changed, to suit the direction of travel, inside the mantle cavity, beyond the siphon, lies the visceral mass, which is covered by a thin, membranous epidermis. Under this are all the internal organs. The giant axon, which may be up to 1 mm in diameter in some species, innervates the mantle. As cephalopods, squid exhibit relatively high intelligence among invertebrates, for example, groups of Humboldt squid hunt cooperatively, using active communication. In females, the ink sac is hidden from view by a pair of white nidamental glands, also, red-spotted accessory nidamental glands are present
