Cheetah




              The cheetah (Acinonyx jubatus) is a large feline (family Felidae, subfamily Felinae) inhabiting most of Africa and parts of the Middle East. It is the only extant member of the genus Acinonyx. The cheetah can run faster than any other land animal— as fast as 112 to 120 km/h (70 to 75 mph) in short bursts covering distances up to 500 m (1,600 ft), and has the ability to accelerate from 0 to 100 km/h (62 mph) in three seconds. Data from 367 runs by three female and two male adults, with an average run distance of 173 m, showed that while hunting cheetahs can run 58 miles (93 km) per hour.
This cat is also notable for modifications in the species' paws. It is one of the few felids with semi-retractable claws. 

Etymology

The word "cheetah" is derived from the Sanskrit word citrakāyaḥ, meaning "variegated", via the Hindi 'चीता' (cītā).

Genetics, Evolution and Classification

Cheetah mother with cub
              The genus name, Acinonyx, means "no-move-claw" in Greek, while the species name, jubatus, means "maned" or "crested" in Latin, a reference to the dorsal crest found in cheetah cubs.
The cheetah has unusually low genetic variability. This is accompanied by a very low sperm count, motility, and deformed flagella. Skin grafts between unrelated cheetahs illustrate the former point, in that there is no rejection of the donor skin. It is thought that the species went through a prolonged period of inbreeding following a genetic bottleneck during the last ice age. This suggests that genetic monomorphism did not prevent the cheetah from flourishing across two continents for thousands of years.
              The cheetah likely evolved in Africa during the Miocene epoch (26 million to 7.5 million years ago), before migrating to Asia. Recent research has placed the last common ancestor of all existing populations as living in Asia 11 million years ago, which may lead to revision and refinement of existing ideas about cheetah evolution.

Cheetah at Maasai Mara National Reserve
              The now-extinct species include: Acinonyx pardinensis (Pliocene epoch), much larger than the modern cheetah and found in Europe, India, and China; Acinonyx intermedius (mid-Pleistocene period), found over the same range. The extinct genus Miracinonyx was extremely cheetah-like, but recent DNA analysis has shown that Miracinonyx inexpectatus, Miracinonyx studeri, and Miracinonyx trumani (early to late Pleistocene epoch), found in North America and called the "North American cheetah" are not true cheetahs, instead being close relatives to the cougar. 

Subspecies
              Although many sources list six or more subspecies of cheetah, the taxonomic status of most of these subspecies is unresolved.[according to whom?] Acinonyx rex—the king cheetah—was abandoned as a subspecies after it was discovered that the variation was caused by a single recessive gene. The subspecies Acinonyx jubatus guttatus, the woolly cheetah, may also have been a variation due to a recessive gene. Some of the most commonly recognized subspecies include:
A Tanzanian cheetah (Acinonyx jubatus raineyii)

 
Portrait of an Asiatic cheetah (A.j. venatecus) by A.N. Kondakov.

                The cheetah's paws have semi-retractable claws (known only in three other cat species: the fishing cat, the flat-headed cat and the Iriomote cat), offering extra grip in its high-speed pursuits. The ligament structure of the cheetah's claws is the same as those of other cats; it simply lacks the sheath of skin and fur present in other varieties, and therefore, with the exception of the dewclaw, the claws are always visible. The dewclaw is much shorter and straighter than that of other cats.
Adaptations that enable the cheetah to run as fast as it does include large nostrils that allow for increased oxygen intake, and an enlarged heart and lungs that work together to circulate oxygen efficiently. During a typical chase, its respiratory rate increases from 60 to 150 breaths per minute. While running, in addition to having good traction due to its semi-retractable claws, the cheetah uses its tail as a rudder-like means of steering to allow it to make sharp turns, necessary to outflank prey animals that often make such turns to escape.


Paws. Note the blunt semi retractible claws


Lion






Male lion
   

Female Lion

              The lion (Panthera leo) is one of the four big cats in the genus Panthera and a member of the family Felidae. With some males exceeding 250 kg (550 lb) in weight, it is the second-largest living cat after the tiger. Wild lions currently exist in sub-Saharan Africa and in Asia (where an endangered remnant population resides in Gir Forest National Park in India) while other types of lions have disappeared from North Africa and Southwest Asia in historic times. Until the late Pleistocene, about 10,000 years ago, the lion was the most widespread large land mammal after humans. They were found in most of Africa, across Eurasia from western Europe to India, and in the Americas from the Yukon to Peru. The lion is a vulnerable species, having seen a major population decline of 30–50% over the past two decades[date missing] in its African range. Lion populations are untenable outside designated reserves and national parks. Although the cause of the decline is not fully understood, habitat loss and conflicts with humans are currently the greatest causes of concern. Within Africa, the West African lion population is particularly endangered.

              Lions live for 10–14 years in the wild, while in captivity they can live longer than 20 years. In the wild, males seldom live longer than 10 years, as injuries sustained from continual fighting with rival males greatly reduce their longevity. They typically inhabit savanna and grassland, although they may take to bush and forest. Lions are unusually social compared to other cats. A pride of lions consists of related females and offspring and a small number of adult males. Groups of female lions typically hunt together, preying mostly on large ungulates. Lions are apex and keystone predators, although they scavenge as opportunity allows. While lions do not typically hunt humans, some have been known to do so. Sleeping mainly during the day, lions are primarily nocturnal, although bordering on crepuscular in nature.
               Highly distinctive, the male lion is easily recognised by its mane, and its face is one of the most widely recognised animal symbols in human culture. Depictions have existed from the Upper Paleolithic period, with carvings and paintings from the Lascaux and Chauvet Caves, through virtually all ancient and medieval cultures where they once occurred. It has been extensively depicted in sculptures, in paintings, on national flags, and in contemporary films and literature. Lions have been kept in menageries since the time of the Roman Empire, and have been a key species sought for exhibition in zoos over the world since the late eighteenth century. Zoos are cooperating worldwide in breeding programs for the endangered Asiatic subspecies. 

A video of a lion and cubs

Giraffe



              The giraffe (Giraffa camelopardalis) is an African even-toed ungulate mammal, the tallest living terrestrial animal and the largest ruminant. Its species name refers to its camel-like appearance and the patches of color on its fur. Its chief distinguishing characteristics are its extremely long neck and legs, its horn-like ossicones and its distinctive coat patterns. It stands 5–6 m (16–20 ft) tall and has an average weight of 1,600 kg (3,500 lb) for males and 830 kg (1,800 lb) for females. It is classified under the family Giraffidae, along with its closest extant relative, the okapi. The nine subspecies are distinguished by their coat patterns.

               The giraffe's scattered range extends from Chad in the north to South Africa in the south, and from Niger in the west to Somalia in the east. Giraffes usually inhabit savannas, grasslands, and open woodlands. Their primary food source is acacia leaves, which they browse at heights most other herbivores cannot reach. Giraffes are preyed on by lions, and calves are also targeted by leopards, spotted hyenas and wild dogs. Adult giraffes do not have strong social bonds, though they do gather in loose aggregations if they happen to be moving in the same general direction. Males establish social hierarchies through "necking", which are combat bouts where the neck is used as a weapon. Dominant males gain mating access to females, which bear the sole responsibility for raising the young.
               The giraffe has intrigued various cultures, both ancient and modern, for its peculiar appearance, and has often been featured in paintings, books and cartoons. It is classified by the International Union for Conservation of Nature as Least Concern, but has been extirpated from many parts of its former range, and some subspecies are classified as Endangered. Nevertheless, giraffes are still found in numerous national parks and game reserves. 

Etymology

               The name "giraffe" has its earliest known origins in the Arabic word zarafa (زرافة), perhaps from some African language. The name is translated as "fast-walker". There were several Middle English spellings such as jarraf, ziraph, and gerfauntz. The word possibly was derived from the animal's Somali name geri. The Italian form giraffa arose in the 1590s. The modern English form developed around 1600 from the French girafe. The species name camelopardalis is from Latin.
Kameelperd is also the name for the species in Afrikaans. Other African names for the giraffe include ekorii (Ateso), kanyiet (Elgon), nduida (Gikuyu), tiga (Kalenjin and Luo), ndwiya (Kamba), nudululu (Kihehe), ntegha (Kinyaturu), ondere (Lugbara), etiika (Luhya), kuri (Ma'di), oloodo-kirragata or olchangito-oodo (Maasai), lenywa (Meru), hori (Pare), lment (Samburu) and twiga (Swahili and others) in the east;:313 and tutwa (Lozi), nthutlwa (Shangaan), indlulamitsi (Siswati), thutlwa (Sotho), thuda (Venda) and ndlulamithi (Zulu) in the south. 

Taxonomy and Evolution

Mounted Shansitherium skeleton from the Beijing Museum of Natural History
The giraffe is one of only two living species of the family Giraffidae, the other being the okapi. The family was once much more extensive, with over 10 fossil genera described. Their closest known relatives are the extinct climacocerids. They, together with the family Antilocapridae (whose only extant species is the pronghorn) belong to the superfamily Giraffoidea. These animals evolved from the extinct family Palaeomerycidae 8 million years ago (mya) in south-central Europe during the Miocene epoch.
While some ancient giraffids like Sivatherium had massive bodies, others like Giraffokeryx, Palaeotragus (possible ancestor of the okapi), Samotherium, and Bohlinia were more elongated. Bohlinia entered China and northern India in response to climate change. From here, the genus Giraffa evolved and, around 7 mya, entered Africa. Further climate changes caused the extinction of the Asian giraffes, while the African ones survived and radiated into several new species. G. camelopardalis arose around 1 mya in eastern Africa during the Pleistocene. Some biologists suggest that the modern giraffe descended from G. jumae; others find G. gracilis a more likely candidate.[9] The main driver for the evolution of the giraffes is believed to have been the change from extensive forests to more open habitats, which began 8 mya. Some researchers have hypothesized this new habitat with a different diet, including Acacia, may have exposed giraffe ancestors to toxins that caused higher mutation rates and a higher rate of evolution. 

The endangered West African giraffe

Closeup of the head of a giraffe at the Melbourne Zoo 


Giant Panda







               The panda (Ailuropoda melanoleuca, lit. "black and white cat-foot"), also known as the giant panda to distinguish it from the unrelated red panda, is a bear native to central-western and south western China. It is easily recognized by the large, distinctive black patches around its eyes, over the ears, and across its round body. Though it belongs to the order Carnivora, the panda's diet is 99% bamboo. Pandas in the wild will occasionally eat other grasses, wild tubers, or even meat in the form of birds, rodents or carrion. In captivity, they may receive honey, eggs, fish, yams, shrub leaves, oranges, or bananas along with specially prepared food.

The giant panda lives in a few mountain ranges in central China, mainly in Sichuan province, but also in the Shaanxi and Gansu provinces. As a result of farming, deforestation and other development, the panda has been driven out of the lowland areas where it once lived.
                The panda is a conservation reliant endangered species. A 2007 report shows 239 pandas living in captivity inside China and another 27 outside the country. Wild population estimates vary; one estimate shows that there are about 1,590 individuals living in the wild, while a 2006 study via DNA analysis estimated that this figure could be as high as 2,000 to 3,000. Some reports also show that the number of pandas in the wild is on the rise. However, the IUCN does not believe there is enough certainty yet to reclassify the species from Endangered to Vulnerable.
While the dragon has often served as China's national emblem, internationally the panda appears at least as commonly. As such, it is becoming widely used within China in international contexts, for example the five Fuwa mascots of the Beijing Olympics. 

Description

              The giant panda has a black-and-white coat. Adults measure around 1.2 to 1.8 m (4 to 6 ft) long, including a tail of about 13 cm (5.1 in), and 60 to 90 cm (2.0 to 3.0 ft) tall at the shoulder. Males can weigh up to 160 kg (350 lb). Females (generally 10–20% smaller than males) can weigh as little as 75 kg (170 lb), but can also weigh up to 125 kg (280 lb). Average adult weight is 100 to 115 kg (220 to 250 lb).
             The giant panda has a body shape typical of bears. It has black fur on its ears, eye patches, muzzle, legs, arms and shoulders. The rest of the animal's coat is white. Although scientists do not know why these unusual bears are black and white, speculation suggests that the bold coloring provides effective camouflage in their shade-dappled snowy and rocky habitat. The giant panda's thick, wooly coat keeps it warm in the cool forests of its habitat. It has large molar teeth and strong jaw-muscles for crushing tough bamboo. 
             The giant panda's paw has a "thumb" and five fingers; the "thumb" - actually a modified sesamoid bone - helps it to hold bamboo while eating. Stephen Jay Gould discusses this feature in his book of essays on evolution and biology, The Panda's Thumb.
The giant panda's tail, measuring 10 to 15 cm (4 to 6 in), is the second-longest in the bear family. (The longest belongs to the sloth bear.)
The giant panda typically lives around 20 years in the wild and up to 30 years in captivity. The oldest captive, a female named Ming Ming, had a recorded age of 34.

Dog







               The domestic dog (Canis lupus familiaris) is a subspecies of the gray wolf (Canis lupus), a member of the Canidae family of the mammalian order Carnivora. The term "domestic dog" is generally used for both domesticated and feral varieties. The dog was the first domesticated animal and has been the most widely kept working, hunting, and pet animal in human history. The word "dog" may also mean the male of a canine species, as opposed to the word "bitch" for the female of the species.

MtDNA evidence shows an evolutionary split between the modern dog's lineage and the modern wolf's lineage around 100,000 years ago but, as of 2013, the oldest fossil specimens genetically linked to the modern dog's lineage date to approximately 33,000–36,000 years ago. Dogs' value to early human hunter-gatherers led to them quickly becoming ubiquitous across world cultures. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. This impact on human society has given them the nickname "Man's Best Friend" in the Western world. In some cultures, however, dogs are also a source of meat. In 2001, there were estimated to be 400 million dogs in the world.
               Most breeds of dogs are at most a few hundred years old, having been artificially selected for particular morphologies and behaviors by people for specific functional roles. Through this selective breeding, the dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal. For example, height measured to the withers ranges from 15.2 centimetres (6.0 in) in the Chihuahua to about 76 cm (30 in) in the Irish Wolfhound; color varies from white through grays (usually called "blue") to black, and browns from light (tan) to dark ("red" or "chocolate") in a wide variation of patterns; coats can be short or long, coarse-haired to wool-like, straight, curly, or smooth. It is common for most breeds to shed this coat.

Taxonomy

In 1753, the father of modern biological taxonomy, Carl Linnaeus, listed among the types of quadrupeds familiar to him, the Latin word for dog, canis. Among the species within this genus, Linnaeus listed the fox, as Canis vulpes, wolves (Canis lupus), and the domestic dog, (Canis canis; see File:Linnaeus - Regnum Animale (1735).png).
In later editions, Linnaeus dropped Canis canis and greatly expanded his list of the Canis genus of quadrupeds, and by 1758 included alongside the foxes, wolves, and jackals and many more terms that are now listed as synonyms for domestic dog, including aegyptius (hairless dog), aquaticus, (water dog), and mustelinus (literally "badger dog"). Among these were two that later experts have been widely used for domestic dogs as a species: Canis domesticus and, most predominantly, Canis familiaris, the "common" or "familiar" dog.
The domestic dog was accepted as a species in its own right until overwhelming evidence from behavior, vocalizations, morphology, and molecular biology led to the contemporary scientific understanding that a single species, the gray wolf, is the common ancestor for all breeds of domestic dogs. In recognition of this fact, the domestic dog was reclassified in 1993 as Canis lupus familiaris, a subspecies of the gray wolf Canis lupus, by the Smithsonian Institution and the American Society of Mammalogists. C. l. familiaris is listed as the name for the taxon that is broadly used in the scientific community and recommended by ITIS, although Canis familiaris is a recognised synonym.
Since that time, C. domesticus and all taxa referring to domestic dogs or subspecies of dog listed by Linnaeus, Johann Friedrich Gmelin in 1792, and Christian Smith in 1839, lost their subspecies status and have been listed as taxonomic synonyms for Canis lupus familiaris.

Elephant



              Elephants are large mammals of the family Elephantidae and the order Proboscidea. Traditionally, two species are recognised, the African elephant (Loxodonta africana) and the Asian elephant (Elephas maximus), although some evidence suggests that African bush elephants and African forest elephants are separate species (L. africana and L. cyclotis respectively). Elephants are scattered throughout sub-Saharan Africa, and South and Southeast Asia. They are the only surviving proboscideans; extinct species include mammoths and mastodons. The largest living terrestrial animals, male African elephants can reach a height of 4 m (13 ft) and weigh 7,000 kg (15,000 lb). These animals have several distinctive features, including a long proboscis or trunk used for many purposes, particularly for grasping objects. Their incisors grow into tusks, which serve as tools for moving objects and digging and as weapons for fighting. The elephant's large ear flaps help to control the temperature of its body. African elephants have larger ears and concave backs while Asian elephants have smaller ears and convex or level backs.
               Elephants are herbivorous and can be found in different habitats including savannahs, forests, deserts and marshes. They prefer to stay near water. They are considered to be keystone species due to their impact on their environments. Other animals tend to keep their distance, and predators such as lions, tigers, hyenas and wild dogs usually target only the young elephants (or "calves"). Females ("cows") tend to live in family groups, which can consist of one female with her calves or several related females with offspring. The latter are led by the oldest cow, known as the matriarch. Elephants have a fission-fusion society in which multiple family groups come together to socialise. Males ("bulls") leave their family groups when they reach puberty, and may live alone or with other males. Adult bulls mostly interact with family groups when looking for a mate and enter a state of increased testosterone and aggression known as musth, which helps them gain dominance and reproductive success. Calves are the centre of attention in their family groups and rely on their mothers for as long as three years. Elephants can live up to 70 years in the wild. They communicate by touch, sight, and sound; elephants use infrasound, and seismic communication over long distances. Elephant intelligence has been compared with that of primates and cetaceans. They appear to have self-awareness and show empathy for dying or dead individuals of their kind.
              African elephants are listed as vulnerable by the International Union for Conservation of Nature (IUCN), while the Asian elephant is classed as endangered. One of the biggest threats to elephant populations is the ivory trade, as the animals are poached for their ivory tusks. Other threats to wild elephants include habitat destruction and conflicts with local people. Elephants are used as working animals in Asia. In the past they were used in war; today, they are often put on display in zoos and circuses. Elephants are highly recognisable and have been featured in art, folklore, religion, literature and popular culture.

Terrestrial Animals



                Terrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, emus), as compared with aquatic animals, which live predominantly or entirely in the water (e.g., fish, lobsters, octopuses), or amphibians, which rely on a combination of aquatic and terrestrial habitats (e.g., frogs). The term terrestrial is also frequently used for species that live primarily on the ground, in contrast to arboreal species, which live primarily in trees.

Taxonomy

               Terrestrial invasion is theorized to be one of the most important events in the history of life. Terrestrial lineages theoretically evolved in several animal phyla, among which vertebrates, arthropods, and mollusks are representatives of more successful groups of the epifaunal terrestrial life.
               Terrestrial animals do not form a unified clade; rather, they share only the fact that they live on land. The transition from an aquatic to terrestrial life has theoretically evolved independently and successfully many times by various groups of animals, though this can't be proven through current scientific data. Most terrestrial lineages are theorized to have originated under mild or tropical climate during the Paleozoic and Mesozoic, whereas few animals became fully terrestrial during the Cenozoic.
               When excluding internal parasites, free living species in terrestrial environments are represented by the following ten phyla; Flatworms (Planaria), Nemertea (ribbon worms), Nematoda (roundworms), Rotifers, Tardigrada (water bears), Onychophora (velvet worms), Arthropods, mollusks (gastropods: land snails and slugs), Annelida and Chordata (tetrapods). Roundworms, tardigrades, and rotifers are microscopic animals that require a film of water to live in, and are not considered truly terrestrial. Flatworms, ribbon worms, velvet worms and annelids all depend on more or less moist habitats, while the three remaining categories, arthropods, gastropods and tetrapods, are the only ones that contain species that have adapted to predominantly dry terrestrial environments.

 Pictures of terresttrial animals:
Planaria worm -
A planarian is one of many non-parasitic flatworms of the Turbellaria class. It is also the common name for a member of the genus Planaria within the family Planariidae. Sometimes it also refers to the genus Dugesia.[2]
Planaria are common to many parts of the world, living in both saltwater and freshwater ponds and rivers. Some species are terrestrial and are found under logs, in or on the soil, and on plants in humid areas.
Some planarians exhibit an extraordinary ability to regenerate lost body parts. For example, a planarian split lengthwise or crosswise will regenerate into two separate individuals. Some planarian species have two eye-spots (also known as ocelli) that can detect the intensity of light, while others have several eye-spots. The eye-spots act as photoreceptors and are used to move away from light sources. Planaria have three germ layers (ectoderm, mesoderm, and endoderm), and are acoelomate (i.e. they have a very solid body with no body cavity). They have a single-opening digestive tract, in Tricladida planarians this consists of one anterior branch and two posterior branches.

Polycelis felina, a freshwater planarian        

Anatomy and physiology

The planarian has very simple organ systems. The digestive system consists of a mouth, pharynx, and a structure called a gastrovascular cavity. The mouth is located in the center of the underside of the body. Digestive enzymes are secreted from the mouth to begin external digestion. The pharynx connects the mouth to the gastrovascular cavity. This structure branches throughout the body allowing nutrients from food to reach all extremities. Planaria eat living or dead small animals that they suck with their muscular mouths. Food passes from the mouth through the pharynx into the intestines where it is digested by the cells lining the intestines. Then its nutrients diffuse to the rest of the body.
Planaria receive oxygen and release carbon dioxide by diffusion. The excretory system is made of many tubes with many flame cells and excretory pores on them. Flame cells energize unwanted liquids from the body by passing them through ducts that lead to excretory pores where waste is released on the dorsal surface of the planarian.

 


scallop







                A scallop (/ˈskɒləp/ or /ˈskæləp/; from Old French escalope, meaning "shell") is a common name applied to many species of marine bivalve mollusks in the family Pectinidae, the scallops. Scallops are a cosmopolitan family, found in all of the world's oceans.

Many scallops are highly prized as a food source; the name "scallop" is also applied to the meat of these animals when it is used as seafood. The brightly colored, fan-shaped shells of some scallops, with their radiating fluted pattern, are valued by shell collectors, and have been used since ancient times as motifs in art and design.

Anatomy

Muscular system: Like the true oysters (family Ostreidae), scallops have a central adductor muscle, and thus the inside of their shells has a characteristic central scar, marking the point of attachment for this muscle. The adductor muscle of scallops is larger and more developed than that of oysters, because they are active swimmers; some species of scallops are known to move en masse from one area to another. In scallops the shell shape tends to be highly regular, and is commonly used as an archetypal form of a seashell. 

Eyes: Scallops have up to 100 simple brilliantly blue eyes arranged around the edges of each of their two mantles like strings of beads. They are reflector eyes, about one millimeter in diameter, with a retina that is more complex than those of other bivalves. Their eyes contain two retina types, one responding to light and the other to abrupt darkness, such as the shadow of a nearby predator. They cannot resolve shapes, but can detect changing patterns of light and motion.
Reflector eyes are an alternative to those with a lens, where the inside of the eye is lined with mirrors which reflect the image to focus at a central point. The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out. The scallop Pecten has up to 100 millimeter-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive eyes.

Digestive system:  Most scallops are filter feeders, and eat plankton. Incidentally, the plankton can include scallop larvae. They lack siphons. Water moves over a filtering structure, where food becomes trapped in mucus. Next, the cilia on the structure move the food toward the mouth. Then, the food is digested in the digestive gland, an organ sometimes misleadingly referred to as the "liver" but which envelops part of the esophagus, intestine, and the entire stomach. Waste is passed on through the intestine (which, near its terminus, enters and leaves the scallop's heart) and exits via the anus.

Nervous system: Like all bivalves, scallops lack an actual brain. Instead, the nervous system is controlled by three paired ganglia located at various points throughout its anatomy. These are termed the cerebral ganglia, the pedal ganglia, and the visceral ganglia. All are yellowish in color; the visceral ganglia are by far the largest and most extensive of the three.

Octopus



               The octopus (/ˈɒktəpʊs/ or /ˈɒktəpəs/; plural: octopuses, octopi, or octopodes; see below) is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms and, like other cephalopods, they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms. Octopuses have no internal or external skeleton (although some species have a vestigial remnant of a shell inside their mantles), allowing them to squeeze through tight places. Octopuses are among the most intelligent and behaviorally flexible of all invertebrates.

The octopus inhabits many diverse regions of the ocean, including coral reefs, pelagic waters, and the ocean floor. They have numerous strategies for defending themselves against predators, including the expulsion of ink, the use of camouflage and deimatic displays, their ability to jet quickly through the water, and their ability to hide. An octopus trails its eight arms behind it as it swims. All octopuses are venomous, but only one group, the blue-ringed octopus, is known to be deadly to humans.
Around 300 species are recognized, which is over one-third of the total number of known cephalopod species. The term 'octopus' may also be used to refer only to those creatures in the genus Octopus.

Biology

              Octopuses are characterized by their eight arms, usually bearing suction cups. The arms of octopuses are often distinguished from the pair of feeding tentacles found in squid and cuttlefish. Both types of limbs are muscular hydrostats. Unlike most other cephalopods, the majority of octopuses – those in the suborder most commonly known, Incirrina – have almost entirely soft bodies with no internal skeleton. They have neither a protective outer shell like the nautilus, nor any vestige of an internal shell or bones, like cuttlefish or squid. The beak, similar in shape to a parrot's beak, and made of chitin, is the only hard part of their bodies. This enables them to squeeze through very narrow slits between underwater rocks, which is very helpful when they are fleeing from moray eels or other predatory fish. The octopuses in the less-familiar Cirrina suborder have two fins and an internal shell, generally reducing their ability to squeeze into small spaces. These cirrate species are often free-swimming and live in deep-water habitats, while incirrate octopus species are found in reefs and other shallower seafloor habitats.

                  Octopuses have a relatively short life expectancy, and some species live for as little as six months. Larger species, such as the giant pacific octopus, may live for up to five years under suitable circumstances. However, reproduction is a cause of death: males can only live for a few months after mating, and females die shortly after their eggs hatch. They neglect to eat during the (roughly) one-month period spent taking care of their unhatched eggs, eventually dying of starvation. In a scientific experiment, removal of both optic glands after spawning was found to result in cessation of broodiness, resumption of feeding, increased growth, and greatly extended lifespans.
               Octopuses have three hearts. Two branchial hearts pump blood through each of the two gills, while the third is a systemic heart that pumps blood through the body. Octopus blood contains the copper-rich protein hemocyanin for transporting oxygen. Although less efficient under normal conditions than the iron-rich hemoglobin of vertebrates, in cold conditions with low oxygen pressure, hemocyanin oxygen transportation is more efficient than hemoglobin oxygen transportation. The hemocyanin is dissolved in the plasma instead of being carried within red blood cells, and gives the blood a bluish color. The octopus draws water into its mantle cavity, where it passes through its gills. As mollusks, their gills are finely divided and vascularized outgrowths of either the outer or the inner body surface.

Types of Octopus:
Octopus species -  There are seven species of bears that remain on the Earth today. While they are all similar in basic ways, there are enough differences for them to each have their own category as well as name.
Atlantic Pygmy Octopus  -The Atlantic Pygmy Octopus is very small, only about 5 ½ inches in length overall. Over 3 inches of that is the arms so the mantle part of the body isn’t very much to work with at all.
Blue Ringed Octopus -  The Blue-Ringed Octopus is one that has a trademark feature about it. They have rings of blue that are around their bodies.
California two Spot Octopus -  The California Two-Spot Octopus offers a very distinct appearance. It is also known by the name Bimac Octopus.
Caribbean  Reef Octopus - The Caribbean Reef Octopus is one that has a fascinating look to it. The combination of blue and green color is something that gets people’s attention
 Common Octopus - There can be quite a difference in the sizes of the Common Octopus. Some of them are only about 12 inches long while others are three times that at 36 inches in length.
East Pacific Red Octopus - There is a good chance you have heard of the East Pacific Red Octopus. They are small in size and have a body that is about three times smaller than the length of their eight arms.
Micmi Octopus -They aren’t very large Octopus with an overall length of two feet when they are fully grown. They have a normal coloring that spans many spans of brown and white.
North Pacific Giant Octopus -The winner of being the largest of all Octopus species in the world is the North Pacific Giant. This one can be close to 150 pound when it is fully mature and be as long as 15 feet.
Seven-arm octopus - What makes the Seven-Arm Octopus stand out from the other 300 species is that it has one less arm than they all do. Well, that is how it appears anyway.  





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