Squid

               Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles. Squid are strong swimmers and certain species can "fly" for short distances out of the water.


Modification and ancestral forms

               Squid have differentiated from their ancestral molluscs such that the body plan has been condensed antero-posteriorly and extended dorso-ventrally. 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, remaining. The pen is a feather-shaped internal structure that supports the squid's mantle and serves as a site for muscle attachment. It is made of a chitin-like material.

Anatomy

               The main body mass is enclosed in the mantle, which has a swimming fin along each side. These fins, unlike in other marine 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, making it practically invisible. 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 mantle cavity, which contains the gills (ctenidia) and openings to the excretory and reproductive systems. 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 major internal organs.

Shrimp

              The term shrimp is used to refer to some decapod crustaceans, although the exact animals covered can vary. Used broadly, it may cover any of the groups with elongated bodies and a primarily swimming mode of locomotion – chiefly Caridea and Dendrobranchiata. In some fields, however, the term is used more narrowly, and may be restricted to Caridea, to smaller species of either group, or to only the marine species. Under the broader definition, shrimp may be synonymous with prawn, covering stalk-eyed swimming crustaceans with long narrow muscular tails (abdomens), long whiskers (antennae) and slender legs. They swim forwards by paddling with swimmerets on the underside of their abdomens. Crabs and lobsters have strong walking legs, whereas shrimp have thin fragile legs which they use primarily for perching.
              Shrimp are widespread and abundant. They can be found feeding near the seafloor on most coasts and estuaries, as well as in rivers and lakes. To escape predators, some species flip off the seafloor and dive into the sediment. They usually live from one to seven years. Shrimp are often solitary, though they can form large schools during the spawning season. There are thousands of species, and usually there is a species adapted to any particular habitat. Any small crustacean which resembles a shrimp tends to be called one. 

Behavior

               There are many variations in the ways different types of shrimp look and behave. Even within the core group of caridean shrimp, the small delicate Pederson's shrimp (above) looks and behaves quite unlike the large commercial pink shrimp or the snapping pistol shrimp. The caridean family of pistol shrimp are characterized by big asymmetrical claws, the larger of which can produce a loud snapping sound. The family is diverse and worldwide in distribution, consisting of about 600 species. Colonies of snapping shrimp are a major source of noise in the ocean and can interfere with sonar and underwater communication. The small emperor shrimp has a symbiotic relationship with sea slugs and sea cucumbers, and may help keep them clear of ectoparasites.

Classification

              Shrimp are swimming crustaceans with long narrow muscular abdomens and long antennae. Unlike crabs and lobsters, shrimp have well developed pleopods (swimmerets) and slender walking legs; they are more adapted for swimming than walking. Historically, it was the distinction between walking and swimming that formed the primary taxonomic division into the former suborders Natantia and Reptantia. Members of the Natantia (shrimp in the broader sense) were adapted for swimming while the Reptantia (crabs, lobsters, etc.) were adapted for crawling or walking. Some other groups also have common names that include the word "shrimp"; any small swimming crustacean resembling a shrimp tends to be called one.

Sea Turtle

               The superfamily Chelonioidea has a world-wide distribution; sea turtles can be found in all oceans except for the polar regions.^{[citation needed]} Some species travel between oceans. The flatback sea turtle is found solely on the northern coast of Australia.

Habitat

               Sea turtles are generally found in the waters over continental shelves. After taking to the water for the first time, males will not return to shore again. During the first three to five years of life, sea turtles spend most time in the pelagic zone floating in seaweed beds. Green sea turtles in particular are often found in Sargassum beds, a brown seaweed in which they find shelter and food. Once the sea turtle has reached adulthood it moves closer to the shore. Females will come ashore to lay their eggs on sandy beaches during the nesting season.   

Respiration

              Sea turtles are almost always submerged, and, therefore, have developed an anaerobic system of energy metabolism. Although all sea turtles breathe air, under dire circumstances they may divert to anaerobic metabolism for long periods of time. When surfacing to breathe, a sea turtle can quickly refill its lungs with a single explosive exhalation and rapid inhalation. Their large lungs have adapted to permit rapid exchange of oxygen and to avoid trapping gases during deep dives.

Life history

              According to SeaWorld Parks & Entertainment, a lifespan of 80 years is feasible for sea turtles. It takes decades for sea turtles to reach sexual maturity. After mating at sea, adult female sea turtles return to land to nest at night. Different species of sea turtles exhibit various levels of philopatry. In the extreme case, females return to the beach where they hatched. This can take place every two to four years in maturity. They make from one to eight nests per season. The mature nesting female hauls herself onto the beach, nearly always at night, and finds suitable sand on which to create a nest. Using her hind flippers, she digs a circular hole 40 to 50 centimetres (16 to 20 in) deep. After the hole is dug, the female then starts filling the nest with a clutch of soft-shelled eggs one by one until she has deposited around 50 to 200 eggs, depending on the species. Some species have been reported to lay 250 eggs, such as the hawksbill. After laying, she re-fills the nest with sand, re-sculpting and smoothing the surface until it is relatively undetectable visually. The whole process takes thirty to sixty minutes. She then returns to the ocean, leaving the eggs untended.

Electric eel

              The electric eel has an elongated, cylindrical body, typically growing to about 2 m (6 ft 7 in) in length, and 20 kg (44 lb) in weight, making it the largest species of the Gymnotiformes. The coloration is dark gray-brown on the back and yellow or orange on the belly. Mature males have a darker color on the belly. They have no scales. The mouth is square, and positioned at the end of the snout. The anal fin extends the length of the body to the tip of the tail. As in other ostariophysan fishes, the swim bladder has two chambers. The anterior chamber is connected to the inner ear by a series of small bones derived from neck vertebrae called the Weberian apparatus, which greatly enhances its hearing capability. The posterior chamber extends along the whole length of the body and is used in buoyancy. Electrophorus has a well-developed sense of hearing. This fish has a vascularized respiratory organ in its oral cavity.^{[citation needed]} As obligate air-breathers, it rises to the surface every 10 minutes or so, and will gulp air before returning to the bottom. Nearly 80% of the oxygen used by the fish is taken in this way.


Physiology

                ^{The electric eel has three abdominal pairs of organs that produce electricity: the main organ, the Hunter's organ, and the Sach's organ. These organs make up four-fifths of its body, and are what give the electric eel the ability to generate two types of electric organ discharges: low voltage and high voltage. These organs are made of electrocytes, lined up so a current of ions can flow through them and stacked so each one adds to a potential difference. When the eel locates its prey, the brain sends a signal through the nervous system to the electrocytes. This opens the ion channels, allowing sodium to flow through, reversing the polarity momentarily. By causing a sudden difference in electric potential, it generates an electric current in a manner similar to a battery, in which stacked plates each produce an electrical potential difference. In the electric eel, some 5,000 to 6,000 stacked electroplaques are capable of producing a shock at up to 500 volts and 1 ampere of current (500 watts). It would be extremely unlikely for such a shock to be deadly for an adult human, due to the very short duration of an eel's discharge (<2 ms). Electrocution death is due to current flow; the level of current would be fatal in humans depending on the path the current takes through the human body, and the duration of current flow. Heart fibrillation (which is reversible via a heart defibrillator) can take place from currents ranging from 70 to 700 mA and higher, provided that the current flows for more than approximately 30 ms.    
                The electric eel is unique among the Gymnotiformes in having large electric organs capable of producing lethal discharges that allows them to stun prey. Larger voltages have been reported, but the typical output is sufficient to stun or deter virtually any other animal. Juveniles produce smaller voltages (about 100 V). They are capable of varying the intensity of the electrical discharge, using lower discharges for "hunting" and higher intensities for stunning prey, or defending themselves. When agitated, they are capable of producing these intermittent electrical shocks over a period of at least an hour without signs of tiring.}

Manta Ray

                Mantas can be found in temperate, subtropical and tropical waters. Both species are pelagic; M. birostris migrates across open oceans, singly or in groups, while M. alfredi tends to be resident and coastal. They are filter feeders and eat large quantities of zooplankton, which they swallow with their open mouths as they swim. Gestation lasts over a year, producing live pups. Mantas may visit cleaning stations for the removal of parasites. Like whales, they breach, for unknown reasons.

Both species are listed as Vulnerable by the International Union for Conservation of Nature. Anthropogenic threats include pollution, entanglement in fishing nets, and direct harvesting for their gill rakers for use in Chinese medicine. Their slow reproductive rate exacerbates these threats. They are protected in international waters by the Convention on Migratory Species of Wild Animals, but are more vulnerable closer to shore. Areas where mantas congregate are popular with tourists. Only a few aquariums are large enough to house them. In general, these large fish are seldom seen and difficult to study.

Appearance and Anatomy

               Manta rays are known for their large size, broad heads, triangular pectoral fins, and the horn-shaped cephalic fins located on either side of their mouths. They have horizontally flattened bodies with eyes on the sides of their heads (behind the cephalic fins) and gill slits on their ventral surfaces. Their tails lack skeletal support and are shorter than their disc-like bodies. The dorsal fins are small and at the base of the tail. The largest mantas can reach 1,350 kg (3,000 lb). In both species the width is approximately 2.2 times the length of the body; M. birostris reaches at least 7 m (23 ft) in width while M. alfredi reaches about 5.5 m (18 ft). Dorsally, mantas are typically black or dark in color with pale markings on their "shoulders". Ventrally, they are usually white or pale with distinctive dark markings by which individual mantas can be recognized. All black color morphs are known to exist. The skin is covered in mucus which protects it from infection.
               Mantas move through the water by the wing-like movements of their pectoral fins, which drive water backwards. Their large mouths are rectangular, and face forward as opposed to other ray and skate species with downward-facing mouths. The spiracles typical of Chondrichthyes are vestigial, and mantas must swim continuously to keep oxygenated water passing over their gills. The cephalic fins are usually spiralled, but flatten during foraging. The fish's gill arches have pallets of pinkish-brown spongy tissue that collect food particles. Mantas track down prey with visual and olfactory senses. They have one of the highest brain-to-body mass ratios of all fish, and their rete mirabiles may serve to keep the brain warm.

Lionfish (Pterois)

             Pterois range in size from 6.2 to 42.4 cm with typical adults measuring 38 cm and weighing an average of 480 g. They are well known for their ornate beauty, venomous spines and unique tentacles. Juvenile lionfish have a unique tentacle located above their eye sockets that varies in phenotype between species. It is suggested that the evolution of this tentacle serves to continually attract new prey; studies also suggest that it plays a role in sexual selection. 


Ecology and Behavior

             Pterois can live from five to fifteen years and have complex courtship and mating behaviors. Females release two mucus-filled egg clusters frequently, which can contain as many as fifteen thousand eggs. Studies on Pterois reproductive habits have increased significantly in the past decade All the species are aposematic: they have conspicuous coloration with boldly contrasting stripes and wide fans of projecting spines, advertising their ability to defend themselves.

Hazard to Humans

             Lionfish are known for their venomous fin rays, a feature that is uncommon among marine fish in the East Coast coral reefs. The potency of their venom makes them excellent predators and poisonous to fishermen and divers. Pterois venom produced negative inotropic and chronotropic effects when tested in both frog and clam hearts and has a depressing effect on rabbit blood pressure. These results are thought to be due to nitric oxide release. In humans, Pterois venom can cause systemic effects such as extreme pain, nausea, vomiting, fever, breathing difficulties, convulsions, dizziness, redness on the affected area, headache, numbness, paresthesia (pins and needles), heartburn, diarrhea, and sweating. Rarely, such stings can cause temporary paralysis of the limbs, heart failure and even death. Fatalities are common in very young children, the elderly, those with a weak immune system or those who are allergic to their venom. Their venom is rarely fatal to healthy humans, but some species have enough venom to produce extreme discomfort for over a period of several days. However, Pterois venom is a danger to allergic victims as they may experience anaphylaxis, a serious and often life threatening condition that requires immediate emergency medical treatment. Severe allergic reactions to Pterois venom include chest pain, severe breathing difficulties, a drop in blood pressure, swelling of the tongue, sweating, runny nose, or slurred speech. Such reactions can be fatal if not treated.

Pufferfish

 

             Pufferfish are generally believed to be the second most poisonous vertebrates in the world, after the golden poison frog. Certain internal organs, such as liver, and sometimes the skin, are highly toxic to most animals when eaten; nevertheless, the meat of some species is considered a delicacy in Japan (as 河豚, pronounced as fugu), Korea (as bok), and China (as 河豚 hétún) when prepared by chefs who know which part is safe to eat and in what quantity.

The Tetraodontidae contain at least 120 species of puffers in 19 genera. They are most diverse in the tropics and relatively uncommon in the temperate zone and completely absent from cold waters. They are typically small to medium in size, although a few species can reach lengths of greater than 100 centimetres (39 in).      

Poisoning

              Pufferfish can be lethal if not served properly. Puffer poisoning usually results from consumption of incorrectly prepared puffer soup, fugu chiri, or occasionally from raw puffer meat, sashimi fugu. While chiri is much more likely to cause death, sashimi fugu often causes intoxication, light-headedness, and numbness of the lips, and is often eaten for this reason.^{[citation needed]} Pufferfish tetrodotoxin deadens the tongue and lips, and induces dizziness and vomiting, followed by numbness and prickling over the body, rapid heart rate, decreased blood pressure, and muscle paralysis. The toxin paralyzes diaphragm muscles and stops the person who has ingested it from breathing. People who live longer than 24 hours typically survive, although possibly after a coma lasting several days.
The source of tetrodotoxin in puffers has been a matter of debate, but it is increasingly accepted that bacteria in the fish's intestinal tract are the source.
Saxitoxin, the cause of paralytic shellfish poisoning and red tide, can also be found in certain puffers.

Evolution

              The tetraodontids have been estimated to diverge from diodontids between 89 and 138 million years ago. There are four major clades, and these diverged during the Cretaceous between 80 and 101 million years ago. The oldest known pufferfish genus is Eotetraodon, from the Lutetian epoch of Middle Eocene Europe, with fossils found in Monte Bolca and the Caucasus Mountains. The Monte Bolca species, E. pygmaeus, coexisted with several other tetraodontiforms, including an extinct species of diodontid, primitive boxfish (Proaracana and Eolactoria), and other, totally extinct forms, such as Zignoichthys and the spinacanthids.

Lobster

       
              Clawed lobsters comprise a family (Nephropidae, sometimes also Homaridae) of large marine crustaceans. They have long bodies with muscular tails, and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, which are usually much larger than the others. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate. Commercially important species include two species of Homarus from the northern Atlantic Ocean, and scampi – the northern-hemisphere genus Nephrops and the southern-hemisphere genus Metanephrops. Although several other groups of crustaceans have the word "lobster" in their names, the unqualified term "lobster" generally refers to the clawed lobsters of the family Nephropidae. Clawed lobsters are not closely related to spiny lobsters or slipper lobsters, which have no claws (chelae), or to squat lobsters. The closest living relatives of clawed lobsters are the reef lobsters and the three families of freshwater crayfish.

               Lobster anatomy includes the cephalothorax which fuses the head and the thorax, both of which are covered by a chitinous carapace, and the abdomen. The lobster's head bears antennae, antennules, mandibles, the first and second maxillae, and the first, second, and third maxillipeds. Because lobsters live in a murky environment at the bottom of the ocean, they mostly use their antennae as sensors. The lobster eye has a reflective structure above a convex retina. In contrast, most complex eyes use refractive ray concentrators (lenses) and a concave retina.The abdomen includes swimmerets and its tail is composed of uropods and the telson.
Lobsters, like snails and spiders, have blue blood due to the presence of haemocyanin which contains copper (in contrast, vertebrates and many other animals have red blood from iron-rich haemoglobin). Lobsters possess a green hepatopancreas, called the tomalley by chefs, which functions as the animal's liver and pancreas.
Lobsters of the family Nephropidae are similar in overall form to a number of other related groups. They differ from freshwater crayfish in lacking the joint between the last two segments of the thorax, and they differ from the reef lobsters of the family Enoplometopidae in having full claws on the first three pairs of legs, rather than just one. The distinctions from fossil families such as Chilenophoberidae are based on the pattern of grooves on the carapace.

Sea Snake

              The Hydrophiinae, also known as coral reef snakes or sea snakes, are a subfamily of venomous elapid snakes that inhabit marine environments for most or all of their lives. Though they evolved from terrestrial ancestors, most are extensively adapted to a fully aquatic life and are unable to move on land, except for the genus Laticauda, which retain ancestral characteristics, allowing limited land movement. They are found in warm coastal waters from the Indian Ocean to the Pacific.
All have paddle-like tails and many have laterally compressed bodies that give them an eel-like appearance. Unlike fish, they do not have gills and must surface regularly to breathe. They are among the most completely aquatic of all air-breathing vertebrates. Among this group are species with some of the most potent venoms of all snakes. Some have gentle dispositions and bite only when provoked, but others are much more aggressive. Currently, 17 genera are described as sea snakes, comprising 62 species.   

             Like other land animals that have adapted to life in a marine environment, sea snakes ingest considerably more salt than their terrestrial relatives through their diets, and when seawater is inadvertently swallowed. This meant they had to evolve a more effective means of regulating the salt concentration of their blood. Mammals have the advantage of being able to pass salt in solution, mostly in the urine, but kidney function in birds and reptiles is too weak to remove salt in sufficient amounts. In birds, such as penguins, salt is removed through nasal glands, just as with the marine iguanas of the Galapagos Islands. Sea turtles' lacrimal glands allow them to produce very salty tears. In sea snakes, the posterior sub lingual glands, located under and around the tongue sheath, evolved to allow them to expel salt with their tongue action.

            Scalation among sea snakes is highly variable. As opposed to terrestrial snake species that have imbricate scales to protect against abrasion, the scales of most pelagic sea snakes do not overlap. Reef-dwelling species, such as Aipysurus, do have imbricate scales to protect against the sharp coral. The scales themselves may be smooth, keeled, spiny or granular, the latter often looking like warts. Pelamis has body scales that are "peg-like", while those on its tail are juxtaposed hexagonal plates.
Aipysurus laevis has been found to have photoreceptors in the skin of its tail, allowing it to detect light and presumably ensuring it is completely hidden, including its tail, inside coral holes during the day. While other species have not been tested, A. laevis possibly is not unique among sea snakes in this respect. Interestingly, dermal light sensitivity is found in all the major animal phyla.

Butterfly Fish

             The butterflyfishes are a group of conspicuous tropical marine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group. Found mostly on the reefs of the Atlantic, Indian and Pacific Oceans, there are approximately 120 species in 10 genera. A number of species pairs occur in the Indian and Pacific Oceans, members of the huge genus Chaetodon.
Butterflyfishes look like smaller versions of angelfish (Pomacanthidae), but unlike these, lack preopercle spines at the gill covers. Some members of the genus Heniochus resemble the Moorish idol (Zanclus cornutus) of the monotypic Zanclidae. Among the paraphyletic Perciformes, the former are probably not too distantly related to butterflyfish, whereas the Zanclidae seem far less close.

Description and Ecology

              Butterflyfishes mostly range from 12 to 22 cm (4.7 to 8.7 in) in length. The largest species, the lined butterflyfish and the saddle butterflyfish, C. ephippium, grow to 30 cm (12 in). The common name references the brightly coloured and strikingly patterned bodies of many species, bearing shades of black, white, blue, red, orange and yellow. Other species are dull in colour. Many have eyespots on their flanks and dark bands across their eyes, not unlike the patterns seen on butterfly wings. Their deep, laterally narrow bodies are easily noticed through the profusion of reef life. The conspicuous coloration of butterflyfishes may be intended for interspecies communication. Butterflyfish have uninterrupted dorsal fins with tail fins that may be rounded or truncated, but are never forked.
             Generally diurnal and frequenting waters of less than 18 m (59 ft) (though some species descend to 180 metres (590 ft)), butterflyfishes stick to particular home ranges. The corallivores are especially territorial, forming mated pairs and staking claim to a specific coral head. Contrastingly, the zooplankton feeders form large conspecific groups. By night, butterflyfish hide in reef crevices and exhibit markedly different coloration.
Their coloration also makes them popular aquarium fish. However, most species feed on coral polyps and sea anemones. Balancing the relative populations of prey and predator is complex, leading hobby aquarists to focus on the few generalists and specialist zooplankton feeders.

Blue Whale

                The blue whale (Balaenoptera musculus) is a marine mammal belonging to the suborder of baleen whales (called Mysticeti).At 30 metres (98 ft) in length and 170 tonnes (190 short tons) or more in weight, it is the largest known animal to have ever existed.
Long and slender, the blue whale's body can be various shades of bluish-grey dorsally and somewhat lighter underneath. There are at least three distinct subspecies: B. m. musculus of the North Atlantic and North Pacific, B. m. intermedia of the Southern Ocean and B. m. brevicauda (also known as the pygmy blue whale) found in the Indian Ocean and South Pacific Ocean. B. m. indica, found in the Indian Ocean, may be another subspecies. As with other baleen whales, its diet consists almost exclusively of small crustaceans known as krill.
Blue whales were abundant in nearly all the oceans on Earth until the beginning of the twentieth century. For over a century, they were hunted almost to extinction by whalers until protected by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 blue whales worldwide, located in at least five groups. More recent research into the Pygmy subspecies suggests this may be an underestimate. Before whaling, the largest population was in the Antarctic, numbering approximately 239,000 (range 202,000 to 311,000).There remain only much smaller (around 2,000) concentrations in each of the eastern North Pacific, Antarctic, and Indian Ocean groups. There are two more groups in the North Atlantic, and at least two in the Southern Hemisphere.

              The blue whale has a long tapering body that appears stretched in comparison with the stockier build of other whales. The head is flat, U-shaped and has a prominent ridge running from the blowhole to the top of the upper lip. The front part of the mouth is thick with baleen plates; around 300 plates (each around one metre (3.2 ft) long) hang from the upper jaw, running 0.5 m (1.6 ft) back into the mouth. Between 70 and 118 grooves (called ventral pleats) run along the throat parallel to the body length. These pleats assist with evacuating water from the mouth after lunge feeding (see feeding below).

              The dorsal fin is small, ranging in height from 8–70 centimeters (3.1–28 in) (usually 20–40 centimeters (7.9–16 in)) and averaging about 28 centimetres (11 in).It is visible only briefly during the dive sequence. Located around three-quarters of the way along the length of the body, it varies in shape from one individual to another; some only have a barely perceptible lump, but others may have prominent and falcate (sickle-shaped) dorsals. When surfacing to breathe, the blue whale raises its shoulder and blowhole out of the water to a greater extent than other large whales, such as the fin or sei whales. Observers can use this trait to differentiate between species at sea. Some blue whales in the North Atlantic and North Pacific raise their tail fluke when diving. When breathing, the whale emits a spectacular vertical single-column spout up to 12 metres (39 ft), typically 9 metres (30 ft). Its lung capacity is 5,000 litres (1320 U.S. gallons). Blue whales have twin blowholes shielded by a large splashguard.

Walrus

                The walrus (Odobenus rosmarus) is a large flippered marine mammal with a discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. This species is subdivided into three subspecies  the Atlantic walrus (O. r. rosmarus) which lives in the Atlantic Ocean, the Pacific walrus (O. r. divergens) which lives in the Pacific Ocean, and O. r. laptevi, which lives in the Laptev Sea of the Arctic Ocean.
Adult walruses are easily recognized by their prominent tusks, whiskers, and bulkiness. Adult males in the Pacific can weigh more than 1,700 kg (3,700 lb) and, among pinnipeds, are exceeded in size only by the two species of elephant seals. Walruses live mostly in shallow waters above the continental shelves, spending significant amounts of their lives on the sea ice looking for benthic bivalve mollusks to eat. Walruses are relatively long-lived, social animals, and they are considered to be a "keystone species" in the Arctic marine regions.
The walrus has played a prominent role in the cultures of many indigenous Arctic peoples, who have hunted the walrus for its meat, fat, skin, tusks, and bone. During the 19th century and the early 20th century, walruses were widely hunted and killed for their blubber, walrus ivory, and meat. The population of walruses dropped rapidly all around the Arctic region. Their population has rebounded somewhat since then, though the populations of Atlantic and Laptev walruses remain fragmented and at low levels compared with the time before human interference.

Etymology

                The origin of the word walrus is thought to derive from a Germanic language, and it has been attributed largely to either the Dutch language or Old Norse. Its first part is thought to derive from a word such as Dutch walvis 'whale'. Its second part has also been hypothesized to come from the Old Norse word for 'horse'. For example, the Old Norse word hrossvalr means 'horse-whale' and is thought to have been passed in an inverted form to both Dutch and the dialects of northern Germany as walros and Walross.An alternate theory is that is comes from the Dutch words wal 'shore' and reus 'giant'.
                 The Norwegian manuscript Konungsskuggsja, thought to date from around 1240 AD refers to the walrus as "rosmhvalr" in Iceland and "rostungr" in Greenland (walruses were by now extinct in Iceland and Norway, while the word evolved on in Greenland). Several place names in Iceland, Greenland and Norway may originate from walrus sites; Hvalfjord, Hvallatrar and Hvalsnes to name some, all being typical walrus breeding grounds.
The archaic English word for walrus—morse—is widely thought to have come from the Slavic languages. Compare морж (morž) in Russian, mursu in Finnish, moršâ in Saami, and morse in French. Olaus Magnus, who depicted the walrus in the Carta Marina in 1539, first referred to the walrus as the ros marus, probably a Latinization of morž, and this was adopted by Linnaeus in his binomial nomenclature.

Sea lion

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                Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, and short, thick hair. Together with the fur seals, they comprise the family Otariidae, eared seals and there are six extant and one extinct species (the Japanese sea lion) in five genera. Their range extends from the subarctic to tropical waters of the global ocean in both the Northern and Southern Hemispheres, with the notable exception of the northern Atlantic Ocean. They have an average life span of 20–30 years. A male California sea lion weighs on an average about 300 kg (660 lb) and is about 8 ft (2.4 m) long, while the female sea lion weighs 100 kg (220 lb) and is 6 ft (1.8 m) long. The largest sea lion is the Steller's sea lion which can weigh 1,000 kg (2,200 lb) and grow to a length of 10 ft (3.0 m). Sea lions consume large quantities of food at a time and are known to eat about 5–8% of their body weight (about 15–35 lb (6.8–16 kg)) at a single feeding.

Taxonomy

                Together with the fur seals, they constitute the Otariidae family, collectively known as eared seals. Until recently, sea lions were grouped under a single subfamily called Otariinae, whereas fur seals were grouped in the subfamily Arcocephalinae. This division was based on the most prominent common feature shared by the fur seals and absent in the sea lions, namely the dense underfur characteristic of the latter. Recent genetic evidence, however, strongly suggests Callorhinus, the genus of the northern fur seal, is more closely related to some sea lion species than to the other fur seal genus, Arctocephalus.Therefore, the fur seal/sea lion subfamily distinction has been eliminated from many taxonomies. Sea lions are related to the walrus and the seal. Nonetheless, all fur seals have certain features in common: the fur, generally smaller sizes, farther and longer foraging trips, smaller and more abundant prey items and greater sexual dimorphism. All sea lions have certain features in common, in particular their coarse, short fur, greater bulk and larger prey than fur seals. For these reasons, the distinction remains useful.

Starfish

             
                Starfish are among the most familiar of marine animals found on the seabed. They typically have a central disc and five arms, though some species have many more arms than this. The aboral or upper surface may be smooth, granular or spiny, and is covered with overlapping plates. Many species are brightly coloured in various shades of red or orange, while others are blue, grey, brown, or drab. Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface. They are opportunistic feeders and are mostly predators on benthic invertebrates. Several species having specialized feeding behaviours, including suspension feeding and adaptations for feeding on specific prey. They have complex life cycles and can reproduce both sexually and asexually. Most can regenerate damaged or lost arms.
The Asteroidea occupy several important ecological roles. Starfish, such as the ochre sea star (Pisaster ochraceus), have become widely known as an example of the keystone species concept in ecology. The tropical crown-of-thorns starfish (Acanthaster planci) is a voracious predator of coral throughout the Indo-Pacific region. Other starfish, such as members of the Asterinidae, are frequently used in developmental biology.

Symmetry

                Starfish are radially symmetric and typically express pentamerism or pentaradial symmetry as adults. However, the evolutionary ancestors of echinoderms are believed to have had bilateral symmetry. Modern starfish, as well as other echinoderms, exhibit bilateral symmetry in their larval forms.
Most starfish have five rays or arms, which radiate from a central disc. However, several species frequently have six or more arms. Several asteroid groups, such as the Solasteridae, have 10 to 15 arms, while some species, such as the Antarctic Labidiaster annulatus can have up to 50. It is not unusual for species that typically have five arms to exceptionally possess six or more through abnormal development.  

Body Wall

               The body wall consists of a thin cuticle, an epidermis consisting of a single layer of cells, a thick dermis formed of connective tissue and a thin coelomic epithelium which contains the longitudinal and circular musculature and the peritoneum. The dermis contains an endoskeleton of plate-like calcium carbonate components known as ossicles. These are honeycombed structures composed of calcite microcrystals arranged in a lattice. They vary in form, some bearing external granules, tubercles and spines, sometimes organised into definite patterns. Some are specialised structures such as the pedicellariae and paxillae. Pedicellariae are compound ossicles with forceps-like jaws and function to remove debris from the body surface, moving about on their flexible stalks in response to physical or chemical stimuli, continually making biting movements.. Paxillae are umbrella-like structures found on starfish which live buried in sediment. They meet edge to edge and form a false cuticle with a water cavity beneath in which the madreporite and delicate gill structures are protected. All the ossicles, including those projecting externally, are covered by the epidermal layer.

Seahorse

           
              Seahorse is the title given to 54 species of marine fish in the genus Hippocampus. "Hippocampus" comes from the Ancient Greek hippos meaning "horse" and kampos meaning "sea monster".

Physical Description

             Seahorses range in size from 0.6 to 14 in (1.5 to 35.5 cm). They are named for their equine appearance. Although they are bony fish, they do not have scales but rather thin skin stretched over a series of bony plates, which are arranged in rings throughout their body. Each species has a distinct number of rings. Seahorses swim upright, another characteristic that is not shared by their close pipefish relatives, who swim horizontally. Razorfish are the only other fish that swim vertically like a seahorse. Unusual among fish, seahorses have a flexible, well-defined neck. They also sport a coronet on the head, which is distinct for each individual.

Location

             Seahorses are mainly found in shallow tropical and temperate waters throughout the world, and prefer to live in sheltered areas such as seagrass beds, estuaries, coral reefs, or mangroves. In Pacific waters from North America to South America there are approximately four species. In the Atlantic, the H. erectus ranges from Nova Scotia to Uruguay. H. zosterae, known as the dwarf seahorse, is found in the Bahamas.
Colonies have been found in European waters such as the Thames Estuary.
Three species live in the Mediterranean Sea: H. guttulatus (the long-snouted seahorse), H. hippocampus (the short-snouted seahorse) and H. fuscus (the sea pony). These species form territories; males stay within 1 square meter (11 sq ft) of their habitat while females range about one hundred times that.

Jellyfish

                          
              Jellyfish or jellies are the major non-polyp form of individuals of the phylum Cnidaria. They are typified as free-swimming marine animals consisting of a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate for locomotion, while stinging tentacles can be used to capture prey.
Jellyfish are found in every ocean, from the surface to the deep sea. A few jellyfish inhabit freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal.

             Jellyfish or jellies are the major non-polyp form of individuals of the phylum Cnidaria. They are typified as free-swimming marine animals consisting of a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate for locomotion, while stinging tentacles can be used to capture prey.
Jellyfish are found in every ocean, from the surface to the deep sea. A few jellyfish inhabit freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal.