Seahorse

This article is about the genus of fish. For the mythological sea-horse, see Hippocamp. For other uses, see Seahorse (disambiguation).

Seahorses comprise the fish genus Hippocampus within the family Syngnathidae, in order Syngnathiformes. Syngnathidae also includes the pipefishes. "Hippocampus" comes from the Ancient Greek hippos meaning “horse” and kampos meaning “sea monster”.

There are about 40 species of seahorse are mainly found in shallow tropical and temperate waters throughout the world. They prefer to live in sheltered areas such as seagrass beds, coral reefs, or mangroves. Colonies have been found in European waters such as the Thames Estuary. From North America down to South America there are approximately four species, ranging from the very small (dwarf seahorses are only about 2.5 centimeters (1 in) to much larger specimens off the Pacific Coast of Central America (the foot-long H. ingens). H. erectus are larger seahorses that range from Nova Scotia to around Uruguay. Three species live in the Mediterranean Sea: H. hippocampus (long snout), H. brevirostris (short snout) and H. fuscus (immigrated from the Red Sea). These fish form territories, with males staying in about 1 square metre (11 sq ft) of their habitat while females range about one hundred times that area. They bob around in sea grass meadows, mangrove stands, and coral reefs where they adopt murky brown and gray patterns to camouflage themselves among the sea grass. During social moments or in unusual surroundings, seahorses turn bright colors.

Description

Seahorses are named for their equine profile. Although they are bony fish, they do not have scales, but rather a thin skin stretched over a series of bony plates 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, which swim horizontally. Seahorses have a coronet on their head, which is distinct to each individual, much like a human fingerprint. They swim very poorly by using a dorsal fin, which they rapidly flutter and pectoral fins, located behind their eyes, which they use to steer. Seahorses have no caudal fin. Since they are poor swimmers, they are most likely to be found resting, with their prehensile tails wound around a stationary object. They have long snouts, which they use to suck up food, and eyes that can move independently of each other, much like a chameleon. Seahorses eat small shrimp, tiny fish and plankton.

Evolution and fossil record

Anatomical evidence, supported by molecular, physical, and genetic evidence, demonstrates that seahorses are highly modified pipefish. The fossil record of seahorses, however, is very sparse. The best known and best studied fossils are specimens of H. guttulatus (though literature more commonly refers to them under the synonym of H. ramulosus), from the Marecchia River Formation of Rimini Province, Italy, dating back to the Lower Pliocene, about 3 million years ago. The earliest known seahorse fossils are of two pipefish-like species, H. sarmaticus and H. slovenicus from the coprolitic horizon of Tunjice Hills, a middle Miocene lagerstätte in Slovenia dating back about 13 million years. Molecular dating finds that pipefish and seahorses separated during the Late Oligocene. This has led to speculation that seahorses evolved in response to large areas of shallow-water, newly created as the result of tectonic events. The shallow water allowed the expansion of seagrass habitats that selected for the camouflage offered by the seahorses’ upright posture.These tectonic changes occurred in the Western Pacific Ocean suggesting an origin there with molecular data suggesting two later and separate invasions of the Atlantic Ocean.

Reproduction

Seahorses are often thought of as being monogamous, though recent research shows this may not be true. The male seahorse is equipped with a brood pouch on the ventral, or front-facing, side. When mating, the female seahorse deposits up to 1,000 the eggs in the male's pouch, which the male then internally fertilizes. The male carries the eggs for about two months until they emerge,expelling fully-developed, miniature seahorses in the water. The father continues to protect the young until they are able to live on their own, however they have been known to eat a few offspring while at it.

Courtship

Before breeding, pairs court for several days, even while others try to interfere. Scientists believe the courtship behavior synchronizes the animals' movements so that the male can receive the eggs when the female is ready to deposit them. During this time they may change color, swim side by side holding tails or grip the same strand of sea grass with their tails and wheel around in unison in what is known as a “pre-dawn dance". They eventually engage in a “true courtship dance" lasting about 8 hours, during which the male pumps water through the egg pouch on his trunk which expands and open to display its emptiness. When the female’s eggs reach maturity, she and her mate let go of any anchors and snout-to-snout, drift upward out of the seagrass, often spiraling as they rise. The female inserts her ovipositor into the male’s brood pouch and deposits dozens to thousands of eggs. As the female releases her eggs, her body slims while his swells. Both animals then sink back into the seagrass and she swims away.

Gestation

The male fertilizes the eggs, which embed in the pouch wall and become enveloped by tissue.[The male supplies the eggs with prolactin, the same hormone responsible for milk production in pregnant mammals. The pouch provides oxygen as well as a controlled environment incubator. The eggs then hatch in the pouch where the salinity of the water is regulated; this prepares the newborns for life in the sea. Throughout gestation, which in most species requires two to four weeks, his mate visits him daily for “morning greetings”. They interact for about 6 minutes, reminiscent of courtship. The female then swims away until the next morning, and the male returns to vacuuming up food through his snout.

Research published in 2007 indicates the male releases sperm into the surrounding sea water during fertilization, and not directly into the pouch as previously thought.

Birth

The number of young released by the male seahorse averages 100-200 for most species, but may be as low as 5 for the smaller species, or as high as 1,500. When the fry are ready to be born, the male expels them with muscular contractions. He typically gives birth at night and is ready for the next batch of eggs by morning when his mate returns. Like almost all other fish species, seahorses do not nurture their young after birth. Infants are susceptible to predators or ocean currents which wash them away from feeding grounds or into temperatures too extreme for their delicate bodies. Fewer than .5% of infants survive to adulthood, explaining why litters are so large. These survival rates are actually fairly high compared to other fish, because of their protected gestation, making the process worth the great cost to the father. The eggs of most other fish are abandoned immediately after fertilization.

Questions surrounding reproductive roles

Reproduction is energetically costly to the male. This brings into question why the sexual role reversal even takes place. In an environment where one partner incurs more energy costs than the other, Bateman's principle suggests that the lesser contributor takes the role of the aggressor. Male seahorses are more aggressive and sometimes “fight” for female attention. According to Amanda Vincent of Project Seahorse, only males tail-wrestle and snap their heads at each other. This discovery prompted further study of energy costs. To estimate the female’s direct contribution, researcher Heather D. Masonjones, associate professor of biology at the University of Tampa, chemically analyzed the energy stored in each egg. To measure the burden on the male, Masonjones measured its oxygen consumption. By the end of incubation, the male consumed almost 33% more oxygen than before mating. The study concluded that the female's energy expenditure while generating eggs is twice that of males during incubation confirming the standard hypothesis.

Why the male seahorse (and other members of Syngnathidae) carries the offspring through gestation is unknown, though some researchers believe it allows for shorter birthing intervals, in turn resulting in more offspring. Given an unlimited number of ready and willing partners, males have the potential to produce 17 percent more offspring than females in a breeding season. Also, females have “time-outs” from the reproductive cycle that are 1.2 times longer than those of males. This seems to be based on mate choice, rather than physiology. When the female’s eggs are ready, she must lay them in a few hours or eject them into the water column. Making eggs is a huge cost to her physically, since they amount to about a third of her body weight. To protect against losing a clutch, the female demands a long courtship. The daily greetings help to cement the bond between the pair.

Monogamy

A study conducted by Amanda Vincent of Project Seahorse demonstrates the importance of the daily greetings ritual in establishing seahorses' monogamous relationships. Vincent kept a female seahorse in a tank with two males. After the female filled one male’s pouch with eggs Vincent removed him and she was left with the unimpregnated male. During the weeks of her mate’s pregnancy, the female and her tankmate greeted each other daily, clinging to the same bit of grass and changing color, but did not display signs of courtship. After the original mate gave birth he was returned to the tank. Both males competed for her attention, but in six of six tests the female presented the next clutch of eggs to the other male.

Although monogamy within species is not common, it does appear to exist for some. In this case, the mate guarding hypothesis may be an explanation. This hypothesis states that “males remain with a single female because of ecological factors that make male parental care and protection of offspring especially advantageous. Because the rates of survival for newborn seahorses are so low, incubation is essential. Though not proven, males could have taken on this role because of the lengthy period the females require to produce their eggs. If males incubate while females prepare the next clutch (amounting to 1/3 of body weight), they can reduce the interval between clutches.

Feeding habits

Seahorses feed on small crustaceans floating in the water or crawling on the bottom. With excellent camouflage and a lot of patience, seahorses ambush prey that float within striking range. Mysid shrimp and other small crustaceans are favorites, but some seahorses have been observed eating other kinds of invertebrates and even larval fish.

In aquaria

While many aquarium hobbyists keep seahorses as pets, seahorses collected from the wild tend to fare poorly in home aquaria. Many eat only live foods such as brine shrimp and are prone to stress, which damages their immune systems and makes them susceptible to disease.

In recent years, however, captive breeding has become more popular. Such seahorses survive better in captivity, and are less likely to carry diseases. They eat frozen mysidacea (crustaceans) that are readily available from aquarium stores,[16] and do not experience the stress of moving out of the wild. Although captive-bred seahorses are more expensive, they take no toll on wild populations.

Seahorses should be kept in an aquarium to themselves, or with compatible tank-mates. Seahorses are slow feeders, and fast, aggressive feeders will leave them without food.[16]

Seahorses can co-exist with many species of shrimp and other bottom-feeding creatures. Gobies also make good tank-mates. Avoid eels, tangs, triggerfish, squid, octopus, and sea anemones.

Animals sold as "freshwater seahorses" are usually the closely related pipefish, of which a few species live in the lower reaches of rivers. The supposed true "freshwater seahorse" called H. aimei was not a real species, but a name sometimes used for Barbour's and Hedgehog seahorses. The latter is a species that can be found in brackish waters, but not actually a freshwater fish.

Use in Chinese medicine

Seahorse populations are thought to have been endangered in recent years by overfishing and habitat destruction. The seahorse is used in traditional Chinese herbology, and as many as 20 million seahorses may be caught each year and sold for this purpose. Medicinal seahorses are not readily bred in captivity as they are susceptible to disease and have somewhat different energetics from aquarium seahorses. Seahorses are also used as medicines by the Indonesians, the Central Filipinos, and a whole host of other racial and ethnic groups around the world.

Import and export of seahorses has been controlled under CITES since May 15, 2004. However, Indonesia, Japan, Norway, and South Korea have chosen to opt out of the trade rules set by CITES.

The problem may be exacerbated by the growth of pills and capsules as the preferred method of ingesting medication as they are cheaper and more available than traditional, individually tailored prescriptions of raw medicinals but the contents are harder to track. Seahorses once had to be of a certain size and quality before they were accepted by TCM practitioners and consumers. But declining availability of the preferred large, pale and smooth seahorses has been offset by the shift towards prepackaged medicines, which make it possible for TCM merchants to sell previously unused juvenile, spiny and dark-coloured animals. Today almost a third of the seahorses sold in China are prepackaged. This adds to the pressure on the species.

Taxonomy

Genus Hippocampus

Big-belly seahorse, H. abdominalis Lesson, 1827 (New Zealand and south and east Australia)
Winged seahorse, H. alatus Kuiter, 2001
West African seahorse, H. algiricus Kaup, 1856
Narrow-bellied seahorse, H. angustus Günther, 1870
Barbour's seahorse, H. barbouri Jordan & Richardson, 1908
Pygmy seahorse, H. bargibanti Whitley, 1970 West Pacific area (Indonesia, Philippines, Papua New Guinea, Solomon Islands, etc)
False-eyed seahorse, H. biocellatus Kuiter, 2001
Réunion seahorse, H. borboniensis Duméril, 1870
Short-head seahorse or knobby seahorse, H. breviceps Peters, 1869 (south and east Australia)
Giraffe seahorse, H. camelopardalis Bianconi, 1854
Knysna seahorse, H. capensis Boulenger, 1900
H. colemani Kuiter, 2003
Tiger tail seahorse, H. comes Cantor, 1850
Crowned seahorse, H. coronatus Temminck & Schlegel, 1850
Denise's pygmy seahorse, H. denise Lourie & Randall, 2003
Lined seahorse, H. erectus Perry, 1810 (east coast of the Americas, between Nova Scotia and Uruguay)
Fisher's seahorse, H. fisheri Jordan & Evermann, 1903
Sea pony, H. fuscus Rüppell, 1838 (Indian Ocean)
Big-head seahorse, H. grandiceps Kuiter, 2001
Long-snouted seahorse, H. guttulatus Cuvier, 1829
Eastern spiny seahorse, H. hendriki Kuiter, 2001
Short-snouted seahorse, H. hippocampus (Linnaeus, 1758) (Mediterranean Sea and Atlantic Ocean)
Thorny seahorse, H. histrix Kaup, 1856 (Indian Ocean, Persian Gulf, Red Sea, and the Far East)
Pacific seahorse, H. ingens Girard, 1858 (Pacific coast of North, Central and South America)
Jayakar's seahorse, H. jayakari Boulenger, 1900
Collared seahorse, H. jugumus Kuiter, 2001
Great seahorse, H. kelloggi Jordan & Snyder, 1901
Common seahorse, H. kuda Bleeker, 1852
Lichtenstein's seahorse, H. lichtensteinii Kaup, 1856
Bullneck seahorse, H. minotaur Gomon, 1997
Japanese seahorse, H. mohnikei Bleeker, 1854
Monte Bello seahorse, H. montebelloensis Kuiter, 2001
Northern spiny seahorse, H. multispinus Kuiter, 2001
H. pontohi Lourie and Kuiter, 2008
High-crown seahorse, H. procerus Kuiter, 2001
Queensland seahorse, H. queenslandicus Horne, 2001
Longsnout seahorse, H. reidi Ginsburg, 1933 (Caribbean coral reefs)
Satomi's pygmy seahorse, H. satomiae Lourie and Kuiter, 2008
Half-spined seahorse, H. semispinosus Kuiter, 2001
H. severnsi Lourie and Kuiter, 2008
Shiho's seahorse, H. sindonis Jordan & Snyder, 1901
Hedgehog seahorse, H. spinosissimus Weber, 1913
West Australian seahorse, H. subelongatus Castelnau, 1873
Longnose seahorse, H. trimaculatus Leach, 1814
White's seahorse, H. whitei Bleeker, 1855 (east Australia)
Zebra seahorse, H. zebra Whitley, 1964
Dwarf seahorse, H. zosterae Jordan & Gilbert, 1882 (Gulf of Mexico and the Caribbean)

Pygmy seahorses

Pygmy Seahorses are less than 15 millimeters (0.6 in) tall and 17 millimeters (0.7 in) wide members of the genus. Previously the term was applied exclusively to the species H. bargibanti but since 1997, discoveries have made this term obsolete. The species H. minotaur, H. denise, H. colemani, H. pontohi, H. severnsi and H. satomiae have been described. Other species that are believed to be unclassified have also been reported in books, dive magazines and on the Internet. They can be distinguished from other species of seahorse by their 12 trunk rings, low number of tail rings (26–29), the location in which young are brooded in the trunk region of males and their extremely small size. Molecular analysis (of ribosomal RNA) of 32 Hippocampus species found that H. bargibanti belongs in a separate clade from other members of the genus and therefore that the species diverged from the other species in the "ancient" past.

Most pygmy seahorses are well camouflaged and live in close association with other organisms including colonial hydrozoans (Lytocarpus and Antennellopsis), coralline algae (Halimeda) sea fans (Muricella, Annella, Acanthogorgia). This combined with their small size accounts for why most species have only been noticed in recent years.

Cultural references

In heraldry, a seahorse is depicted as a creature with the foreparts of a horse and the hindparts of a fish. See, for example, the right supporter of the Isle of Wight Arms, the supporters on either side of the crest of the city of Newcastle upon Tyne, or the coincidental arms of the University of Newcastle, Australia.
The seahorse is prominent in the badge of Italian football club A.C. Cesena.
The seahorse is prominent in the logo of Waterford Crystal and the logotype of illustrator W. W. Denslow.
In the Seri culture of northwestern Mexico, the legend is that the seahorse is a person who, to escape his pursuers, fled into the sea, placing his sandals in his waistbelt at his back.
The National Society for Epilepsys seahorse mascot is named Caesar (after the Roman dictator, Julius Caesar, who was believed to have had epilepsy). The seahorse mascot was chosen because the hippocampus, a part of the brain that is vulnerable to damage from epileptic seizures, resembles a seahorse in shape.
In Hawaiian culture the seahorse signals eternal friendship.
The Japanese anime company, Tatsunoko Production, has a seahorse in its logo.
Four schools in the United States are known to use a seahorse as a mascot:
The Avery Coonley School (in Downers Grove, Illinois)
Burlington High School (of Burlington, Vermont)
Christchurch School (of Christchurch, Virginia)
Frederick Douglass Academy VI High School (in Queens, New York)

Name of the Body parts for sea horse.



Source:http://en.wikipedia.org/wiki/Sea_horse

Dolphin

For other uses, see Dolphin (disambiguation). This article is semi-protected. Bottlenose Dolphin breaching in the bow wave of a boat. Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in seventeen genera. They vary in size from 1.2 m (4 ft) and 40 kg (90 lb) (Maui's Dolphin), up to 9.5 m (30 ft) and 10 tonnes (9.8 LT; 11 ST) (the Orca or Killer Whale). They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating fish and squid. The family Delphinidae is the largest in the Cetacean order, and relatively recent: dolphins evolved about ten million years ago, during the Miocene. Dolphins are among the most intelligent animals and their often friendly appearance and seemingly playful attitude have made them popular in human cultu

Origin of the name

The name is originally from Ancient Greek (delphís; "dolphin"), which was related to the Greek (delphys; "womb"). The animal's name can therefore be interpreted as meaning "a 'fish' with a womb". The name was transmitted via the Latin delphinus, Middle Latin dolfinus and the Old French daulphin, which reintroduced the ph into the word. The word is used in a few different ways. It can mean: * Any member of the family Delphinidae (oceanic dolphins), * Any member of the families Delphinidae and Platanistoidea (oceanic and river dolphins), * Any member of the suborder Odontoceti (toothed whales; these include the above families and some others), * Used casually as a synonym for Bottlenose Dolphin, the most common and familiar species of dolphin. This article uses the second definition and does not describe Porpoises (suborder Odontoceti, family Phocoenidae). Orcas and some closely related species belong to the Delphinidae family and therefore qualify as dolphins, even though they are called whales in common language. A group of dolphins is called a "school" or a "pod". Male dolphins are called "bulls", females "cows" and young dolphins are called "calves".

Taxonomy

Suborder Odontoceti, toothed whales Family Delphinidae, oceanic dolphins Genus Delphinus Long-Beaked Common Dolphin, Delphinus capensis Short-Beaked Common Dolphin, Delphinus delphis Genus Tursiops Common Bottlenose Dolphin, Tursiops truncatus Indo-Pacific Bottlenose Dolphin, Tursiops aduncus Genus Lissodelphis Northern Rightwhale Dolphin, Lissodelphis borealis Southern Rightwhale Dolphin, Lissodelphis peronii Genus Sotalia Tucuxi, Sotalia fluviatilis Costero, Sotalia guianensis Genus Sousa Indo-Pacific Hump-backed Dolphin, Sousa chinensis Chinese White Dolphin (the Chinese variant), Sousa chinensis chinensis Atlantic Humpbacked Dolphin, Sousa teuszii Genus Stenella Atlantic Spotted Dolphin, Stenella frontalis Clymene Dolphin, Stenella clymene Pantropical Spotted Dolphin, Stenella attenuata Spinner Dolphin, Stenella longirostris Striped Dolphin, Stenella coeruleoalba Genus Steno Rough-Toothed Dolphin, Steno bredanensis Genus Cephalorhynchus Chilean Dolphin, Cephalorhynchus eutropia Commerson's Dolphin, Cephalorhynchus commersonii Heaviside's Dolphin, Cephalorhynchus heavisidii Hector's Dolphin, Cephalorhynchus hectori Genus Grampus Risso's Dolphin, Grampus griseus Genus Lagenodelphis Fraser's Dolphin, Lagenodelphis hosei Genus Lagenorhynchus Atlantic White-Sided Dolphin, Lagenorhynchus acutus Dusky Dolphin, Lagenorhyn chus obscurus Hourglass Dolphin, Lagenorhynchus cruciger Pacific White-Sided Dolphin, Lagenorhynchus obliquidens Peale's Dolphin, Lagenorhynchus australis White-Beaked Dolphin, Lagenorhynchus albirostris Genus Orcaella Australian Snubfin Dolphin, Orcaella heinsohni Irrawaddy Dolphin, Orcaella brevirostris Genus Peponocephala Melon-headed Wha le, Peponocephala electra Genus Orcinus Killer Whale (Orca), Orcinus orca Genus Feresa Pygmy Killer Whale, Feresa attenuata Genus Pseudorca False Killer Whale, Pseudorca crassidens Genus Globicephala Long-finned Pilot Whale, Globicephala melas Short-finned Pilot Whale, Globicephala macrorhynchus Genus †Australodelphis †Australodelphis mirus Family Platanistidae Ganges and Indus River Dolphin, Platanista gangetica with two subspecies Ganges River Dolphin (or Susu), Platanista gangetica gangetica Indus River Dolphin (or Bhulan), Platanista gangetica minor Family In iidae Amazon River Dolphin (or Boto), Inia geoffrensis Family Lipotidae Baiji (or Chinese River Dolphin), Lipotes vexillifer (possibly extinct, since December 2006) Family Pontoporiidae La Plata Dolphin (or Franciscana), Pontoporia blainvillei Six species in the family Delphinidae are commonly called "whales" but genetically are dolphins. They are sometimes called blackfish. Melon-headed Whale, Peponocephala electra Killer Whale (Orca), Orcinus orca Pygmy Killer Whale, Feresa attenuata Wolphin Kawili'Kai at the Sea Life Park in Hawaii. False Killer Whale, Pseudorca crassidens Long-finned Pilot Whale, Globicephala melas Short-finned Pilot Whale, Globicephala macrorhynchus

Hybrid dolphins

In 1933, three strange dolphins beached off the Irish coast; they appeare d to be hybrids between Risso's and Bottlenose Dolphins. This mating was later repeated in captivity producing a hybrid calf. In captivity, a Bottlenose Dolphin and a Rough-toothed Dolphin pro

duced hybrid offspring. A Common-Bottlenose hybrid lives at SeaWorld California. Other dolp hin hybrids live in captivity around the world or have been reported in the wild, s uch as a Bot tlenose- Atlantic Spotted hybrid. The best known hybrid is the Wolphin, a False Killer Whale-Bottlenose Dolphin hybrid. The Wolphin is a fertile hybrid. Two Wolphins currently live at the Sea Life Park in Hawaii; the first was born in 1985 from a male False Killer Whale and a female Bottlenose. Wolphins have also been observed in the wild.

Evolution and anatomy

Evolution

See also: Evolution of cetaceans Dolphins, along with whales and porpoises, are descendants of terrestrial mammals, most likely of the Artiodactyl order. The ancestors of the modern day dolphins entered the water roughly fifty million years ago, in the Eocene epoch. Hind Limb Buds on Dolphins. An embryo of a Spotted Dolphin in the fifth week of developme nt. The hind limbs are present as small b umps (hind limb buds) near the base of the tail. The pin is approximately 2.5 cm (1.0 in) long. Modern dolphin skeletons have two small, rod-shaped pelvic bones thought to be vestigial hind limbs. In October 2006 an unusual Bottlenose Dolphin was captured in Japan; it had small fins on each side of its genital slit which scientists believe to be a more pronounced development of these vestigial hind limbs.

Anatomy

Dolphins have a streamlined fusiform body, adapted for fast swimming. The tail fin, called the fluke, is used for propulsion, while the pectoral fins together with the entire tail section provide directional control. The dorsal fin, in those species that have one, provides

stability while swimming. Though it varies per species, basic coloration patterns are shades of grey usually with a lighter underside, often with lines and patches of different hue and contrast. The head contains the melon, a round organ used for echolocation. In many species, elongated jaws form a distinct beak; species such as the Bottlenose have a curved mouth which looks like a fixed smile. Some species have up to 250 teeth. Dolphins breathe through a blowhole on top of their head. The trachea is anterior to the brain. The dolphin brain is large and highly complex and is different in structure from that of most land mammals. Unlike most mammals, dolphins do not have hair, except for a few hairs around the tip of their rostrum which they lose shortly before or after birth. The only exception to this is the Boto river dolphin, which has persistent small hairs on the rostrum. Dolphin’s reproductive organs are located on the underside of the body. Males have two slits, one concealing the penis and one further behind for the anus. The female has one genital slit, housing the vagina and the anus. A mammary slit is positioned on either side of the female's genital slit. A recent study at the US National Marine Mammal Foundation revealed that dolphins are the only animals other than humans that develop a natural form of Type 2 Diabetes, which may lead to a better understanding of the disease and new treatments for both humans and dolphins.

Senses


Most dolphins have acute eyesight, both in and out of the water, and they can hear frequencies ten times or more above the upper limit of adult human hearing. Though they have a small ear opening on each side of their head, it is believed that hearing underwater is also if not exclusively done with the lower jaw, which conducts sound to the middle ear via a fat-filled cavity in the lower jaw bone. Hearing is also used for echolocation, which all dolphins have. It is believed that dolphin teeth function as an antenna to receive incoming sound and to pinpoint the exact location of an object. The dolphin's sense of touch is also well-developed, with free nerve endings densely packed in the skin, especially around the snout, pectoral fins and genital area. However, dolphins lack an olfactory nerve and lobes and thus are believed to have no sense of smell. They do have a sense of taste and show preferences for certain kinds of fish. Since dolphins spend most of their time below the surface, tasting the water could function like smelling, in that substances in the water can signal the presence of objects that are not in the dolphin’s mouth. Though most dolphins do not have hair, they do have hair follicles that may perform some sensory function. The small hairs on the rostrum of the Boto river dolphin are believed to function as a tactile sense possibly to compensate for the Boto's poor eyesight.

Behavior

See also: Whale surfacing behaviour Dolphins are often regarded as one of Earth's most intelligent animals, though it is hard to say just how intelligent. Comparing species' relative intelligence is complicated by differences in sensory apparatus, response modes, and nature of cognition. Furthermore, the difficulty and expense of experimental work with large aquatic animals has so far prevented some tests and limited sample size and rigor in others. Compared to many other species however, dolphin behavior has been studied extensively, both in captivity and in the wild. See cetacean intelligence for more details

Social behavior

Dolphins are social, living in pods of up to a dozen individuals. In places with a high abundance of food, pods can merge temporarily, forming a superpod; such groupings may exceed 1,000 dolphins. Individuals communicate using a variety of clicks, whistles and other vocalizations. They make ultrasonic sounds for echolocation. Membership in pods is not rigid; interchange is common. However, dolphins can establish strong social bonds. Dolphins will stay with injured or ill individuals, even helping them to breathe by bringing them to the surface if needed. This altruism does not appear to be limited to their own species however. The dolphin Moko in New Zealand has been observed guiding a female Pygmy Sperm Whale together with her calf out of shallow water where they had stranded several times. They have also been seen protecting swimmers from sharks by swimming circles around the swimmers or charging the sharks to make them go away. Dolphins also display culture, something long believed to be unique to humans (and possibly other primate species). In May 2005, a discovery in Australia found Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) teaching their young to use tools. They cover their snouts with sponges to protect them while foraging. This knowledge is mostly transferred by mothers to daughters, unlike simian primates, where knowledge is generally passed on to both sexes. Using sponges as mouth protection is a learned behavior. Another learned behavior was discovered among river dolphins in Brazil, where some male dolphins use weeds and sticks as part of a sexual display. Dolphins engage in acts of aggression towards each other. The older a male dolphin is, the more likely his body is to be covered with bite scars. Male dolphins engage in such acts of aggression apparently for the same reasons as humans: disputes between companions and competition for females. Acts of aggression can become so intense that targeted dolphins sometimes go into exile as a result of losing a fight. Male Bottlenose Dolphins have been known to engage in infanticide. Dolphins have also been known to kill porpoises for reasons which are not fully understood, as porpoises generally do not share the same diet as dolphins and are therefore not competitors for food supplies.

Reproduction and sexuality

Dolphin copulation happens belly to belly and though many species engage in lengthy foreplay, the actual act is usually brief, but may be repeated several times within a short timespan. The gestation period varies per species; for the small Tucuxi dolphin, this period is around 11 to 12 months, while for the Orca the gestation period is around 17 months. They usually become sexually active at a young age, even before reaching sexual maturity. The age of sexual maturity varies by species and gender.

Dolphins are known to have sex for reasons other than reproduction, sometimes also engaging in homosexual behavior. Various species sometimes engage in sexual behavior including copulation with other dolphin species. Sexual encounters may be violent, with male dolphins sometimes showing aggressive behavior towards both females and other males. Occasionally, dolphins behave sexually towards other animals, including humans.

Feeding

Various methods of feeding exist among and within species, some apparently exclusive to a single population. Fish and squid are the main food, but the False Killer Whale and the Killer Whale also feed on other marine mammals.

One common feeding method is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball. Individual members then take turns plowing through the ball, feeding on the stunned fish. Coralling is a method where dolphins chase fish into shallow water to more easily catch them. In South Carolina, the Atlantic Bottlenose Dolphin takes this further with strand feeding, driving prey onto mud banks for easy access. In some places, Orcas come to the beach to capture sea lions. Some species also whack fish with their fluke, stunning them and sometimes knocking them out of the water.

Reports of cooperative human-dolphin fishing date back to the ancient Roman author and natural philosopher Pliny the Elder. A modern human-dolphin partnership currently operates in Laguna, Santa Catarina, Brazil. Here, dolphins drive fish towards fishermen waiting along the shore and signal the men to cast their nets. The dolphins’ reward is the fish that escape the nets.

Vocalizations

Dolphins are capable of making a broad range of sounds using nasal airsacs located just below the blowhole. Roughly three categories of sounds can be identified: frequency modulated whistles, burst-pulsed sounds and clicks. Dolphins communicate with their whistles and burst-pulsed sounds, though the nature and extent of that ability is not known. At least some dolphin species can identify themselves using a signature whistle.The clicks are directional and are for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Dolphin echolocation clicks are amongst the loudest sounds made by marine animals.

Jumping and playing

Dolphins occasionally leap above the water surface, sometimes performing acrobatic figures (e.g. the Spinner Dolphin). Scientists are not certain about the purpose(s) of the acrobatics. Possibilities include locating schools of fish by looking at above-water signs like feeding birds, communicating with other dolphins, dislodging parasites or simple amusement.

Play is an important part of dolphin culture. Dolphins play with seaweed and play-fight with other dolphins. At times they harass other local creatures, like seabirds and turtles. Dolphins enjoy riding waves and frequently surf coastal swells and the bow waves of boats, at times “leaping” between the dual bow waves of a moving catamaran. Occasionally, they playfully interact with swimmers.

Sleeping

Source:http://en.wikipedia.org/wiki/Dolphin

Star fish

Starfish or sea stars are echinoderms belonging to the class Asteroidea. The names "starfish" and "sea star" essentially refer to members of the Class Asteroidea. However, common usage frequently finds "starfish" and "sea star" also applied to ophiuroids which are correctly referred to as "brittle stars" or "basket stars".

There are 2,000 living species of starfish that occur in all the world's oceans, including the Atlantic, Pacific, Indian as well as in the Arctic and the Southern Ocean (i.e., Antarctic) regions. Starfish occur across a broad depth range from the intertidal to abyssal depths (>6000 m).

Starfish are among the most familiar of marine animals and possess a number of widely known traits, such as regeneration and feeding on mussels. Starfish possess a wide diversity of body forms and feeding methods. The extent that Asteroidea can regenerate varies with individual species. Broadly speaking, starfish are opportunistic feeders, with several species having specialized feeding behavior, including suspension feeding and specialized predation on specific prey.

The Asteroidea occupy several important roles throughout ecology and biology. Sea stars, such as the Ochre sea star (Pisaster ochraceus) have become widely known as the example of the keystone species concept in ecology. The tropical Crown of Thorns starfish (Acanthaster planci) are voracious predators of coral throughout the Indo-Pacific region. Other starfish, such as members of the Asterinidae are frequently used in developmental biology.

Appearance

Starfish express pentamerism or pentaradial symmetry as adults. However, the evolutionary ancestors of echinoderms are believed to have had bilateral symmetry. Starfish, as well as other echinoderms, do exhibit bilateral symmetry, but only as larval forms. Most starfish typically have five rays or arms, which radiate from a central disk. However, several species frequently have six or more arms. Several asteroid groups, such as the Solasteridae, have 10-15 arms whereas some species, such as the Antarctic Labidiaster annulatus can have up to 50. It is not unusual for species that typically have five-rays to exceptionally possess five or more rays due to developmental abnormalities. The bodies of starfish are composed of calcium carbonate components, known as ossicles. These form the endoskeleton, which takes on a variety of forms that are externally expressed as a variety of structures, such as spines and granules. The architecture and individual shape/form of these plates which often occur in specific patterns or series, as well as their location are the source of morphological data used to classify the different groups within the Asteroidea. Terminology referring to body location in sea stars is usually based in reference to the mouth to avoid incorrect assumptions of homology with the dorsal and ventral surfaces in other bilateral animals. The bottom surface is often referred to as the oral or actinal surface whereas the top surface is referred to as the aboral or abactinal side. The body surface of sea stars often has several structures that comprise the basic anatomy of the animal and can sometimes assist in its identification. The madreporite can be easily identified as the light-colored circle, located slightly off center on the central disk. This is a porous plate which is connected via a calcified channel to the animal's water vascular system in the disk. Its function is, at least in part, to provide additional water for the animal's needs, including replenishing water to the water vascular system. Several groups of asteroids, including the Valvatacea but especially the Forcipulatacea possess small bear-trap or valve-like structures known as pedicellariae. These can occur widely over the body surface. In forcipulate asteroids, such as Asterias or Pisaster, pedicellariae occur in pom-pom like tufts at the base of each spine, whereas in goniasterids, such as Hippasteria, pedicellariae are scattered over the body surface. Although the full range of function for these structures is unknown, some are thought to act to act as defense where others have been observed to aid in feeding. The Antarctic Labidiaster annulatus uses its large, pedicellariae to capture active krill prey. The North Pacific Stylasterias has been observed to capture small fish with its pedicellariae. Other types of structures vary by taxon. For example, Porcellanasteridae employ additional cribriform organs which occur among their lateral plate series, which are thought to generate current in the burrows made by these infaunal sea star.

Internal anatomy

As echinoderms, starfish possess a hydraulic water vascular system that aids in locomotion. The water vascular system has many projections called tube feet on the ventral face of the sea star's arms which function in locomotion and aid with feeding. Tube feet emerge through openings in the endoskeleton and are externally expressed through the open grooves present along the bottom of each arm. The body cavity not only contains the water vascular system that operates the tube feet, but also the circulatory system, called the hemal system. Hemal channels form rings around the mouth (the oral hemal ring), closer to the top of the sea star and around the digestive system (the gastric hemal ring). A portion of the body cavity called the axial sinus connects the three rings. Each ray also has hemal channels running next to the gonads. On the end of each arm or ray there is a microscopic eye (ocellus), which allows the sea star to see, although it only allows it to see light and dark, which is useful to see movement. Only part of the cells are pigmented (thus a red or black color) and there is no cornea or iris. This eye is known as a pigment spot ocellus. Several types of toxins and secondary metabolites have been extracted from several species of sea star. Research into the efficacy of these compounds for possible pharmacological or industrial use occurs worldwide.

Digestive system

The mouth of a starfish is located on the underside of the body, and opens through a short esophagus into firstly a cardiac stomach, and then, a second, pyloric stomach. Each arm also contains two pyloric caeca, long hollow tubes branching outwards from the pyloric stomach. Each pyloric caecum is lined by a series of digestive glands, which secrete digestive enzymes and absorb nutrients from the food. A short intestine runs from the upper surface of the pyloric stomach to open at an anus in the center of the upper body.

Many sea stars, such as Astropecten and Luidia swallow their prey whole, and start to digest it in the stomachs before passing it into the pyloric caeca. However, in a great many species, the cardiac stomach can be everted out of the organism's body to engulf and digest food. In these species, the cardiac stomach fetches the prey then passes it to the pyloric stomach, which always remains internal.

Some species are able to use their water vascular systems to force open the shells of bivalve mollusks such as clams and mussels by injecting their stomachs into the shells. With the stomach inserted inside the shell, the sea star is able to digest the mollusk in place. The cardiac stomach is then brought back inside the body, and the partially digested food is moved to the pyloric stomach. Further digestion occurs in the intestine. Waste is excreted through the anus on the aboral side of the body.

Because of this ability to digest food outside of its body, the sea star is able to hunt prey that are much larger than its mouth would otherwise allow, such as clams and oysters, arthropods, small fish, and mollusks. However, some species are not pure carnivores, and may supplement their diet with algae or organic detritus. Some of these species are grazers, but others trap food particles from the water in sticky mucus strands that can be swept towards the mouth along ciliated grooves.

Some echinoderms can live for several weeks without food under artificial conditions. Scientists believe that they may receive some nutrients from organic material dissolved in seawater.

Nervous system

Echinoderms have rather complex nervous systems, but lack a true centralized brain. All echinoderms have a network of interlacing nerves called a nerve plexus which lies within, as well as below, the skin. The esophagus is also surrounded by a central nerve ring which sends radial nerves into each of the arms, often parallel with the branches of the water vascular system. The ring nerves and radial nerves coordinate the sea star's balance and directional systems.
Although the echinoderms do not have many well-defined sensory inputs, they are sensitive to touch, light, temperature, orientation, and the status of water around them. The tube feet, spines, and pedicellariae found on sea stars are sensitive to touch, while eyespots on the ends of the rays are light-sensitive. The tube feet, especially those at the tips of the rays, are also sensitive to chemicals and this sensitivity is used in locating odor sources, such as food.
The eyespots each consist of a mass of ocelli, consisting of pigmented epithelial cells that respond to light and narrow sensory cells lying between them. Each ocellus is covered by a thick, transparent, cuticle that both protects them and acts as a lens. Many starfish also possess individual photoreceptor cells across their body and are able to respond to light even when their eyespots are covered.

Source:http://en.wikipedia.org/wiki/Starfish

Shark

Sharks (superorder Selachimorpha) are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs. Since that time, sharks have diversified into 440 species, ranging in size from the small dwarf lanternshark, Etmopterus perryi, a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark, Rhincodon typus, the largest fish, which reaches approximately 12 metres (39 ft 4 in) and which feeds only on plankton, squid, and small fish through filter feeding. Sharks are found in all seas and are common down to depths of 2,000 metres (6,562 ft). They generally do not live in freshwater, with a few exceptions such as the bull shark and the river shark which can live both in seawater and freshwater. They respire with the use of five to seven gill slits. Sharks have a covering of dermal denticles that protect their skin from damage and parasites and improve fluid dynamics so the shark can move faster. They have several sets of replaceable teeth. Well-known species such as the great white shark, tiger shark, and the hammerhead are apex predators, at the top of the underwater food chain. Their extraordinary skills as predators fascinate and frighten humans, even as their survival is under serious threat from fishing and other human activities.

Physical characteristics:

Shark skeletons are very different from those of bony fish and terrestrial vertebrates. Sharks and other cartilaginous fish (skates and rays) have skeletons made of cartilage and connective tissue. Cartilage is flexible and durable, yet has about half the density of bone. This reduces the skeleton’s weight, saving energy. Sharks have no rib cage and therefore on land a shark's own weight can literally crush it.

Jaw

Like its relatives, rays and skates, the shark's jaw is not attached to the cranium. The jaw's surface, like the shark's vertebrae and gill arches, needs extra support due to its heavier exposure to physical stress and its need for strength. It has a layer of tiny hexagonal plates called "tesserae", which are crystal blocks of calcium salts arranged as a mosaic. This gives these areas much of the same strength found in the real bony tissue found in other animals. Generally there is only one layer of tesserae in sharks, but the jaws of large specimens, such as the bull shark, tiger shark, and the great white shark, have two to three layers or more, depending on body size. The jaws of a large white shark may have up to five layers. In the rostrum (snout), the cartilage can be spongy and flexible to absorb the power of impacts.

Teeth

Main article: Shark teeth The teeth of sharks are embedded in the gums rather than directly fixed to the jaw, and are constantly replaced throughout the shark's life. Multiple rows of replacement teeth are grown in a groove on the inside of the jaw and moved forward in a "conveyor belt"; some sharks lose 30,000 or more teeth in their lifetime. The rate of tooth replacement varies from once every 8–10 days to several months. In most species teeth are replaced one at a time, while in the cookiecutter sharks the entire row of teeth is replaced simultaneously. The shape of a shark's tooth depends on its diet: those that feed on mollusks and crustaceans have dense flattened teeth for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey such as mammals have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. The teeth of plankton-feeders such as the basking shark are greatly reduced and non-functional.

Fins

The fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling the horny keratin in hair and feathers. Sharks can only drift away from objects directly in front of them because their fins do not allow them to swim backwards.

Dermal denticles

Main article: Dermal denticle Unlike bony fish, sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body. This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy. In the past, sharkskin has been used as sandpaper. Their dermal teeth give them hydrodynamic advantages as they reduce turbulence when swimming.

Tails

Sharks have very distinctive tails. The tails (caudal fins) of sharks vary considerably between species and are adapted to the lifestyle of the shark. The tail provides thrust and so speed and acceleration are dependent on tail shape. Different tail shapes have evolved in sharks adapted for different environments. Sharks possess a heterocercal caudal fin in which the dorsal portion is usually noticeably larger than the ventral portion. This is due to the fact that the shark's vertebral column extends into that dorsal portion, allowing for a greater surface area for muscle attachment which would then be used for more efficient locomotion among the negatively buoyant cartilaginous fishes. This is in contrast to most bony fishes, which possess a homocercal caudal fin.

The tiger shark's tail has a large upper lobe which delivers the maximum amount of power for slow cruising or sudden bursts of speed. The tiger shark must be able to twist and turn in the water easily when hunting to support its varied diet, whereas the porbeagle, which hunts schooling fish such as mackerel and herring has a large lower lobe to help it keep pace with its fast-swimming prey. Some tail adaptations have other purposes. The thresher feeds on fish and squid, which it herds and stuns with its

Physiology

Buoyancy

Unlike bony fish, sharks do not have gas-filled swim bladders for buoyancy. Instead, sharks rely on a large liver, filled with oil that contains squalene and the fact that cartilage is about half as dense as bone. The liver constitutes up to 30% of their body mass. The liver's effectiveness is limited, so sharks employ dynamic lift to maintain depth and then sink when they stop swimming. Sand tiger sharks are also known to store air in their stomachs, using the stomach as a swim bladder. Most sharks need to constantly swim in order to breathe and cannot sleep very long, if at all, or they will sink. However certain shark species, like the nurse shark, are capable of pumping water across their gills, allowing them to rest on the ocean bottom.

Some sharks, if inverted or stroked on the nose, enter a natural state of tonic immobility. Researchers can use this condition to handle sharks safely.

Respiration

Like other fish, sharks extract oxygen from seawater as it passes over their gills. Unlike other fish, shark gill slits are not covered, but lie in a row behind the head. A modified slit called a spiracle lies just behind the eye; the spiracle assists water intake during respiration and plays a major role in bottom dwelling sharks. Spiracles are reduced or missing in active pelagic sharks. While the shark is moving, water passes through the mouth and over the gills in a process known as "ram ventilation". While at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move. Obligate ram ventilation is also true of some pelagic bony fish species.

The respiration and circulation process begins when deoxygenated blood travels to the shark's two-chambered heart. Here the shark pumps blood to its gills via the ventral aorta artery where it branches off into afferent brachial arteries. Reoxygenation takes place in the gills and the reoxygenated blood flows into the efferent brachial arteries, which come together to form the dorsal aorta. The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from the body then flows through the posterior cardinal veins and enters the posterior cardinal sinuses. From there blood enters the heart ventricle and the cycle repeats.

Thermoregulation

Most sharks are "cold-blooded", or more precisely poikilothermic, meaning that their internal body temperature matches that of their ambient environment. Members of the family Lamnidae, such as the shortfin mako shark and the great white shark, are homeothermic and maintain a higher body temperature than the surrounding water. In these sharks, a strip of aerobic red muscle located near the center of the body generates the heat, which the body retains via a countercurrent exchange mechanism by a system of blood vessels called the rete mirabile ("miraculous net"). The common thresher shark has a similar mechanism for maintaining an elevated body temperature, which is thought to have evolved independently.

Osmoregulation

In contrast to bony fish, with the exception of the Coelacanth, the blood and other tissue of sharks and Chondrichthyes in general is isotonic to their marine environments because of the high concentration of urea and trimethylamine N-oxide (TMAO), allowing them to be in osmotic balance with the seawater. This adaptation prevents most sharks from surviving in fresh water, and they are therefore confined to marine environments. A few exceptions to this rule exist, such as the bull shark which has developed a way to change its kidney function to excrete large amounts of urea. When a shark dies the urea is broken down to ammonia by bacteria — because of this, the dead body will gradually start to smell strongly of ammonia.

Senses

Smell

Sharks have keen olfactory senses, located in the short duct (which is not fused, unlike bony fish) between the anterior and posterior nasal openings, with some species able to detect as little as one part per million of blood in seawater. They are more attracted to the chemicals found in the guts of many species, and as a result often linger near or in sewage outfalls. Some species, such as nurse sharks, have external barbels that greatly increase their ability to sense prey.

Sight

Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retinas, though their eyesight is well adapted to the marine environment with the help of a tissue called tapetum lucidum. This means that sharks can contract and dilate their pupils, like humans, something no teleost fish can do. This tissue is behind the retina and reflects light back to it, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger nocturnal adaptations. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some species have nictitating membranes. This membrane covers the eyes during predation, and when the shark is being attacked. However, some species, including the great white shark (Carcharodon carcharias), do not have this membrane, but instead roll their eyes backwards to protect them when striking prey. The importance of sight in shark hunting behavior is debated. Some believe that electro- and chemoreception are more significant, while others point to the nictating membrane as evidence that sight is important. Presumably, the shark would not protect its eyes were they unimportant. The use of sight probably varies with species and water conditions. In effect the shark's field of vision can swap between monocular and stereoscopic at any time.

Hearing

Although it is hard to test sharks' hearing, they may have a sharp sense of hearing and can possibly hear prey many miles away. A small opening on each side of their heads (not to be confused with the spiracle) leads directly into the inner ear through a thin channel. The lateral line shows a similar arrangement, which is open to the environment via a series of openings called lateral line pores. This is a reminder of the common origin of these two vibration- and sound-detecting organs that are grouped together as the acoustico-lateralis system. In bony fish and tetrapods the external opening into the inner ear has been lost.

Source:http://en.wikipedia.org/wiki/Shark