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105-473: Centrostephanus is a genus of echinoderms belonging to the family Diadematidae . The genus has almost cosmopolitan distribution . Species: Echinoderm See taxonomy An echinoderm ( / ɪ ˈ k aɪ n ə ˌ d ɜːr m , ˈ ɛ k ə -/ ) is any animal of the phylum Echinodermata ( / ɪ ˌ k aɪ n oʊ ˈ d ɜːr m ə t ə / ), which includes starfish , brittle stars , sea urchins , sand dollars and sea cucumbers , as well as

210-554: A gastrula or even a blastula stage. New larvae can develop from the preoral hood (a mound like structure above the mouth), the side body wall, the postero-lateral arms, or their rear ends. Cloning is costly to the larva both in resources and in development time. Larvae undergo this process when food is plentiful or temperature conditions are optimal. Cloning may occur to make use of the tissues that are normally lost during metamorphosis. The larvae of some sand dollars clone themselves when they detect dissolved fish mucus, indicating

315-427: A yolk-feeding larva. The provision of a yolk-sac means that smaller numbers of eggs are produced, the larvae have a shorter development period and a smaller dispersal potential, but a greater chance of survival. Echinoderms are globally distributed in almost all depths, latitudes and environments in the ocean. Adults are mainly benthic , living on the seabed, whereas larvae are often pelagic , living as plankton in

420-844: A backbone, make up a huge portion of all life in the sea. Invertebrate sea life includes Cnidaria such as jellyfish and sea anemones ; Ctenophora ; sea worms including the phyla Platyhelminthes , Nemertea , Annelida , Sipuncula , Echiura , Chaetognatha , and Phoronida ; Mollusca including shellfish , squid , octopus ; Arthropoda including Chelicerata and Crustacea ; Porifera ; Bryozoa ; Echinodermata including starfish ; and Urochordata including sea squirts or tunicates . Over 10,000 species of fungi are known from marine environments. These are parasitic on marine algae or animals, or are saprobes on algae, corals, protozoan cysts, sea grasses, wood and other substrata, and can also be found in sea foam . Spores of many species have special appendages which facilitate attachment to

525-433: A co-ordinated way, propelled by the other four arms. During locomotion, the propelling arms can made either snake-like or rowing movements. Starfish move using their tube feet, keeping their arms almost still, including in genera like Pycnopodia where the arms are flexible. The oral surface is covered with thousands of tube feet which move out of time with each other, but not in a metachronal rhythm ; in some way, however,

630-403: A defensive mechanism when attacked. Echinoderms possess a unique water vascular system, a network of fluid-filled canals modified from the coelom (body cavity) that function in gas exchange, feeding, sensory reception and locomotion. This system varies between different classes of echinoderm but typically opens to the exterior through a sieve-like madreporite on the aboral (upper) surface of

735-547: A huge community of life, including the corals themselves, their symbiotic zooxanthellae , tropical fish and many other organisms. Much attention in marine biology is focused on coral reefs and the El Niño weather phenomenon. In 1998, coral reefs experienced the most severe mass bleaching events on record, when vast expanses of reefs across the world died because sea surface temperatures rose well above normal. Some reefs are recovering, but scientists say that between 50% and 70% of

840-474: A large stomach and a rectum with the anus at the apex of the test. Sea cucumbers are mostly detritivores , sorting through the sediment with modified tube feet around their mouth, the buccal tentacles. Sand and mud accompanies their food through their simple gut, which has a long coiled intestine and a large cloaca . Crinoids are suspension feeders , passively catching plankton which drift into their outstretched arms. Boluses of mucus-trapped food are passed to

945-620: A little in front of the midpoint. The two halves each regenerate their missing organs over a period of several months, but the missing genital organs are often very slow to develop. The larvae of some echinoderms are capable of asexual reproduction. This has long been known to occur among starfish and brittle stars, but has more recently been observed in a sea cucumber, a sand dollar and a sea urchin. This may be by autotomising parts that develop into secondary larvae, by budding , or by splitting transversely . Autotomised parts or buds may develop directly into fully formed larvae, or may pass through

1050-478: A main line of defence against potential pathogens. Depending on the class, echinoderms may have spherule cells (for cytotoxicity, inflammation, and anti-bacterial activity), vibratile cells (for coelomic fluid movement and clotting), and crystal cells (which may serve for osmoregulation in sea cucumbers). The coelomocytes secrete antimicrobial peptides against bacteria, and have a set of lectins and complement proteins as part of an innate immune system that

1155-430: A pore (or a pair of pores in sea urchins) to the exterior, forming a podium or tube foot . The water vascular system assists with the distribution of nutrients throughout the animal's body; it is most visible in the tube feet which can be extended or contracted by the redistribution of fluid between the foot and the internal ampulla. The organisation of the water vascular system is somewhat different in ophiuroids, where

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1260-449: A sea urchin has an 'echinopluteus' larva while a brittle star has an 'ophiopluteus' larva. A starfish has a ' bipinnaria ' larva, which develops into a multi-armed ' brachiolaria ' larva. A sea cucumber's larva is an 'auricularia' while a crinoid's is a 'vitellaria'. All these larvae are bilaterally symmetrical and have bands of cilia with which they swim; some, usually known as 'pluteus' larvae, have arms. When fully developed they settle on

1365-541: A sea urchin is overturned, it can extend its tube feet in one ambulacral area far enough to bring them within reach of the substrate and then successively attach feet from the adjoining area until it is righted. Some species bore into rock, usually by grinding away at the surface with their mouthparts. Sea cucumbers are generally sluggish animals. Many can move on the surface of the seabed or burrow through sand or mud using peristaltic movements; some have short tube feet on their under surface with which they can creep along in

1470-402: A single limb. Geologically, the value of echinoderms is in their ossified dermal endoskeletons , which are major contributors to many limestone formations and can provide valuable clues as to the geological environment. They were the most used species in regenerative research in the 19th and 20th centuries. Further, some scientists hold that the radiation of echinoderms was responsible for

1575-538: A sudden encirclement by their flexible arms. The limbs then bend under the disc to transfer the food to the jaws and mouth. Many sea urchins feed on algae, often scraping off the thin layer of algae covering the surfaces of rocks with their specialised mouthparts known as Aristotle's lantern. Other species devour smaller organisms, which they may catch with their tube feet. They may also feed on dead fish and other animal matter. Sand dollars may perform suspension feeding and feed on phytoplankton , detritus, algal pieces and

1680-459: A tip shaped like a suction pad in which a vacuum can be created by contraction of muscles. This combines with some stickiness from the secretion of mucus to provide adhesion. The tube feet contract and relax in waves which move along the adherent surface, and the animal moves slowly along. Brittle stars are the most agile of the echinoderms. Any one of the arms can form the axis of symmetry, pointing either forwards or back. The animal then moves in

1785-409: A transition zone between freshwater river environments and saltwater maritime environments. They are subject both to marine influences—such as tides, waves, and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment. The shifting flows of both sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among

1890-543: A very small number of species, the eggs are retained in the coelom where they develop viviparously , later emerging through ruptures in the body wall. In some crinoids, the embryos develop in special breeding bags, where the eggs are held until sperm released by a male happens to find them. One species of seastar , Ophidiaster granifer , reproduces asexually by parthenogenesis . In certain other asterozoans , adults reproduce asexually until they mature, then reproduce sexually. In most of these species, asexual reproduction

1995-537: Is a complex three-dimensional world, covering approximately 71% of the Earth's surface. The habitats studied in marine biology include everything from the tiny layers of surface water in which organisms and abiotic items may be trapped in surface tension between the ocean and atmosphere, to the depths of the oceanic trenches , sometimes 10,000 meters or more beneath the surface of the ocean. Specific habitats include estuaries , coral reefs , kelp forests , seagrass meadows ,

2100-446: Is a special kind of tissue known as catch connective tissue . This collagen -based material can change its mechanical properties under nervous control rather than by muscular means. This tissue enables a starfish to go from moving flexibly around the seabed to becoming rigid while prying open a bivalve mollusc or preventing itself from being extracted from a crevice. Similarly, sea urchins can lock their normally mobile spines upright as

2205-452: Is also becoming understood that the well-being of marine organisms and other organisms are linked in fundamental ways. The human body of knowledge regarding the relationship between life in the sea and important cycles is rapidly growing, with new discoveries being made nearly every day. These cycles include those of matter (such as the carbon cycle ) and of air (such as Earth's respiration , and movement of energy through ecosystems including

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2310-416: Is by transverse fission with the disc splitting in two. Both the lost disc area and the missing arms regrow, so an individual may have arms of varying lengths. During the period of regrowth, they have a few tiny arms and one large arm, and are thus often known as "comets". Adult sea cucumbers reproduce asexually by transverse fission. Holothuria parvula uses this method frequently, splitting into two

2415-471: Is closely linked to oceanography , especially biological oceanography , and may be regarded as a sub-field of marine science . It also encompasses many ideas from ecology . Fisheries science and marine conservation can be considered partial offshoots of marine biology (as well as environmental studies ). Marine chemistry , physical oceanography and atmospheric sciences are also closely related to this field. An active research topic in marine biology

2520-496: Is especially common in cold water species where planktonic larvae might not be able to find sufficient food. These retained eggs are usually few in number and are supplied with large yolks to nourish the developing embryos. In starfish, the female may carry the eggs in special pouches, under her arms, under her arched body, or even in her cardiac stomach. Many brittle stars are hermaphrodites; they often brood their eggs, usually in special chambers on their oral surfaces, but sometimes in

2625-456: Is extreme and there is no sunlight, but some life still exists. A white flatfish , a shrimp and a jellyfish were seen by the American crew of the bathyscaphe Trieste when it dove to the bottom in 1960. In general, the deep sea is considered to start at the aphotic zone , the point where sunlight loses its power of transference through the water. Many life forms that live at these depths have

2730-426: Is limited to bending (their stems can bend) and rolling and unrolling their arms; a few species can relocate themselves on the seabed by crawling. The sea feathers are unattached and usually live in crevices, under corals or inside sponges with their arms the only visible part. Some sea feathers emerge at night and perch themselves on nearby eminences to better exploit food-bearing currents. Many species can "walk" across

2835-402: Is no true heart , and the blood often lacks any respiratory pigment. Gaseous exchange occurs via dermal branchiae or papulae in starfish, genital bursae in brittle stars, peristominal gills in sea urchins and cloacal trees in sea cucumbers. Exchange of gases also takes place through the tube feet. Echinoderms lack specialized excretory (waste disposal) organs and so nitrogenous waste , chiefly in

2940-441: Is still being characterised. Echinoderms have a simple radial nervous system that consists of a modified nerve net of interconnected neurons with no central brain , although some do possess ganglia . Nerves radiate from central rings around the mouth into each arm or along the body wall; the branches of these nerves coordinate the movements of the organism and the synchronisation of the tube feet. Starfish have sensory cells in

3045-426: Is still much more to learn about the deeper parts of the ocean . In biology, many phyla, families and genera have some species that live in the sea and others that live on land. Marine biology classifies species based on their environment rather than their taxonomy. For this reason, marine biology encompasses not only organisms that live only in a marine environment, but also other organisms whose lives revolve around

3150-482: Is synchronised in some species, usually with regard to the lunar cycle. In other species, individuals may aggregate during the reproductive season, increasing the likelihood of successful fertilisation. Internal fertilisation has been observed in three species of sea star, three brittle stars and a deep-water sea cucumber. Even at abyssal depths , where no light penetrates, echinoderms often synchronise their reproductive activity. Some echinoderms brood their eggs . This

3255-794: Is to discover and map the life cycles of various species and where they spend their time. Technologies that aid in this discovery include pop-up satellite archival tags , acoustic tags , and a variety of other data loggers . Marine biologists study how the ocean currents , tides and many other oceanic factors affect ocean life forms, including their growth, distribution and well-being. This has only recently become technically feasible with advances in GPS and newer underwater visual devices. Most ocean life breeds in specific places, nests in others, spends time as juveniles in still others, and in maturity in yet others. Scientists know little about where many species spend different parts of their life cycles especially in

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3360-426: Is widespread and very diverse under the ocean. Microscopic photosynthetic algae contribute a larger proportion of the world's photosynthetic output than all the terrestrial forests combined. Most of the niche occupied by sub plants on land is actually occupied by macroscopic algae in the ocean, such as Sargassum and kelp , which are commonly known as seaweeds that create kelp forests . Plants that survive in

3465-529: The Mesozoic Marine Revolution . The name echinoderm is from Ancient Greek ἐχῖνος ( ekhînos )  'hedgehog' and δέρμα ( dérma )  'skin'. The name Echinodermata was originated by Jacob Theodor Klein in 1734, but only in reference to echinoids . It was expanded to the phylum level by Jean Guillaume Bruguière , first informally in 1789 and then in formal Latin in 1791. In 1955, Libbie Hyman attributed

3570-535: The chordates , as well as the largest marine-only phylum. The first definitive echinoderms appeared near the start of the Cambrian . The echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in the biotic desert of the deep sea , as well as shallower oceans . Most echinoderms are able to reproduce asexually and regenerate tissue, organs and limbs; in some cases, they can undergo complete regeneration from

3675-553: The crown-of-thorns starfish are long and sharp and can cause a painful puncture wound as the epithelium covering them contains a toxin. Because of their catch connective tissue, which can change rapidly from a flaccid to a rigid state, echinoderms are very difficult to dislodge from crevices. Some sea cucumbers have a cluster of cuvierian tubules which can be ejected as long sticky threads from their anus to entangle and permanently disable an attacker. Sea cucumbers occasionally defend themselves by rupturing their body wall and discharging

3780-635: The epipelagic , mesopelagic , bathypelagic , abyssopelagic , and hadopelagic zones. Zones which vary by the amount of light they receive include the photic and aphotic zones . Much of the aphotic zone's energy is supplied by the open ocean in the form of detritus . The deepest recorded oceanic trench measured to date is the Mariana Trench , near the Philippines , in the Pacific Ocean at 10,924 m (35,840 ft). At such depths, water pressure

3885-405: The marine environment are often called seabirds . Examples include albatross , penguins , gannets , and auks . Although they spend most of their lives in the ocean, species such as gulls can often be found thousands of miles inland. There are five main types of marine mammals: cetaceans ( toothed whales and baleen whales ); sirenians such as manatees ; pinnipeds including seals and

3990-456: The microorganisms within the ocean; looking at how they are affected by their environment and how that affects larger marine creatures and their ecosystem. Biological oceanography is similar to marine biology, but it studies ocean life from a different perspective. Biological oceanography takes a bottom up approach in terms of the food web, while marine biology studies the ocean from a top down perspective. Biological oceanography mainly focuses on

4095-760: The order Apodida have a single statocyst adjoining each radial nerve, and some have an eyespot at the base of each tentacle. The gonads at least periodically occupy much of the body cavities of sea urchins and sea cucumbers, while the less voluminous crinoids, brittle stars and starfish have two gonads in each arm. While the ancestors of modern echinoderms are believed to have had one genital aperture, many organisms have multiple gonopores through which eggs or sperm may be released. Many echinoderms have great powers of regeneration . Many species routinely autotomize and regenerate arms and viscera . Sea cucumbers often discharge parts of their internal organs if they perceive themselves to be threatened, regenerating them over

4200-588: The saltwater crocodile . Most extant marine reptiles, except for some sea snakes, are oviparous and need to return to land to lay their eggs. Thus most species, excluding sea turtles, spend most of their lives on or near land rather than in the ocean. Despite their marine adaptations, most sea snakes prefer shallow waters nearby land, around islands, especially waters that are somewhat sheltered, as well as near estuaries. Some extinct marine reptiles, such as ichthyosaurs , evolved to be viviparous and had no requirement to return to land. Birds adapted to living in

4305-426: The sea-lily Comaster schlegelii has two hundred. Genetic studies have shown that genes directing anterior-most development are expressed along ambulacra in the center of starfish rays, with the next-most-anterior genes expressed in the surrounding fringe of tube feet. Genes related to the beginning of the trunk are expressed at the ray margins, but trunk genes are only expressed in interior tissue rather than on

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4410-441: The walrus ; sea otters ; and the polar bear . All are air-breathing, meaning that while some such as the sperm whale can dive for prolonged periods, all must return to the surface to breathe. The marine ecosystem is large, and thus there are many sub-fields of marine biology. Most involve studying specializations of particular animal groups, such as phycology , invertebrate zoology and ichthyology . Other subfields study

4515-598: The Asteroidea ( starfish , with some 1,745 species), Ophiuroidea ( brittle stars , with around 2,300 species), Echinoidea ( sea urchins and sand dollars , with some 900 species), Holothuroidea ( sea cucumbers , with about 1,430 species), and Crinoidea ( feather stars and sea lilies , with around 580 species). Echinoderms evolved from animals with bilateral symmetry . Although adult echinoderms possess pentaradial symmetry, their larvae are ciliated , free-swimming organisms with bilateral symmetry. Later, during metamorphosis,

4620-446: The ability to create their own light known as bio-luminescence . Marine life also flourishes around seamounts that rise from the depths, where fish and other sea life congregate to spawn and feed. Hydrothermal vents along the mid-ocean ridge spreading centers act as oases , as do their opposites, cold seeps . Such places support unique biomes and many new microbes and other lifeforms have been discovered at these locations.There

4725-421: The animal. The madreporite is linked to a slender duct, the stone canal, which extends to a ring canal that encircles the mouth or oesophagus . The ring canal branches into a set of radial canals, which in asteroids extend along the arms, and in echinoids adjoin the test in the ambulacral areas. Short lateral canals branch off the radial canals, each one ending in an ampulla. Part of the ampulla can protrude through

4830-597: The anus located in the centre of the aboral body surface. With a few exceptions, the members of the order Paxillosida do not possess an anus. In many species of starfish, the large cardiac stomach can be everted to digest food outside the body. Some other species are able to ingest whole food items such as molluscs . Brittle stars, which have varying diets, have a blind gut with no intestine or anus; they expel food waste through their mouth. Sea urchins are herbivores and use their specialised mouthparts to graze, tear and chew their food, mainly algae . They have an oesophagus,

4935-417: The area that extends from the shoreline to the edge of the continental shelf . Most marine life is found in coastal habitats, even though the shelf area occupies only seven percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf. Alternatively, marine habitats can be divided into pelagic and demersal habitats. Pelagic habitats are found near

5040-400: The areas that are close to the shore, are constantly being exposed and covered by the ocean's tides . A huge array of life can be found within this zone. Shore habitats span from the upper intertidal zones to the area where land vegetation takes prominence. It can be underwater anywhere from daily to very infrequently. Many species here are scavengers, living off of sea life that is washed up on

5145-537: The arms of sea stars, brittle stars and crinoids. The ossicles may bear external projections in the form of spines, granules or warts and they are supported by a tough epidermis . Skeletal elements are sometimes deployed in specialized ways, such as the chewing organ called " Aristotle's lantern " in sea urchins, the supportive stalks of crinoids, and the structural "lime ring" of sea cucumbers. Although individual ossicles are robust and fossilize readily, complete skeletons of starfish, brittle stars and crinoids are rare in

5250-485: The bacterial layer surrounding grains of sand. Sea cucumbers are often mobile deposit or suspension feeders, using their buccal podia to actively capture food and then stuffing the particles individually into their buccal cavities. Others ingest large quantities of sediment, absorb the organic matter and pass the indigestible mineral particles through their guts. In this way they disturb and process large volumes of substrate, often leaving characteristic ridges of sediment on

5355-448: The body surface. This means that a starfish body can more-or-less be considered to consist only of a head. Echinoderms have a mesodermal skeleton in the dermis, composed of calcite -based plates known as ossicles . If solid, these would form a heavy skeleton, so they have a sponge-like porous structure known as stereom. Ossicles may be fused together, as in the test of sea urchins, or may articulate to form flexible joints as in

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5460-489: The brittle stars, six-armed species such as Ophiothela danae , Ophiactis savignyi , and Ophionotus hexactis exist, and Ophiacantha vivipara often has more than six. Echinoderms have secondary radial symmetry in portions of their body at some stage of life, most likely an adaptation to a sessile or slow-moving existence. Many crinoids and some seastars are symmetrical in multiples of the basic five; starfish such as Labidiaster annulatus possess up to fifty arms, while

5565-417: The course of several months. Sea urchins constantly replace spines lost through damage, while sea stars and sea lilies readily lose and regenerate their arms. In most cases, a single severed arm cannot grow into a new starfish in the absence of at least part of the disc. However, in a few species a single arm can survive and develop into a complete individual, and arms are sometimes intentionally detached for

5670-418: The development of marine protected areas . This data is important to both scientists and fishermen because they are discovering that, by restricting commercial fishing in one small area, they can have a large impact in maintaining a healthy fish population in a much larger area. The study of marine biology dates to Aristotle (384–322 BC), who made many observations of life in the sea around Lesbos , laying

5775-607: The distinction between plants and animals often breaks down in very small organisms. Other zooplankton include cnidarians , ctenophores , chaetognaths , molluscs , arthropods , urochordates , and annelids such as polychaetes . Many larger animals begin their life as zooplankton before they become large enough to take their familiar forms. Two examples are fish larvae and sea stars (also called starfish ). Microscopic algae and plants provide important habitats for life, sometimes acting as hiding places for larval forms of larger fish and foraging places for invertebrates. Algal life

5880-399: The ecological roles of adults are the grazing of sea urchins, the sediment processing of heart urchins, and the suspension and deposit feeding of crinoids and sea cucumbers. Some sea urchins can bore into solid rock, destabilising rock faces and releasing nutrients into the ocean. Coral reefs are also bored into in this way, but the rate of accretion of carbonate material is often greater than

5985-500: The ecosystem of the ocean with an emphasis on plankton : their diversity (morphology, nutritional sources, motility, and metabolism); their productivity and how that plays a role in the global carbon cycle; and their distribution (predation and life cycle). Biological oceanography also investigates the role of microbes in food webs, and how humans impact the ecosystems in the oceans. Marine habitats can be divided into coastal and open ocean habitats. Coastal habitats are found in

6090-596: The environment. Marine life is a vast resource, providing food, medicine, and raw materials, in addition to helping to support recreation and tourism all over the world. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms contribute significantly to the oxygen cycle , and are involved in the regulation of the Earth's climate . Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land. Many species are economically important to humans, including both finfish and shellfish. It

6195-451: The epithelium and have simple eyespots and touch-sensitive tentacle-like tube feet at the tips of their arms. Sea urchins have no particular sense organs but do have statocysts that assist in gravitational orientation, and they too have sensory cells in their epidermis, particularly in the tube feet, spines and pedicellariae . Brittle stars, crinoids and sea cucumbers in general do not have sensory organs, but some burrowing sea cucumbers of

6300-405: The erosion produced by the sea urchin. Echinoderms sequester about 0.1 gigatonnes of carbon dioxide per year as calcium carbonate , making them important contributors in the global carbon cycle . Marine biology A large proportion of all life on Earth lives in the ocean. The exact size of this "large proportion" is unknown, since many ocean species are still to be discovered. The ocean

6405-447: The form of ammonia , diffuses out through the respiratory surfaces. The coelomic fluid contains the coelomocytes , or immune cells. There are several types of immune cells, which vary among classes and species. All classes possess a type of phagocytic amebocyte, which engulf invading particles and infected cells, aggregate or clot, and may be involved in cytotoxicity . These cells are usually large and granular, and are believed to be

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6510-441: The fossil record. On the other hand, sea urchins are often well preserved in chalk beds or limestone. During fossilization, the cavities in the stereom are filled in with calcite that is continuous with the surrounding rock. On fracturing such rock, paleontologists can observe distinctive cleavage patterns and sometimes even the intricate internal and external structure of the test. The epidermis contains pigment cells that provide

6615-476: The foundation for many future discoveries. In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum , the first work dedicated to marine algae and the first book on marine biology to use the new binomial nomenclature of Linnaeus . It included elaborate illustrations of seaweed and marine algae on folded leaves. The British naturalist Edward Forbes (1815–1854) is generally regarded as

6720-510: The founder of the science of marine biology. The pace of oceanographic and marine biology studies quickly accelerated during the course of the 19th century. The observations made in the first studies of marine biology fueled the Age of Discovery and exploration that followed. During this time, a vast amount of knowledge was gained about the life that exists in the oceans of the world. Many voyages contributed significantly to this pool of knowledge. Among

6825-416: The great quantity of eggs and larva that they produce form part of the zooplankton , consumed by many marine creatures. Crinoids, on the other hand, are relatively free from predation. Antipredator defences include the presence of spines, toxins (inherent or delivered through the tube feet), and the discharge of sticky entangling threads by sea cucumbers. Although most echinoderm spines are blunt, those of

6930-399: The gut and internal organs. Starfish and brittle stars may undergo autotomy when attacked, detaching an arm; this may distract the predator for long enough for the animal to escape. Some starfish species can swim away from danger. Echinoderms are numerous invertebrates whose adults play an important role in benthic ecosystems , while the larvae are a major component of the plankton. Among

7035-423: The home to many exotic biological materials that may inspire biomimetic materials . Through constant monitoring of the ocean, there have been discoveries of marine life which could be used to create remedies for certain diseases such as cancer and leukemia. In addition, Ziconotide, an approved drug used to treat pain, was created from a snail which resides in the ocean. Marine biology is a branch of biology . It

7140-411: The infant and juvenile years. For example, it is still largely unknown where juvenile sea turtles and some sharks in the first year of their life travel. Recent advances in underwater tracking devices are illuminating what we know about marine organisms that live at great ocean depths. The information that pop-up satellite archival tags gives aids in fishing closures for certain times of the year and

7245-512: The left side of the body grows at the expense of the right side, which is eventually absorbed. The left side then grows in a pentaradially symmetric fashion, in which the body is arranged in five parts around a central axis. Within the Asterozoa , there can be a few exceptions from the rule. Most starfish in the genus Leptasterias have six arms, although five-armed individuals can occur. The Brisingida also contain some six-armed species. Amongst

7350-452: The madreporite may be on the oral surface and the podia lack suckers. In holothuroids, the system is reduced, often with few tube feet other than the specialised feeding tentacles, and the madreporite opens on to the coelom. Some holothuroids like the Apodida lack tube feet and canals along the body; others have longitudinal canals. The arrangement in crinoids is similar to that in asteroids, but

7455-774: The majority of starfish are active hunters. Crinoids catch food particles using the tube feet on their outspread pinnules, move them into the ambulacral grooves, wrap them in mucus, and convey them to the mouth using the cilia lining the grooves. The exact dietary requirements of crinoids have been little researched, but in the laboratory, they can be fed with diatoms. Basket stars are suspension feeders, raising their branched arms to collect zooplankton , while other brittle stars use several methods of feeding. Some are suspension feeders, securing food particles with mucus strands, spines or tube feet on their raised arms. Others are scavengers and detritus feeders. Others again are voracious carnivores and able to lasso their waterborne prey with

7560-478: The manner of a starfish. Some species drag themselves along using their buccal tentacles, while others manage to swim with peristaltic movements or rhythmic flexing. Many live in cracks, hollows and burrows and hardly move at all. Some deep-water species are pelagic and can float in the water with webbed papillae forming sails or fins. The majority of crinoids are motile, but sea lilies are sessile and attached to hard substrates by stalks. Movement in most sea lilies

7665-516: The most productive natural habitats in the world. Reefs comprise some of the densest and most diverse habitats in the world. The best-known types of reefs are tropical coral reefs which exist in most tropical waters; however, reefs can also exist in cold water. Reefs are built up by corals and other calcium -depositing animals, usually on top of a rocky outcrop on the ocean floor. Reefs can also grow on other surfaces, which has made it possible to create artificial reefs . Coral reefs also support

7770-422: The most significant were the voyages of HMS  Beagle where Charles Darwin came up with his theories of evolution and on the formation of coral reefs . Another important expedition was undertaken by HMS Challenger , where findings were made of unexpectedly high species diversity among fauna stimulating much theorizing by population ecologists on how such varieties of life could be maintained in what

7875-536: The mouth, which is linked to the anus by a loop consisting of a short oesophagus and longer intestine. The coelomic cavities of echinoderms are complex. Aside from the water vascular system, echinoderms have a haemal coelom , a peri visceral coelom, a gonadal coelom and often also a perihaemal coelom. During development, echinoderm coelom is divided into the metacoel, mesocoel and protocoel (also called somatocoel, hydrocoel and axocoel, respectively). The water vascular system, haemal system and perihaemal system form

7980-536: The movement and remodelling of existing tissues to replace lost parts. Direct transdifferentiation of one type of tissue to another during tissue replacement is also observed. Echinoderms become sexually mature after approximately two to three years, depending on the species and the environmental conditions. Almost all species have separate male and female sexes , though some are hermaphroditic . The eggs and sperm cells are typically released into open water, where fertilisation takes place. The release of sperm and eggs

8085-586: The name to "Bruguière, 1791 [ex Klein, 1734]." This attribution has become common and is listed by the Integrated Taxonomic Information System (ITIS), although some workers believe that the ITIS rules should result in attributing "Klein, 1778" due to a 2nd edition of his work published by Leske in that year. While Echinodermata has been in common use since the mid-1800s, several other names had been proposed. Notably, F. A. Bather called

8190-440: The ocean). Large areas beneath the ocean surface still remain effectively unexplored. Marine biology can be contrasted with biological oceanography . Marine life is a field of study both in marine biology and in biological oceanography . Biological oceanography is the study of how organisms affect and are affected by the physics , chemistry , and geology of the oceanographic system . Biological oceanography mostly focuses on

8295-459: The often vivid colours of echinoderms, which include deep red, stripes of black and white, and intense purple. These cells may be light-sensitive, causing many echinoderms to change appearance completely as night falls. The reaction can happen quickly: the sea urchin Centrostephanus longispinus changes colour in just fifty minutes when exposed to light. One characteristic of most echinoderms

8400-526: The open ocean. Some holothuroid adults such as Pelagothuria are however pelagic. Some crinoids are pseudo-planktonic, attaching themselves to floating logs and debris, although this behaviour was exercised most extensively in the Paleozoic, before competition from organisms such as barnacles restricted the extent of the behaviour. Echinoderms primarily use their tube feet to move about, though some sea urchins also use their spines. The tube feet typically have

8505-424: The ovary or coelom. In these starfish and brittle stars, development is usually direct to the adult form, without passing through a bilateral larval stage. A few sea urchins and one species of sand dollar carry their eggs in cavities, or near their anus, holding them in place with their spines. Some sea cucumbers use their buccal tentacles to transfer their eggs to their underside or back, where they are retained. In

8610-417: The phylum "Echinoderma" (apparently after Latreille , 1825 ) in his 1900 treatise on the phylum, but this name now refers to a fungus . There are about 7,600 extant species of echinoderm as well as about 13,000 extinct species. All echinoderms are marine , but they are found in habitats ranging from shallow intertidal areas to abyssal depths. Five extant classes of echinoderms are generally recognized:

8715-531: The physical effects of continual immersion in sea water and the ocean in general, adaptation to a salty environment, and the effects of changing various oceanic properties on marine life. A subfield of marine biology studies the relationships between oceans and ocean life, and global warming and environmental issues (such as carbon dioxide displacement). Recent marine biotechnology has focused largely on marine biomolecules , especially proteins , that may have uses in medicine or engineering. Marine environments are

8820-425: The presence of predators. Asexual reproduction produces many smaller larvae that escape better from planktivorous fish, implying that the mechanism may be an anti-predator adaptation. Development begins with a bilaterally symmetrical embryo, with a coeloblastula developing first. Gastrulation marks the opening of the "second mouth" that places echinoderms within the deuterostomes, and the mesoderm, which will host

8925-459: The purpose of asexual reproduction . During periods when they have lost their digestive tracts, sea cucumbers live off stored nutrients and absorb dissolved organic matter directly from the water. The regeneration of lost parts involves both epimorphosis and morphallaxis . In epimorphosis stem cells—either from a reserve pool or those produced by dedifferentiation —form a blastema and generate new tissues. Morphallactic regeneration involves

9030-808: The role of viruses in marine ecosystems is barely being explored even in the beginning of the 21st century. The role of phytoplankton is better understood due to their critical position as the most numerous primary producers on Earth. Phytoplankton are categorized into cyanobacteria (also called blue-green algae/bacteria), various types of algae (red, green, brown, and yellow-green), diatoms , dinoflagellates , euglenoids , coccolithophorids , cryptomonads , chrysophytes , chlorophytes , prasinophytes , and silicoflagellates . Zooplankton tend to be somewhat larger, and not all are microscopic. Many Protozoa are zooplankton, including dinoflagellates, zooflagellates , foraminiferans , and radiolarians . Some of these (such as dinoflagellates) are also phytoplankton;

9135-408: The sea are often found in shallow waters, such as the seagrasses (examples of which are eelgrass, Zostera , and turtle grass, Thalassia ). These plants have adapted to the high salinity of the ocean environment. The intertidal zone is also a good place to find plant life in the sea, where mangroves or cordgrass or beach grass might grow. As on land, invertebrates , or animals that lack

9240-407: The sea. As inhabitants of the largest environment on Earth, microbial marine systems drive changes in every global system. Microbes are responsible for virtually all photosynthesis that occurs in the ocean, as well as the cycling of carbon , nitrogen , phosphorus and other nutrients and trace elements. Microscopic life undersea is incredibly diverse and still poorly understood. For example,

9345-449: The seabed to undergo metamorphosis, and the larval arms and gut degenerate. The left-hand side of the larva develops into the oral surface of the juvenile, while the right side becomes the aboral surface. At this stage the pentaradial symmetry develops. A plankton-eating larva, living and feeding in the water column, is considered to be the ancestral larval type for echinoderms, but in extant echinoderms, some 68% of species develop using

9450-470: The seabed, raising their body with the help of their arms, or swim using their arms. Most species of sea feather, however, are largely sedentary, seldom moving far from their chosen place of concealment. The modes of feeding vary greatly between the different echinoderm taxa. Crinoids and some brittle stars tend to be passive filter-feeders, enmeshing suspended particles from passing water. Most sea urchins are grazers; sea cucumbers are deposit feeders; and

9555-441: The seabed. Some sea cucumbers live infaunally in burrows, anterior-end down and anus on the surface, swallowing sediment and passing it through their gut. Other burrowers live anterior-end up and wait for detritus to fall into the entrances of the burrows or rake in debris from the surface nearby with their buccal podia. Nearly all starfish are detritus feeders or carnivores, though a few are suspension feeders. Small fish landing on

9660-412: The sessile sea lilies or "stone lilies". While bilaterally symmetrical as larvae , as adults echinoderms are recognisable by their usually five-pointed radial symmetry (pentamerous symmetry), and are found on the sea bed at every ocean depth from the intertidal zone to the abyssal zone . The phylum contains about 7,600 living species , making it the second-largest group of deuterostomes after

9765-424: The shore. Many land animals also make much use of the shore and intertidal habitats. A subgroup of organisms in this habitat bores and grinds exposed rock through the process of bioerosion . Estuaries are also near shore and influenced by the tides . An estuary is a partially enclosed coastal body of water with one or more rivers or streams flowing into it and with a free connection to the open sea. Estuaries form

9870-416: The skeleton, migrates inwards. The secondary body cavity, the coelom, forms by the partitioning of three body cavities. The larvae are often planktonic , but in some species the eggs are retained inside the female, while in some the female broods the larvae. The larvae pass through several stages, which have specific names derived from the taxonomic names of the adults or from their appearance. For example,

9975-649: The soft body parts. As the adductor muscle of the bivalve relaxes, more stomach is inserted and when digestion is complete, the stomach is returned to its usual position in the starfish with its now liquefied bivalve meal inside it. Other starfish evert the stomach to feed on sponges, sea anemones, corals, detritus and algal films. Despite their low nutrition value and the abundance of indigestible calcite, echinoderms are preyed upon by many organisms, including bony fish , sharks , eider ducks , gulls , crabs , gastropod molluscs , other echinoderms, sea otters , Arctic foxes and humans. Larger starfish prey on smaller ones;

10080-423: The substratum. A very diverse range of unusual secondary metabolites is produced by marine fungi. A reported 33,400 species of fish , including bony and cartilaginous fish , had been described by 2016, more than all other vertebrates combined. About 60% of fish species live in saltwater. Reptiles which inhabit or frequent the sea include sea turtles , sea snakes , terrapins , the marine iguana , and

10185-426: The surface or in the open water column , away from the bottom of the ocean and affected by ocean currents , while demersal habitats are near or on the bottom. Marine habitats can be modified by their inhabitants. Some marine organisms, like corals, kelp and sea grasses, are ecosystem engineers which reshape the marine environment to the point where they create further habitat for other organisms. Intertidal zones ,

10290-448: The surrounds of seamounts and thermal vents , tidepools , muddy, sandy and rocky bottoms, and the open ocean ( pelagic ) zone, where solid objects are rare and the surface of the water is the only visible boundary. The organisms studied range from microscopic phytoplankton and zooplankton to huge cetaceans (whales) 25–32 meters (82–105 feet) in length. Marine ecology is the study of how marine organisms interact with each other and

10395-411: The tube feet are coordinated, as the animal glides steadily along. Some burrowing starfish have points rather than suckers on their tube feet and they are able to "glide" across the seabed at a faster rate. Sea urchins use their tube feet to move around in a similar way to starfish. Some also use their articulated spines to push or lever themselves along or lift their oral surfaces off the substrate. If

10500-430: The tube feet lack suckers and are used in a back-and-forth wafting motion to pass food particles captured by the arms towards the central mouth. In the asteroids, the same motion is employed to move the animal across the ground. Echinoderms possess a simple digestive system which varies according to the animal's diet. Starfish are mostly carnivorous and have a mouth, oesophagus, two-part stomach, intestine and rectum, with

10605-403: The tubular coelomic system. Echinoderms are unusual in having both a coelomic circulatory system (the water vascular system) and a haemal circulatory system, as most groups of animals have just one of the two. Haemal and perihaemal systems are derived from the original coelom, forming an open and reduced circulatory system. This usually consists of a central ring and five radial vessels. There

10710-447: The upper surface may be captured by pedicilaria and dead animal matter may be scavenged but the main prey items are living invertebrates, mostly bivalve molluscs. To feed on one of these, the starfish moves over it, attaches its tube feet and exerts pressure on the valves by arching its back. When a small gap between the valves is formed, the starfish inserts part of its stomach into the prey, excretes digestive enzymes and slowly liquefies

10815-420: The world's coral reefs are now endangered and predict that global warming could exacerbate this trend. The open ocean is relatively unproductive because of a lack of nutrients, yet because it is so vast, in total it produces the most primary productivity. The open ocean is separated into different zones, and the different zones each have different ecologies. Zones which vary according to their depth include

10920-721: The world, Station biologique de Roscoff , was established in Concarneau, France founded by the College of France in 1859. In the United States, the Scripps Institution of Oceanography dates back to 1903, while the prominent Woods Hole Oceanographic Institute was founded in 1930. The development of technology such as sound navigation and ranging , scuba diving gear, submersibles and remotely operated vehicles allowed marine biologists to discover and explore life in deep oceans that

11025-465: Was thought to be such a hostile environment. This era was important for the history of marine biology but naturalists were still limited in their studies because they lacked technology that would allow them to adequately examine species that lived in deep parts of the oceans. The creation of marine laboratories was important because it allowed marine biologists to conduct research and process their specimens from expeditions. The oldest marine laboratory in

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