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Encyclopedia > Echinoderm
Echinoderms
Fossil range: Late Ediacaran?-Recent
A brittle star resting on a brain coral
A brittle star resting on a brain coral
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Superphylum: Deuterostomia
Phylum: Echinodermata
Klein, 1734
Subphyla & Classes
  • Homalozoa Gill & Caster, 1960
Homostelea
Homoiostelea
Stylophora
Ctenocystoidea Robison & Sprinkle, 1969
  • Crinozoa
Crinoidea
Paracrinoidea † Regnéll, 1945
Cystoidea †von Buch, 1846
  • Asterozoa
Ophiuroidea
Asteroidea
  • Echinozoa
Echinoidea
Holothuroidea
Ophiocistioidea
Helicoplacoidea †
Arkarua
Homalozoa
  • Pelmatozoa †
Edrioasteroidea
  • Blastozoa †
Blastoidea
Eocrinoidea †Jaekel, 1899

† = extinct The Ediacaran[5][6]  â€¢  â€¢  | Neoproterozoic (last æon of the Precambrian) Phanerozoic Axis scale: millions of years ago. ... Image File history File links Size of this preview: 800 × 527 pixelsFull resolution (1796 × 1184 pixel, file size: 1. ... Orders ME Oegophiurida Ophiurida Phrynophiurida Brittle stars are echinoderms, closely related to starfish. ... Genera 24 genera, the most common being: FaviaIts behavior is semi-aggressive and it will sting other corals with its extended sweeper tentacles during the night Montastrea Wikispecies has information related to: Brain coral Brain coral ( ) is a collection of species of coral characterized by the spheroid shape of their... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... For other uses, see Animal (disambiguation). ... subgroups Ctenophora Cnidaria Bilateria Eumetazoa is a clade comprising all major animal groups except sponges. ... Phyla Chaetognatha Echinodermata Hemichordata Chordata Deuterostomes (from the Greek: second the mouth) are one of the two superphyla of animals in the taxonomic branch bilateria, the other being the protostomes. ... Daniel Gralath (* 30 May 1708 in Danzig (Gdansk); † 23 July 1767 in Danzig) was a German physicist and Bürgermeister (mayor) of Danzig. ... The Stylophora are a class within the subphylum Homalozoa of the Phylum Echinodermata. ... Orders Articulata Cladida (extinct) Flexibilia (extinct) Camerada (extinct) Disparida (extinct) Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). ... Brittle stars are echinoderms, closely related to starfish. ... A database query syntax error has occurred. ... Slate pencil urchin (cidaroid) Group of black, long-spined Caribbean sea urchins, Diadema antillarum (Philippi) Sea urchin roe. ... Orders Subclass Apodacea  Apodida  Molpadiida Subclass Aspidochirotacea  Aspidochirotida  Elasipodida Subclass Dendrochirotacea  Dactylochirotida  Dendrochirotida The sea cucumber is an echinoderm of the class Holothuroidea, with an elongated body and leathery skin. ... Helicoplacus (often misspelt Heiloplacus) is the earliest well-studied fossil echinoderm. ... Arkarua is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of 5 small dots from the middle of the disk center. ... The Cothurnocystis along with all the Stylophora, are a disputed organism in its relationship with other species. ... The Edrioasteroids are an extinct class of echinoderm that lived from the Cambrian to the Carboniferous periods of geologic time. ... Subclasses Fissiculata Spiraculata Blastoids (class Blastoidea) are an extinct type of stemmed echinoderm. ... Otto Max Johannes Jaekel, born 1863, died 1929, was a German paleontologist. ...

Echinoderms (Phylum Echinodermata, from the Greek for spiny skin) are a phylum of marine animals found at all ocean depths. Aside from the problematic Arkarua, the first definitive members of the phylum appeared near the start of the Cambrian period, and contains about 7,000 living species, making it the second largest grouping of deuterostomes, after the chordates; they are the largest phylum without freshwater or terrestrial representatives. Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... Marine is an umbrella term for things relating to the ocean, as with marine biology, marine geology, and as a term for a navy, etc. ... For other uses, see Animal (disambiguation). ... Arkarua is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of 5 small dots from the middle of the disk center. ... For other uses, see Cambrian (disambiguation). ... For other uses, see Species (disambiguation). ... Typical Classes Subphylum Urochordata - Tunicates Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with...


The Echinoderms are important both biologically and geologically: biologically because few other groupings are so abundant in the biotic desert of the deep sea, as well as the shallower oceans, and geologically as their ossified skeletons are major contributors to many limestone formations, and can provide valuable clues as to the geological environment. Further, it is held by some that the radiation of echinoderms was responsible for the Mesozoic revolution of marine life. Mesozoic Era is one of three geologic eras of the Phanerozoic eon. ...


Two main subdivisions of Echinoderms are traditionally recognised: the more familiar, motile Eleutherozoa, which encompasses the Asteroidea (starfish), Ophiuroidea (brittle stars), Echinoidea (sea urchin and sand dollar) and Holothuroidea (sea cucumbers); and the sessile Pelmatazoa, which consist of the crinoids. Some crinoids, the feather stars, have secondarily re-evolved a free-living lifestyle. Orders Forcipulatida Paxillosida Notomyotida Spinulosida Valvatida Velatida Brisingida Starfish redirects here. ... Brittle stars are echinoderms, closely related to starfish. ... Subclasses Subclass Perischoechinoidea Order Cidaroida (pencil urchins) Subclass Euechinoidea Superorder Atelostomata Order Cassiduloida Order Spatangoida (heart urchins) Superorder Diadematacea Order Diadematoida Order Echinothurioida Order Pedinoida Superorder Echinacea Order Arbacioida Order Echinoida Order Phymosomatoida Order Salenioida Order Temnopleuroida Superorder Gnathostomata Order Clypeasteroida (sand dollars) Order Holectypoida Wikispecies has information related to... Suborders and families See text. ... Orders Subclass Apodacea  Apodida  Molpadiida Subclass Aspidochirotacea  Aspidochirotida  Elasipodida Subclass Dendrochirotacea  Dactylochirotida  Dendrochirotida The sea cucumber is an echinoderm of the class Holothuroidea, with an elongated body and leathery skin. ... Orders Articulata Cladida (extinct) Flexibilia (extinct) Camerada (extinct) Disparida (extinct) Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). ... Orders Articulata Cladida (extinct) Flexibilia (extinct) Camerada (extinct) Disparida (extinct) Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). ...


A fifth class of Eleutherozoa consisting of just two species, the Concentricycloidea (sea daisies), were recently[1] merged into the Asteroidea. The fossil record contains a host of other classes which do not appear to fall into any extant crown group. Genera Xyloplax Sea daisies (order Concentricycloidea) make up a small group belonging to the echinoderms, with only one genus (Xyloplax) 2 species actually known. ... A crown group is a living monophyletic group or clade, consisting of the last common ancestor of all living examples, plus all of its descendants. ...

Contents

Physiology

Echinoderms evolved from animals with bilateral symmetry; although adult echinoderms possess radial symmetry. Echinoderms' larvae are ciliated, free-swimming organisms that organize in a bilaterally symmetric fashion that makes them look like embryonic chordates. Later, 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. The elaborate patterns on the wings of butterflies are one example of bilateral symmetry. ... The elaborate patterns on the wings of butterflies are one example of bilateral symmetry. ... cross-section of two cilia, showing 9+2 structure A cilium (plural cilia) is a fine projection from a eukaryotic cell that constantly beats in one direction. ... Typical Classes See below Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates. ... In biology, pentamerism, also known as pentaradial symmetry, is a unique body symmetry exhibited primarily by starfish. ...


All echinoderms exhibit fivefold radial symmetry in portions of their body at some stage of life, even if they have secondary bilateral symmetry. Many crinoids and some starfish exhibit symmetry in multiples of the basic five, with starfish such as Helicoilaster spp. known to possess up to 50 arms, and the sea-lily Comanthina schlegelii boasting 200.


Describing a radially symmetrical organism

With a radially symmetrical animal, the traditional designation of a front and back, posterior and anterior becomes troublesome - what does one term the front? To get around this, a different terminology is used with the Echinoderms. The mouth and anus of the developing adult migrate simultaneously from the front and back of the larvum to opposite ends of the organism, allowing the description of an "oral" (containing the mouth) and opposite "aboral" side. Grazing organisms such as sea urchins tend to have their mouth on the substrate upon which they are feeding, and their anus on their "top" surface; burrowers such as sea cucumbers have their mouth at their front, and the anus behind their direction of travel. Hence the sea-cucumbers appear to have evolved from a sea-urchin-like organism which gradually tipped on its side and lengthened.
The individual limbs can be named on the basis of a break in the symmetry provided by the "filter plate". This lies beside the anus on the aboral plate, between two of the radial arms; the radial limbs are designated letters a to e in a clockwise direction from this marker.


Skin and skeleton

Some urchins display large spines.
Some urchins display large spines.

In spite of their potentially misleading name and sometimes foreboding appearance, the echinoderms do not possess an external skeleton. Rather, a thin outermost skin covers a mesodermal endoskeleton made of tiny calcified plates and spines, which forms a rigid support contained within tissues of the organism. Some groups, such as the sea urchins, also possess calcareous spines that serve to protect the organism from predation and colonisation by encrusting organisms; the sea cucumbers secondarily use these spines for locomotion. These spines too are covered by a thin layer of epidermis. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Organs derived from each germ layer. ... Calcium carbonate is a chemical compound, with the chemical formula CaCO3. ...


The calcite grown by the organisms is diagnostically rich in the element magnesium; they may consist of 3 to 15 % magnesium oxide. The abundance of this small element property confers them a higher skeletal density, and the chemical properties of magnesium encourage it to form stronger bonds - making for a stronger, more resistant skeleton. The feeding apparatus of the echinoderms is particularly enriched in magnesium; the rock-grazing lifestyle of the sea urchins makes their mandibles especially prone to wear, thus the extra strength provides a significant advantage, outweighing the metabolic costs involved in concentrating the magnesium.


Despite the robustness of the individual skeletal modules, complete echinoderm skeletons are rare in the fossil record. This is because they quickly disarticulate once the encompassing skin rots away, and in the absence of tissue there is nothing to hold the plates together. The modular construction is a result of the growth system employed by echinoderms, which adds new segments at the centre of the radial limbs, pushing the existing plates outwards in the fashion of a conveyor belt. The spines of sea urchins are most readily lost, as they are not even attached to the main skeleton in life. Each spine can be moved individually and is thus only loosely attached in life; a walk above a rocky shore will often reveal a large number of spineless but otherwise complete sea urchin skeletons.


Skeletal elements are also deployed in some specialised ways; as well as the famous feeding organ of the sea urchins, the "Aristotle's lantern", crinoids' stalks and the supportive "lime ring" of sea cucumbers consist of specialised calcite plates. A highly complex internal apparatus used for feeding, and is only present in some sea urchins. ...


The epidermis itself consists of cells responsible for the support and maintenance of the skeleton, as well as pigment cells, mechanoreceptor cells, which detect motion on the animal's surface, and sometimes gland cells which secrete sticky fluids or even toxins.

Echinoderms exhibit a wide range of colours.
Echinoderms exhibit a wide range of colours.

The varied and often vivid colours of the echinoderms are produced by the action of the skin pigment cells. These may be light sensitive, and as a result many species change appearance completely as night falls. The reaction can happen very quickly — the sea urchin Centrostephanus discolours longispinus changes from jet black to grey-brown in just 50 minutes when exposed to light. The colours are produced by a variable combination of coloured pigments, such as the dark Melanin, red Carotinoids, and Carotinproteins, which can be blue, green or violet. Image File history File links Size of this preview: 800 × 549 pixelsFull resolution (1800 × 1236 pixel, file size: 1,002 KB, MIME type: image/jpeg) Kachemak Bay National Estuarine Research Reserve. ... Image File history File links Size of this preview: 800 × 549 pixelsFull resolution (1800 × 1236 pixel, file size: 1,002 KB, MIME type: image/jpeg) Kachemak Bay National Estuarine Research Reserve. ...


The water vascular system

Echinoderms possess a unique water vascular system, a network of fluid-filled canals that function in gas exchange, feeding, and secondarily in locomotion. This system may have allowed them to function without the gill slits found in other Deuterostomes. The system comprises a central ring, the hydrocoel, and radial ambulacra stretching along each limb of the organism. As well as assisting with the distribution of nutrients through the animal, the system is most obviously expressed in the "tube-feet" of most echinoderms. These are extensions of the water vascular system which poke through holes in the skeleton and can be extended or contracted by the redistribution of fluid between the foot and internal sac. In the crinoids, these tube feet waft food particles captured on the radial limbs towards the central mouth; in the asteroids, the same wafting motion is employed to move the animal across the ground. Sea urchins use their feet to prevent the larvae of encrusting organisms from settling on their surfaces; potential settlers are moved to the urchin's mouth and eaten. Some burrowing sea stars poke their tube feet through the surface of the sand or mud above them into the water column and use them to attain oxygen from the water column. The water vascular system is a hydraulic system used by echinoderms, such as starfish and sea urchins, for locomotion, food and waste transportation, and respiration[1]. The system is composed of canals connecting numerous tube feet. ...


Other organs

Although echinoderms possess a complete digestive tube (tubular gut), it is very simple, often simply leading directly from mouth to anus. It can generally be divided into a throat, stomach, intestine and rectum. They also possess an open and reduced circulatory system — consisting of a central ring and five radial vessels, but no heart. For transport in plants, see Vascular tissue. ...


They have a simple radial nervous system that consists of a modified nerve net — interconnected neurons with no central brain (although some do possess ganglia. Nerves radiate from central rings around the mouth into each arm; the branches of these nerves coordinate the movements of the organism. The nervous system is a highly specialized network whose principal components are nerves called neurons. ... A nerve net is a type of simple nervous system that is found in members of the phylum cnidaria. ... For other uses, see Brain (disambiguation). ... GÃ…NGLÃŽÃ… is a 1 man electronic grindcore band from Los Angeles California that began in August of 1999. ...


The gonads of the organisms occupy the entire body cavities of sea urchins and sea cucumbers; the less voluminous crinoids, brittle stars and starfish having two gonads per arm. Whilst the primitive condition is considered to be one genital aperture, many organisms have multiple holes through which eggs or sperm may be released. The gonad is the organ that makes gametes. ...


Sexual reproduction

Echinoderms become sexually mature after approximately two to three years, depending on the species and the environmental conditions. The eggs and sperm cells are released into open water, where fertilization takes place. The release of sperm and eggs is co-ordinated temporally in some species, and spatially in others. Internal fertilization has currently been observed in three species of starfish, three brittle stars and a deep water sea cucumber.


In some species of feather star, the embryos develop in special breeding bags, where the eggs are held until sperm released by a male happen to find them and fertilize the contents. This can also be found among sea urchins and sea cucumbers, where exhibit care for their young can occur, for instance in a few species of sand dollars who carry their young between the pricks of their oral side, and heart urchins possess breeding chambers. With brittle stars, special chambers can be developed near the stomach bags, in which the development of the young takes place. Species of sea cucumbers with specialized care for their offspring may also nurse the young in body cavities or on their surfaces. In rare cases, direct development without passing through a bilateral larval stage can occur in some starfish and brittle stars.[citation needed] Another strategy that has evolved in some starfish and brittle stars is the ability to reproduce asexually by dividing in two halves while they are small juveniles, while turning to sexual reproduction when they have reached sexual maturity.[verification needed] These species have six arms.[citation needed]


Larval development

The larva of a sea urchin
The larva of a sea urchin

The development of an echinoderm begins with a bilaterally symmetrical embryo, with a coeloblastula developing first. Gastrulation marks the opening of the "second mouth" that places them within the deuterostomes, and the mesoderm, which will host the skeleton, migrates inwards. The secondary body cavity, the coelom, forms by the partitioning of three body cavities. Pluteus larva of echinoderm Scanned from 11th edition of the Encyclopaedia Brittannica, 1911; in public domain. ... Pluteus larva of echinoderm Scanned from 11th edition of the Encyclopaedia Brittannica, 1911; in public domain. ... It has been suggested that epiboly be merged into this article or section. ...


Upon metamorphosis, each taxon produces a distinct larvum, the left hand side of which develops into the adult organism, the right hand side eventually being absorbed; the left hand side typically becomes the oral plate.


F.M. Balfour[2] and D.I. Williamson[3] hold that no echinoderms acquired larvae until after the classes of the phylum were established, i.e. after the Ordovician. Some modern brittle stars and heart urchins have no larvae, and they develop as protostomes. H.B. Fell [4] and Williamson (2003) argue that the original echinoderms were radial protostomes and the bilateral larvae were later additions. Artist impression of the Ordovician Sea. ... Orders ME Oegophiurida Ophiurida Phrynophiurida Brittle stars are echinoderms, closely related to starfish. ... Phyla Mollusca Arthropoda Annelida Protostomes (from the Greek: first the mouth) are a superphylum of animals in the taxonomic group bilateria, and include animals such as arthropods, mollusks, and nematodes. ...


Asexual reproduction

Many echinoderms have remarkable powers of regeneration. Some sea stars are capable of regenerating lost arms. In some cases, lost arms have been observed to regenerate a second complete sea star. Sea cucumbers often discharge parts of their internal organs if they perceive danger. The discharged organs and tissues are quickly regenerated. Sea urchins are constantly losing their spines through damage--all parts are replaceable. Some starfish populations can reproduce entirely asexually purely by the shedding of arms for long periods of time. In biology, regeneration is an organisms ability to replace body parts. ...


Distribution and habitat

Echinoderms are globally distributed in almost all depths, latitudes and environments in the ocean. They reach highest diversity in reef environments but are also widespread on shallow shores, around the poles — refugia where crinoids are at their most abundant — and throughout the deep ocean, where bottom-dwelling and burrowing sea cucumbers are common — sometimes accounting for up to 90 % of organisms. Whilst almost all echinoderms are benthic — that is, they live on the sea floor — some sea-lilies can swim at great velocity for brief periods of time, and a few deep-sea sea cucumbers are fully floating. 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 such organisms as barnacles restricted the extent of the behaviour. Some sea cucumbers employ a similar strategy, hitching lifts by attaching to the sides of fish.


The larvæ of many echinoderms, especially starfish and sea urchins, are pelagic, and with the aid of ocean currents can swim great distances, reinforcing the global distribution of the phylum.


Mode of life

Feeding

The modes of feeding vary greatly between the constituent taxa. Crinoids and some brittle stars tend to be passive filter-feeders, absorbing suspended particles from passing water; sea urchins are grazers, sea cucumbers deposit feeders, and starfish active hunters.


Crinoids employ a large net-like structure to sieve water as it is swept by currents, and to adsorb any particles of matter sinking from the ocean overhead. Once a particle touches the arms of the creature, the tube feet act to swish it to the central mouth of the crinoid, where it is ingested, nutrients removed, and the remains egested through its anus to the underlying water column.


Many sea urchins graze on the surfaces of rocks, scraping off the thin layer of algae covering the surfaces. Other toothless breeds devour smaller organisms, which they may catch with their tube feet, whole. Sand dollars may perform suspension feeding.


Sea cucumbers may be suspension feeders, sucking vast quantities of sea water through their guts and absorbing any useful matter. Others use their feeding apparatus to actively capture food from the sea floor. Yet others deploy their feeding apparatus as a net, in which smaller organisms become ensnared.


Whilst some starfish are detritovores, extracting the organic material from mud, and others mimic the crinoids' filter feeding, most are active hunters, attacking other starfish or shellfish. The latter are seized and held by the tube feet; starfish then stiffen their legs, expanding the shell. The starfish can use catch connective tissue to lock their arms in place and maintain a force on the prey whilst exerting minimal effort; the unfortunate victim must expend energy resisting the force with its abductor muscle. When the abductor tires, the starfish can insert its stomach through the opening and release gastric juices, digesting the prey alive.


Avoiding predation

Despite their low nutrition value and the abundance of indigestable calcite, many organisms, such as Crabs, sharks, sea birds and larger starfish, make a living by feeding on echinoderms. Defensive strategies employed include the presence of spines, toxins, which can be inherent or delivered through the tube feet, and the discharge of sticky entangling threads by sea cucumbers. For other uses, see Crab (disambiguation). ... For other uses, see Shark (disambiguation). ...


Ecology

The Ordovician cystoid Echinosphaerites from northeastern Estonia; approximately 5 cm in diameter.
The Ordovician cystoid Echinosphaerites from northeastern Estonia; approximately 5 cm in diameter.

Echinoderms provide a key ecological role in ecosystems. For example, the grazing of sea urchins reduces the rate of colonisation of bare rock; the burrowing of sand dollars and sea cucumbers depleted the sea floor of nutrients and encouraged deeper penetration of the sea floor, increasing the depth to which oxygenation occurs and allowing a more complex ecological tiering to develop. Starfish and brittle stars prevent the growth of algal mats on coral reefs, which would obstruct the filter-feeding constituent organisms. Some sea urchins can bore into solid rock; this bioerosion can destabilise rock faces and release nutrients into the ocean. Bioerosion describes the erosion of hard ocean substrates by living organisms by a number of mechanisms. ...


The echinoderms are also the staple diet of many organisms, most notably the otter; conversely, many sea cucumbers provide a habitat for parasites, including crabs, worms and snails. The extinction of large quantities of echinoderms appears to have caused a subsequent overrunning of ecosystems by seaweed, or the destruction of an entire reef. This article is about the carnivorous mammals. ...


Evolution

Early Echinoderms (?)
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Arkarua
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Helicoplacus
(approx.)
Carpoids
Neoproterozoic
(last æon of the Precambrian)

Palæozoic The Ediacaran[5][6]  â€¢  â€¢  | Neoproterozoic (last æon of the Precambrian) Phanerozoic Axis scale: millions of years ago. ... For other uses, see Cambrian (disambiguation). ... Arkarua is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of 5 small dots from the middle of the disk center. ... Helicoplacus is the earliest well-studied fossil echinoderm. ... Few fossils of Ediacaran animals are so compellingly bizarre as this unusual disc-shaped form with three-part (triradial) symmetry. ... The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... In general usage, an eon (sometimes spelled aeon) is a very long period of time. ... The Precambrian (Pre-Cambrian) is an informal name for the supereon comprising the eons of the geologic timescale that came before the current Phanerozoic eon. ...

(first æon of the Phanerozoic)
Axis scale: millions of years ago.
Fossil crinoid crowns.
Fossil crinoid crowns.

The first universally accepted echinoderms appear in the Cambrian period around 535 million years ago.[verification needed] Echinoderms left behind an extensive fossil record. Despite this, there are numerous conflicting hypotheses on their phylogeny. Based on their bilateral larvae, many zoologists argue that echinoderm ancestors were bilateral and that their coelom had three pairs of spaces (trimeric). During the Phanerozoic the biodiversity shows a steady but not monotonic increase from near zero to several thousands of genera. ... Image File history File links Size of this preview: 537 × 599 pixelsFull resolution (748 × 835 pixel, file size: 860 KB, MIME type: image/jpeg) Released under GFDL on de-wikipedia. ... Image File history File links Size of this preview: 537 × 599 pixelsFull resolution (748 × 835 pixel, file size: 860 KB, MIME type: image/jpeg) Released under GFDL on de-wikipedia. ... Subclasses Articulata (540 species) Cladida (extinct) Flexibilia (extinct) Camerata (extinct) Disparida (extinct) Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). ... For other uses, see Cambrian (disambiguation). ...


Some have proposed that radial symmetry arose in a free-moving echinoderm ancestor and that sessile groups were derived several times independently from free-moving ancestors. Unfortunately, this view does not address the significance of radial symmetry as an adaptation for a sessile existence.


The more traditional view is that the first echinoderms were sessile, became radial as an adaptation to that existence, and then gave rise to free-moving groups. This view perceives the evolution of endoskeletal plates with stereom structure and of external ciliary grooves for feeding as early echinoderm developments.


The extinct members of Class Homalozoa, commonly referred to as carpoids, had stereom ossicles but were not radially symmetrical, and the status of their water-vascular system is not known. Further, extinct members of the Class Helicoplacoidea possessed three, true ambulacral grooves, and their mouth was on the side of their body.


Attachment to a substratum would have selected for radial symmetry and may have marked the origin of the Class Crinoidea. Members of Crinoidea, along with the extinct members of Class Cystoidea, were primitively attached to a substratum by an aboral stalk. An ancestor that became free-moving might have given rise to Asteroidea, Ophiuroidia, Holothuroidea, and Echinoidea.


Economic importance

Most humans know the Echinoderms rather from the unpleasant side: if one finds oneself near the coast, on a rocky shore or reef, one must beware the poisonous prick of a sea urchin. Because of their fine, circular structure they often break off when removed, and need patience — or the physician — to fully remove. But in the kitchens of some countries, Echinoderms are regarded as a delicacy; and for children sea-urchin skeletons are as popular a collecting object as brightly coloured starfish are fascinating.


The economic impact of Echinoderms is primarily local. Around 50,000 tons of sea urchins are captured each year, the gonads of which are consumed particularly in Japan, Peru and in France. The taste is described as soft and melting, like a mix of seafood and fruit. The quality depends on the color, which can range from light yellow to bright orange. The gonad is the organ that makes gametes. ...


Sea cucumbers are also considered a delicacy in some countries of south east Asia; particularly popular are the pineapple roller Thelenota ananas (susuhan) and the red Halodeima edulis. They are well known as bêche de mer or Trepang in China and Indonesia. The sea cucumbers are dried, and the potentially poisonous entrails removed. The strong poisons of the sea cucumbers are often psychoactive, but their effects are not well studied. It does appear that some sea cucumber toxins restrain the growth rate of tumour cells, which has sparked interest from cancer researchers. For other uses, see Pineapple (disambiguation). ...


The calcareous tests of echinoderms are used as a source of lime by farmers in areas where limestone is unavailable; indeed 4,000 tons of the animals are used annually for this purpose. This trade is often carried out in conjunction with shellfish farmers, for whom the starfish pose a major irritation by eating their stocks.


Classification

The orange gonads of a sea urchin
The orange gonads of a sea urchin

Echinoderms, like chordates, are deuterostomes and are therefore thought to be the most closely related of the major phyla to the chordates, being a sister group to chordates plus hemichordates. (Some believe that acorn worms are more closely related to echinoderms than chordates.) Because of a controversial interpretation of Homalozoa, a minority of classifiers place the echinoderms into the Chordata). Williamson (2003) disputes the links to hemichordates and chordates. They are based on larvae, which (Williamson claims) were later additions to life-histories. And pteropod hemichordates have larvae resembling trochophores, which would link them with annelids and molluscs. The phylogeny below is based on Smith (2005). Sea urchin disected and about to be devoured. ... Sea urchin disected and about to be devoured. ... Typical Classes Subphylum Urochordata - Tunicates Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with... Phyla Chaetognatha Echinodermata Hemichordata Chordata Deuterostomes (from the Greek: second the mouth) are one of the two superphyla of animals in the taxonomic branch bilateria, the other being the protostomes. ... Classes Enterepneusta Pterobranchia Planctosphaeroidea Hemichordata is a phylum of worm-shaped marine deuterostome animals, generally considered the sister group of our own, the chordates. ... Families Harrimaniidae Protoglossidae Ptychoderidae Saxipendiidae Spengelidae Torquaratoridae The Acorn worms or Enteropneusta are a hemichordate class of invertebrates. ...


Chordates Typical Classes See below Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates. ...




Hemichordates




Cincta




Cornutes



Mitrates





Solutes A substance is soluble in a fluid if it dissolves in the fluid. ...




Crinoids Orders Articulata Cladida (extinct) Flexibilia (extinct) Camerada (extinct) Disparida (extinct) Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). ...


ELEUTHEROZOA
Asterozoa

Asteroids Asteroids is a popular vector-based video arcade game released in 1979 by Atari. ...



†Somasteroidea





Ophiuroids


Echinozoa

Holothuroideas Orders Subclass Apodacea  Apodida  Molpadiida Subclass Aspidochirotacea  Aspidochirotida  Elasipodida Subclass Dendrochirotacea  Dactylochirotida  Dendrochirotida The sea cucumber is an echinoderm of the class Holothuroidea, with an elongated body and leathery skin. ...



Echinoids Subphyla & Classes Homalozoa Gill & Caster, 1960 Homostelea Homoiostelea Stylophora Ctenocystoidea Robison & Sprinkle, 1969 Crinozoa Crinoidea Eocrinoidea Jaekel, 1899 Paracrinoidea Regnéll, 1945 Cystoidea von Buch, 1846 Asterozoa Ophiuroidea Asteroidea Echinozoa Echinoidea Holothuroidea Ophiocistioidea Helicoplacoidea † Arkarua † Homalozoa † Pelmatozoa Edrioasteroidea† Cystoidea † Eocrinoidea † Edriaosteroidea † Blastozoa † † = extinct Echinoderms (Phylum Echinodermata, from the Greek for...









Bibliography

  1. ^ Siera104. Echinodermata. Retrieved on 15-03-2008.
  2. ^ 1880-81. A Treatise on Comparative Embryology. 2 vols. Macmillan,London
  3. ^ 2003. The Origins of Larvae. Kluwer, Dordrecht
  4. ^ 1948. Echinoderm embryology and the origin of chordates. Biological Reviews 23: 81-107
  • Black, R M (1973). The Elements of Palaeontology, 3rd impression. Cambridge University Press, 340pp + xviii, ISBN 0-521-09615-4. (Chapter 9 deals with Echinoids).
  • Clark, A M (1968). Starfishes and their relations, 2nd edition. Trustees of the British Museum (Natural History), 120pp nickel
  • Clarkson, E N K (1993). Invertebrate Palaeontology and Evolution, 3rd edition. Chapman & Hall, 434pp + ix, ISBN 0-412-47990-7. (Chapter 9 covers Echinoderms).
  • Nichols, D (1969). Echinoderms, 4th (revised) edition. Hutchinson University Library, 192pp, ISBN 0-09-065994-5. (This is the same Nichols who produced the seminal work on the mode of life of the irregular echinoid, Micraster, in the English chalk).
  • Shrock R R & Twenhofel W H (1953). Principles of Invertebrate Paleontology, 2nd edition. McGraw Hill International Series on the Earth Sciences, 816pp + xx, LCC 52-5341. (Chapter 14 covers Echinoderma).
  • Smith, A.B. (2006). "The pre-radial history of echinoderms". Geological Journal 40: 255-280. doi:10.1002/gj.1018. 
  • Williamson D I (2003). "The Origins of Larvae", xviii + 261 pp, ISBN 1-4020-1514-3. Kluwer. Dordrecht. (Chaps 8-12 cover echinoderm larvae).
  • This article was initially translated from the Wikipedia article Stachelhäuter, specifically from this version.

The Chalk Formations of Europe are thick deposits of chalk, a soft porous white limestone, deposited in a marine environment during the upper Cretaceous Period. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

External links

Wikispecies has information related to:
Echinodermata
Wikimedia Commons has media related to:
Echinodermata

Image File history File links Wikispecies-logo. ... Wikispecies is a wiki-based online project supported by the Wikimedia Foundation that aims to create a comprehensive free content catalogue of all species (including animalia, plantae, fungi, bacteria, archaea, and protista). ... For other similarly-named museums see Museum of Natural History. ... The Tree of Life Web Project is an ongoing Internet project and providing information about the diversity and phylogeny of life on Earth. ...


  Results from FactBites:
 
Echinoderm (99 words)
"Echinoderms are truly strange animals because none of them has a head, or eyes, or other kinds of things we associate with animals.
All are built on a five-sided body plan, probably most obvious in the gorgeous starfish that you see in front of you.
Predators, detritus feeders, filter feeders, herbivores • Some are keystone species (exerting a disproportiante effect on their ecostystem's structure through their predation) • Humans use echinoderms as food, as a source of medicines, and as research subjects in developemental biology.
Echinoderm - MSN Encarta (482 words)
Echinoderm, common name for about 6000 living species constituting a phylum of marine animals, such as starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers.
An echinoderm such as the starfish typically has a mouth surrounded by five arms that bear minute, fleshy tube feet with which the animal clings and crawls.
Echinoderms are common on the ocean bottom at all depths; in the deep sea they often make up the bulk of living material.
  More results at FactBites »

 
 

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