NationMaster - Encyclopedia: Sea star

Sea Stars (commonly known as starfish) are marine invertebrates belonging to the phylum Echinodermata, class Asteroidea. The names sea star and starfish are also (incorrectly) used for the closely related brittle stars, which make up the class Ophiuroidea. They exhibit a superficially radial symmetry. Starfish typically have five or more "arms" which radiate from an indistinct disk (pentaradial symmetry). In fact, their evolutionary ancestors are believed to have had bilateral symmetry, and sea stars do exhibit some superficial remnant of this body structure. Starfishes are a group of marine invertebrates. ... Invertebrate is a term coined by Chevalier de Lamarck to describe any animal without a backbone or vertebra, like insects, squids and worms. ... 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. ... Classes Asteroidea Blastoidea (extinct) Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Echinoderms (Phylum Echinodermata, from the Greek for spiny skin) are a phylum of marine animals found at all depths. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Orders Oegophiurida Ophiurida Phrynophiurida Brittle starfishs are echinoderms, closely related to sea stars. ... Brittle stars are echinoderms, closely related to starfish. ... The elaborate patterns on the wings of butterflies are one example of biological symmetry. ... The elaborate patterns on the wings of butterflies are one example of biological symmetry. ... The elaborate patterns on the wings of butterflies are one example of biological symmetry. ...

Sea stars do not have movable skeletons, but instead possess a hydraulic water vascular system. The water vascular system has many projections called tube feet, located on the ventral face of the sea star's arms, which function in locomotion and aid with feeding. A human skeleton - (endoskeleton) In biology, the skeleton (from Greek ÏƒÎºÎµÎ»ÎµÏ„ÏŒÏ‚, dried-up) or skeletal system is the biological system providing physical support in living organisms. ... The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. ... The tube feet can be clearly seen on this sea star Tube feet are the many small tubular projections found most famously on the ventral face of a sea stars arms, but are characteristic of the water vascular system of the echinoderm phylum which also includes sea urchins, sand... In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ... In a general sense, locomotion simply means active movement or travel, applying not just to biological individuals. ... Feeding is the process by which organisms, typically animals, obtain food. ...

Distribution

There are about 1,800 living species of sea star, and they occur in all of the Earth's oceans. The greatest variety of sea stars are found in the tropical Indo-Pacific. Areas known for their great diversity include the tropical-temperate regions around Australia, the tropical East Pacific, and the cold-temperate water North Pacific (California to Alaska). Asterias is a common genus found in European waters and on the eastern coast of the United States; Pisaster, along with Dermasterias ("leather star"), are usually found on the western coast. Habitats could range from tropical coral reefs, kelp forests to deep-sea floor, although none of them live within the water column; all species of sea stars found are living as benthos. Echinoderms need a delicate internal balance in their body, no sea stars are found in freshwater environments. Image File history File links Download high resolution version (1273x829, 236 KB) Astropecten foliota Photo: Channel Islands NMS. Printing resolution: 300 DPI. Downloaded from http://www. ... Image File history File links Download high resolution version (1273x829, 236 KB) Astropecten foliota Photo: Channel Islands NMS. Printing resolution: 300 DPI. Downloaded from http://www. ... Species Asterias is a genus of the Asteriidae family of starfish (also known as sea stars). ... World map showing Europe A satellite composite image of Europe Europe is one of the seven traditional continents of the Earth. ... The tropics are the geographic region of the Earth centered on the equator and limited in latitude by the two tropics: the Tropic of Cancer in the north and the Tropic of Capricorn in the southern hemisphere. ... Part of a coral reef. ... Kelp Forest Kelp forests are a type of marine ecosystem established around colonies of kelp; they contain rich biodiversity. ... In oceanography, marine geology and biology, benthos are the organisms and habitats of the sea floor; in freshwater biology they are the organisms and habitats of the bottoms of lakes, rivers, and creeks. ... Classes Asteroidea Blastoidea (extinct) Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Echinoderms (Phylum Echinodermata, from the Greek for spiny skin) are a phylum of marine animals found at all depths. ... For the village on the Isle of Wight, see Freshwater, Isle of Wight. ...

External anatomy

Sea stars are composed of a central disc from which arms sprout in radial symmetry. Most starfish have five arms, however some have more or less; in fact some starfish can have different numbers of arms even within one species. The mouth is located underneath the sea star on the oral or ventral surface, while the anus is located on the top of the animal. The spiny upper surface covering the species is called the aboral or dorsal surface. On the aboral surface there is a structure called the madreporite, which acts as a water filter and supplies the sea star's water vascular system with water to move. Additional parts like cribriform organs present exclusively in Porcellanasteridae are used to generate current in the burrows made by these infaunal sea stars. Image File history File links Download high resolution version (1800x1286, 744 KB) Red-knobbed Starfish Protoreaster linckii at Bristol Zoo Aquarium, Bristol, England. ... Image File history File links Download high resolution version (1800x1286, 744 KB) Red-knobbed Starfish Protoreaster linckii at Bristol Zoo Aquarium, Bristol, England. ... The term aboral refers to the side of a radially symmetrical animal, such as a starfish, that does not contain the mouth. ... Small red or yellow button-like structure that often looks like a small wart on a sea stars central disk. ...

Sea stars, while having their own basic body plan, radiate diversely in shapes and colors and the morphology differs between each species; for example, a species of sea star may have rows of spines on their arms as means of protection. Ranging from nearly pentagonal (example: Indo-pacific cushion star, Culcita novaeguineae) to gracile stars like those on Zoroaster genus.

Sea stars have a simple photoreceptor eyespot at the end of each arm. The eye is able to "see" only differences of light and dark, which is useful in detecting movement. Starfish on the sea floor. ... Starfish on the sea floor. ... Image File history File linksMetadata Download high-resolution version (1728x2304, 989 KB) Blood star (Henricia sanguinolenta). ... Image File history File linksMetadata Download high-resolution version (1728x2304, 989 KB) Blood star (Henricia sanguinolenta). ... The New England Aquarium is a major aquarium located in the city of Boston, Massachusetts. ...

On the surface of the sea star, surrounding the spines, are small white objects known as pedicellariae. There are large numbers of these pedicellariae on the external body which serve to prevent encrusting organisms from colonising the sea star. The radial canal which is across each arm of the sea star has tooth-like structures called ampullae, which surround the radial canal. The aboral surface is also covered with papulae that are involved with the sea star's respiratory system. Pedicellariae are commonly found on Echinoderms. ... The ampulla of Vater is a sphincter (a small muscle) where the common bile duct enters the duodenum. ...

Sea stars are often brightly colored, usually from reddish hues to violet, and unusual colors such as green and blue exist in some species, but come in muted colors as well. Patterns including mosaic-like tiles formed by ossicles, stripes, interconnecting net between spines, pustules with bright colors, mottles or spots. These mainly serve as camouflage or warning coloration displayed by many other marine animals as means of protection against predation. Several types of toxins and secondary metabolites have been extracted from several species of sea stars and now being subjected into research worldwide for pharmacy or other uses such as pesticides. The ossicles (also called auditory ossicles) are the three smallest bones in the human body. ... For a list of biologically injurious substances, including toxins and other materials, as well as their effects, see poison. ... Secondary metabolites are those chemical compounds in organisms that are not directly involved in the normal growth, development or reproduction of organisms. ... A cropduster spreading pesticide. ...

Internal anatomy

The body cavity also contains the water vascular system that operates the tube feet, and the hemal system. Hemal channels form rings around the mouth (the oral hemal ring), closer to the top of the starfish and around the digestive system (the gastric hemal ring). The axial sinus, a portion of the body cavity, connects the three rings. Each ray also has hemal channels running next to the gonads. Image File history File links Download high resolution version (800x735, 108 KB) Summary Dissection of Asterias rubens. ... Image File history File links Download high resolution version (800x735, 108 KB) Summary Dissection of Asterias rubens. ...

Digestion and excretion

Sea star digestion is carried out in two separate stomachs. They are called the cardiac stomach and the pyloric stomach. The cardiac stomach, which is a sack like stomach located at the center of the body may be everted - pushed out of the organism's body and used to engulf and digest food. Some species take advantage of the great endurance of their water vascular systems to force open the shells of bivalve mollusks such as clams and mussels, and inject their stomachs into the shells. Once the stomach is inserted inside the shell it digests 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 and waste is excreted through the anus on the aboral side of the body. This article or section does not cite its references or sources. ... In anatomy, the stomach (in ancient Greek ÏƒÏ„ÏŒÎ¼Î±Ï‡Î¿Ï‚) is an organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. ... Orders Subclass Protobranchia Solemyoida Nuculoida Subclass Pteriomorphia - oysters Arcoida Mytiloida Pterioida Subclass Paleoheterodonta - mussels Trigoinoida Unionoida Subclass Heterodonta - clams, zebra mussels Veneroida Myoida Subclass Anomalosdesmata Pholadomyoida Animals of the Class Bivalvia are known as bivalves because they typically have two-part shells, with both parts being more or less symmetrical. ... Classes Caudofoveata Aplacophora Polyplacophora Monoplacophora Bivalvia Scaphopoda Gastropoda Cephalopoda â€ Rostroconchia The mollusks or molluscs are the large and diverse phylum Mollusca, which includes a variety of familiar creatures well-known for their decorative shells or as seafood. ... Littleneck clams: Rocks with food inside. ... Subclasses Pteriomorpha (marine mussels) Palaeoheterodonta (freshwater mussels) Heterodonta (zebra mussels) The term mussel is used for several families of bivalve mollusks inhabiting lakes, rivers, and creeks, as well as intertidal areas along coastlines worldwide. ...

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 including arthropods, and even small fish in addition to mollusks. Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... A giant grouper at the Georgia Aquarium Fish are aquatic vertebrates that are typically cold-blooded; covered with scales, and equipped with two sets of paired fins and several unpaired fins. ...

Some echinoderms have been shown to live for several weeks without food under artificial conditions—it is believed 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 nerve plexus (a network of interlacing nerves), which lies within as well as below the skin. The esophagus is also surrounded by a number of nerve rings, which send radial nerves that are often parallel with the branches of the water vascular system. The ring nerves and radial nerves coordinate the starfish'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 starfish are sensitive to touch, while eyespots on the ends of the rays are light-sensitive. Image File history File linksMetadata Download high resolution version (2272x1704, 2781 KB) Summary This is a picture of a star fish taken in MontaÃ±a de Oro State Park, California. ... Image File history File linksMetadata Download high resolution version (2272x1704, 2781 KB) Summary This is a picture of a star fish taken in MontaÃ±a de Oro State Park, California. ... The nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. ... In animals, the brain, or encephalon (Greek for in the head), is the control center of the central nervous system. ... The esophagus (also spelled oesophagus/Å“sophagus), or gullet is an organ in vertebrates which consists of a muscular tube through which food passes from the mouth area to the stomach. ...

Behavior

Diet

Most sea star species are generalist predators, some eating bivalves like mussels, clams, and oysters; or any animal slow enough to be unable to evade the attack (e.g. dying fish). Some species are detritivores, eating decomposed animal and plant material, or organic films attached to substrate. The others may consume coral polyps (the best-known example for this is the infamous Acanthaster planci), sponges or even suspended particles and planktons (sea stars from the Order Brisingida). The process of feeding or capture may or may not be aided by special parts; Pisaster brevispinus or Short-spined Pisaster from the west coast of America may use a set of specialized tube feet capable of extending itself deep into the soft substrata, hauling out the prey (usually clams) from within^[1]. Image File history File linksMetadata Starfish0048. ... Image File history File linksMetadata Starfish0048. ... Binomial name Linckia laevigata (Linnaeus, 1758) The Blue Linckia, Linckia laevigata is a species of sea star in the shallow waters of tropical Indo-Pacific. ... This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ... Mussels A mussel is a bivalve shellfish that can be found in lakes, rivers, creeks, intertidal areas, and throughout the ocean. ... Categories: Pages needing attention | Animal stubs ... The name oyster is used for a number of different groups of mollusks which grow for the most part in marine or brackish water. ... A giant grouper at the Georgia Aquarium Fish are aquatic vertebrates that are typically cold-blooded; covered with scales, and equipped with two sets of paired fins and several unpaired fins. ... Subclasses Alcyonaria Zoantharia See text for orders. ... Binomial name Acanthaster planci (Linnaeus, 1758) The crown-of-thorns starfish (Acanthaster planci) is a red-colored starfish with thorn-like spines sprouting all over its body for protection. ... This article is about the animal. ... This article or section does not cite its references or sources. ... The tube feet can be clearly seen on this sea star Tube feet are the many small tubular projections found most famously on the ventral face of a sea stars arms, but are characteristic of the water vascular system of the echinoderm phylum which also includes sea urchins, sand... Littleneck clams: Rocks with food inside. ...

Reproduction

Sea stars are capable of both sexual and asexual reproduction. Individual sea stars are male or female. Fertilization takes place externally, both male and female releasing their gametes into the environment. Resulting fertilised embryos form part of the zooplankton. Ochre sea star, PhotoCD image from film taken June 2003 by k. ... Ochre sea star, PhotoCD image from film taken June 2003 by k. ... Olympic National Park is located in the U.S. state of Washington, in the far northwestern part of the state known as the Olympic Peninsula. ... Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ... Photomontage of plankton organisms Plankton is the aggregate community of weakly swimming but mostly drifting small organisms that inhabit the water column of the ocean, seas, and bodies of freshwater. ...

Sea stars are developmentally (embryologically) known as deuterostomes. Their embryo initially develops bilateral symmetry, indicating that sea stars probably share a common ancestor with the chordates, which includes the fish. Later development takes a very different path however as the developing sea star settles out of the zooplankton and develops the characteristic radial symmetry. Some species reproduce cooperatively, using environmental signals to coordinate the timing of gamete release; in other species, one to one pairing is the norm. It has been suggested that embryology be merged into this article or section. ... Phyla Echinodermata Hemichordata Chordata Xenoturbellida Chaetognatha (uncertain) Vetulicolia â€ Deuterostomes (taxonomic term: Deuterostomia; from the Greek: second mouth) are a superphylum of animals. ... 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... A giant grouper at the Georgia Aquarium Fish are aquatic vertebrates that are typically cold-blooded; covered with scales, and equipped with two sets of paired fins and several unpaired fins. ...

Some species of sea star also reproduce asexually by fragmentation, often with part of an arm becoming detached and eventually developing into an independent individual sea star. This has led to some notoriety. Sea stars can be pests to fishermen who make their living on the capture of clams and other mollusks at sea as sea stars prey on these. The fishermen would presumably kill the sea stars by chopping them up and disposing of them at sea, ultimately leading to their increased numbers until the issue was better understood. A sea star arm can only regenerate into a whole new organism if some of the central ring of the sea star is part of the chopped off arm.

Image File history File linksMetadata Download high-resolution version (2048x1536, 460 KB)Copyright H.J.Moyes. ... Image File history File linksMetadata Download high-resolution version (2048x1536, 460 KB)Copyright H.J.Moyes. ... The tone of this article is inappropriate for an encyclopedia. ...

Locomotion

Sea stars move using a water vascular system. Water comes into the system via the madreporite. It is then circulated from the stone canal to the ring canal and into the radial canals. The radial canals carry water to the ampullae and provide suction to the tube feet. The tube feet latch on to surfaces and move in a wave, with one body section attaching to the surfaces as another releases. Most sea stars cannot move quickly. However, some burrowing species like sea stars from genus Astropecten and Luidia are quite capable of rapid, creeping motion - it "glides" across the ocean floor. This motion results from their pointed tubefeet adapted specially for excavating local area of sand. Image File history File links Stachelhaeuter_fg01. ... Image File history File links Stachelhaeuter_fg01. ...

Image File history File linksMetadata Download high-resolution version (2048x1536, 593 KB)Schmedelian pin-cushion sea star. ... Image File history File linksMetadata Download high-resolution version (2048x1536, 593 KB)Schmedelian pin-cushion sea star. ... The tone of this article is inappropriate for an encyclopedia. ...

Regeneration

Some species of sea star have the ability to regenerate lost arms and can regrow an entire new arm in time. Most species must have the central part of the body intact to be able to regenerate, but a few can grow an entire starfish from a single ray. Included in this group are the red and blue linkia star. The regeneration of these stars is possible due to the vital organs kept in their arms.

Image File history File linksMetadata Download high-resolution version (2048x1536, 734 KB)Copyright H.J.Moyes. ... Image File history File linksMetadata Download high-resolution version (2048x1536, 734 KB)Copyright H.J.Moyes. ... The tone of this article is inappropriate for an encyclopedia. ...

Geological history

Fossil sea stars and brittle stars are first known from rocks of Ordovician age indicating that two groups probably diverged in the Cambrian. However, Ordovician examples of the two groups show many similarities and can be difficult to distinguish. Complete fossil sea stars are very rare, but where they do occur they may be abundant. Most fossil sea stars consist of scattered individual plates or segments of arms. This is because the skeleton is not rigid, as in the case of echinoids (sea urchins), but is composed of many small plates (or ossicles) which quickly fall apart and are scattered after death and the decay of the soft parts of the creature. Scattered sea star ossicles are reasonably common in the Cretaceous Chalk Formation of England. Image File history File links Starfish_Roentgen_X-Ray_01_Nevit. ... Image File history File links Starfish_Roentgen_X-Ray_01_Nevit. ... The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. ... The Cambrian is a major division of the geologic timescale that begins about 542 Â± 1. ... Subclasses 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 Perischoechinoidea Order Cidaroida (pencil urchins) Sea urchins are spiny sea creatures of... The Cretaceous Period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i. ... 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. ... Motto: (French for God and my right) Anthem: God Save the King/Queen Capital London (de facto) Largest city London Official language(s) English (de facto) Unification - by Athelstan AD 927 Area - Total 130,395 kmÂ² (1st in UK) 50,346 sq mi Population - 2006 est. ...

Contents

Distribution

External anatomy

Internal anatomy

Digestion and excretion

Nervous system

Behavior

Diet

Reproduction

Locomotion

Regeneration

Geological history

See also

References

Resources

Contents

Distribution GA_googleFillSlot("encyclopedia_square");

External anatomy

Internal anatomy

Digestion and excretion

Nervous system

Behavior

Diet

Reproduction

Locomotion

Regeneration

Geological history

See also

References

Resources

Distribution