StarFish

Sea stars (also often called "starfish") are echinoderms belonging to the class Asteroidea.Mooi, Rich. "Classification of the Extant Echinodermata." California Academy of Sciences - Research. . The names "sea star" and "starfish" essentially refer to members of the Class Asteroidea. However, common usage frequently finds "sea star" and "starfish" also applied to ophiuroids which are correctly referred to as "brittle stars or "basket stars".

There are over 1800 species of living species of sea stars that occur in all the world's oceans, including the Atlantic, Pacific, Indian as well as in the Arctic and the Southern Ocean (i.e., Antarctic) regions. Sea stars occur across a broad depth range from the intertidal to abyssal depths (>6000 m).

Sea stars are among the most familiar of marine animals and possess a number of widely known traits,such as regeneration and feeding on mussels that are largely based on the frequently encountered Atlantic Asterias. Sea stars possess a wide diversity of body forms and feeding methods. The extent that asteroids can regenerate varies with individual species. Broadly speaking, sea stars are opportunistic feeders, with several species having specialized feeding behavior, including suspension feeding and specialized predation on specific prey.

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

Brittle stars, or ophiuroids, are echinoderms, closely related to sea stars. They crawl across the seafloor using their flexible arms for locomotion. The ophiuroids generally have five long slender, whip-like arms which may reach up to in length on the largest specimens. They are also known as serpent stars.

Ophiuroidea contains two large clades, Ophiurida (brittle stars) and Euryalida (basket stars). Many of the ophiuroids are rarely encountered in the relatively shallow depths normally visited by humans, but they are a diverse group.

There are some 1,500 species of brittle stars living today, and they are largely found in deep waters more than 500 metres (1,650 feet) down.

The Crown-of-Thorns Starfish (Acanthaster planci) is a large nocturnal sea star that preys upon coral polyps. The Crown-of-Thorns receives its name from venomous thorn-like spines that cover its body.

The Crown-of-Thorns is endemic to tropical coral reefs in the Red Sea, the Indian Ocean, and the Pacific Ocean. As solitary animals, they feed alone and maintain constant distance between themselves and other members of their species.

The Crown-of-Thorns is the second largest sea star in the world. Only the Giant Sunstar is larger.

Category: File - :Protoreaster nodosus 1.jpg|left|350px|thumb|Prague sea aquarium

Protoreaster nodosus is a species of sea star found in the warm, shallow waters of Indo-Pacific region. Also known as "horned" or "Chocolate Chip"Shedd Aquarium sea stars, they possess rows of spines or "horns"; black conical points arranged in a single row, radially on the dorsal side, which may erode and becoming blunt.These dark protrusions are used to scare away possible predators, by looking frightening or dangerous. On the ventral side, tube feet, purple in color(or pale, transparent pink), are arranged in rows on each arm. Most horned sea stars found are roughly rigid five-pointed star-shape with tapering arms to the end, although there are anomalies like four or six-armed specimens; they may grow up to 30 centimetres in diameter. The sea stars are usually colored in shades of red or brown, but can be light tan, the color of cookie dough. This appearance, combined with the small horns on its dorasl side, give the sea star a look similar to that of a bumpy cookie. Horned sea stars prefer sheltered, sandy or slightly muddy bottoms more than hard substrata such as coral reef, and are frequently sighted conspicuously between the leaves of seagrasses on sea grass meadows or on blank stretch of coral sand. In shallow water, this species can be seen intertidally, occasionally exposed to the low tide. they do not withstand rapid changes well, however, and usually keep themselves underwater. In aquariums, these sea stars like to climb around on glass and also filters, which they can disrupt. Sometimes, many individuals of this species can be seen gathering on soft bottom with reason not very well known, probably to increase the chance of fertilization when spawning or simply a suitable feeding ground.

Horned sea stars seem to be opportunistic carnivores; adults are known to predate on most sessile life forms including hard corals and sponges in aquarium.In this same setting, they will hunt down snails and eat them. An individual of horned sea star is also has been observed eating a sea urchin in their natural habitat Gremli MS, Newman HE, Insight Guides Underwater: Marine Life In the South China Sea, page 159. APA Publications GmbH & Co. Verlag KG., 1993. In public aquariums, these stars are sometimes target-fed with chopped squids, clams or shrimps, and are popular animals for touch pools as it is moderately large in number in some undisturbed areas. Horned sea stars need perfect water condition, suitable diet and proper acclimatization to thrive - thus, these sea stars did not fare very well caused by several factors mentioned before in many home aquariums. In reef aquariums, they are regarded as undesirable as they have destructive tendencies of toppling decors and digesting patches of corals and sessile organisms; they are reasonably safe if kept in a fish-only aquarium. However, the sea stars are desirable for their cute appearance and relatively non-aggressive behavior.

In many tropical Asian and Pacific countries, horned sea stars are collected for sea shell trade for their ornate skeletons. In some areas overharvesting is an issue and reduces greatly the population of the echinoderms. Related to this species, the Atlantic Oreaster reticulatus or commonly known as Bahama Sea Star, is also a previously-abundant species reduced in number due to the continuous harvesting by the industry and tourists alike.

As with other tropical echinoderms, commensal animals like shrimps (of genus Periclimenes), tiny brittle stars and even juvenile filefish can be found on the surfaces of a horned sea star. This may be attributed to its protective nature, as there are few predators would dare to eat this echinoderm.

Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). Crinoidea comes from the Greek word krinon, "a lily", and eidos, "form". Websters New Universal Unabridged Dictionary.'' 2nd ed. 1979. They live both in shallow water and in depths as great as 6,000 meters.

Crinoids are characterized by a mouth on the top surface that is surrounded by feeding arms. They have a U-shaped gut, and their anus is located next to the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognized, most crinoids have many more than five arms. Crinoids usually have a stem used to attach themselves to a substrate, but many live attached only as juveniles and become free-swimming as adults.

There are only a few hundred known modern forms, but crinoids were much more numerous both in species and numbers in the past. Some thick limestone beds dating to the mid- to late-Paleozoic are almost entirely made up of disarticulated crinoid fragments.

Sea urchins or urchins are small, spiny, globular animals that compose part of class Echinoidea. They are found in all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull shades of green, olive, brown, purple, and red. They move slowly, feeding mostly on algae. Sea otters, wolf eels, and other predators feed on urchins. Humans harvest them and serve their roe as a delicacy.

Sea urchins are members of the phylum Echinodermata, which also includes sea stars, sea cucumbers, brittle stars, and crinoids. Like other echinoderms they have fivefold symmetry (called pentamerism) and move by means of hundreds of tiny, transparent, adhesive "tube feet". The symmetry is not visually obvious, but is easily visible in the dried test.

Together with sea cucumbers (Holothuroidea), they make up the subphylum Echinozoa, which is characterized by a globoid shape without arms or projecting rays. Sea cucumbers and the irregular echinoids have secondarily evolved diverse shapes. Although many sea cucumbers have branched tentacles surrounding the oral opening, these have originated from modified tube feet and are not homologous to the arms of the crinoids, sea stars, and brittle stars.

Holothuroidea are a class of marine animals (phylum Echinodermata) with an elongated body and leathery skin, which is found on the sea floor worldwide. Many holothurian species and genera, informally known as sea cucumbers, are targeted for human consumption. The harvested product is also referred to as sea cucumber, or as trepang, bêche-de-mer, balate, or sea slug. The body contains a single, branched gonad.

Like all echinoderms, sea cucumbers have an endoskeleton just below the skin, calcified structures that are usually reduced to isolated microscopic ossicles (or sclerietes) joined by connective tissue. These can sometimes be enlarged to flattened plates, forming an armour. In pelagic species such as Pelagothuria natatrix (Order Elasipodida, family Pelagothuriidae), the skeleton and a calcareous ring are absentPelagic sea cucumber: Information from Answers.com.