What Are Two Animals In The Echinoderm Phylum
Introduction to Phylum Echinodermata
Echinoderms are named for the spines or bumps covering the outer surface of the bodies of many of them (Greek root word echino- meaning spiny; Latin root word -derm significant peel). Examples of echinoderms include sea stars, body of water urchins, body of water cucumbers, brittle stars, and feather stars (Fig. 3.83). Although they may appear very unlike, echinoderms all have two major defining characteristics that ready them apart from all other animals: a water vascular system and five-sided radial symmetry.
The water vascular organisation is a complex serial of canals running through an echinoderm's body (Fig. 3.84). Information technology is a hydraulic pressure arrangement that aids in movement. The canals are h2o-filled tubes that open to the outside through a skeletal plate called the madreporite (from Latin root words madre meaning mother and pori meaning small pigsty) lying on the surface well-nigh the anal opening. Water enters and leaves the tubes through this sieve-like plate. An echinoderm moves by using many tube feet. Tube feet are small, fragile projections attached along the side of a water-filled tube chosen a radial canal. Figure 3.85 shows some examples of echinoderm tube anxiety. Tube feet extend through the small holes in the skeleton to the outside. These feet are grouped in five regions. Virtually sea stars, sea urchins, and sea cucumbers have suction cups at the tips of their tube feet. In some sea stars and brittle stars the tube feet are shaped like piffling paddles. H2o gets from the madreporite to the tube anxiety through the radial canal. Valves continue water from flowing back into the radial canal (Fig. 3.84). The ampullae of the tube feet human action like the bulbs of eyedroppers. When a valve closes and the ampulla muscles contract, squeezing the ampulla, water shoots into the tube pes, extending it (Fig. 3.85). When the tube foot comes in contact with hard substrate, its centre withdraws, forming a cup and producing a vacuum much equally a rubber suction cup does. The tube human foot clings to the substrate considering the water pressure level on its outside border is greater than the force per unit area within its suction loving cup. When the muscles of the ampulla relax, water moves back into the ampulla, flattening the cup and releasing the vacuum in Fig. iii.85.
Echinoderms are radically symmetrical, and the body is normally divided into five parts or multiples of 5. This five-sided radial structure of echinoderms makes the trunk strong (Fig. three.86). A five-sided skeleton is stronger than a 4- or half-dozen-sided one because the line of weakness cannot run directly across the body. Fifty-fifty a three-sided body plan is weaker than a v-sided one.
Most animals that move around have bilateral symmetry, as described in the previous sections on molluscs, worms, and arthropods. But echinoderms, although they also move, are radially symmetrical, so the terms inductive, posterior, dorsal, and ventral practice not use. In the echinoderms there are 2 surfaces. One is the oral surface, where the rima oris is and the tube feet project. The tube anxiety on the oral surface are express to distinct regions called the ambulacral regions. The other surface is the aboral, which typically contains the anal opening of the digestive system. All echinoderms are variations on this oral-aboral trunk plan (Fig. three.83). Bounding main stars (class Asteroidea) and brittle stars (course Ophiuroidea) have apartment bodies with a broad aboral surface facing up and an oral surface facing down. Both groups have arms projecting from a cardinal trunk disc and the ambulacral regions with the projecting tube feet extending forth each of the arms (Fig. 3.83 B and Fig. three.83 C). Like sea stars, the feather stars and sea lilies (class Crinoidea) have arms, just the oral surface faces upwards, abroad from the bottom (Fig. 3.83 Due east). The tube feet extend upward from the oral surface to capture particles of nutrient floating past. Plumage stars grasp the substrate with a series of rootlike projections from the aboral surface and bounding main lilies have long, stalk-like projections from the aboral surface with which they permanently adhere themselves to the bottom. Bounding main urchins (class Echinoidea) have no arms (Fig. three.83 A). The radial body plan is spherical. The oral surface, with ambulacral regions and tube anxiety, covers virtually of the sphere. The aboral surface is just a small disc at the top. In most sea urchins, spines also extend from the oral surface, ordinarily betwixt the rows of tube feet. The radial body program of bounding main cucumbers (form Holothuroidea) is tube-shaped, with the aboral surface just a small-scale region at the finish reverse the mouth (Fig. 3.85 D). Most of the long torso is covered by the oral surface, with tube anxiety projecting in five rows. Many of the tube feet around the oral fissure take the form of long tentacles, used for gathering nutrient. The body lies on its side, giving the advent of bilateral symmetry. The tube anxiety touching the bottom commonly carry suction cups and are used for locomotion. The tube feet on the "upper" part of the body are oft elementary pointed structures.
All echinoderms also lack any kind of central nervous organisation or brain, simply have a nervus ring. Echinoderms as well have calcium carbonate endoskeletons, ranging from microscopic spicules in bounding main cucumbers to visible plates in ocean stars and urchins. Most echinoderms take a consummate digestive organisation and a big coelom. They have split sexes, ordinarily with gonads in sets of five, showing internal pentaradial symmetry. All echinoderm species alive in the ocean; in that location are no freshwater or terrestrial echinoderms.
Class Echinoidea
Sea urchins belong to the class Echinoidea, named for the movable spines projecting from their body like a hedgehog'due south spines (from the Greek word echinoid meaning like a hedgehog). Sea urchins (Fig. iii.83 A) are mutual around the world, from the bounding main'south shoreline to great depths and from tropical waters to polar waters. Ocean urchins are relatively small-scale; nigh species could fit in the palm of your hand. The spines are adaptations that protect the urchins from predators. Spines and tube anxiety help urchins motility and go food. The long, sparse, precipitous spines of some ocean urchins hands penetrate flesh and in some species, toxic chemicals on the tissue covering the sharp spines brand its stab extremely painful (Fig. 3.87 A and B). Other species, with short, thick, or blunt spines are safe to handle (Fig. 3.87 C and D). A few species that have adjusted to live in the moving ridge surge zone of rocky coastlines have flattened spines (Fig. 3.87 D). Flat, broad plate spines give these urchins a low profile and preclude them from getting swept away by powerful waves. Sand dollars have fine velvet-textured spines that help these animals burrow into sand (Fig. 3.87 E). Pedicellariae are modest jaw-like pincher appendages establish on many species of bounding main urchins and sea stars (Fig. 3.88). They are typically attached to the echinoderm trunk at the base of the spines. The proper name pedicellaria comes from the Latin root words ped- meaning foot and -icellus pregnant lilliputian. A pedicellaria snaps open if something touches its outer surface; it snaps close if information technology is touched on its inner surface. Some pedicellariae are toxic, containing a pocket-size poison gland. Others have powerful jaws that can vanquish small organisms.
The soft inner organs of sea urchins are protected by a hard structure called a test. An urchin exam is a difficult internal skeleton composed of calcium carbonate (CaCO3) plates (Fig. 3.89 A). The plates interlock in a tight geometric pattern that makes the skeleton rigid. Because the test is covered by very thin skin or epidermis, it is considered to be an endoskeleton. Most of the plates take tiny pores through which internal organs of respiration protrude into the seawater. The spines attach to the plates on tubercles, ball-and-socket joints with muscles attached effectually the base that support and motion the spines. The mouthparts of urchins are called Aristotle'southward lantern (Fig. 3.89 B and Fig. 3.89 C). Nigh sea urchins are herbivores and scrape algae from hard substrates with v tooth-similar structures in the mouth on the lower surface of the torso. Minor bits of food move through a long digestive tube to be digested and absorbed. Indigestible textile passes out through the anus, opposite the mouth (Figs. iii.90 A and C).
Class Asteroidea
Ocean stars belong to the form Asteroidea (from the Greek word asteroid pregnant like a star; Fig. 3.90). Like sea urchins, sea stars inhabit the oceans worldwide, from nearshore tide pools to deep bounding main seafloors. Sea stars come in a range of sizes, reaching upward to i meter (yard) in length, but almost are much smaller. Ocean stars may be red, blue, or many other colors. Almost sea stars have a central disk with five radial artillery; some species have 15 to twoscore artillery. A few species have artillery so short that they barely beetle. Their bodies look similar pin cushions.
The sea star's skeleton, like the sea urchin's, is an endoskeleton consisting of small-scale plates of calcium carbonate embedded in the epidermis. These plates, called ossicles, are much smaller than those of bounding main urchins. The sea star's ossicles are continued by muscles and connective tissue to form a network that lets the arms curve and twist into shapes to fit rocky contours. Some body of water stars have spines extending from the ossicles, to help defend them from predators. Body of water stars accept a h2o vascular system and tube feet much like those of the sea urchins. Ambulacral grooves (from the Latin root ambul meaning walk) are narrow channels in the oral surface of a sea star filled with tube feet. The tube anxiety are used mainly for grabbing and locomotion. In some sand-dwelling sea stars the tips of tube anxiety are paddle-shaped, making them efficient for "walking" and burrowing. Sea stars have remarkable powers of regeneration. Many species tin can regenerate a whole arm that breaks off (Fig. three.91 A). These regenerated pieces are chosen comets (Fig. 3.91 B).
Image courtesy of Ahmed Abdul Rahman and Frédéric Ducarm, Marine Discovery Eye Seamarc Maldives
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Ocean stars are voracious predators, itch over the ocean bottom in search of prey. They feed non only on sessile molluscs such as clams, oysters, and mussels, but besides on dead organisms lying on the bottom. The crown-of-thorns starfish (Acanthaster planci) consumes so much live coral that it is considered a significant threat to coral reefs in the tropical Indo-Pacific region. The mouth of a ocean star opens into the stomach in the central disc. The anus is on the upper surface (Fig. three.90 A). Most sea stars are carnivores. Although a sea star has no teeth, it can eat coral polyps and molluscs by pushing its tum out of the body, spreading it over its prey, and digesting it. To consume a clam, the sea star grasps the bivalve in its arms, attaches its suction cups to both shells, pulls steadily until the shells open up slightly, and extends its tum into the mollusk. In this way information technology preys on clams whose shells are open up as fiddling as 0.i mm. Later on the sea star digests and absorbs the tissue of its prey, it sucks its tummy back into its own body.
Class Ophiurodea
Breakable stars are the most arable echinoderms. About 2,000 species inhabit the sea floor worldwide, from the shoreline to keen depths. In some areas, clusters of millions of breakable stars thickly carpet the lesser. This group is active just at night, hiding under rocks and in crevices during the day. Brittle stars have long, flexible arms fastened to a small central disc (Figs. iii.83 C and 3.92). Skeletal ossicles class a serial of scaly plates forth the arms, and a serial of large cylindrical ossicles runs through the eye of each arm. These ossicles look somewhat like the row of vertebrae in a fish skeleton. They are connected past muscles that contract, producing a snakelike action. This characteristic movement gives the class its name, Ophiuroidea (from the Greek root words ophio- pregnant ophidian and -uroid pregnant tail-like). Information technology is also the basis for another common name, serpent star. Moving breakable stars can appear to exist dangerous, but they are harmless to humans. A row of movable spines projecting from the sides of the artillery helps the animal move along the lesser. Although the arms appear to be radial, one or ii of them unremarkably lead in pulling the animal forth while the others trail (Fig. 3.93). These animals got the name breakable star because an arm oftentimes breaks off if they are captured. The cleaved arm is left fluctuant equally the rest of the brittle star scoots abroad. The missing arm regenerates quickly. Most brittle stars are minor with a key disc diameter less than three centimeters, simply the arms may be upwards to x centimeters long.
Breakable stars feed on detritus—small particles of food—on the bottom. Some breakable stars curve their arms up to collect food particles suspended in the water. The tube feet, shaped like pointed tentacles, are used mainly for collecting food. Ane tube pes passes particles to another toward the mouth. The nutrient then passes into the stomach, where it is digested. Unlike the other echinoderms, breakable stars take no anus; they eject undigested textile through the oral fissure.
Class Holothuroidea
The class Holothruoidea is improve known past every bit the sea cucumbers. Sea cucumbers are cylindrical echinoderm animals with feathery tentacles at the oral cavity end of their bodies. They are often mistakenly called worms. Some species resembles fatty pickles a few centimeters long (Fig. iii.94 A). Others are like thin tubes over a meter long (Fig. 3.94 B). These animals are mutual residents of reefs and rocky shorelines worldwide. A few species swim constantly in the water, seldom touching the bottom; they are the merely members of this phylum to do and so. Some Pacific islanders collect sea cucumbers, remove their intestines, and dry the muscular body wall, making a nutrient eaten in many countries.
Dissimilar other groups of echinoderms, ocean cucumbers have no large plates or ossicles forming a rigid skeleton. Their skeletal structures are microscopic spicules embedded in the animal's peel. Considering the spicules differ by species, they are useful in identification. Muscles in the body wall of many bounding main cucumbers are developed enough to aid in locomotion. When the muscles contract, the body becomes firm and rigid. In some species the muscles are then thin that the internal organs prove through the body wall. When these animals are taken from the water, the body wall collapses like thin plastic tubing.
The digestive system has a mouth at one end, a digestive tube down the center, and an anus at the other end (Fig. 3.95). The mouth is ringed with tentacles that are modified tube anxiety. Some species use their tentacles to accept in sediment particles rich in plant and animate being matter (Fig. 3.94 B). Other body of water cucumbers extend their tentacles to snatch passing nutrient particles (detritus and plankton) (Fig. iii.94 A). This beliefs makes them await somewhat similar sea anemones, and and so this grade is named Holothuroidea (from the Greek root discussion holothuroid pregnant similar a polyp). The digestive tube has a stomach and a long, sparse, coiled intestine where food is digested. Indigestible sand and other particles are expelled through the anus. Much the aforementioned happens in earthworms, which literally eat their way through soil.
The respiratory system of sea cucumbers is unusual in its organization. They breathe through an internal construction called a respiratory tree, which is attached to the intestine (Fig. 3.95). Seawater taken in through the anus fills this branching structure, where trunk fluids absorb the oxygen. The water is so "exhaled" through the anus. Because the anus is often open during this respiratory process, other organisms—small crabs and fish amid them—sometimes enter and take up residence in the lower digestive tract and respiratory tree (Fig. 3.72 A). A few species of sea cucumbers have a set of molar-like projections around the anus to ward off invaders.
Some sea cucumbers have some other bizarre fashion of protecting themselves. Cuverian tubules are branches of sea cucumber respiratory copse in the form of long, slender threads (Fig. three.95). These Cuverian tubules contain both sticky and toxic chemicals. When these sea cucumbers are disturbed, they can eject these viscous threads out the anus, thoroughly entangling any attacking predator (Fig. 3.94 D). The ejected tubules wait like strands of limp spaghetti but stick like cobwebs. Nether favorable conditions, these internal organs soon regenerate.
Class Crinoidea
The bounding main lilies and feather stars reside within the course Crinoidea (from the Greek root word crino significant lily). Sea lilies are sessile organisms attached to the substrate by a flexible stem (Figs. iii.96 A and B). The digestive organs are in a bud at the tiptop of the stalk called the calyx. The artillery of the crinoid extend out from the calyx. These arms are made up of the calcareous plates seen in other echinoderms. Similar the brittle stars, they are jointed for flexibility. Each arm has am ambulacral groove containing tube anxiety in the center and is lined on each side with tubular extensions chosen pinnules. The feathery arms are used to collect food from the water, thus crinoids are filter feeders. Feather stars are similar in body grade to sea lilies (Fig. 3.96 C and D). Rather than an attached stalk, feather stars take pocket-sized flexible appendages called cirri at the base of the calyx. These appendages allow feather stars to move around. Some feather star species tin can even use their artillery to actively swim (Fig. three.96 East).
Source: https://manoa.hawaii.edu/exploringourfluidearth/biological/invertebrates/phylum-echinodermata
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