Echinoderm - Wikipedia
Echinoderms are the largest phylum with no freshwater or terrestrial forms. The sea urchin shown below is exhibiting this trait, covering itself with shells from other organisms. .. Echinodermata: Life History and Ecology. however there is doubt as to their phylogenetic relationship within the tree itself. Nowadays, marine organisms are being given a lot of attention in . comparison with other classes of echinoderms discussed herein, we will .. Relationship. Marine symbiotic relationships are an amazing part of nature! symbiosis, meaning both organisms benefit from having the other around.
Depending on the species the water depth and movement will vary. Echinoderms are generally found in shallow water near shores or in reef environments but can also live in great depths of water. Below is a photo of a tank for marine animals. This tank contains brittle stars, sea cucumbers, and sea urchins along with non-echinoderm animals.
In the tank are rocks, plants and other things to help give shelter and protection to the animals. This picture is of a tank in a classroom at Ohio State University.
In this tank there is a species of brittle stars, sea urchins and sea cucumbers. There are also other animals such as a shrimp and some small fish. Not to mention the plants and sponges present. Brittle stars Ophio coma lead a cryptic lifestyle. They avoid predation by spending much of their day hiding within holes in coral and rocks found in their environment Zubi, In the picture shown below, a brittle star is almost completely concealed under a sponge.
When sea urchins are found in environments not conducive to burrowing, like the marine tank shown above, they have been know to cover themselves with objects found in the environment for protection Carefoot, The sea urchin shown below is exhibiting this trait, covering itself with shells from other organisms. The photo on the left is of a brittle star hiding out under a sponge in the tank at Ohio State. The photo on the right is of a sea urchin in the same tank carrying around a shell of another organism.
Though many Echinoderm species undergo sexual reproduction, a few species reproduce asexually. The bulk of echinoderm species are diecious, meaning that there are male and female individuals. The type of reproduction that an echinoderm goes through depends on the species and the environment Mulcrone, Sexual reproduction refers to the combination of genetic material from two separate individuals, of different sexes, resulting in a new organism.
The males provide the sperm and the females provide the eggs for reproduction. The sperm and eggs are propagated into the water column, and fertilization generally happens in the open water. Certain species of sea stars, brittle stars, and sea cucumbers go through internal fertilization. This is a recent observation and little information is known about this phenomenon.
The release of the eggs and sperm is synchronized in two different ways. Some species have a breeding season where individuals congregate to increase the chances of fertilization. Some species such as the Slender Sea Star Leptasterias tenera brood their eggs. This means that they carry their eggs with them until they are ready to hatch. When sexual reproduction occurs, the resulting eggs go through either direct or indirect development.
When indirect development occurs, the fertilized eggs of echinoderms will develop into larvae known as planktonic larvae. In most cases, this stage occurs when the fertilized egg consists of a lower yolk volume. For example, a sea urchin has an 'echinopluteus' larva while a brittle star has an 'ophiopluteus' larva. A starfish has a 'bipinnaria' larva but this later develops into a multi-armed 'brachiolaria' larva. A sea cucumber larva is an 'auricularia' while a crinoid one is a 'vitellaria'.
All these larvae are bilaterally symmetrical and have bands of cilia with which they swim and some, usually known as 'pluteus' larvae, have arms.
When fully developed they settle on the seabed to undergo metamorphosis and the larval arms and gut degenerate. The left hand side of the larva develops into the oral surface of the juvenile while the right side becomes the aboral surface.
At this stage the bilateral symmetry is lost and radial symmetry develops. There seems to be an evolutionary trend towards a "lower-risk—lower-gain" strategy of direct development.
While 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. The tube feet typically have a tip shaped like a suction pad in which a vacuum can be created by contraction of muscles. This along with some stickiness provided by the secretion of mucus provides adhesion.
Waves of tube feet contractions and relaxations move along the adherent surface and the animal moves slowly along.
Echinoderm - New World Encyclopedia
The two forward arms grip the substrate with their tube feet, the two side arms "row", the hindermost arm trails and the animal moves in jerks. The arm spines provide traction and when moving among objects, the supple arms can coil around things. A few species creep around on pointed tube feet. The movement of multiple tube feet, coordinated in waves, moves the animal forward, but progress is slow. Some also use their articulated spines to push or lever themselves along or lift their oral surfaces off the substrate.
If a sea urchin is overturned, it can extend its tube feet in one ambulacral area far enough to bring them within reach of the substrate and then successively attach feet from the adjoining area until it is righted. Some species bore into rock and they usually do this by grinding away at the surface with their mouthparts.
Many can move on the surface or burrow through sand or mud using peristaltic movements and some have short tube feet on their under surface with which they can creep along in the manner of a starfish. Some species drag themselves along by means of their buccal tentacles while others can expand and contract their body or rhythmically flex it and "swim". Many live in cracks, hollows and burrows and hardly move at all.
Some deep water species are pelagic and can float in the water with webbed papillae forming sails or fins. These stems can bend and the arms can roll and unroll and that is about the limit of the sea lily's movement, although a few species can relocate themselves on the seabed by crawling.
The sea feathers are unattached and usually live in crevices, under corals or inside sponges with their arms the only visible part. Some sea feathers emerge at night and perch themselves on nearby eminences to better exploit the food-bearing current. Many species can "walk" across the seabed, raising their body with the help of their arms. Many can also swim with their arms but most are largely sedentary, seldom moving far from their chosen place of concealment.
Crinoids and some brittle stars tend to be passive filter-feeders, enmeshing suspended particles from passing water; most sea urchins are grazers, sea cucumbers deposit feeders and the majority of starfish are active hunters.
Crinoids are suspension feeders and spread their arms wide to catch particles floating past. These are caught by the tube feet on the pinnules, moved into the ambulacral grooves, wrapped in mucus and conveyed to the mouth by the cilia lining the grooves.
Some are suspension feeders, securing food particles with mucus strands, spines or tube feet on their raised arms. Others are scavengers and feeders on detritus. Others again are voracious carnivores and able to lasso their waterborne prey with a sudden encirclement by their flexible arms. The limbs then bend under the disc to transfer the food to the jaws and mouth.
Other species devour smaller organisms, which they may catch with their tube feet.
There was a problem providing the content you requested
They may also feed on dead fish and other animal matter. Others ingest large quantities of sediment, absorb the organic matter and pass the indigestible mineral particles through their guts. In this way they disturb and process large volumes of substrate, often leaving characteristic ridges of sediment on the seabed.
Some sea cucumbers live infaunally in burrows, anterior-end down and anus on the surface, swallowing sediment and passing it through their gut. Other burrowers live anterior-end up and wait for detritus to fall into the entrances of the burrows or rake in debris from the surface nearby with their buccal podia.
Small fish landing on the upper surface may be captured by pedicilaria and dead animal matter may be scavenged but the main prey items are living invertebrates, mostly bivalve molluscs. To feed on one of these, the starfish moves over it, attaches its tube feet and exerts pressure on the valves by arching its back.
When a small gap between the valves is formed, the starfish inserts part of its stomach into the prey, excretes digestive enzymes and slowly liquefies the soft body parts.
As the adductor muscle of the shellfish relaxes, more stomach is inserted and when digestion is complete, the stomach is returned to its usual position in the starfish with its now liquefied bivalve meal inside it. The same everted stomach process is used by other starfish to feed on sponges, sea anemones, corals, detritus and algal films.
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. Although most echinoderm spines are blunt, those of the crown-of-thorns starfish are long and sharp and can cause a painful puncture wound as the epithelium covering them contains a toxin. Certain sea cucumbers have a cluster of cuvierian tubules which can be ejected as long sticky threads from their anus and entangle and permanently disable an attacker.Echinodermata - Class Diversity
Another defensive strategy sometimes adopted by sea cucumbers is to rupture the body wall and discharge the gut and internal organs. The animal has a great regenerative capacity and will regrow the lost parts later. Some starfish species can "swim" away from what may be danger, foregoing the regrowth by not losing limbs. The burrowing of sand dollarssea cucumbers and some starfish stirs up the sediment and depletes the sea floor of nutrients. Their digging activities increases the depth to which oxygen can seep and allows a more complex ecological tier-system to develop.
Starfish and brittle stars prevent the growth of algal mats on coral reefs, which might otherwise obstruct the filter-feeding constituent organisms. Coral reefs are also bored into in this way but the rate of accretion of carbonate material is often greater than the erosion produced by the sea urchin.
Armless, elongated, generally soft-bodied small exoskeleton animals, resembling slugs retaining partial bilateral symmetry as adults ; about 1, species. Ophiuroidea brittle stars and basket stars: The physically largest of echinoderms; about 1, species, the largest echinoderm class.
Primarily bottom feeders, and have long, narrow arms that allow relatively fast movement. Extinct forms known from fossils include blastoids, edrioasteroids, and several early Cambrian animals, such as Helicoplacus, carpoids, Homalozoa, and possibly machaerids.
Physiology The tube feet can be seen on this sea star. Echinoderms appeared to have evolved from animals with bilateral symmetrybut whose later forms were lopsided. They undergo metamorphosis from larva with bilateral symmetry to a bottom-dwelling adult with radial symmetry Towle 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.
Echinoderms (starfish, brittle star, sea urchin, feather star, sea cucumber)
All echinoderms exhibit fivefold radial symmetry, or multiples thereof, in portions of their body at some stage of life, even if they have secondary bilateral symmetry. The worm-like sea cucumbers retain partial bilateral symmetry into their adult form. Live sand dollar on a beach Echinoderms also have a mesodermal endoskeleton made of tiny calcified plates and spines, which forms a rigid support contained within tissues of the organism.
Some groups have modified spines, called pedicellariae, that keep the animal free of debris. The spines from which echinodermata gets its name are actually part of this internal skeleton and are covered by epidermis skin. Echinoderms possess a hydraulic water vascular system, a network of fluid-filled canals that function in locomotion, feeding, and gas exchange.
Echinoderms typically have hundreds of transparent, adhesive tube feet.
These tube feet extend from the canals, and can be extended or retracted by means of water pressure from the water vascular system. The tube feet, or podia, are sucker-like and can be used for movement and to grip objects. Echinoderms possess an open and reduced circulatory systemand have a complete digestive tube tubular gut.