ECHINODERMATA
Discription:
Echinodermata has approximately 7000 living species and about 13,000 extinct species. This phylum is the largest without any freshwater or terrestrial forms.
Geographic Range:
Mainly a marine group, echinoderms are found in all the oceans.
Habitat:
Except for a few species, all echinoderms are found in marine environments. Echinoderms inhabit depths ranging from shallow waters at tide lines to the deep sea. Habitat Regions: temperate, tropical, polar, saltwater or marine, and Aquatic Biomes
Characteristics :
All echinoderms are marine organisms. In the larval stage, most echinoderms are bilaterally symmetrical. Most adults are radially symmetrical. They have a ventral mouth, an internal skeleton of calcium carbonate plates, and a water vascular system consisting of tube feet, radial canals, and a ring canal for movement.
Classification:
Members of the class Crinoidea include sea lilies and feather stars. Members of the class Stelleroidea include sea stars and brittle stars. Members of the class Echinoidea include sea urchins and sand dollars. Members of the class Holothuroidea include sea cucumbers.
Reproduction:
Echinoderms have the ability to regenerate new parts asexually. They also have separate sexes with sex organs in each arm. Sexual reproduction involves releasing gametes into the water (external fertilization).
ORGANISIMS
Sea Stars Reproduction:
The majority of sea stars are carnivorous and feed on sponges, bryozoans, ascidians and molluscs. Other starfishes are detritus feeders (detritus = organically enriched film that covers rocks) or scavengers. Some starfish are specialized feeders, for example the crown-of-thorns that feeds on life coral polyps. Starfish have no hard mouthparts to help them capture prey. The stomach is extruded over the prey, thus surrounding the soft parts with the digestive organs. Digestive juices are secreted and the tissue of the prey liquefied. The digested food mass, together with the stomach is then sucked back in. This method can be observed, if you turn around a starfish that sits on prey or sand - you will see the stomach retreating. Starfish are well known for their powers of regeneration. A complete new animal can grow from a small fragment such as an arm. In some species (Linckia multifora and Echinaster luzonicus) one of the arms will virtually pull it away, regenerates and forms a new animal. Autotomy (self amputation) usually is a protective function, losing the body part to escape a predator rather than being eaten. But here it serves as a form of asexual reproduction. In other species of sea stars (Allostichaster polyplax and Coscinasterias calamaria) the body is broken into unequal parts (= fission) then the missing limbs regenerate.
Sea Urchins Reproduction:
Locomotion by tube feet but also by movement of the spines on the underside of the body. Sea urchins are generally nocturnal, during the day they hide in crevices. However some sea urchins such as Diadema sometimes form large aggregations in open exposed areas. Despite their sharp spines sea urchins are easy game for some fishes, particularly triggerfishes and puffers. A triggerfish grabs the sea urchin with its hard beak like mouth by the spines or it blows some water towards the sea urchin and turns it on its back. The underside of a sea urchin has much shorter spines and those are easily crushed. During the breeding season the body cavity is crammed with eggs or sperms. This is one of the main reasons urchins are so attractive to fish predators (Japanese also like them for the same reason). Some sea urchins are camouflaged. They hold on with their tube feet onto some bottom debris like rubble or pieces of sea grass and carry them on their back. Some even carry live soft corals or anemones. Most sea urchins are algal grazers but some feed on sponges, bryozonans and ascidians and others on detritus (detritus = organically enriched film that covers rocks). The sexes are separate and the young are formed indirectly by the fusion of sperm and eggs released into the water. Many animals live in symbiotic relation with sea urchins. Even on the poisonous spines of the fire urchin (Asthenosoma varium) small shrimps (Periclimenes colemani) can be found. One shrimp (Stegopontonia commensalis) is striped black and white lengthwise and perfectly camouflaged and lives in spines of the long-spined sea urchin (Diadema setosum). Some cardinal fishes and juvenile shrimpfishes also like to take shelter in-between these spines, but even small cuttlefish hide there. It has been observed, that they change their coloring also to black and white. Some flatworms wrap around the thicker spines of the diadema sea urchin.
Sea Cucumbers Reprodution:
Most species feed on the rich organic film coating sandy surfaces. The crawl over the bottom ingesting sand. The edible particles (organic matter such as plankton, foraminifera and bacteria) are extracted when passing through their digestive tract and the processed sand is expelled from the anus (as worm-like excrements). Sea cucumbers move by means of tube feet, which extend in rows from the underside of the body. The tentacles surrounding the mouth are actually tube feet that have been modified for feeding. Other holothurians feed on current-borne zooplankton. They bury in sand extruding their featherlike tentacles (Pseudocolochirus violaceus, Neothyondium magnum or Pentacta crassa). The tentacles have the same shape as soft corals or some anenemones. Large congregations of some small species are found on sponges. They apparently feed on substances secreted by the sponges as well as detritus from the surface. Some species of holothurians have separate sexes others are hermaphrodites. The sea cucumbers hold on to exposed rocks or corals, raise their body to an upright position, rock back and forth and release the sperm and eggs into the sea. Sea cucumbers have a remarkable capacity for regenerating their body parts. When attacked they shed a sticky thread like structure which is actually parts of their guts. The so called Cuverian threads are toxic (the poison is called holothurin) and can dissuade many potential predators. These structures quickly regenerate.