phylum ECHINODERMATA
All echinoderms are solely marine organisms. Members of this phylum include sea stars, brittle stars, sea urchins, and sea cucumbers, With a few exceptions, echinoderms are all bottom-dwellers.
ECOLOGICAL ROLE
Echinoderms are usually an intricate part of their ecosystems. Some groups are keystone species, whereas others are efficient scavengers of decaying matter on the seafloor, and a prey upon small organisms helping to regulate the number of them. However, when certain groups get large in number, such as sea urchins, they can devastate seagrass beds due to overgrazing which affects the rest of the ecosystem.
Echinoderms are usually an intricate part of their ecosystems. Some groups are keystone species, whereas others are efficient scavengers of decaying matter on the seafloor, and a prey upon small organisms helping to regulate the number of them. However, when certain groups get large in number, such as sea urchins, they can devastate seagrass beds due to overgrazing which affects the rest of the ecosystem.
MOVEMENT STRUCTURES/TYPE
Some echinoderms have podia or tube feet which are sucker-like appendages that the echinoderm can be used as levers, stepping along surfaces, or as attachment mechanisms that pull the animal. These tube feet are extended and retracted by hydraulic pressure in the water-vascular system. Echinoderms are able to move via water vascular system. Other groups tend to move by thrashing the arms in a rowing motion in strokes. Sea Cucumbers move by both the tube feet and by contraction and expansion of the body.
Some echinoderms have podia or tube feet which are sucker-like appendages that the echinoderm can be used as levers, stepping along surfaces, or as attachment mechanisms that pull the animal. These tube feet are extended and retracted by hydraulic pressure in the water-vascular system. Echinoderms are able to move via water vascular system. Other groups tend to move by thrashing the arms in a rowing motion in strokes. Sea Cucumbers move by both the tube feet and by contraction and expansion of the body.
BODY COVERING; CELL LAYERS; LEVEL OF ORGANIZATION; PROTECTION
All adult echinoderms have five part radial symmetry, an internal skeleton and a water-vascular system derived from the coelom (central cavity). Characterized by being invertebrates with hard, spiny covering or skin. The water vascular system performs many important functions in echinoderms, including locomotion, respiration, sensory reception and feeding. Echinoderms have a true coelom (an open, fluid-filled body cavity lined with tissue), large gonads, and a complete gut. Projections from the skeleton sometimes resembling spikes, which are typical of echinoderms. Different echinoderms can protect themselves from predation by having a firm skeleton, spines, poisonous pincer like organs, and by releasing toxic chemicals or sticky tangling threads. Part of the body cavity or coelom is a water vascular system, consisting of fluid filled vessels that are pushed out from the body surface as tube feet, papillae, and other structures that are used in locomotion, feeding, respiration, and sensory perception. typically opens to the exterior through a sieve-like madreporite on the aboral (upper) surface of the animal. The madreporite is linked to a slender duct, the stone canal, which extends to a ring canal that encircles the mouth or oesophagus. From this, radial canals extend along the arms of asteroids and adjoin the test in the ambulacral areas of echinoids. Short lateral canals branch off the radial canals, each one ending in an ampulla. Part of the ampulla can protrude through a pore (or a pair of pores in sea urchins) to the exterior and is known as a podium or tube feet.
All adult echinoderms have five part radial symmetry, an internal skeleton and a water-vascular system derived from the coelom (central cavity). Characterized by being invertebrates with hard, spiny covering or skin. The water vascular system performs many important functions in echinoderms, including locomotion, respiration, sensory reception and feeding. Echinoderms have a true coelom (an open, fluid-filled body cavity lined with tissue), large gonads, and a complete gut. Projections from the skeleton sometimes resembling spikes, which are typical of echinoderms. Different echinoderms can protect themselves from predation by having a firm skeleton, spines, poisonous pincer like organs, and by releasing toxic chemicals or sticky tangling threads. Part of the body cavity or coelom is a water vascular system, consisting of fluid filled vessels that are pushed out from the body surface as tube feet, papillae, and other structures that are used in locomotion, feeding, respiration, and sensory perception. typically opens to the exterior through a sieve-like madreporite on the aboral (upper) surface of the animal. The madreporite is linked to a slender duct, the stone canal, which extends to a ring canal that encircles the mouth or oesophagus. From this, radial canals extend along the arms of asteroids and adjoin the test in the ambulacral areas of echinoids. Short lateral canals branch off the radial canals, each one ending in an ampulla. Part of the ampulla can protrude through a pore (or a pair of pores in sea urchins) to the exterior and is known as a podium or tube feet.
SUPPORT
Echinoderm skeletons are made up of interlocking plates or ossicles(spines). This skeleton is enclosed by the epidermis, making it an exoskeleton. In some species, the plates are tightly fit together such as in sea urchins. In other species the plates are more loosely bound such as in starfish. The plates are not solid blocks but are fine networks of calcium carbonate forming a sponge like micro structure called a stereom. The general shape of echinoderms may be that of a star with arms extending from a central disk or with branched and feathery arms extending from a body.
Echinoderm skeletons are made up of interlocking plates or ossicles(spines). This skeleton is enclosed by the epidermis, making it an exoskeleton. In some species, the plates are tightly fit together such as in sea urchins. In other species the plates are more loosely bound such as in starfish. The plates are not solid blocks but are fine networks of calcium carbonate forming a sponge like micro structure called a stereom. The general shape of echinoderms may be that of a star with arms extending from a central disk or with branched and feathery arms extending from a body.
OBTAINING NUTRIENTS
Different groups have different feeding habits. Echinoderms consist of filter or suspension feeders, herbivores, detritivores, predators and scavengers. Many starfish have the ability to feed by turning the stomach inside out through the mouth. Many echinoderms have hard plates which retract and grasp like teeth, arranged in a structure known as “Aristotle’s lantern”. This allows sea urchins to graze on algae.
Different groups have different feeding habits. Echinoderms consist of filter or suspension feeders, herbivores, detritivores, predators and scavengers. Many starfish have the ability to feed by turning the stomach inside out through the mouth. Many echinoderms have hard plates which retract and grasp like teeth, arranged in a structure known as “Aristotle’s lantern”. This allows sea urchins to graze on algae.
RESPIRATION
Echinoderms lack a well-developed respiratory system. Some groups respire through simple gills, their tube feet, or through diffusion.
Echinoderms lack a well-developed respiratory system. Some groups respire through simple gills, their tube feet, or through diffusion.
CIRCULATION
Echinoderms have a network of fluid-filled canals that function in gas exchange feeding and in movement. The network contains a central ring and areas which contain the tube feet which stretch along the body or arms. The tube feet poke through holes in the skeleton and can be extended or contracted. They do not have a true heart and the blood often lacks any respiratory pigment.
Echinoderms have a network of fluid-filled canals that function in gas exchange feeding and in movement. The network contains a central ring and areas which contain the tube feet which stretch along the body or arms. The tube feet poke through holes in the skeleton and can be extended or contracted. They do not have a true heart and the blood often lacks any respiratory pigment.
EXCRETION
Most echinoderms possess a simple digestive system with a stomach, intestine, rectum and anus, although not all groups have each part. Some echinoderms such as brittle stars expel waste through their mouths, sea urchins expel waste through their anus, while other groups excrete through the process of diffusion.
Most echinoderms possess a simple digestive system with a stomach, intestine, rectum and anus, although not all groups have each part. Some echinoderms such as brittle stars expel waste through their mouths, sea urchins expel waste through their anus, while other groups excrete through the process of diffusion.
RESPONSE
Echinoderms do not have a centralised nervous system, allowing them to sense their environment from all sides. Most sensory neurons are located at the termini of podia (tube feet). They do not have brains, but have nerves running from the mouth into each arm or along the body. They have tiny eye spots at the end of each arm which only detect light or dark. Some of their tube feet are also sensitive to chemicals and this allows them to find the source of smells.
Echinoderms do not have a centralised nervous system, allowing them to sense their environment from all sides. Most sensory neurons are located at the termini of podia (tube feet). They do not have brains, but have nerves running from the mouth into each arm or along the body. They have tiny eye spots at the end of each arm which only detect light or dark. Some of their tube feet are also sensitive to chemicals and this allows them to find the source of smells.
REPRODUCTION
Echinoderms are mainly of separate sexes and reproduce sexually by external fertilization. Eggs and sperm are freely released into the water. The eggs are fertilized on the seafloor. A few sea urchins hold fertilized eggs in special pouches, but they provide no parental care. Some groups of echinoderms also reproduce asexually, by fragmentation and regeneration.
Echinoderms are mainly of separate sexes and reproduce sexually by external fertilization. Eggs and sperm are freely released into the water. The eggs are fertilized on the seafloor. A few sea urchins hold fertilized eggs in special pouches, but they provide no parental care. Some groups of echinoderms also reproduce asexually, by fragmentation and regeneration.
classes of echinoderms
Asteroidea (starfish & sea stars): flat, pentagonal or star shaped body, oral surface is directed downwards and the aboral surface upwards, 5-50 rays or ams radiating symmetrically from the central disc, mouth and anus are seperate, podia for feet, flexible endoskeleton, seperate sexes, reproduce by papulae.
Holothuroidea (sea cucumbers): calcareous ring that encircles the throat that serves as an attachment point for muscles, circlet of oral tentacles, the skeleton is reduced to microscpoic ossicles, some possess organs not found in other vertebrates Cuvierian tubules, respiratory trees for gas exhchange that attach to the intestine near the anus cloacal breathing, tentacles instead of arms, soft body wall, dioecious.
Echinoidea (sea urcins & sand dollars): no arms, hemispherical in shape, round on top flat from bottom, pentaradially symmetrical, calcareous skeleton made of tightly packed or fused plates, mouth contains Artistotles lantern composed of five jaws, spines and tube feet for movement, seperate sexes, mouth is on the aboral surface and anus is on the oral surface.
Holothuroidea (sea cucumbers): calcareous ring that encircles the throat that serves as an attachment point for muscles, circlet of oral tentacles, the skeleton is reduced to microscpoic ossicles, some possess organs not found in other vertebrates Cuvierian tubules, respiratory trees for gas exhchange that attach to the intestine near the anus cloacal breathing, tentacles instead of arms, soft body wall, dioecious.
Echinoidea (sea urcins & sand dollars): no arms, hemispherical in shape, round on top flat from bottom, pentaradially symmetrical, calcareous skeleton made of tightly packed or fused plates, mouth contains Artistotles lantern composed of five jaws, spines and tube feet for movement, seperate sexes, mouth is on the aboral surface and anus is on the oral surface.