Response and Movement

Nervous and sensory systems are generally poorly developed in echinoderms. There is a simple nervous system sensitive to temperature, light, and vibrations. They lack specialized sense organs nose, eyes, and ears. No brain, or head but they do have a nerve net and a nerve ring. Their nerve cells can detect light and touch. Starfish have eyespots (which are a cluster of nerve cells) at the tips of each arm that sense each ray for light.
The water-vascular system supplies water through canals of small muscular tubes to the tube feet (ambulacral feet). As the tube feet press against a moving object, water is withdrawn from them, resulting in a suction effect. When water returns to the canals, suction is released. Sea stars, sea cucumbers, and sea urchins move by alternately extending and retracting groups of tube feet, gripping with the suction cups and pulling themselves along. The resulting locomotion is generally very slow, but effective.

Respiration

Echinoderms lack respiratory systems. Tube feet and skin gills are used for gas exchange.
Tube feet immensely contribute to the respiratory function in most echinoderms; the tissue’s outer thin wall forms the main respiratory surface. The paper-like wall is suitable for the diffusion of oxygen into the body cavity and the diffusion outward of carbon dioxide and wastes. However, many groups have developed skin gills (auxiliary respiratory structures).

Reproduction!

Echinoderms have separate sexes, male or female, although some are hermaphroditic. The males and females discharge their eggs and sperm through broadcast spawning into the water where they are fertilized. Fertilization is external; the gametes are simply shed into the water. A female can release one hundred million eggs at once. The floating embryo develops into a ciliated, free-swimming, bilaterally symmetrical larva, which undergoes radical metamorphosis into the radial symmetrical adult. In some species, the whole digestive system is changed during metamorphosis, and the organism acquires a new mouth and anus. Regeneration is achieved by means of asexual binary fission. If a piece of certain echinoderms is cut off or injured, their great ability to regenerate quickly creates a new body part or even a new echinoderm can grow.

Feeding

This phylum is known for its diversity in its feeding. Echinoderms are carnivores, herbivores, filter feeders, and detritus feeders. All echinoderms are heterotrophs (including active, omnivorous, scavenging, selective predators and mud swallowing). Many carnivorous echinoderms, like the sea star, use their tube feet to force open shells, particularly mussels, clams and scallops. Once the shell has been pried open, the echinoderm expels its stomach out of the mouth, releasing enzymes into the preys open cavity. The enzymes then liquefy the meat, and the prey is digested in its own shell. The herbivorous sea urchin scrapes algae from rocks with their five-part jaw arranged in a structure known as "Aristotle's lantern." Many echinoderm filter feeders, such as sea lilies and basket stars feed on small suspended organisms that are floating in the water or the bottom of the ocean floor. The sea cucumber, a detritus feeder slowly moves across the ocean floor ingesting a combination of detritus and sand, and digest the organic material leaving the sand grains behind.

Habitat and Adaptations

Echinoderms are marine, although few can survive being washed on the shore by a tide for several hours. They are the only phylum with no freshwater or land animals. There is no fossil evidence that shows any exception to this. Within the marine waters echinoderms can survive in a variety of habitats. The habitat use of echinoderms also depends on the area where their communities are developed. One study counted twenty-eight species on the rocky bottom while thirty-eight species were found on the sandy bottom. Many echinoderm species such as sea stars or sea cucumbers cling to rocks and therefore prefer rocky areas, while other echinoderm species prefer it to be sandy where they can burry themselves in order to remain concealed. There are also many echinoderms that enjoy living in mud. In addition, echinoderms are known to commonly use other animals as homes such as sponges or the skin of other fishes. Echinoderms are found in all marine waters except the Arctic. Within the marine waters, echinoderms are located in different areas depending on their preferred temperatures. Sea cucumbers have adapted to face predators without a calcium carbonate endoskeleton. When threatened, they are able to release all internal organs into their surroundings. This confuses the predator and gives the sea cucumber an escape route. Many echinoderms are sand, coral or reef coloured to camoflauge themselves in their habitat.

General Anatomy

Echinoderms are characterized by radial symmetry, radiating from a central body (pentamerous). It can be expressed in different body forms such as five arms, a five-part jaw, and five radial canals. The body consists of five equal segments, each containing a duplicate set of various internal organs. They have an endoskelteon that is made from hard calcium carbonate (CaCO3). They have no heart, brain, or eyes, but some brittle stars have light sensitive areas on their arms. Their mouth is situated on the underside and their anus on upper body (except feather stars, sea cucumbers and some urchins).Echinoderms have tentacle-like structures called tube feet with suction pads situated on their extremities. They are many small, flexible, fluid filled tubes that project from the body and are used in locomotion, feeding, gas exchange, and nitrogen excretion. These tube feet are hydraulically controlled by a remarkable water-vascular system. The madreporite is a sieve-like opening on the aboral surface of a sea star through which water enters the water vascular system and connects to a circular ring canal. Five radial canal branch from the ring canal and a portion of the sea star’s water vascular system that runs along inside the ambulacral ridge in each arm. The body is covered by many ossicles, which are small calcium carbonate plates that forms the endoskeleton.