INTRODUCTION

The name echinoderm literally means "spiny skin." Echinoderms are characterized by their pentaradial symmetry, internal skeletons, a water vascular system, and tube feet. The phylum Echinodermata is split into 5 main classes. Asteroidea which includes sea stars, Crinoidea with the sea lillies and feather stars, Echinoidea including the sea urchins and sand dollars, Holothuroidea with the sea cucumbers and Ophiuroidea including brittle stars and basket stars. Echinodermata is the only phylum the exists exlusively in marine habitats.

Read more about the classes: click here.
http://www.cyhaus.com/marine/Echinoderm.htm

GENERAL ANATOMY

Echinoderms have radial symmetry, which means they are divided into 5 equal sections, radiating from a central point. In each segment, there is an identical set of internal organs. The closest thing to eyes in the phylum is the light sensitive spots on their arms. Along with having no eyes, Echinoderms also have no heart or brain. Each tentacle-like structure is called a tube foot and aids in respiration and movement. Echinoderms are coelomates, which means they have a large body cavity completely lined with tissue.

EXCRETION

Nearly all echinoderms release their solid wastes through the anus. It will then be released in the form of feces, except with the organism brittle stars, because they do no require an anus and thus leaving them to excrete through the mouth. Wastes are excreted through the tube feet and skin gills on the body, and also contain nitrogen in the form of ammonia.

REPRODUCTION

All echinoderms are capable of sexual and asexual reproduction. Most are ethier male or female, but in some cases could be hermaphodites. Fertilization takes place externally, by both males and females realeasing their gametes into the environment during the reproductive season. The animals will release their sperm and eggs into the sea and detect gametes of their own species and then later, they will release theirs. Soon after this process, larvae will begin to swim around, along with plankton. Afterwards, the larvae, which have bilateral symmetry, swim to the floor of the ocean and start to mature and matamorphosose into adults which contain radial symmetry. Sea stars are unbelievable animals. They have the ability to heal themselves when been attacted by predators. Interesting fact, sea stars are able to regenerate into a brand new organism if pulled apart, but only as long as it has a portion of the middle area on the body. Sea stars are incredible and clever creatures that cause a lot of trouble for fisherman, especially the ones who earn their living catching mollusks.

To view a diagram of the reproduction and life cycle of a Sea Star, click here and scroll down the website:
http://www.oceaninn.com/guides/echino.htm

RESPONSE AND MOVEMENT

Echinoderms have a very uncomplicated nervous system. Most species have a nerve ring that surrounds the mouth with radial nerves that connect the central ring to other parts of the body. Some echinoderms also have sensory cells that recognize chemicals released by potential prey. Sea stars also have up to 200 light sensitive eye spots on the end of each arm able to detect whether they are in light or dark. Star fish and other echinoderms also have statocysts which tell the animal if it is upside down. Most echinoderms are motile except for sea lillies and feather stars who attach to rocks. Echinoderms use tube and thin layers of muscle latched onto plates of the endoskelton to move around. With the pumping of water in and out of the water vascular system the tube feet act as suction cups and make it extremely hard to move a sea star from where it is. To protect themselves from predators echinoderms have numerous defenses. Sea urchins have tons of long spikes (sometimes containing poison) which help to keep enemies away. Others, like the sand dollar, burrow away in the sand and mud where as the brittle stars shed a leg whenever they feel a predator close.

INTERNAL TRANSPORT AND CIRCULATION

The task of internal transport relys on many different systems in the echinoderms. Gas exchange (respiration) and the elimination of wastes is taken care of by skin gills and tube feet. Tube feet are an essential part of the water vascular system, this is used for many things, one of which is the transportation of waste. It is made of channels connectig to several tube feet. Water first enters the madroporite, located on the dorsal side of the echinoderm, and then continues through the stone canal and is greeted by the ring canal. The water then diverges into five different radial canals, that further transform into a bubble like structure called, ampullae. The final exit point is the tube feet, which are connected to the ampullae. Echinoderms have an open circulatory system, which means blood does not travel within blood vessels.

RESPIRATION

Echinoderms, not unlike many other animals, have to exchange carbon dioxide for oxygen. In most echinoderms the outer tissue of the tube feet creates the main surface for respiration. In other echinoderms the exchange of carbon dioxide and oxygen occurs through skin gills or in respiratory trees.

FEEDING

Echinoderms are heterotrophs and have several methods of feeding. Some are carnivores while others are herbivores. Carnivores use their tube feet to pry open the shells of bivalve mollusks such as clams and scallops. Once the shell has been broken open, the starfish flips its somach out of its mouth, pours out enzymes, and digests its prey in the prey's own shell. After the sea stars haave finished eating, it removes its stomach from the shell and moves it back into his mouth. Sea stars usually eat snails, corals, and even other echinoderms. Some echinoderms are also herbivores, such as sea urchins, scrape algae from rocks by using their 5-part jaw. Sea lilies, basket stars, and some brittle stars, use tube feet on flexible arms to capture plankton that float by on ocean currents. This method of feeding is called filter feeding. The last method is the detritus feeders. The move as a large suction and pick up half sand and detritus. Later, they will digest organic materials and excrete the sand grains.

HABITAT AND ADAPTATIONS

Echinoderms live in marine habitats, although they can occasionally survive being washed up and dried on shore. Within marine habitats, Echinoderms can survive in a wide variety of places. Sea Stars and sea cucumbers, for instance, prefer rocky areas while others often reside in sandy areas where they can bury themselves. Some Echinoderms even use other animals as homes such as the skin of other fish. In order to stay concealed during the day, Echinoderms have adapted to match the colour of their surroundings. Also, to protect and structure their bodies, Echinoderms such as sea urchins have interlocking plates of Calcium Carbonate which form a very hard internal skeleton. Others, such as sea stars and brittle stars have slightly more flexible internal skeletons to allow them to flex and bend their arms. Sea cucumbers have barely any Calcium Carbonate, resulting in a very flexible body containing only remnants of a sturdy internal skeleton. Anther adaptation the Echinoderms have is that they can regenerate body parts. This means that if, for example, a sea star's leg gets cut off by a predator, over time it can form a new one.

DIGESTION

When an echinoderm ingests food, the first step on the path it takes is the mouth, which is on the bottom of the organism. After the mouth, the food travels through the esophagus and into one of the two stomachs of an echinoderm; the cardiac stomach. Some echinoderms can actually take their cardiac stomachs outside of their body. For example, starfish open a bivalve with their strong water-vascular system and push their stomachs inside to digest their prey. Next, the food travels into the pyloric stomach where it is continued to be digested. The last steps of digestion take place in the intestine and digestive glands. Waste is then excreted through the anus.

CONNECTIONS TO OTHER PHYLA

Echinodermata is a very unique phyla in that its organisms live in marine habitats only. Organisms belonging to crustecea, a subphylum of arthropoda, also live in water only, but can be found in fresh water as well as salt water. Other phylums that are strictly aquatic are cnidaria and porifera, but once again these organisms can be found in fresh water and marine habitats. However the phyla with the most similar habitat characertistics is mollusca.
Organisms of the phyla echinodermata all have penta radial symetry, similarly to this cnidarians have radial symetry. Another characteristic they hold is thier endoskeleton, certain members of phyla mollusca also share this characteristic, such as the squid.
A similar function between annelids and echinoderms is that they both have specialized segments of the body. Echinoderms all have an intersection like center, where a majority of their internal organs are found. Annelids too have a specialized first few segments that carry their eyes or antennae. Both starfishes and sea stars from echinodermata have a similar function to octopus's from the phyla mollusca. Both these organisms have suction like appendages, though they are not controlled by the same kind of system their suction like charactaristics make them comparable.

IMPORTANT VOCABULARY

View this link to read some interesting vocabulary about echinoderms: Once link has appeared, click on MOLLUSKS VOCAB ONLY (it is actually echinoderms vocabulary):
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLG,GGLG:2005-24,GGLG:en&q=vocab+on+echinoderms

INTERESTING FACTS

Some sea cucumbers have the ability to bring all of their internal mass out of their body to scare away predators. Sea stars are able to regenerate their arms when bitten by a preditor and in some case the whole body has been able to be regenerated from a single arm. The cushion star (top right) releases huge amounts of mucus when threatened by an enemy.