1. Explain the classification and the phylogeny of each phyla.

Members of the Phylum Echinodermata ("spiny skin") include the sea stars, brittle stars, sand dollars, and sea cucumbers. They inhabit marine environments ranging from shallow coastal waters to ocean trenches over 10000 m deep. They range in size from 1 cm to 1 m in diameter and often have brilliant coloring.

Echinoderms bear an important evolutionary relationship to vertebrates. Evidence indicates that the echinoderms may share a common ancestor with the lower chordates and hence the vertebrates.

The characteristics of the echinoderms include the following, most of which are not shared by any other invertebrate phylum:

• Most undergo metamorphosis from a free-swimming, bilaterally symmetrical larva to a bottom-dwelling adult with radial symmetry. Most echinoderms have five radii or multiples thereof. Such a symmetry is called pentaradial symmetry.

• They have an internal skeleton called an endoskeleton, composed of calcium plates, which may include protruding spines.

• They have a water-vascular system, which is a network of water-filled canals

• They have numerous small, movable protrusions called tube feet that aid in movement, feeding, respiration, and excretion

• They have no circulatory, respiratory, or excretory systems

• They have a nervous system but have no head or brain.

• They have two sexes, and reproduce sexually or asexually

The fossil record of echinoderms dates back to the Cambrian period, over 500 million years ago. Because echinoderm larvae are bilaterally symmetrical, scientists infer that they evolved from bilaterally symmetrical ancestors.

The fossil record also indicates that the early adult forms of the early echinoderms were probably sessile, not free-living as most modern forms are. Scientists infer that radial symmetry evolved as an adaptation to this sessile existence. Conditions may have later favored free-living species, yet most modern echinoderms have retained radial symmetry. Taxonomists have divided the 6000 species of echinoderms into five classes: Crinoidea, Asteroidea, Ophiuroidea, Echinoidea, and Holothuroidea.

The class Crinoidea ("lilylike"), which includes sea lilies and feather stars, most closely resembles the fossils of Cambrian echinoderms. Crinoids are sessile. They have a long stalk that is attached to rocks or to the sea bottom. The five arms that extend form the body branch out to form many more arms - up to 200 in some feather star species. Sticky tube feet located at the end of each arm capture food and serve as respiratory surface.

The sea stars, belong to the class Asteroidea ("starlike"). They live all over the world in coastal waters and along rocky shores. They are economically important because they pray on oysters, clams, and other organisms used as food by people.

The 2000 species of basket stars and brittle stars belong to the class Ophiuroidea ("snakelike"), the largest echinoderm class. Basket stars and brittle stars live primarily on the sea bottom, often beneath stones or in the crevices and holes of coral reefs.

Ophiuroids are distinguished by their long, narrow arms, which allow them to move very quickly. The thin, flexible arms of basket stars resemble a tangle of snakes. Brittle stars, so named because parts of their arms break off readily, can regenerate missing parts. Ophiuroids feed by raking in food with their arms; by gathering food from the ocean bottom with their tube feet; or by trapping suspended particles with their tube feet or with the aid of mucous strands found between their spines.

About 900 species of sea urchins and sand dollars belong to the class Echinoidea ("hedgelike"). In Echinoids the internal organs are enclosed with a compact, rigid endoskeleton called a test. Most species of Echinoids grind their food with a complex jawlike mechanism called Aristotle’s lantern.

The spherical sea urchins are well adapted to life on hard sea bottoms. These echinoids use their tube feet for locomotion and feed by scraping algae from hard surfaces with teethlike structures that are part of Aristotle’s lantern. They have barbs on their long spines and in some species venom that protects sea urchins from predators.

Sand dollars live along seacoasts. As their name implies, they live in sandy areas and have the flat, round shape of a silver dollar, which is an adaptation for shallow burrowing. The short spines of the sand dollar aid in locomotion and burrowing and help clean the surface of the body. Sand dollars use their tub feet to move and to scoop up food.

The armless sea cucumbers belong to the Class Holothuroidea. Most reside on the sea bottom. Because they do not have a large endoskeleton, their bodies are soft. Tube feet are present on their aboral side. A fringe of tentacles, actually modified tube feet, surrounds the mouth and sweeps up sediment and water. Sea cucumbers then stuff their tentacles in to their mouths and clean the food off them.

When threatened, many sea cucumbers eject their internal organs through the anus, a defense mechanism called evisceration. They later regenerate their lost parts.

Phylum Echinodermata: Pentaradilly symmetrical; adults covered with spiny or calcareous plates; most forms with tube feet for locomotion; radial cleavage in early development; digestive tract and nervous system; endoskeleton; marine: Echinoderms

Class Crinoidea: Five branched rays and pinnules; tube feet without suckers; most forms with stalk; many fossil forms: sea lily, feather star.

Class Asteroidea: Body usually with five rays and double rows of tube feet in each ray; eyespots: starfish

Class Ophiuroidea: Usually with five slender arms or rays; brittle stars, basket stars.

Class Echinoidea: Body spherical, oval, or diskshaped; rays lacking; tube feet with suckers: sea urchin, sand dollar.

Class Holothuroidea: Elongated, thickened body with tentacles around the mouth; no rays or spines: sea cucumber

2. Describe the characteristics typical for the diversity shown by this phyla.

Since the anatomy and behavior of the sea star represents many echinoderms I will use it as an example for the structure and function of many Echinoderms.

The sea star’s mouth is located on the underside of the body, called the oral surface. The top of the body is called the aboral surface. While some invertebrates have an external skeleton, a sea star, like all echinoderms, has an endoskeleton - a skeleton found within the body. The sharp, protective spines on the aboral surface form from calcium plates called ossicles, which are covered with a thin epidermal layer of cells. Groups of pedicellariae surround the spines. Pedicellariae, which resemble tiny forceps, help protect and clean the surface of the body.

While most invertebrates swim, wiggle, or use appendages for movement, sea stars use a water-vascular system. This is a network of canals in which muscle contractions create hydrostatic pressure, which in turn permits movement. Water enters the sieve plate, a small opening on the aboral surface. It passes through the madreporite and down the stone canal. I will trace the path of water from the ring canal encircling the mouth to the five radial canals extending into each arm.

The radial canals carry water to hundreds of paired, hollow tube feet. The upper end of each foot connects to a bulblike sac called an ampulla. Muscles in the tube feet contract, forcing water into the ampullae and creating suction, which causes suckers at the tip of the feet to grip the surface. When the ampullae contract, water enters the feet, releasing the suction and causing the feet to extend. These coordinated muscle contractions enable the sea star to climb slippery rocks or to capture prey.

Sea stars use their tube feet to obtain food - usually mollusks, worms, and other slow moving animals. The sea star attaches the suckers of its tube feet to both halves of a clamshell and pulls until the shell opens a crack. The sea star then turns its stomach inside out through its mouth and inserts its stomach into the clam.

Enzymes secreted by the sea star’s stomach digest the clam’s soft parts while they are still in shell. The sea star then withdraws the stomach, containing the partially digested food, back into its body, where the digestive process is complete.

The sea star has no circulatory, excretory, or respiratory systems. Fluid in the coelom bathes the organs and distributes nutrients and oxygen. Gas exchange and waste excretion take place by diffusion through the thin walls of the tube feet and through the skin gills, hollow tubes that project from the coelom lining.

The sea star has no head or brain. A nerve ring surrounds the mouth and branches off into nerve cords that extend into each arm. Each arm has an eye spot that responds to light and tentacle that responds to touch. The tube feet also respond to touch.

Each arm of the sea star has two gonads, which produce eggs in females and sperm in males. Fertilization occurs externally. Females produce up to 200 million eggs in one season. Each fertilized egg develops into a bilaterally symmetrical, free-swimming larva called a bipinnaria. After about two years the larva settles to the bottom, and metamorphosis begins. During metamorphosis the sea star develops into a pentaradially symmetrical adult.

Sea stars can also reproduce asexually by regenerating lost parts. In fact, a completely new star may grow from a segment of an arm as

3. List all the animals  which are used as examples in class.

Class Crinoidea. Crinoids, sea lilies - Antedon, Ptilocrinus, Comactinia

Class Stelleroidea. Sea stars, brittle stars - Asterias, Ctenodiscus, Luidia, Oreaster, Asteronyx, Amphioplus, Ophiothrix, Ophioderma, Ophiura

Class Echinoidea. Sea Urchins, sand dollars, heart urchins. Cidaris, Arbacia, Strongylocentrotus, Echinanthus, Echinarachnius, Moira

Class Holothuroidea. Sea cucumbers. Cucumaria, Thyone, Caudina, Synapa

4. Make a vocabulary list and briefly define them. Use all words printed in bold print.

1. Pentaradial symmetry - a symmetry of having five radii or multiples thereof.

2. endoskeleton - internal skeleton

3. Water-vascular system - network of water filled canals in Echinoderms

4. Tube feet - numerous small, movable protrusions that aid echinoderms in movement, feeding, respiration, and excretion.

5. Test - a compact, rigid endoskeleton that encloses the internal organs of Echinoids

6. Aristotle’s lantern - a complex jawlike mechanism used to grind up food in most species of echinoids

7. Evisceration - the ejection of internal organs though the anus used as defense in the members of Class Holothuroidea

8. Oral surface - the underside of a sea star

9. Aboral surface - the top of the body of a sea star

10. Ossicles - calcium plats from which protective spines on the aboral surface form

11. Pedicellarie - resemble tiny forceps, help protect and clean the surface of the sea stars body

12. Sieve plate - a small opening on the aboral surface of a sea star through which water passes

13. Stone canal - a canal which transports water from the sieve plate and madreporite

14. Ring canal - the water continues from the stone canal to the ring canal which encircles the sea stars mouth

15. Radial canals - canals that extend into each of the sea stars arms and lead water from the ring canal

16. Ampulla - a bulblike sac which is located in the upper end of the sea stars tube feet, ampulla is used to create suction on the stars feet which can be used for capturing prey and movement

17. Skin gills - hollow tubes that project from the coelom lining in a sea star which enable part of gas exchange and excretion

18. Nerve ring - A system of nerves that extends throughout the sea star

19. Bipinnaria - after fertilization and the release of fertilized eggs in sea stars each egg develops into a bilaterally symmetrical, free-swimming larva called bipinnaria