Echinodermata

Phylum Enchinodermata  By Meaghan Perry



__Diagnostic Characteristics That Define Echinoderms__ Echinoderms are slow moving, marine animals. Unique to the taxa Echinodermata is the **water vascular system**. The water vascular system is how Echinoderms move, feed and exchange gas. Echinoderms have a network of hydraulic canals that branch into **tube feet**. Echinoderms also have thin skin layers that cover a skeleton composed of hard, callous plates. The prickly touch Echinoderms have, come from skeletal bumps and spines. Echinoderms are best distinguished by their **radial symmetry**, which emerge when the animal reaches adulthood, but stems from a **bilateral** larvae. There are six classes of which 7,000 or so Echinoderms are separated into: 1. //Astrerodiea// 2. //Ophiuroidea// 3. //Echinoidea// 4. //Crinoidea// 5. //Holothuriodea// 6. //Concertricycloidea// These are five of the six classes of Echinoderms mentioned above. (RG) [|(13)]

(ZS) The six classes of Echinoderms.

//Class Asterordiea// The type of Echinoderm that falls under the class Asterordiea are sea stars. Sea stars have five arms that radiate from a central disk. If a sea star lost one of its arms, it would be able to re-grow that arm, and members of one genus are able to re-grow their entire body from one arm. On the underside of each arm, the tube feet act like suction disks, where the suction can either be released or created by a complex set of muscle and hydraulic actions. In order to move, the star fish affixes its tube feet to adhere to rocks, and by repeated motions of extend, grip, contract, release, the star fish creeps along. The tube feet of a star fish are also used to catch prey like clams and oysters. Star fish turn themselves inside out in order to eat. The tube feet catch hold of the prey, and tightly embrace the prey of which they are about to eat. Then the star fish turns its stomach inside out and the digestion begins. Pedicellaria, tiny pincer-like structures, make sure that the surface of the starfish's is free of algae. (20)(SM)

//Class Ophiuroidea// The type of Echinoderms that is classified under //Ophiuroidea// are the brittle stars. Brittle Stars have arms that are long and flexible and a distinct central disk. Their tube feet lack suction so in order to move, they have to lash their arms in a serpent like fashion. In order to feed, some brittle stars are suspension feeders while others are predators or scavengers. They have five arms that are supported by an internal skeleton of calcium carbonate plates called vertebral ossicles that superficially look like a back bone. (KL)([|12])

//Class Echinoidea1// In the class //Echinoidea//, there are two types of enchinoderms; the seas urchins and the sand dollar. Sea urchins are spherical in shape, while sand dollars are flat with a disk shape. Both types of //Enchinoidea// have no arms but have five rows of tube feet that function in slow movement. Sea urchins have extra aid for moving because they have muscles that help pivot their long spines. A sea urchin has a complex jawlike structure that helps in eating seaweeds and other food.

//Class Crinoidea// In the class //Crinoide//a the type of echinoderms that is put under the class is the sea lily and feather stars. Sea lilies live attached to the substratum by stalks and feather stars move by crawling using their long, flexible arms. Crinods use their arms in suspension feed; the arms circle the mouth which is upward away from the substratum. The stalked forms of Crinidea live deep in the oceans, whereas stalkless forms are usually found in shallower depths. (AC)(8)

//Class Holothuroidea// The sea cucumber is classified as an echinoderms contrary to the way it looks. Sea cucumbers have five rows of tube feet, which is found in the water vascular system which is unique to echinoderms. Some of the tube feet of the sea cucumbers act as feeding tentacles, these tube feet are found around the mouth. Sea cucumbers look like they don't belong in the group echinoderms because they lack a spins and have a reduced hard endoskeleton. Below is an image of the anatomy of a sea cucumber: (MT)

Class Concerntricycloidea The last branch of echinoderms that is put into the last class is the sea daisies. Sea daisies were discovered very recently. Sea daisies live on waterlogged wood in the deep sea. "The sea daisies, which were discovered in 1986, have disk-shaped flat bodies and are less than 0.39 in. (1 cm) in diameter. The two known species were located on wood found in deep waters off the coasts of New Zealand and the Bahamas. They have a water-vascular system, with tube feet on the body surface around the edge of the disk. They have no obvious arms or mouth, and appear to absorb nutrients through the membrane surrounded their bodies." [MS] [|6]

__The Process of Acquiring and Digesting Food__ In order for an Echinoderm to acquire energy from food, the echinoderms must turn first capture its prey. Using the sea star as an example of an type of echinoderm, prey like clams and oysters are captured and then tightly embraced by the tube feet. Then the star fish turns its stomach inside out through the mouth and into the narrow opening between the shelves of the bivalve. A short digestive tract runs from the moth on the bottom of the central disk to the top of central disk. Once the stomach is turned inside out, the digestive system of the sea star produce juices that begin digesting the soft body of the mollusk (clam, oyster) within its own shell.

The method of acquisition of food varies considerably among different types of echinoderms. Holothurians (sea cucumbers) use tentacles to bring food to their mouth, while urchins use a device called "Aristotle's lantern", which is used to rub hard surfaces like stones to acquire detritus that will serve as food. (NI) [|1]



(YA)(10)

__How Do Echinoderm Sense the Environment?__  Echinoderms sense their evironment through touch. The nervous system of echinoderms consists of a central nerve ring that surrounds the gut, radial nerves, and a ganglia. The central nerve ring is composed of fiber tracks that connect the radial nerves. There is no brain, but ganglia are present along the radial nerves in some echinoderms. (DB) (4)s "Echinoderms have few well-defined sense organs, however, they are sensitive to touch, light intensity, temperature, orientation, and the surrounding water. The tube feet, spine, and skin are sensitive to touch. Light-sensitive organs have been found in echinoids, holothurians, and asteroids." (AK) (5)

__The Movement of Echinoderms__ Each class has their own methods for moving. The sea star moves by attaching its tube feet to rocks with the suction the tube feet utilize. Then through repetition of extend, grip, contract and release, the sea star is able to move. Brittle stars use their long arms and thrash about in order to move. The same kind of tube feet present in sea stars are present in seas urchins and sand dollars and help aid in the moving even though sea urchins and sand dollars lack arms. Sea urchins also have muscles that help aid in the process of moving. Feather stars are another example of organisms that use long arms in order to move. The only type of echinoderm that does not move is the sea lilies because they stay attached by stalks. Tube feet are small projections that are arranged in grooves along each arm and whivh operate through hydrolic pressure. (KS)10

Some good looking tube feet. (RL)(23) __The Process of Respiration__ Sea stars, the most populous of the echinoderms have small gills that cover most of the surface that allows for gas exchanges. Because the sea stars live in the water there is no problem keeping the surface of the skin dry, but the warmer and saltier the water, less dissolved oxygen is available to be absorbed.Gas exchange occurs by a diffusion across the surface of the gills, and the fluid that is inside the body cavity circulates in and out of the gills. Therefore, the gills have to be very effective to obtain oxygen. **Ventilation** helps to increase the flow of the water over the skin. As previously mentioned echinoderms have a water vascular system. gas exchange is performed by the movement of water through the canals. These canals, connected to tube feet, work by transmitting a pressure from one area to another. (ORS 21)

__All Animals Remove Waste, Including Those in the Water__ Echinoderms excrete waste products through the anus. The anus is located on the top of the central disk. Ameoboid cells are what carry the wastes out of the body.(CW)(6) The gills also dispel nitrogenous waste through gas respiration as water flows through them. (JS) [|(7)]

__Circulation__ Echinoderms do not need a circular system. A body wall, that is two cells thick, encloses a central gastrovascular cavity that serves for both distribution of substances through the body and digestion. The fluid that is in the cavity is continuous with the water outside through a single opening; the inner and outside tissue layers are covered with liquid. Because digestion begins in the cavity, once the cells of the inner layer have direct access to the nutrients are are released through digestion.

__Guard Yourself__ Echinoderms are protected from predators thanks to their surface. The surface of a sea star is covered by spines, which hurt any predators who would want to eat the star fish. Sea urchins have very prominent spines that act like a porcupines spikes, very painful to the predators who would think of attempting to eat an urchin. Echinderms tend to me very vulnerable when they are in their larval stage. However as adults the subclass asteroids can regenerate an arm or leg when they lose it. This serves as an anti-predator adaption. Also, the class holothurians are able to discharge cuvierian tubules, sticky tubules, at any potential predators. (15)(MF)

This video explains starfish renegeration very well and is rather fascinating: http://www.youtube.com/watch?v=f7cXeWxxfD4&feature=fvw

(CSR 16)

__Osmotic Balance__ Echinoderms pass water through their gills.Sea stars, typically do not lose or gain water to their environment.

Echinoderms maintain osmotic balance through simple diffusion of gaseous waters. Most echinoderms are marine osmoconformers, which maintaining internal levels of water and salinity equal to the levels outside of the organism. (SI)(17)

The natural inner salinity of a sea-star equals that of the ocean and is in fact made up primarily of ocean water, as it can diffuse through its outer membrane. Because of this, sea stars need a very specific salinity for osmotic regulations and can therefor only live in oceanic salt water. It is so exact in fact, that the sea star can't even survive in an estuary.(GR)([|18])

__Maintaining Temperature__ Sea stars have no distinct method of maintaining temperature balance. There are no special adaptations that would help aid in homeostasis. In addition, they have body temperatures that are similar to their environments and produce very little body heat. (SR) (22)

__Interesting Facts__
 * 1) Sexual reproduction of echinoderms involves separate male and female individuals, that release their games into the water.
 * 2) The opening of a sea star's water vascular system is not central, but off to one side.
 * 3) "The water vascular system of echinoderms is responsible for their movement and ability to clean to surfaces for long periods of time."(CW)(6)
 * 4) Sea stars are able to regenerate their limbs if one is damaged or cut off.(MLK) [|9]

Reproduction: Echinoderms can either be male or female. The males discharge their sperm and the females discharge their eggs into the water. Here, they fertilize. A female echinoderm can release a hundred million eggs at once. Echinoderms are regenerative. If a piece of their bodies is removed, it can grow and develop into a new organisms. (LW) (14)

Review Questions  1) How does turning its stomach inside out allow a sea star to digest a hard shelled organism such as a mollusk? (SD) 2) Why don't echinoderms need circulation systems? (CC) 3) Do echinoderms have other ways of defending themselves other than spines? (ZXU) 4) If a sea star wasn't getting enough oxygen from its environment, what would it do, and why? (TM) 5) How do Echinoderms protect themselves? (MC) 6) Explain how the size and structure of star fish is beneficial to their aquiring of food. (NG)

__Souces__ 1. Campbell, Neil A., and Jane B. Reece. Biology. Sixth Edition. Boston: Benjamin-Cummings Company, 2002. 2. http://www.carolguze.com/images/animals/echinoderm.jpg-Photo of a Sea Star 3. http://media.pearsoncmg.com/bc/bc_campbell_biology_6/cipl/stu/33/33-38-SeaStarAnatomy-L.jpg-Anatomy of a Sea Star 4. [] 5. [] 6. [] 7. [] 8. http://www.palaeos.com/Invertebrates/Echinoderms/Crinoidea/Crinoidea.htm 9. [] 10. [] 11. [] 12. [] 13. [] 14. ([]LW) 15. http://animaldiversity.ummz.umich.edu/site/accounts/information/Echinodermata.html (MF) 16. http://www.youtube.com/watch?v=f7cXeWxxfD4&feature=fvw (CSR) 17. http://faculty.vassar.edu/mehaffey/academic/animalstructure/outlines/echinodermata.html 18.http://books.google.com/books?id=HHaDGynAz1EC&pg=PA291&lpg=PA291&dq=starfish+osmotic+regulation&source=bl&o (GR) 19.http://myphliputil.pearsoncmg.com/media/ebcampbell7/chapter33/ebcampbell7_33_77big.jpg (ZS) 20. [] (SM) 21.[](ORS) 22. http://www.users.on.net/~jamesmosby/starfish/index.html 23. http://yhsbiology.wikispaces.com/file/view/Stachelhaeuter_fg01.jpg/59322612/Stachelhaeuter_fg01.jpg (RL)