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Ophiuroidea

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S: Basket and Brittle Stars

FC: Discover the World of Brittle and Basket Stars Kendall McPheeters

1: Discover the World of Brittle and Basket Stars Kendall McPheeters Second Period

3: Table of Contents What is an Echinoderm?.....................1 ClassOphiuroidea...............................3 Physical Characteristics.....................5 Anatomy of a Brittle Star.....................6 Range and Habitat..............................7 Disc and Internal Organs....................9 Nervous System.................................10 Digestive System and Diet................11 Respiration.........................................13 Locomotion........................................13 Skeletal and Muscular Structure......14 Reproduction.....................................15 Puzzles................................................17 Sources of Information......................20

4: What is an Echinoderm? The phylum Echinodermata contains many species of invertebrates such as sea stars, sand dollars, sea urchins, and sea cucumbers. There are about 7000 described living species and about 13,000 extinct species whose fossils date back more than 500 million years ago. Echinoderms, members of this phylum, live in marine environments ranging from shallow tide pools to deep trenches. Most are radically symmetric; however, they develop from bilaterally symmetric larvae generally called bipinnaria. Developing from a bilateral larva and being deuterostomes makes this phylum different from other invertebrates. In fact, echinoderms are closely related to chordates in reference to the phylogenic tree. Echinoderms share three major characteristics that differ from other phyla. First, echinoderms have an exoskeleton composed of calcium carbonate plates called ossicles. The ossicles can be attached to spines that cover the external surface of the skin. Secondly, echinoderms have a water-vascular system. This system is composed of a network of water-filled canals inside their body that help aid in locomotion and other functions. Third, they have tube feet. Tube feet are small, movable extensions of the water-vascular system which aids in movement, feeding, respiration, and excretion. | The phylogenic tree of kingdom Animalia demonstrates the close relationship between phyla Echinodermata and Chordata. Both phyla are classified as deuterostomes and share a common ancestor on the branches of the tree. | 1

5: The phylum Echinodermata is divided into five major classes. The first class is Crinoidea, consisting of sea lilies and feather stars. Most crinoids, meaning “lily-like”, are sessile as adults, however, feather stars can swim or crawl as adults. They have sticky tube feet that filter small organisms from the water, aid in respiration, and transport food to the mouth of the organism. The second class is Echinoidea, meaning “spinelike”. This class consists of about 900 species of sea urchins and sand dollars. Sea urchins have barbed spine sand contain a venom poisonous to predators. They use their tube feet for locomotion and feed with a device called Aristotle’s lantern, a complex jawlike mechanism. Class Holothuroidea, the third class, consists of species of sea cucumbers. They are armless and live on the ocean floor where they crawl or burrow. Their bodies are soft due to the fact that their ossicles are not attached to one another. Their body shape resembles that of a polyp, which is why the name Holothuroidea means “water polyp”. The fourth class, Asteroidea, meaning “starlike”, consists of starfish. Starfish live in coastal waters all over the world. They are economically important because they prey on oysters, clams, and other organisms. The fifth class is Ophiuroidea, the class of basket and brittle stars. This class will be described in detail throughout the remainder of this book. | Sea Lily of the Class Crinoidea | Starfish of Class Asteroidea | Sea Urchin of Class Echinoidea | Sea Cucumber of Class Holothuroidea | 2

6: Class Ophiuroidea | The class Ophiuroidea contains about 2000 known species of organisms identified as brittle stars and basket stars. These organisms are starlike echinoderms whose bodies display radial symmetry and are supported by a hard exoskeleton made of calcium salt. The name brittle star is derived from their habit of breaking off arms in order to defend themselves from predators. Basket stars earn their name from the basket like structure they create with their branching arms. These animals, known collectively as ophioroids, are also called serpent stars because their long arms resemble snakes. | The class Ophiuroidea contains two major clades: the clade Ophiurida includes brittle stars and the most abundant species of ophioroids, and Euryalida is made up of basket stars. Brittle stars usually have five arms that are long and flexible. Basket stars have a similar structure to brittle stars, however they usually are larger and have arms that are highly branched and even more flexible than those of brittle stars. | Did you know? | A brittle star clings to a rock in the shallow waters off the Australian coast. | Ophis means snake in Greek, giving ophioroids the name serpent stars. | 3

7: Ophioroids can be distinguished from starfish of the class Asteroidea because they have a rounded central disk which is easily distinguishable from the arms. Although brittle stars do have the water-vascular system and tube feet like all other echinoderms, they lack ambulacral grooves on the aboral surface of their arms and their tube feet function as tactile organs and are not used for locomotion. | The Northern Brittle Star is an inhabitant of deep marine waters from the Arctic to Cape Cod, Massachusetts. | The Red Basket Star has sensory hairs protruding from its skin to help sense prey and chemicals in the water. | A brittle star clings to a rock in the shallow waters off the Australian coast. | The brittle star (left) is pictured in a habitat of shallow waters among a coral reef, displaying the relationships that ophioroids have with other organisms. The brittle star (above) is ironically known as the Green Serpent Star due to the fact that they are green as juveniles. | 4

8: Physical Characteristics | Members of the class Ophiuroidea display an immense variety of physical characteristics. Most have five long, thin, jointed arms covered with spines but some may have up to eight arms. Brittle stars can be as large as two feet in diameter or as small as a few millimeters. Ophioroids are usually a drab green, grey or brown, but some have multicolored color patterns. | Members of the class Ophiuroidea display an immense variety of physical characteristics. Most have five long, thin, jointed arms covered with spines but some may have up to eight arms. Brittle stars can be as large as two feet in diameter or as small as a few millimeters. Ophioroids are usually a drab green, grey or brown, but some have multicolored color patterns. | Ophioroids also have the water-vascular system found in all echinoderms. The water vascular system consists of madreporite which is a pore that regulates the water flow into the system. After water enters this pore, it passes through the stone canal into the ring canal in the central disk. From the ring canal, the water disperses into the radial canals located along each of the arms. The water exits through the ampullae and tube feet and the system is completed. | The Northern basket star exhibits characteristics common in the class Ophiuroidea Australian coast. | The water-vascular system. | 5

9: The Anatomy of a Brittle Star | The anatomy of a brittle star is unique, especially in relation to an echinoderm, because brittle stars bear no anus, have small or nonexistent pedicellaria, only have one stomach, and the digestive gland is modified into the bursae. | 6

10: Range and Habitat | The first members of the class Ophiuroidea first diverged in the Early Ordovician, about 500 million years ago. These ancient and now extinct creatures most resembled modern brittle stars in form and function. | Today, brittle and basket stars are found on the seabed in all of the world’s oceans. They inhabit the dark, high pressure environments on the floor of the abyssal zone (the deepest part of the ocean where few living things can survive), as well as the shallow waters often visited by humans snorkeling and scuba diving. In fact, six families live at least two meters deep and three genera range below four meters. A few species can even tolerate brackish water which is extremely rare in the phylum Echinodermata. Individuals are relatively small, the average size being less than one inch across the central disk. This enables ophioroids to live under rocks, among seaweed, or buried in the sand, leaving only their arms protruding. | Taxonomy There are about 2000 species of ophioroids in about 230 genera. They are grouped into three currently living orders: Oegophiurida, Phrynophiurida, and Ophiurida. There is even a Paleozoic order named the Stenurida. | Did you know? | Some ophioroids even glow in the dark and a bright green luminescence appears if they are disturbed. | TThe size range of brittle stars is so vast that some are hard to see with the naked eye while some are the size of a pumpkin. | 7

11: LETS GO BACK IN TIME The Paleozoic order of the class Ophiuroidea named the Stenurida differ from modern day ophioroids. This extinct order contained species that had a double row of plates that could be found across the arm axis either directly opposite one another or slightly offset in comparison to today’s modern species only having one row of arm plates. Also, stenurids lack the dorsal and ventral arm shields that are found in most ophioroids. The arms of most stenurids are broader and comparatively stiff and the central disk is larger than modern species. The content of the order is poorly established and there are fewer than ten genera known. | Fast Fact | Many species of the ophioroids are rarely encountered in the depths visited by humans. Scientists estimate that there could be over 100 species not yet discovered in the deep abysses. | The Northern basket star exhibits characteristics common in the class Ophiuroidea Australian coast. | Members of Ophiroidiea can inhabit regions ranging from the euphotic zone to the upper aphotic zones. | 8

12: Disc and Internal Organs | Like all echinoderms, the members of the class Ophiuroidea contain a skeleton of calcium carbonate in the form of calcite. These bone-like structures are called ossicles. In ophioroids, the calcite ossicles are fused together to form plates that are known as tests. | The Central Disk The central disk is sharply marked off from the arms. The disk contains all the internal organs of digestion, and reproduction. These organs never enter the arms as they do in starfish. The arms of brittle stars are attached to the central disk that houses, on the underside the mouth, the viscera. The mouth is surrounded by five moveable jaw segments, making the opening look like a star. | Internal Organs Internal organs include Gonads Digestive gland Bursae Pyloric stomach Cardiac stomach Sensory Cilia Bursae | The aboral side of the central disk of ophioroids houses many important structures that aid in feeding and locomotion. | The bleaching of starfish removes all fleshy covering to reveal only the ossicles. | 9

13: Nervous System | The nervous system of ophioroids is primitive compared to those of vertebrates. The nervous system consists of a main nerve ring that runs around the central disk. At the base of each arm, the ring attaches to a radial nerve that runs down the length of each arm. Ophioroids have no eyes but they do have the ability to sense light through receptors in the epidermis. Tube feet, in some species, can sense light as well. Due to their sensitivity of light, many ophioroids tend to avoid light and prefer to hide in dark crevices and become more active at night. Other simply inhabit the ocean depths where it is always dark. | The body and arms of ophioroids in some species consist of arrays of mircolenses that focus light onto a nerve bundle, acting like a compound eye. | Did you know? | The magnified image (above) displays the thousands of sensory cilia and plates that help ophioroids sense their environment. The brittle star (below) is able to sense chemical changes like the spawning of polyps on the coral reef. | 10

14: Digestive System and Diet | The digestive system of members of the class Ophiuroidea is one of the most complex systems of the ophioroids. The path of food is very easy to track in these simple organisms. The food first enters the mouth, where the jaw apparatus rips it into smaller pieces. Then it is moved down the esophagus and into a stomach cavity that occupies much of the dorsal half of the body. Once the food enters the stomach, and since there is no intestine and no true anus, digestion and absorption take place in the bursae located at the base of each of the arms. The bursae are pouch like structures that are essentially ceca. | Did you know? | The mouth of the ophioroids functions for ingesting as well as an anus for egesting | The aboral side of the central disk of ophioroids houses many important structures that aid in feeding and locomotion. | The mouth of the brittle star has jaws that tear food and create a star like shape. | 11

15: Most ophioroids are carnivorous and scavengers, while others feed on small particles of plankton. Brittle stars tend to feed on detritus and small living or dead animals. The arms move the larger food masses to the mouth where the food it torn by the jaws. Tube feet move smaller particles to the mouth. They feed on organisms such as mollusks, worms, and sometimes even small fish. Basket stars, in particular, are capable of suspension feeding. They use mucus coating on their arms to trap plankton and bacteria as well as a series of rings of sharp hooks to capture food and bring it to their mouth. | Fast Fact | The species Pectinura will consume beech pollen n the New Zealand seaweed. | Ophioroids eat organisms such as small crustaceans (top), marine worms (second), filter plankton (third), and sometimes even large shrimp (bottom). | 12

16: Respiration | Respiration in ophioroids is very primitive. Since they have no gills and no lungs, oxygen must be diffused directly through the skin. Usually, gas exchange occurs through the cilia lined sacs called bursae. Each of the bursae opens into areas between the arm bases of the oral surface of the disc. Oxygen then is transported throughout the body. Food is also deoxygenated once it enters the body. This function provides the ophioroids with much of the oxygen that their body needs to function. Without oxygen, the animals would begin to shrivel and would lose water. This results in death for the animal. | Locomotion | Locomotion is vital to the survival of brittle and basket stars. They must be able to move in order to escape predators, capture food, and operate the water-vascular system. Ophioroids use their arms for locomotion in contrast to starfish that depend on their tube feet for movement. Brittle stars move fairly rapidly by wriggling their arms to enable the animals to make either snake like or rowing movements. Although they do tend to attach themselves to the seafloor or to sponges or cnidarians, such as coral, ophioroids have mastered the art of movement. | 13

17: Skeletal and Muscular Structure | Did you know? | Brittle stars only move horizontally and basket stars only move vertically due to the coordination of their muscles. | Skeleton Members of the class Ophiuroidea typically have bodies supported by fused ossicles called tests. Their five long, slender, whip-like arms are supported by an internal skeleton of calcium carbonate plates that are referred to as vertebral ossicles. These functional “vertebrae” move in a ball-in-socket joint and are controlled by muscles. In ancient species, these ossicles corresponded to the parallel ambulacral plates, however, modern species the vertebrae run along the median of the arm. The skeletal system is also composed of spines that protect the primitive vertebrae. The spines, made of calcite, compose a rigid border to the arm edges. | Muscular In living ophioroids, the vertebrae of the skeletal system are linked by longitudinal muscles. The larger the vertebrae and the smaller the muscles, the less spasmodic the movements are. Because of the muscles in their body structure, ophioroids are able to grip prey and substrate surfaces. They are even able to keep this grip after death. They also have the ability of coordinated movements. | When brittle stars dry out and their bodies lose all water, their flesh disintegrates leaving only the calcite test. | 14

18: Reproduction | Members of the class Ophiuroidea have separate sexes, although few have been found to be hermaphroditic, and reproduce through both asexual and sexual means. They are able to regenerate lost body parts through a way of asexual reproduction and are able to produce young through the fertilization of an egg by sperm. In sexual reproduction, fertilization sometimes occurs in the open sea after gametes have been discharged. The discharging of gametes is called spawning. This action usually takes place during the summer. Gametes are shed by the way of the bursal sacs and when fertilized, develop into a larval stage called the ophiopluteus which undergoes an intense metamorphosis before becoming a mature adult. The parents of this larva provide no parental care after they spawn. However, in another form of sexual reproduction, some specie’s gametes do not open into bursae and are paired in a chain along the basal arm joints. Many species actually brood their larvae in the bursae. Brittle stars generally sexually mature in two years, become full grown in three to four years, and live up to five years. | A brittle star spawning, releasing gametes into the water to be fertilized. | The intermingling of brittle stars usually marks the beginning of the mating ritual which can last for over 2 hours in some species. | 15

19: Regeneration Ophioroids can readily regenerate lost arms or arm segments unless all the arms are lost. This is due to the fact that the disk houses all the vital organs of the organism. Ophioroids regenerate in order to escape predators. When they feel threatened, they are easily able to unattach an arm that has been attacked. Also, the six armed species, Ophiactidae, exhibit transverse fission. Fission is the deliberate splitting of a body part in order to form a new and similar structure. Ophiactidae members go through fission and yield three large arms and three small arms. | Fast Fact | The species Pectinura will consume beech pollen n the New Zealand seaweed. | The ophiopluteus is the larva form of the brittle star adult. It displays bilateral symmetry making it close in relation to chordates. | Starfish and brittle stars both have the amazing power of regeneration and fission. In the picture (right), a starfish is undergoing fission by splitting one of its arms in two. | 16

20: Echinodermata Cross Word Puzzle | Across 1. invertebrates with a hard skeleton, no head, mouth in center and tube feet 5. aid in locomotion and feeding 8. pincher like structures surrounding spines on starfish skin 9. having coloring and patterns that blend in with surroundings 11. the larvae form the starfish 13. an animal lives by preying on other animals 14. has a flattened body with arms that form a star shape Down 2. located underneath the body in the center of the disk 3. some starfish break into two parts, then each grows its missing parts 4. armless echinoderms that live on the sea bottom 6. have poison in spines that can be poisonous to predators 7. rigid and sharp projection from the skin of a starfish 10. has a flat body with a small circle shaped disk and very long, thin arms 12. five arms protruding from a central body | 17

21: Echinodermata Word Search J A W Z X C P E T S R O T A Y E X E S J V W O I Y Z A N U M T F H D M E G E W M A B P Y I I A B T U C D K H T G J S S R A E D I O R U H T O L O H H C R M I R E G E N E R A T I O N H U C A A N H L X N U E T Z I F A K R N X C A N F A C V F U T E E F E B U T Y E C L S B Y U D N I A W Z O Y R P U U M A A E D I O R E T S A S T R H G Y R R N Z L O C F I B C U F R R A D I A L Q G A J A T F Y G E E O P I O L I D L Z U C W I S J R Z X M O Y K Q V I B S L V P Y I F P S E J K T M F J S Q K J W P E F G B J R R Z W R O O A A D H I E C J E B G L T S Q N W A M T A G S E B Q E B I R E I O E F B L I P E J E O P E S J P P O J R Y T E N D F F I D X N P A S T E D R G F T F F B B Z A H S N D A C T J E F T I I C R V K M V K E O P L C G M P X T P Q S E W V X C K M E O S E G K W H H G T P U E R W T G Z W G J C I Y J H A S K C N S A M A T W C R K J Q S H B B W W V J H E N C I M Z A D I I R R I Q H C L J C E D L S C F V J D I P T U N L N R Z V O R E V N A L O E U E G Q A C N W Z M N D U H O E R E Q I R Z C M P R Q R U W V D N O N J C K Z O H V X D L Q B O S R T U S U E O E B I I O M T O T L M T I Q D T E I L M F B Z Y Y Q C C I M H D A D U L I V E A V D C F C R S D V K U S C V U S V N O J E D X S M E L H R P E I U E M S N G B L R U M M Y G N T L B E Z C N K U N W N A P T B A E B Q W H V C F X E H P S N D I D A K K F E P S R Y A X T S B I S N C Q H P N H O O S K I N G I L L S P T S R B L A I Q X T D G D F I P L X R D I U O I S J A L U Z V H J H W H A I W B R X T V N G X E D W U N S D F S X M U X Y S V S A Y X K L N Z Z S E Y M T D I R D T C Q L M Q V U P G W H Z X K P P U Q H J C F M U R X W J I B E L N K R R Z B M A Z K E X A G R L J P P S E N M J Q O E H B W Z V X G F I B A A I R Y S M W S R C W D O D Y S F Q F B Z F C R O M L J O N R E Z A A R C B Z R M R A E K Y M I J E Y Z W N J G Q U D L U AMPULLAE ARISTOTLES LANTERN ASTEROIDEA BASKET BIPINNARIA BRITTLE CRINOIDEA CUCUMBER DEUTEROSTOME ECHINODERMATA ECHINOIDEA HOLOTHUROIDEA MADREPORITE NERVE RING OPHIUROIDEA OSSICLES PEDICELLARIAE RADIAL REGENERATION SESSILE SKIN GILLS STARFISH TUBE FEET URCHIN WATER VASCULAR | 18

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23: Sources of Information | "Brittlestar." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. 22 Feb. 2010 . Morris, M. and D. Fautin. "Ophiuroidea" (On-line), Animal Diversity Web. 2001. 22 Feb. 2010 . http://www.absoluteastronomy.com/topics/Brittle_star http://www.ucmp.berkeley.edu/echinodermata/ophiuroidea.html http://seawrold.org/animal-info/animal-bytes/animalia/eumetazoa/coelomates/deuterostomes/echinodermata/brittle-stars http://library.thinkquest.org/26153/marine/sketch/785.jpg http://www.enchantedlearning.com/bgifs/Brittlestar http://www.geo.arizona.edu/geo3xx/geo308_fall2002/5echinos_files/image032 http://www.mcz.harvard.edu/Departments/InvertPaleo/Trenton/Intro/PaleoPage/Terminology&Morphology/Images/AsterozoaDiagram2.jpg | 20

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