Reading Essentials for Biology Glencoe (794133), страница 80
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The arms of a sea star arecalled rays. The skin of a sea cucumber is made of soft tissue thatdoes not appear spiny. The small platelike structures that cover asea cucumber’s skin have replaced true spines.Create a ChartHighlight the text thatdescribes the body parts orcharacteristics that make anechinoderm unique. In a different color, highlight thebody parts or characteristicsthat make one echinodermspecies different fromanother. Use the highlightedtext to create a chart thatshows these unique features.1. What are sea stars’ armscalled?________________________________________________________________________READING ESSENTIALSChapter 29351NameDateClassSection29.1Echinoderms, continuedSome of the spines found on the skin of sea stars and sea urchinshave been modified into pincerlike appendages.
These appendagesare called a pedicellariae (PEH dih sih LAHR ee ay; singular,pedicellaria). An echinoderm uses its pedicellariae to protect itself.It also uses the pedicellariae to clean the surface of its body.How do echinoderms benefit fromradial symmetry?As you will recall, radial symmetry means that the parts of theanimal’s body are arranged regularly around a central axis. Radialsymmetry is an advantage to animals that move slowly or that donot move freely from place to place. Radial symmetry allowsechinoderms to sense possible food or predators that might benearby. Radial symmetry also allows echinoderms to sense otherconditions of their environment from all directions.________________________________________________________________________352Chapter 29What is a water vascular system?Echinoderms have a water vascular system. A water vascularsystem is a hydraulic system that operates under water pressure.Water comes in and goes out of a sea star through the water vascular system.
This system allows sea stars to move, to catch theirfood, to exchange gases, and to excrete wastes.As the water goes through the sea star, it passes through themadreporite. The madreporite (mah druh POHR ite) is a diskshaped opening on the upper surface of the animal. It functionslike a strainer that fits into a kitchen sink drain and keeps largebits of material from going into the drain pipes.
The madreporiteprevents large particles from entering the echinoderm’s body.Sea stars and other echinoderms have tube feet. Tube feet arehollow tubes with thin walls. They look like tiny medicine droppers. The end of a tube foot works like a tiny suction cup. Theround, muscular structure is called an ampulla (AM pew lah). Itlooks like the bulb of the dropper. The ampullae contract andrelax, creating a strong suction action.
The total suction actionof ampullae in tube feet is so strong that a sea star can open aclam shell. Each tube foot works independently of the other tubefeet. Echinoderms move by pushing out and then pulling in theirtube feet.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.2. How do echinoderms usea water vascular system?NameDateClassSection29.1Echinoderms, continuedTube feet also carry out gas exchange and excretion.
Gases areexchanged and some wastes are excreted by diffusion through thethin walls of the tube feet.What does an echinoderm eat?All echinoderms have a mouth, stomach, and intestines. Theway echinoderms catch their food differs from one species toanother. Sea stars are carnivores, or meat-eaters. They eat wormsand mollusks such as clams and oysters. Most sea urchins areherbivores. They eat algae. Brittle stars, sea lilies, and sea cucumbers feed on dead and decaying matter on the ocean floor.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Do echinoderms have a nervous system?An echinoderm has a simple nervous system. It consists of anerve ring that surrounds the mouth.
Echinoderms do not haveheads or brains. Nerves extend from the nerve ring down intoeach ray. Nerves in the rays are called radial nerves. The radialnerves branch out into a network of nerves. This nerve networkprovides sensory information to the animal.Most echinoderms do not have sensory organs. They have cellsthat detect touch and light. Sea stars, however, do have sensoryorgans. A sea star’s body is composed of long rays that extendfrom the animal’s central disk.
On the underside of each arm orray is an eyespot. Eyespots consist of a cluster of light-detectingcells. They help sea stars detect the intensity of light. Most seastars use their eyespots to help them move toward light. The tubefeet of sea stars have chemical receptors. When a sea star senses achemical signal from a prey animal, it moves in the direction ofthe ray that most strongly senses the chemical.3. What purposes do tubefeet serve?________________________________________________________________________4. What kind of nervous system does an echinodermhave?________________________________________________________________________Do echinoderm larvae have radial orbilateral symmetry?The larval stages of echinoderms have bilateral symmetry.
Thelarvae are free swimming, and they go through metamorphosis.During metamorphosis, the larvae undergo many changes both intheir body parts and in their symmetry. Remember that the adultforms of echinoderms have radial symmetry.READING ESSENTIALSChapter 29353NameDateClassSection29.1Echinoderms, continuedAre echinoderms protostomes or deuterostomes?A protostome is an animal with a mouth that develops fromthe opening in the gastrula. A deuterostome is an animal witha mouth that develops from cells elsewhere on the gastrula.Echinoderms are deuterostomes. Echinoderms have a close relationship to chordates because chordates also are deuterostomes.________________________________________________Diversity of EchinodermsAbout 6000 species of echinoderms exist today.
About 1500 ofthese belong to the class Asteroidea (AS tuh ROY dee uh). Seastars belong to this class. The six classes of echinoderms and anexample of a species in each class are as follows:________________________ClassExample of Speciesin ClassAsteroidea(AS tuh ROY dee uh)Sea starsOphiuroidea(OH fee uh ROY dee uh)Brittle starsEchinoidea(eh kihn OY dee uh)Sea urchinsHolothuroidea(HOH loh thuh ROY dee uh)Sea cucumbersCrinoidea(cry NOY dee uh)Sea liliesConcentricycloidea(kon sen tri sy CLOY dee uh)Sea daisiesWhat are sea stars?Sea stars are probably the best-known echinoderm. Most seastars have only five rays. Some sea stars, however, have more than40 rays. Sea stars have all the common characteristics of echinoderms.
They have an endoskeleton made of calcium carbonateplates. The sea star can change from a rigid structure to a flexibleone by contracting or relaxing the muscles that connect the plates.As shown in the illustration on page 355, they have tube feetwith ampullae and use eyespots on each ray to distinguishbetween light and dark. Sea stars have a stomach.
In order to eat,354Chapter 29READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.5. How many classes andhow many species ofechinoderms exist today?NameDateClassSection29.1Echinoderms, continueda sea star pushes its stomachout of its mouth and spreadsits stomach over the food.Enzymes secreted by thedigestive gland turn solidfood into liquid. The stomach absorbs this liquid. Thesea star then pulls its stomach back into its body.
Thesea star has an anus for ridding its body of waste. Italso has pedicellariae that ituses to keep the surface ofits body clean.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What are brittlestars?PedicellariaeRayMadreporiteAnusRingRadial canalcanalNerveringStomachRadialAmpullaeBrittle stars are fragile.nerveIf you pick up a brittle star,parts of its rays will breakTube feetoff in your hand. That ishow this star got its name.If a predator tries to attackEyespotsa brittle star, rays will breakoff and the brittle star canescape.
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