Bài giảng Biology - Chapter 33: Invertebrates

Chapter 33InvertebratesOverview: Life Without a BackboneInvertebratesAre animals that lack a backboneAccount for 95% of known animal speciesFigure 33.1 A review of animal phylogenyAncestral colonialchoanoflagellateEumetazoaBilateriaDeuterostomiaPoriferaCnidariaOther bilaterians (includingNematoda, Arthropoda,Mollusca, and Annelida)EchinodermataChordataFigure 33.2 Exploring invertebrate diversityPORIFERA (5,500 species)A spongeCNIDARIA (10,000 species)A jellyPLACOZOA (1 species)KINORHYNCHA (150 species)0.5 mmA placozoan (LM)A kinorhynch (LM)250 µmPLATYHELMINTHES (20,000 species)ROTIFERA (1,800 species)A marine flatwormA rotifer (LM)ECTOPROCTA (4,500 species)PHORONIDA (20 species)EctoproctsPhoronidsFigure 33.3Exploring invertebrate diversityBRACHIOPODA (335 species)NEMERTEA (900 species)A brachiopodA ribbon wormACANTHOCEPHALA (1,100 species)CTENOPHORA (100 species)An acanthocephalanA ctenophore, or comb jellyMOLLUSCA (93,000 species)ANNELIDA (16,500 species)An octopusA marine annelidLORICIFERA (10 species)PRIAPULA (16 species)5 mm50 µmA loriciferan (LM)A priapulanFigure 33.3Exploring invertebrate diversityNEMATODA (25,000 species)ARTHROPODA (1,000,000 + species)A roundwormA scorpion (an arachnid)CYCLIOPHORA (1 species)TARDIGRADA (800 species)100 µm100 µmA cycliophoran (colorized SEM) Tardigrades (colorized SEM)ONYCHOPHORA (110 species)HEMICHORDATA (85 species)An onychophoranAn acorn wormECHINODERMATA (7,000 species)CHORDATA (52,000 species)A sea urchinA tunicateFigure 33.3Sponges are sessile and have a porous body and choanocytesSponges, phylum PoriferaLive in both fresh and marine watersLack true tissues and organsSponges are suspension feedersCapturing food particles suspended in the water that passes through their bodyAzure vase sponge (Callyspongia plicifera)OsculumSpiculesWaterflowFlagellumCollarFood particlesin mucusChoanocytePhagocytosis offood particlesAmoebocyte Choanocytes. The spongocoel is lined with feeding cells called choanocytes. By beating flagella, the choanocytes create a current that draws water in through the porocytes. Spongocoel. Water passing through porocytes enters a cavity called the spongocoel. Porocytes. Water enters the epidermis through channels formed by porocytes, doughnut-shaped cells that span the body wall. Epidermis. The outer layer consists of tightly packed epidermal cells. Mesohyl. The wall of this simple sponge consists of two layers of cells separatedby a gelatinous matrix, themesohyl (“middle matter”). The movement of the choanocyte flagella also draws water through its collar of fingerlike projections. Food particles are trapped in the mucus coating the projections, engulfed by phagocytosis, and either digested or transferred to amoebocytes. Amoebocyte. Amoebocytes transport nutrients to other cells ofthe sponge body and also produce materials for skeletal fibers (spicules).5674321Figure 33.4Choanocytes, flagellated collar cellsGenerate a water current through the sponge and ingest suspended foodMost sponges are hermaphroditesMeaning that each individual functions as both male and femaleConcept 33.2: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytesAll animals except spongesBelong to the clade Eumetazoa, the animals with true tissuesPhylum CnidariaIs one of the oldest groups in this cladeCnidariansHave diversified into a wide range of both sessile and floating forms including jellies, corals, and hydrasBut still exhibit a relatively simple diploblastic, radial body planThe basic body plan of a cnidarianIs a sac with a central digestive compartment, the gastrovascular cavityA single openingFunctions as both mouth and anusThere are two variations on this body planThe sessile polyp and the floating medusaMouth/anusTentacleGastrovascularcavityGastrodermisMesogleaEpidermisTentacleBodystalkMouth/anusMedusaPolypFigure 33.5Tentacle“Trigger”NematocystCoiled threadDischargeOf threadCnidocytePreyFigure 33.6Cnidarians are carnivoresThat use tentacles to capture preyThe tentacles are armed with cnidocytesUnique cells that function in defense and the capture of preyThe phylum Cnidaria is divided into four major classesTable 33.1Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa(a) These colonial polyps are members of class Hydrozoa.(b) Many species of jellies (classScyphozoa), including thespecies pictured here, are bioluminescent. The largest scyphozoans have tentaclesmore than 100 m long dangling from a bell-shaped body up to 2 m in diameter.(c) The sea wasp (Chironex fleckeri) is a member of class Cubozoa. Its poison,which can subdue fish andother large prey, is more potent than cobra venom.(d) Sea anemones and othermembers of class Anthozoaexist only as polyps.Figure 33.7a–dHydrozoansMost hydrozoansAlternate between polyp and medusa formsFeeding polypReproductivepolypMedusabudASEXUALREPRODUCTION(BUDDING)GonadMedusaMEIOSISFERTILIZATIONSEXUALREPRODUCTIONEggSpermDevelopingpolypPortion ofa colonyof polypsMaturepolypPlanula(larva)KeyHaploid (n)Diploid (2n)1 mmZygoteFigure 33.8A colony ofinterconnectedpolyps (inset,LM) resultsfrom asexualreproductionby budding.1 Some of the colony’s polyps, equipped with tentacles, are specialized for feeding.2 Other polyps, specialized for reproduction, lack tentacles and produce tiny medusae by asexual budding.3 The medusae swim off, grow, and reproduce sexually.4 The zygote develops into a solid ciliated larva called a planula.5 The planula eventually settles and develops into a new polyp.6ScyphozoansIn the class ScyphozoaJellies (medusae) are the prevalent form of the life cycleCubozoansIn the class Cubozoa, which includes box jellies and sea waspsThe medusa is box-shaped and has complex eyesAnthozoansClass Anthozoa includes the corals and sea anemonesWhich occur only as polypsConcept 33.3: Most animals have bilateral symmetryThe vast majority of animal species belong to the clade BilateriaWhich consists of animals with bilateral symmetry and triploblastic developmentFlatwormsMembers of phylum PlatyhelminthesLive in marine, freshwater, and damp terrestrial habitatsAre flattened dorsoventrally and have a gastrovascular cavityAlthough flatworms undergo triploblastic developmentThey are acoelomatesFlatworms are divided into four classesTable 33.2TurbellarianTurbellariansAre nearly all free-living and mostly marineFigure 33.9The best-known turbellarians, commonly called planariansHave light-sensitive eyespots and centralized nerve netsPharynx. The mouth is at thetip of a muscular pharynx thatextends from the animal’sventral side. Digestive juicesare spilled onto prey, and thepharynx sucks small pieces offood into the gastrovascularcavity, where digestion continues.Digestion is completed withinthe cells lining the gastro-vascular cavity, which hasthree branches, each withfine subbranches that pro-vide an extensive surface area.Undigested wastesare egestedthrough the mouth.Ganglia. Located at the anterior endof the worm, near the main sourcesof sensory input, is a pair of ganglia,dense clusters of nerve cells.Ventral nerve cords. Fromthe ganglia, a pair ofventral nerve cords runsthe length of the body.GastrovascularcavityEyespotsFigure 33.10Monogeneans and TrematodeMonogeneans and trematodesLive as parasites in or on other animalsParasitize a wide range of hostsTrematodes that parasitize humansSpend part of their lives in snail hostsThese larvae penetratethe skin and blood vessels of humans working in irrigated fields contaminated with infected human feces.Asexual reproduction within a snail results in another type of motilelarva, which escapes from the snail host.Blood flukes reproduce sexually in the human host. The fertilized eggs exit the host in feces.The eggs develop in water into ciliated larvae. These larvaeinfect snails, the intermediate hosts.Snail host1 mmFemaleMale5234Figure 33.11Mature flukes live in the blood vessels of the human intestine. A female fluke fits into a groove running the length of the larger male’s body, as shown in the light micrograph at right.1Most monogeneansAre parasites of fishTapewormTapewormsAre also parasitic and lack a digestive systemProglottids withreproductive structures200 µmHooksSuckerScolexFigure 33.12RotifersRotifers, phylum RotiferaAre tiny animals that inhabit fresh water, the ocean, and damp soilRotifers are smaller than many protistsBut are truly multicellular and have specialized organ systems0.1 mmFigure 33.13Rotifers have an alimentary canalA digestive tube with a separate mouth and anus that lies within a fluid-filled pseudocoelomRotifers reproduce by parthenogenesisIn which females produce more females from unfertilized eggsLophophorates: Ectoprocts, Phoronids, and BrachiopodsLophophorates have a lophophoreA horseshoe-shaped, suspension-feeding organ bearing ciliated tentaclesEctoproctsAre colonial animals that superficially resemble plantsLophophoreEctoprocts, such as this sea mat (Membraniporamembranacea), are colonial lophophorates.(a)Figure 33.14aPhoronidsAre tube-dwelling marine worms ranging from 1 mm to 50 cm in lengthLophophoreIn phoronids such as Phoronis hippocrepia, the lophophore and mouth are at one end of an elongated trunk.(b)Figure 33.14bBrachiopods superficially resemble clams and other hinge-shelled molluscsBut the two halves of the shell are dorsal and ventral rather than lateral, as in clamsLophophoreBrachiopods have a hinged shell. The two parts of the shell are dorsal and ventral.(c)Figure 33.14cNemerteansMembers of phylum NemerteaAre commonly called proboscis worms or ribbon wormsFigure 33.15The nemerteans unique proboscisIs used for defense and prey captureIs extended by a fluid-filled sacNemerteans also have a closed circulatory systemIn which the blood is contained in vessels distinct from fluid in the body cavityConcept 33.4: Molluscs have a muscular foot, a visceral mass, and a mantlePhylum MolluscaIncludes snails and slugs, oysters and clams, and octopuses and squidsMost molluscs are marineThough some inhabit fresh water and some are terrestrialMolluscs are soft-bodied animalsBut most are protected by a hard shellAll molluscs have a similar body plan with three main partsA muscular footA visceral massA mantleVisceral massMantleFootCoelomIntestineGonadsMantlecavityAnusGillNervecordsEsophagusStomachShellRadulaMouthMouthNephridium. Excretory organs called nephridia remove metabolic wastes from the hemolymph.Heart. Most molluscs have an open circulatory system. The dorsally located heart pumps circulatory fluid called hemolymph through arteries into sinuses (body spaces). The organs of the mollusc are thus continually bathed in hemolymph. The long digestive tract is coiled in the visceral mass.Radula. The mouth region in many mollusc species contains a rasp-like feeding organ called a radula. This belt of backward-curved teeth slides back and forth, scraping and scooping like a backhoe. The nervous system consists of a nerve ring around the esophagus, from which nerve cords extend.Figure 33.16Most molluscs have separate sexesWith gonads located in the visceral massThe life cycle of many molluscsIncludes a ciliated larval stage called a trochophoreThere are four major classes of molluscsTable 33.3ChitonsClass Polyplacophora is composed of the chitonsOval-shaped marine animals encased in an armor of eight dorsal platesFigure 33.17GastropodsAbout three-quarters of all living species of molluscsBelong to class GastropodaA land snail (a)A sea slug. Nudibranchs, or sea slugs, lost their shell during their evolution. (b)Figure 33.18a, bMost gastropodsAre marine, but there are also many freshwater and terrestrial speciesPossess a single, spiraled shellSlugs lack a shellOr have a reduced shellThe most distinctive characteristic of this classIs a developmental process known as torsion, which causes the animal’s anus and mantle to end up above its headAnusMantlecavityStomachIntestineMouthFigure 33.19BivalvesMolluscs of class BivalviaInclude many species of clams, oysters, mussels, and scallopsHave a shell divided into two halvesFigure 33.20The mantle cavity of a bivalveContains gills that are used for feeding as well as gas exchangeHinge areaGutCoelomHeartAdductormuscleAnusExcurrentsiphonWaterflowIncurrentsiphonGillMantlecavityFootPalpMouthShellMantleFigure 33.21CephalopodsClass Cephalopoda includes squids and octopusesCarnivores with beak-like jaws surrounded by tentacles of their modified footMost octopusesCreep along the sea floor in search of preyFigure 33.22a(a) Octopuses are considered among the most intelligent invertebrates.Squids use their siphonTo fire a jet of water, which allows them to swim very quicklyFigure 33.22b(b) Squids are speedy carnivores with beaklike jaws and well-developed eyes.`One small group of shelled cephalopodsThe nautiluses, survives todayFigure 33.22c(c) Chambered nautiluses are the only living cephalopods with an external shell.Concept 33.5: Annelids are segmented wormsAnnelidsHave bodies composed of a series of fused ringsThe phylum Annelida is divided into three classesTable 33.4OligochaetesOligochaetes (class Oligochaeta)Are named for their relatively sparse chaetae, or bristles made of chitinInclude the earthworms and a variety of aquatic speciesEarthworms eat their way through the soil, extracting nutrients as the soil moves through the alimentary canalWhich helps till the earth, making earthworms valuable to farmersAnatomy of an earthwormMouthSubpharyngealganglionPharynxEsophagusCropGizzardIntestineMetanephridiumVentralvesselNervecordsNephrostomeIntestineDorsalvesselLongitudinalmuscleCircularmuscleEpidermisCuticleSeptum(partitionbetweensegments)AnusEach segment is surrounded by longitudinal muscle, which in turn is surrounded by circular muscle. Earthworms coordinate the contraction of these two sets of muscles to move (see Figure 49.25). These muscles work against the noncompressible coelomic fluid, which acts as a hydrostatic skeleton.Coelom. The coelom of the earthworm is partitioned by septa.Metanephridium. Each segment of the worm contains a pair of excretory tubes, called metanephridia, with ciliated funnels, called nephrostomes. The metanephridia remove wastes from the blood and coelomic fluid through exterior pores.Tiny blood vessels are abundant in the earthworm’s skin, which functions as its respiratory organ. The blood contains oxygen-carryinghemoglobin.Ventral nerve cords with segmental ganglia. The nerve cords penetrate the septa and run the length of the animal, as do the digestive tract and longitudinal blood vessels.The circulatory system, a network of vessels, is closed. The dorsal and ventral vessels are linked by segmental pairs of vessels. The dorsal vessel and five pairs of vessels that circle the esophagus of an earthworm are muscular and pump blood through the circulatory system.Cerebral ganglia. The earthworm nervous system features a brain-like pair of cerebral ganglia above and in front of the pharynx. A ring of nerves around the pharynx connects to a subpharyngeal ganglion, from which a fused pair of nerve cords runs posteriorly.Chaetae. Each segment has four pairs of chaetae, bristles that provide traction for burrowing. Many of the internal structures are repeated within each segment of the earthworm. Giant Australian earthwormClitellumTable 33.23PolychaetesMembers of class PolychaetaPossess paddlelike parapodia that function as gills and aid in locomotionParapodiaFigure 33.24LeechesMembers of class HirudineaAre blood-sucking parasites, such as leechesFigure 33.25Concept 33.6: Nematodes are nonsegmented pseudocoelomates covered by a tough cuticleAmong the most widespread of all animals, nematodes, or roundwormsAre found in most aquatic habitats, in the soil, in moist tissues of plants, and in the body fluids and tissues of animalsThe cylindrical bodies of nematodes (phylum Nematoda)Are covered by a tough coat called a cuticle25 µmFigure 33.26Some species of nematodesAre important parasites of plants and animals50 µmEncysted juvenilesMuscle tissueFigure 33.27Concept 33.7: Arthropods are segmented coelomates that have an exoskeleton and jointed appendagesTwo out of every three known species of animals are arthropodsMembers of the phylum ArthropodaAre found in nearly all habitats of the biosphereGeneral Characteristics of ArthropodsThe diversity and success of arthropodsAre largely related to their segmentation, hard exoskeleton, and jointed appendagesEarly arthropods, such as trilobitesShowed little variation from segment to segmentFigure 33.28As arthropods evolvedThe segments fused, and the appendages became more specializedThe appendages of some living arthropodsAre modified for many different functionsAntennae(sensoryreception)HeadThoraxSwimmingappendagesWalking legsMouthparts (feeding)Pincer (defense)AbdomenCephalothoraxFigure 33.29The body of an arthropodIs completely covered by the cuticle, an exoskeleton made of chitinWhen an arthropod growsIt molts its exoskeleton in a process called ecdysisArthropods have an open circulatory systemIn which fluid called hemolymph is circulated into the spaces surrounding the tissues and organsA variety of organs specialized for gas exchangeHave evolved in arthropodsMolecular evidence now suggestsThat living arthropods consist of four major lineages that diverged early in the evolution of the phylumTable 33.5CheliceriformsCheliceriforms, subphylum CheliceriformesAre named for clawlike feeding appendages called cheliceraeInclude spiders, ticks, mites, scorpions, and horseshoe crabsMost of the marine cheliceriforms are extinctBut some species survive today, including the horseshoe crabsFigure 33.30Scorpions have pedipalps that are pincers specialized for defense and the capture of food. The tip of the tail bears a poisonous stinger.(a)Dust mites are ubiquitous scavengers in human dwellings but are harmless except to those people who are allergic to them (colorized SEM).(b)Web-building spiders are generally most active during the daytime.(c)50 µmFigure 33.31a–cMost modern cheliceriforms are arachnidsA group that includes spiders, scorpions, ticks, and mitesArachnids have an abdomen and a cephalothoraxWhich has six pairs of appendages, the most anterior of which are the cheliceraeDigestiveglandIntestineHeartStomachBrainEyesPoisonglandPedipalpCheliceraBook lungSpermreceptacleGonopore(exit for eggs)Silk glandSpinneretsAnusOvaryFigure 33.32MyriapodsSubphylum MyriapodaIncludes millipedes and centipedesMillipedes, class DiplopodaHave a large number of legsEach trunk segmentHas two pairs of legsFigure 33.33Centipedes, class ChilopodaAre carnivores with jaw-like mandiblesHave one pair of legs per trunk segmentFigure 33.34InsectsSubphylum Hexapoda, insects and their relativesAre more species-rich than all other forms of life combinedLive in almost every terrestrial habitat and in fresh waterThe internal anatomy of an insectIncludes several complex organ systemsCompound eyeAntennaeAnusVaginaOvaryDorsalarteryCropAbdomenThoraxHeadThe insect body has three regions: head, thorax, and abdomen. The segmentation of the thorax and abdomen are obvious, but the segments that form the head are fused. Heart. The insect heart drives hemolymph through an open circulatory system.Cerebral ganglion. The two nerve cords meet in the head, where the ganglia of several anterior segments are fused into a cerebral ganglion (brain). The antennae, eyes, and other sense organs are concentrated on the head.Tracheal tubes. Gas exchange in insects is accomplished by a tracheal system of branched, chitin-lined tubes that infiltrate the body and carry oxygen directly to cells. The tracheal system opens to the outside of the body through spiracles, pores that can control air flow and water loss by opening or closing.Nerve cords. The insect nervous system consists of a pair of ventral nerve cords with several segmental ganglia.Insect mouthparts are formed from several pairs of modified appendages. The mouthparts include mandibles, which grasshoppers use for chewing. In other insects, mouthparts are specialized for lapping, piercing, or sucking.Malpighian tubules. Metabolic wastes areremoved from the hemolymph by excretory organs called Malpighian tubules, which are out-pocketings of the digestive tract.Figure 33.35Flight is obviously one key to the great success of insectsAn animal that can flyCan escape predators, find food, and disperse to new habitats much faster than organisms that can only crawlMany insectsUndergo metamorphosis during their developmentIn incomplete metamorphosis, the young, called nymphsResemble adults but are smaller and go through a series of molts until they reach full sizeInsects with complete metamorphosisHave larval stages specialized for eating and growing that are known by such names as maggot, grub, or caterpillarThe larval stageLooks entirely different from the adult stageMetamorphosis from the larval stage to the adult stageOccurs during a pupal stageLarva (caterpillar)(a)(b) Pupa(c) Pupa(d) Emerging adult(e) AdultFigure 33.6a–eInsects are classified into about 26 ordersORDERBlattodea 4,000Cockroaches have a dorsoventrally flattened body, with legs modified for rapid running. Forewings, when present, areleathery, whereas hind wings are fanlike. Fewer than 40 cock-roach species live in houses; the rest exploit habitats ranging from tropical forest floors to caves and deserts.Beetles comprise the most species-rich order of insects. They have two pairs of wings, one of which is thick and leathery, theother membranous. They have an armored exoskeleton andmouthparts adapted for biting and chewing. Beetles undergocomplete metamorphosis.Earwigs are generally nocturnal scavengers. While some species are wingless, others have two pairs of wings, one of which is thick and leathery, the other membranous. Earwigshave biting mouthparts and large posterior pincers. They un-dergo incomplete metamorphosis.Dipterans have one pair of wings; the second pair has become modified into balancing organs called halteres. Their head islarge and mobile; their mouthparts are adapted for sucking,piercing, or lapping. Dipterans undergo complete metamorpho-sis. Flies and mosquitoes are among the best-known dipterans, which live as scavengers, predators, and parasites.Hemipterans are so-called “true bugs,” including bed bugs, assassin bugs, and chinch bugs. (Insects in other orders aresometimes erroneously called bugs.) Hemipterans have two pairs of wings, one pair partly leathery, the other membranous.They have piercing or sucking mouthparts and undergoincomplete metamorphosis.Ants, bees, and wasps are generally highly social insects. Theyhave two pairs of membranous wings, a mobile head, and chewing or sucking mouthparts. The females of many species have a posterior stinging organ. Hymenopterans undergo com-plete metamorphosis.Termites are widespread social insects that produce enormous colonies. It has been estimated that there are 700 kg oftermites for every person on Earth! Some termites have twopairs of membranous wings, while others are wingless. They feed on wood with the aid of microbial symbionts carried in specialized chambers in their hindgut.Coleoptera 350,000 Dermaptera1,200Diptera151,000Hemiptera85,000Hymenoptera125,000Isoptera2,000APPROXIMATENUMBER OFSPECIESMAIN CHARACTERISTICSEXAMPLESGermancockroachJapanesebeetleEarwigHorseflyLeaf-FootedbugCicada-killer waspTermiteFigure 33.37Insects are classified into about 26 ordersLepidoptera120,000Butterflies and moths are among the best-known insects. They have two pairs of wings covered with tiny scales. To feed, theyuncoil a long proboscis. Most feed on nectar, but some species feed on other substances, including animal blood or tears.Odonata5,000Dragonflies and damselflies have two pairs of large, membran-ous wings. They have an elongated abdomen, large, compound eyes, and chewing mouthparts. They undergo incomplete meta-morphosis and are active predators.Orthoptera13,000Grasshoppers, crickets, and their relatives are mostly herbi-vorous. They have large hind legs adapted for jumping, twopairs of wings (one leathery, one membranous), and biting or chewing mouthparts. Males commonly make courtship sounds by rubbing together body parts, such as a ridge on their hind leg. Orthopterans undergo incomplete metamorphosis.Phasmida2,600Stick insects and leaf insects are exquisite mimics of plants. The eggs of some species even mimic seeds of the plants on which the Insects live. Their body is cylindrical or flattened dorsoventrally. They lack forewings but have fanlike hind wings. Their mouthparts are adapted for biting or chewing.Phthiraptera2,400Commonly called sucking lice, these insects spend their entire life as an ectoparasite feeding on the hair or feathers of a singlehost. Their legs, equipped with clawlike tarsi, are adapted forclinging to their hosts. They lack wings and have reduced eyes.Sucking lice undergo incomplete metamorphosis.Siphonaptera2,400Fleas are bloodsucking ectoparasites on birds and mammals. Their body is wingless and laterally compressed. Their legs are modified for clinging to their hosts and for long-distance jumping. They undergo complete metamorphosis.Thysanura450Silverfish are small, wingless insects with a flattened body and reduced eyes. They live in leaf litter or under bark. They can also infest buildings, where they can become pests.Trichoptera7,100The larvae of caddisflies live in streams, where they make houses from sand grains, wood fragments, or other material held to-gether by silk. Adults have two pairs of hairy wings and chewingor lapping mouthparts. They undergo complete metamorphosis.SwallowtailbutterflyDragonflyKatydidStick insectHumanBodylouseFleaSilverfishCaddisflyORDERAPPROXIMATENUMBER OFSPECIESMAIN CHARACTERISTICSEXAMPLEFigure 33.37CrustaceansWhile arachnids and insects thrive on landCrustaceans, for the most part, have remained in marine and freshwater environmentsCrustaceans, subphylum CrustaceaTypically have biramous, branched, appendages that are extensively specialized for feeding and locomotionDecapods are all relatively large crustaceansAnd include lobsters, crabs, crayfish, and shrimpGhost crabs (genus Ocypode) live on sandy ocean beaches worldwide. Primarily nocturnal, they take shelter in burrows during the day.(a)Figure 33.38aPlanktonic crustaceans include many species of copepodsWhich are among the most numerous of all animalsPlanktonic crustaceans known as krill are consumed in vast quantities by whales.(b)Figure 33.38bBarnacles are a group of mostly sessile crustaceansWhose cuticle is hardened into a shellThe jointed appendages projecting from the shellsof these barnacles capture organisms and organic particles suspended inthe water.(c)Figure 33.38cConcept 33.8: Echinoderms and chordates are deuterostomesAt first glance, sea stars and other echinoderms, phylum EchinodermataMay seem to have little in common with phylum Chordata, which includes the vertebratesChordates and echinoderms share characteristics of deuterostomesRadial cleavageDevelopment of the coelom from the archenteronFormation of the mouth at the end of the embryo opposite the blastoporeEchinodermsSea stars and most other echinodermsAre slow-moving or sessile marine animalsA thin, bumpy or spiny skinCovers an endoskeleton of hard calcareous platesUnique to echinoderms is a water vascular systemA network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchangeStomachAnusRingcanalGonadsAmpullaPodiumRadialnerveTubefeetSpineGillsA short digestive tract runs from the mouth on the bottom of the central disk to the anus on top of the disk.The surface of a sea star is covered by spines that help defend against predators, as well as by small gills that provide gas exchange.Madreporite. Water can flow in or out of the water vascular system into the surrounding water through the madreporite.Branching from each radial canal are hundreds of hollow, muscular tube feet filled with fluid. Each tube foot consists of a bulb-like ampulla and suckered podium (foot portion). When the ampulla squeezes, it forces water into the podium and makes it expand. The podium then contacts the substrate. When the muscles in the wall of the podiumcontract, they force water back into the ampulla, making the podium shorten and bend.Radial canal. The water vascular system consists of a ring canal in the central disk and five radial canals, each running in a groove down the entire length of an arm.Digestive glands secrete digestive juices and aid in the absorption and storage of nutrients.Central disk. The central disk has a nerve ring and nerve cords radiating from the ring into the arms.Figure 33.39The radial anatomy of many echinodermsEvolved secondarily from the bilateral symmetry of ancestorsLiving echinoderms are divided into six classesTable 33.6Sea StarsSea stars, class AsteroideaHave multiple arms radiating from a central diskThe undersurfaces of the armsBear tube feet, each of which can act like a suction disk(a) A sea star (class Asteroidea)Figure 33.40aBrittle StarsBrittle stars have a distinct central diskAnd long, flexible arms(b) A brittle star (class Ophiuroidea)Figure 33.40bSea Urchins and Sand DollarsSea urchins and sand dollars have no armsBut they do have five rows of tube feet that function in movement(c) A sea urchin (class Echinoidea)Figure 33.40cSea Lilies and Feather StarsSea lilies Live attached to the substrate by a stalkSea CucumbersFeather starsCrawl about using their long, flexible arms(d) A feather star (class Crinoidea)Figure 33.40dSea CucumbersSea cucumbersUpon first inspection do not look much like other echinodermsLack spines, and their endoskeleton is much reduced(e) A sea cucumber (class Holothuroidea)Figure 33.40eSea DaisiesSea daisies were discovered in 1986And only two species are known(f) A sea daisy (class Concentricycloidea)Figure 33.40fChordatesChordatesPhylum ChordataConsists of two subphyla of invertebrates as well as the hagfishes and the vertebratesShares many features of embryonic development with echinodermsA summary of animal phylaTable 33.7