flatworms, roundworms, and rotifers. germ layers layers of cells that originate in the developing...
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Flatworms, Roundworms, and Rotifers
Germ Layers
Layers of cells that originate in the developing embryo and become specific structuresEctoderm - outerMesoderm - middleEndoderm - inner
Acoelomate
Without a coelom2 germ layersEctoderm and endodermNot separated by a cavityLeast complex body planSponges and cnidarians
Body Plans
3 Layer Acoelomate
3 germ layersEndoderm, mesoderm and ectodermNot separated by a cavityFlatworms
Pseudocoelomate
PseudocoelomCavity formed between mesoderm and endodermRoundworms and rotifers
Coelomate
Cavity developed within the mesodermMost complex body planMollusks, annelids, arthropods, echinoderms, and chordates
Phylum Platyhelminthes - Flatworms
13,000 speciesBilaterally symmetricalCephalization3 classes (Turbellaria, Trematoda, and Cestoda)Trematodes and cestodes parasiticParasites live in or on other organisms (host)
Parasitic Flatworms
Originated from free livingSome organs modified for parasitismLack mouthsWell developed digestive system
Hooks or suckers Tegument- thick covering of cellsCuticle- nonliving layer secreted by epidermis
Class Turbellaria
3000 speciesMost marineEx. Planaria (fresh water)
Planaria
Anterior end spade shapedPosterior end taperedBody covered with cilia
External anatomy
Movement
Move by undulative motion orLaying down mucus layer and beating cilia
Digestion and Excretion
Scavenger (carrion)Predator (small prey)
Digestion
Muscular pharynx extended out of mouthFood sucked inPassed into intestines (branched)Nutrients absorbed through intestinal wall or phagocytosisUndigested food excreted through pharynx and mouth
Excretion
Chemical wastes and excess water eliminated by network of ducts (pores and canals)Contains flame cellsFlame cells enclose a tuft of beating ciliaCilia moves wastes into the ducts ->Excretory pores -> out
Nervous Control
Organized and cephalizedSense light intensity and directionTwo anterior eyespots (photosensitive cells)Touch, taste, and smell receptors
Two anterior ganglia (clusters of nerves) -> simple brainTwo longitudinal nerves connected by transverse nervesCapable of simple "learning"Memory stored chemically
Reproduction
HermaphroditesSexual reproductionSimultaneous fertilizationProtective encapsulated eggs stick to rockHatch 2-3 weeks
Asexual (summer)Attach to rock surface with posterior endStretch until they tear into twoEach half regenerates lost parts
Class Trematoda
6,000 speciesParasitic - both endoparasites and ectoparasitesLeaf shaped
Structure and Reproduction of Flukes
Parasites1 cm long (oval shaped)Unciliated tegument
2 sucker mouths (anterior and ventral)Cling to hostAnterior sucker sucks in blood, cells and fluids of host
Nervous and Excretory System
Turbellarian likeReproductionComplex reproductive life cycleHermaphroditicLong coiled uterus (stores eggs (10,000+)Eggs released through genital pore -> larvae
Life Cycle
Adults live in sheep liver and gall bladder where they mate and produce eggsEggs enter intestines ->Eliminated with feces ->Eggs hatch in water ->
Larvae invade snail ->Multiply asexually ->Leave snail and form cysts ->Cysts dormant larvae with hard protective covering
Ingested by sheep ->Hatch in digestive tract ->Bore through intestines into blood ->Mature and reproduce in liver
Schistosomiasis
Blood fluke - schistosomaInfects 200-300 million people (asia, africa, and so. America)Around lakes and riversSpread via irrigation ditches and reservoirs
Adults live in human bloodstreamEggs lodge in veins, lungs, intestines, bladder, and liverBlock blood vesselsCause internal bleeding and tissue decay
Class Cestoda - Tapeworms
1,500 speciesMost parasitic (7 in humans)Adapted for parasitic lifeTough outer tegument
Hooks and suckersNervous system extends length of bodyLack sense organs, mouth, and digestive tract
Absorb nutrients directly through heavily folded tegumentKnoblike head with hooks and suckers (scolex)Grows by producing body segments (proglottids)Oldest proglottids at posteriorExcretory system drains proglottids of wasteLife cycle and reproduction
Proglottids contain both male and female reproductive organsCross fertilization is typical between individuals or proglottidsAfter fertilization - proglottids break off and are eliminated with feces
Beef tapeworm
Cattle eat grass with proglottids and eggsLarvae hatchBore through cow's intestine -> blood stream
Burrow into muscle tissue and form cystsHuman eats beef (muscle) -> intestineCysts wall dissolves and bladder worm releasedDevelops into an adult beef tapeworm
Nematoda and Rotifera
PseudocoelomLined on the inside by endoderm and outside by mesodermFluid filledContains organs
Supports the bodyProvides hydrostatic pressure against which muscles can contractServes as a storage area for wastes or eggs and sperm
Phylum Nematoda - Roundworms
10,000 - 80,000 (million) speciesLong slender bodies that taper at both endsFlexible protective cuticle
Digestive tract with two opening (1 way)Anterior mouth Posterior anusSexes distinct in most species Guinea worm female = 120 cmMale = 2.5 cm)
Excretory wastes collected by system of tubesExpelled through excretory pore in posterior endLongitudinal muscles, lack circular muscle -> thrashing motionMost free living
Many plant and animal parasites (enormous economic damage)Humans host 50 speciesMore than 1/3 of humans infected
Ascaris
Found in the intestines of pigs, horses, and humansEnter body in contaminated food or waterHatch in intestinesLarvae bore into the blood stream
Carried to the lungs and throatCoughed up, swallowed, returned to intestinesMature and mateBlock intestines -> death
Larvae in lungs cause respiratory illnessFemales produce 200,000 eggs/day (contain 27 million eggs)Shed through genital poreExit in hosts feces
Ancylostoma and Necator - Hookworms
Ancylostoma - effects 40 million peopleNecator - effects 360 million peopleBoth tropical and semi-tropicalCutting plates hook into intestinal wallFeed on hosts blood -> anemia
Attached to intestinal wall
Migrating larvae
Travels via blood to lungs and throat where swallowed ->Mate in intestines ->Eggs shed in feces ->Hatch on moist soil ->Larvae bore through feet or new host
Trichinella
Causes trichinosisUndercooked pork contaminated with cysts Cysts released larvaeLarvae burrow into wall of small intestines
Mature into adults ->Adults produce larvae ->Pass into blood and form cysts in muscles ->Causing pain and suffering ->
Rotifera
1,750 speciesTransparent, free swimming and microscopicFreshwater and marineCrown of cilia surrounding mouth
Cilia sweep food into mouthLook like rotating wheelFeed on unicellular algae, bacteria, and protozoaMoves through pharynx -> mastaxMastax (muscular organ) chops up food
Hydrostatic pressure inside pseudocoelomNervous system composed of anterior ganglia and two long longitudinal nervesTwo anterior eye spots
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