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