Flatworms, Roundworms, and Rotifers
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Flatworms, Roundworms, and Rotifers. Germ Layers. Layers of cells that originate in the developing embryo and become specific structures Ectoderm - outer Mesoderm - middle Endoderm - inner. Body Plans. Acoelomate. Without a coelom 2 germ layers Ectoderm and endoderm

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Flatworms, Roundworms, and Rotifers

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Flatworms, Roundworms, and Rotifers


Germ Layers

  • Layers of cells that originate in the developing embryo and become specific structures

  • Ectoderm - outer

  • Mesoderm - middle

  • Endoderm - inner


Body Plans

Acoelomate

  • Without a coelom

  • 2 germ layers

  • Ectoderm and endoderm

  • Not separated by a cavity

  • Least complex body plan

  • Sponges and cnidarians


3 Layer Acoelomate

  • 3 germ layers

  • Endoderm, mesoderm and ectoderm

  • Not separated by a cavity

  • Flatworms


Pseudocoelomate

  • Pseudocoelom

  • Cavity formed between mesoderm and endoderm

  • Roundworms and rotifers


Coelomate

  • Cavity developed within the mesoderm

  • Most complex body plan

  • Mollusks, annelids, arthropods, echinoderms, and chordates


Phylum Platyhelminthes - Flatworms

  • 13,000 species

  • Bilaterally symmetrical

  • Cephalization

  • 3 classes (Turbellaria, Trematoda, and Cestoda)

  • Trematodes and cestodes parasitic

  • Parasites live in or on other organisms (host)


Parasitic Flatworms

  • Originated from free living

  • Some organs modified for parasitism

  • Lack mouths

  • Well developed digestive system


  • Hooks or suckers

  • Tegument- thick covering of cells

  • Cuticle- nonliving layer secreted by epidermis


Class Turbellaria

  • 3000 species

  • Most marine

  • Ex. Planaria (fresh water)


Planaria

External anatomy

  • Anterior end spade shaped

  • Posterior end tapered

  • Body covered with cilia


Movement

  • Move by undulative motion or

  • Laying down mucus layer and beating cilia


Digestion and Excretion

  • Scavenger (carrion)

  • Predator (small prey)


Digestion

  • Muscular pharynx extended out of mouth

  • Food sucked in

  • Passed into intestines (branched)

  • Nutrients absorbed through intestinal wall or phagocytosis

  • Undigested food excreted through pharynx and mouth


Excretion

  • Chemical wastes and excess water eliminated by network of ducts (pores and canals)

  • Contains flame cells

  • Flame cells enclose a tuft of beating cilia

  • Cilia moves wastes into the ducts ->

  • Excretory pores -> out


Nervous Control

  • Organized and cephalized

  • Sense light intensity and direction

  • Two anterior eyespots (photosensitive cells)

  • Touch, taste, and smell receptors


  • Two anterior ganglia (clusters of nerves) -> simple brain

  • Two longitudinal nerves connected by transverse nerves

  • Capable of simple "learning"

  • Memory stored chemically


Reproduction

  • Hermaphrodites

  • Sexual reproduction

  • Simultaneous fertilization

  • Protective encapsulated eggs stick to rock

  • Hatch 2-3 weeks


  • Asexual (summer)

  • Attach to rock surface with posterior end

  • Stretch until they tear into two

  • Each half regenerates lost parts


Class Trematoda

  • 6,000 species

  • Parasitic - both endoparasites and ectoparasites

  • Leaf shaped


Structure and Reproduction of Flukes

  • Parasites

  • 1 cm long (oval shaped)

  • Unciliated tegument


  • 2 sucker mouths (anterior and ventral)

  • Cling to host

  • Anterior sucker sucks in blood, cells and fluids of host


Nervous and Excretory System

  • Turbellarian like

  • Reproduction

  • Complex reproductive life cycle

  • Hermaphroditic

  • Long 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 eggs

  • Eggs 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 - schistosoma

  • Infects 200-300 million people (asia, africa, and so. America)

  • Around lakes and rivers

  • Spread via irrigation ditches and reservoirs


  • Adults live in human bloodstream

  • Eggs lodge in veins, lungs, intestines, bladder, and liver

  • Block blood vessels

  • Cause internal bleeding and tissue decay


Class Cestoda - Tapeworms

  • 1,500 species

  • Most parasitic (7 in humans)

  • Adapted for parasitic life

  • Tough outer tegument


  • Hooks and suckers

  • Nervous system extends length of body

  • Lack sense organs, mouth, and digestive tract


  • Absorb nutrients directly through heavily folded tegument

  • Knoblike head with hooks and suckers (scolex)

  • Grows by producing body segments (proglottids)

  • Oldest proglottids at posterior

  • Excretory system drains proglottids of waste

  • Life cycle and reproduction


  • Proglottids contain both male and female reproductive organs

  • Cross fertilization is typical between individuals or proglottids

  • After fertilization - proglottids break off and are eliminated with feces


Beef tapeworm

  • Cattle eat grass with proglottids and eggs

  • Larvae hatch

  • Bore through cow's intestine -> blood stream


  • Burrow into muscle tissue and form cysts

  • Human eats beef (muscle) -> intestine

  • Cysts wall dissolves and bladder worm released

  • Develops into an adult beef tapeworm


Nematoda and Rotifera

  • Pseudocoelom

  • Lined on the inside by endoderm and outside by mesoderm

  • Fluid filled

  • Contains organs


  • Supports the body

  • Provides hydrostatic pressure against which muscles can contract

  • Serves as a storage area for wastes or eggs and sperm


Phylum Nematoda - Roundworms

  • 10,000 - 80,000 (million) species

  • Long slender bodies that taper at both ends

  • Flexible protective cuticle


  • Digestive tract with two opening (1 way)

  • Anterior mouth

  • Posterior anus

  • Sexes distinct in most species

  • Guinea worm female = 120 cm

  • Male = 2.5 cm)


  • Excretory wastes collected by system of tubes

  • Expelled through excretory pore in posterior end

  • Longitudinal muscles, lack circular muscle -> thrashing motion

  • Most free living


  • Many plant and animal parasites (enormous economic damage)

  • Humans host 50 species

  • More than 1/3 of humans infected


Ascaris

  • Found in the intestines of pigs, horses, and humans

  • Enter body in contaminated food or water

  • Hatch in intestines

  • Larvae bore into the blood stream


  • Carried to the lungs and throat

  • Coughed up, swallowed, returned to intestines

  • Mature and mate

  • Block intestines -> death


  • Larvae in lungs cause respiratory illness

  • Females produce 200,000 eggs/day (contain 27 million eggs)

  • Shed through genital pore

  • Exit in hosts feces


Ancylostoma and Necator - Hookworms

  • Ancylostoma - effects 40 million people

  • Necator - effects 360 million people

  • Both tropical and semi-tropical

  • Cutting plates hook into intestinal wall

  • Feed 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 trichinosis

  • Undercooked pork contaminated with cysts

  • Cysts released larvae

  • Larvae 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 species

  • Transparent, free swimming and microscopic

  • Freshwater and marine

  • Crown of cilia surrounding mouth


  • Cilia sweep food into mouth

  • Look like rotating wheel

  • Feed on unicellular algae, bacteria, and protozoa

  • Moves through pharynx -> mastax

  • Mastax (muscular organ) chops up food


  • Hydrostatic pressure inside pseudocoelom

  • Nervous system composed of anterior ganglia and two long longitudinal nerves

  • Two anterior eye spots


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