Unit 4 - Phylums Platyhelminthes and Nematoda Flatworms and Roundworms

Unit 4 - Phylums Platyhelminthes and Nematoda

Flatworms and Roundworms

Phylum Platyhelminthes

• Largest group of acoelomate (no body cavity) worms

• Flatworms with middle tissue layer- mesodermmesoderm• Tissues organized into organs• Bilaterally symmetrical and flat• Cells lie close to exterior enabling efficient diffusion

of oxygen and carbon dioxide• Highly branched gastrovascular cavity runs close to

all tissues giving cells ready access to food• No respiratory or circulatory systems

Coelom – Body Cavity

• The coelom usually performs multiple functions, including one or more of the following:

Provides room for organ developmentSurfaces for diffusion of gases, nutrients,

and wastesStorageHydrostatic support

Phylum Platyhelmithes

• Flatworms– Liver Flukes, Planaria and tapeworms– Marine flatworms– Characteristics:

• Ribbon-like bodies• Bilateral symmetry• Branched digestive system• No skeleton• Asexual (fission); Hermaphrodites (sexual)• Free movement• Skin breathing


• Class Turbellaria

– Most free-living; marine

• Dugesia- Freshwater planarians

– Digestion- Nutrients absorbed by intestinal wall and waste goes out through mouth

• Muscular pharynx comes out of central mouth to feed


• Reproduction- Mostly asexual by attaching posterior end to stationary object and pulling into two

• Hermaphrodites can reproduce sexually• Nervous system: Brain, two nerve cords, and

light-sensitive eye spots• Water balance- Water continually enters by

osmosis • Flame cells with cilia draw water to the outside


• Marine flatworm


Planarian


• Many parasitic– Endoparasite- internal– Ectoparasite- external

• Class Cestoidea• Subclass Eucestoda- Parasitic flatworms

(tapeworms)– Suckers and hooks on scolex (head) attach to

walls of intestines and food absorbed from host’s intestines directly through the tapeworm’s skin


• String of rectangular body sections (proglottids)

• Each proglottid is a reproductive unit

• Added continually through life

• May grow up to 12 m (40 ft.) long


• Most occur in vertebrates

• Dozen types in humans

• Taenia saginata- Beef tapeworm– Live in cow muscles in cysts– High temp. kills larvae– Subclass Cestodaria

• Body not subdidvided into proglottids

• Larvae in crustaceans; adults in fish

Scolex Examples

Phylum Platyhelmithes

Proglottid – reproductive structure


• Largest flatworm class, Trematoda– Parasitic worms called flukesflukes– Endoparasites Endoparasites or ectoparasitesectoparasites

• Subclass Aspidogastrea Subclass Aspidogastrea (Aspidobothrea)- Endoparasite of (Aspidobothrea)- Endoparasite of mollusksmollusks

• Subclass Digenea- Endoparasites of Subclass Digenea- Endoparasites of vertebratesvertebrates


• Tegument- thick protective covering prevents them from being digested

• Take nourishment directly from hosts

• Use suckers to attach and the muscular pharynx to suck nourishment from host’s body fluids


• Complex life cycles involve more than one host• Ex: Schistosoma- Responsible for schistosomiasis• From contaminated water• Larvae bore into host skin into blood vessels of

intestines• Block vessels causing bleeding and damage to

liver• Snail is intermediate host


• Class Monogenea –

– Monogenetic flukes

– One life cycle in one host

– Mostly ectoparasites on vertebrates


Liver fluke

•

Phylum Nematoda

• Roundworms- have a pseudopseudocoelomcoelom (body cavity between endoderm & mesoderm)– Fluid movement serves as circulatory and gas

exchange system – Fluid also distributes nutrients to cells from

digestive system

Phylum Nematoda

• Long, cylindrical bodies

• Majority microscopic and free-living

• One-way digestive system

• Thick, flexible epidermis protects and gives shape

• Layer of muscle underneath pulls at epidermis and pseudocoelem for whip-like movement

Phylum Nematoda

• Roundworms– Ascaris, Trichinella and hookworms

– Characteristics:• Flattened bodies

• Bilateral symmetry

• Many are parasites

• Fluid-filled body cavity called a pseudocoelem

• Digestive tube

• No skeleton

• Sexual reproduction (Internal fertilization)– Sperm is amoeboid

• Free movement

• Skin breathing

Phylum Nematoda• Class Secernentea (Phasmidea)- Phasmids (sensory structures) in tail

– Ascaris, Enterobius, Rhabditis, Turbutrix, Necator, and Wuchereria

• Class Adenophorea (Aphasmidia)- No phasmids– Dioctophyme, Trichinella, Trichuris

• 50 species are parasitic• Plant parasites feed on living plant cells in all parts of plant, causing

wilting and withering• 14 species affect humans

– Ex: Enterobius (pinworms), Ascaris lumbricoides, Trichinella spiralis, Necator (hookworms)

Phylum Nematoda

• Trichinella infects pigs and causes trichinosistrichinosis (serious disease caused by eating undercooked pork)

• Necator live in warm, moist soils of the tropics– Hookworm larvae enter

bloodstream through soles of feet

Phylum Nematoda

• Ascaris – Carried in human waste– After ingestion, eggs hatch

into larvae in intestines– Larvae bore through blood

vessels, enter blood stream and then lungs (causes respiratory distress)

– Larvae may enter gallbladder or pancreas causing blockages

– Return to intestines to mature and mate

– May grow up to 1 ft. in length

Phylum Nematoda

• Ascaris

• Trichinella

Trichinosis

• Trichinella spiralis is found in pork

• Trichinosis is a disease caused by the Trichinella worm.– Eggs hatch in the host’s gut– Symptoms:

• Diarrhea• Fever• Muscle pain• Death

Common Parasitic Roundworms • Hookworms attach to

the inside of the digestive tract

• Often found in pets

• Pinworms- most common

• Heartworms- transmitted to dogs by mosquitos

• Filarial worms- live in blood where they block blood vessels or lymph vessels causing severe swelling (Elephantitis)

• Guinea worm- Ingested with contaminated water– Cause dracunculiasis

– Only found when exiting skin

– Found in Africa, India and Pakistan

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Unit 4 - Phylums Platyhelminthes and Nematoda Flatworms and Roundworms