BIOL 316 Phylum Platyhelminthes 1

Biology 11 – Kingdom Animalia

Study of the Primitive Worms

Phylum Platyhelminthes: Flatworms

Phylum Nematoda: Roundworms

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Phylum Platyhelminthes – the Flatworms

The Planarians

The Flukes

The Tapeworms

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Importance of the Flatworms to Evolution

Bilateral body plan – left side mirror image of right

Cephalization – development of the head sense organs and nerves concentrated in head region

Centralization of nervous system: Nerve cord accompanies cephalization and bilateral symmetry.

Advanced muscle tissue present;

Primitive excretory system allows removal of metabolic wastes

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Flatworms (Phylum Platyhelminthes)

Definition:

Flatworms are soft, flattened worms that have tissues and internal organ systems.

They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, and cephalization

Flatworms are acoelomates, meaning “without a coelom”

coelom = a fluid-filled body cavity that is lined with mesoderm

mesoderm = middle germ layer that gives rise to muscles, circulatory, reproductive, and excretory systems

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Phylum Platyhelminthes Characteristics

Bilateral symmetry; anterior and posterior ends.

Body flattened Well-developed epidermis

No internal body cavity other than digestive tube (acoelomate)

Parenchyma (connective tissue) fills space between organs.

Incomplete digestive system Still one opening This critter eats and poops out of its

mouth – mmmm, pass the popcorn

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Cross Section of a Flatworm

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Advantage of Being Flat

Surface area to volume ratio is important for organisms.

Many substances enter and leave through body surface.

Faster absorption and release of wastes

3mm

3mm3mm

Volume = 3 x 3 x 3 = 27mm2

Area = 6(3 x 3) = 54mm3

9mm

3mm

1mm

Volume = 9 x 3 x 1 = 27mm2

Area = 2(9 x 1) + 2(3 x 1) + 2(3x9) = 78mm3

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Nutrition and Digestion

Typical digestive system includes a mouth, a pharynx, and an intestine.

Parasitic Tapeworms and Flukes lack a digestive system Parasitic flatworms, such as the

Tapeworm absorb molecules from host. Free living flatworms (Planarians) are

carnivorous; suck prey into pharynx with mouth. Undigested food goes out mouth. Yes,

folks, they eat and excrete out the same hole

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Flatworm Respiratory, Circulatory, and Excretory System

Lack circulatory, respiratory, and excretory systems.

Flatworms rely on diffusion to transport oxygen and nutrients throughout the body, to remove CO2 and other wastes

Some flatworms have flame cells – specialized cells that remove excess water and metabolic wastes

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Nervous System and Sense Organs

Have a nerve-net.

Most have more complex system.

Cerebral ganglion = primitive brain coordinates impulses.

“Ladder” system carries impulses throughout body

Many sense organs present Eyespots Chemoreceptors, touch sensors

and rheoreceptors (sense direction) also common

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Note: Free-living vs. Parasitic

Free-living (eg Planarians) have well developed digestive and nervous systems to seek-out and process food

Parasitic Tapeworms – rely on host’s digestive system to process food, which absorb. No need for advancement of nervous system – not needed.

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Reproduction – in Free-living Flatwormssuch as Planarians

May reproduce sexually or asexually

Asexual: Binary fission – split in two

Sexual: Both sexes present in same

flatworm (hermaphrodites). Fertilization internal, eggs

produced Embryos emerge as juveniles

resembling adults.

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Reproduction in theTapeworm!

Lack digestive system

Sucker and hooks on anterior end for attachment

Neck produces new segments Called proglottids

Each proglottid contains male and female gonads

Reproductive output high Many proglottids per worm Many eggs per proglottid

Groups of Flatworms

Turbellarians

Free-living, e.g. planarian Flukes (Trematoda)

Parasites Tapeworms (Cestoda)

Parasites

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Tapeworm - Life Cycle

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Flukes -- Life Cycle of a Liver Fluke

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The Coelom or Body Cavity Advances

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Another Look at the Coelom

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Phylum Nematoda (Roundworms)

Definition: Roundworms are unsegmented worms that have

pseudocoeloms and digestive systems with two openings – a mouth and an anus

Pseudocoelom = “false coelom” Is a body cavity between the endoderm and mesoderm tissues,

partially lined with mesoderm tissue

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Form and Function in Roundworms

Feeding: free-living carnivores; or eat algae, fungi, decaying organic matter

Respiration: gases diffuse through body walls Circulation: no internal transport system

diffusion Excretion: metabolic wastes diffuse through body

walls

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Form and Function in Roundworms

Response: ganglia from the head and run through length of body; sense organs to detect chemicals of other organisms

Movement: muscles and fluid of the pseudocoelom function as a hydrostatic skeleton; allows movement (swimming or pushing through soil)

Reproduction: sexual reproduction; internal fertilization, were male deposits sperm inside the female’s reproductive tract

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Roundworm Ecological Roles

Omnivores that catch and eat algae, fungi, decaying matter

Recyclers Parasites of Plants – eg. The Golden

Nematode attacks potato crops, causing severe devastation

Parasites of animals

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Ascaris – Parasitic Roundworm of Pigs and Humans

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Unfortunately, they can Grow quite Big!

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Parasites: Your Pet's Enemies

Tiny parasites that pose a gigantic threat

  Heart worms inside the dog's heart, can grow to a length of 14".

What they do:Restrict blood flow and cause organ damage. Symptoms include coughing. labored breathing, heart failure. Untreated, heart worm disease can kill a dog. Death may occur within 72 hours.

How they spread:Transmitted by over 70 species of mosquitoes. Virtually all dogs are at risk.

Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.

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Adult roundworms live in the dog's small intestine.

What they do:Cause diarrhea, vomiting, stunted growth, rough coat, bloated belly.

How they spread:Almost all puppies get roundworms from their mothers. Dogs can also pick up roundworms from the soil.

Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.

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Enlarged hook worm mouth showing 'teeth'.

What they do:Attach to the dog's intestinal lining, leaving

bleeding internal wounds. Cause blood loss, anemia, and diarrhea. As few as 100 hook

worms can kill a puppy.

How they spread:Eggs pass through the feces of an infected

dog into the soil where they are easily swallowed or can penetrate through a dog's

feet.

Defending against them: Once a month prevention is recommended, contact your

local veterinarian for advice.

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Symptoms:

Larvae digested enter bloodstream

and burrow into organs, causing

absolutely horrendous pain

and in some cases death.

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Filarial (threadlike worms) are nematodes that may block the passage of Fluids in the Body

Disease: Elephantitis

The disease is caused by parasitic worms, including Wuchereria bancrofti, Brugia malayi, and B. timori, all transmitted by mosquitoes. Lymphatic filariasis currently affects 120 million people worldwide, and 40 million

Blocks Lymphatic nodes which drain fluid to and from the blood.

Tropics, Africa and Asia

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Phylum Annelida (Earthworms)

Annelida annellus, meaning “little ring”

Definition: Annelids are worms with segmented bodies.

They have a true coelom that is lined with tissue derived from mesoderm.

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Body Plan

The body of an annelid is divided into segments separated by septa (singular: septum) Septum – internal walls between each segment Most segments contain the same organs (eyes,

antennae, sense), while others are specialized Most segments have bristles called setae

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Feeding and Digestion

Annelids may be filter feeders or predators (carnivorous)

Annelids use their pharynx (with jaws) to bring food into the esophagus. The food then go into the crop (food storage) and then to the gizzard (food is ground up). Then food is absorbed in the intestine.

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Circulation

Annelids have a closed circulatory system. Closed circulatory system:

Blood is contained in a network of blood vessels

•Blood circulates through a dorsal vessel and a ventral vessel, and smaller blood vessels through each segment

•Dorsal vessel helps pump blood

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Respiration

Annelids can respire through: Gills (worms that live in water) Diffusion through skin (earthworms)

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Excretion

Digestive waste passes out anus

Metabolic waste is filtered out by nephridia

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Response

Most annelids have a well-developed nervous system with a brain and nerve cords

Other sense organs: Sense receptors, chemical receptors, sensors

that detect gravity

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Movement

Hydrostatic skeleton Contraction of longitudinal and circular muscles

Annelids can burrow, use setae, or parapodia (paddlelike appendages for swimming or crawling)

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Reproduction

Sexual reproduction May have separate sexes and external fertilization

OR Annelids are hermaphrodites and exchange sperm with

another worm Two worms attach, exchange sperm, and store it in

sacs A clitellum (a thick band) secretes a mucus ring

where the egg and sperm are released and fertilization takes place inside this ring

The ring falls off the worm and forms a cocoon, where the eggs will hatch

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Ewwwwwwwwwwwwwwwwwwwwwwwww!

Ah, but they are sooooooo in love, don’t you think?

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Class Oligochaeta

Earthworms Streamlined bodies, few setae, live in soil or water

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Class Hirudinea

• Leeches

• External parasites that suck blood and body fluids of host

• Medical uses: reduce swelling, helps blood clotting

• Have suckers at one or both ends for attachment. Produce a chemical in saliva called HIRUDIN, which is an anti-coagulant

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Leech Anatomy 101

Mmmm – lunch!

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Leeches Used in Medicine

Successful reattachment

of severed ear, as blood

continued to flow and carry nutrients to

the damaged region

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Class Polychaeta

Sandworms, blood worms Marine annelids with parapodia (paired paddlelike

appendages)

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Ecology of Annelids

Annelids are important for our environment because they: Burrow through the soil, aerating and mixing it Decompose plant matter Food source (for birds, moles, toads, snakes,

etc.)