VS.

http://upload.wikimedia.org/wikipedia/commons/d/d2/A-ferox_digenean1.jpg

Flatworms demonstrate a bilaterally symmetrical body plan

They are dorsoventrally flattened and lack a skeleton

They have a highly branched gastrovascular cavity .

There is only one opening which serves the function of both the mouth and anus (not excretion)

They have three germ layers: Ectoderm: Outside Endoderm: Inside Mesoderm: Middle layer of tissue between

the ectoderm and the endoderm

Though Flatworms have three germ layers they are acoelomates and have no body cavity

Flatworms do have true organs and primitive organ systems that are used for digestion and excretion

• Flatworms are also the most primitive organisms to show cephalization.

• The head region of Flatworms contains a concentration of nerve tissue called ganglia (singular=ganglion) that resembles a primitive brain.

Cephalization

They have two nerve cords that run from the ganglia in the head region along the ventral side of the worm to the tale region

In the head region of Flatworms are two eye-spots

They also have lobes on the side of their head called auricles

Auricles

Flatworms have a mouth/anus which is connected to the gastrovascular system through a long muscular pharynx.

Small invertebrates or the remains of dead animals are taken into the mouth/anus by the muscular pharynx

The food is then digested in the highly branched gastrovascular cavity

The nutrients moves from the gut into the body cells by diffusion

Respiration occurs by diffusion

Nutrients and oxygen in the gut are simply absorbed into the body cells by the process of diffusion

Most undigested food is released directly out of the anus/mouth: Pharynx

A flame cell is a specialized excretory cell

Flame cells function like a kidney, removing waste materials.

The beating of cilia resembles a flame, giving the cell its name.

Flatworms are able to sense and respond to at least three forms of stimuli: Sense and respond to light: The eye-spots

can detect light and allow the Flatworms to respond to it

Sense and respond to chemicals: Pits on the side of their head regions can sense chemicals in the water and allow the Flatworms to respond (like “smelling”)

Sense and respond to touch: The auricles on either side of the head region can sense touch and allow the Flatworms to respond

The ganglia in the head region relay messages from the sensory organs down the nerve cords to the rest of the body. The nerve cords can control muscles in the body which allow the Flatworms to move or eat.

Auricles

The flatworms move across a surface using cilia on their ventral surface

They can also move by contracting circular and longitudinal muscles that lay just below the ectoderm. These muscles are controlled by the nerve cords.

Asexual Reproduction: Flatworms can asexually reproduce

through a process called fission. The anterior and posterior ends hold a surface and the midsection constricts. This results in two new flatworms, one from the anterior end of the original flatworm and the other from the posterior end of the original flatworm.

• Flatworms can also regenerate parts they have lost.

Sexual Reproduction: Flatworms are hermaphroditic After two flatworms have copulated they

release sacs of fertilized eggs and attach them to a surface

The tapeworm has an anterior end called a scolex with complicated hooks for attaching to the intestines of its host.

The tapeworm does not have a mouth or digestive system. Instead they bath in the pre-digested fluids of their host and absorb nutrients directly into their body cells

Proglottids

Hooks

Scolex

Suckers

Phylum Phylum PlatyPlatyhelmintheshelminthes

The “flat” “worms”The “flat” “worms”

www.onacd.ca

4 Classes of Phylum Platyhelminthes4 Classes of Phylum Platyhelminthes

TREMATODA – flukes CESTODA – tapeworms

MONOGENEA – small, parasitic flatworms

TURBELLARIA - small, free-living flatworms

Identifying Characteristics of the Identifying Characteristics of the Phylum PlatyhelminthesPhylum Platyhelminthes

Acoelomate Exhibit bilateral symmetry Have a bilateral nervous system with cephalization at

the head end. Some species exhibit eyespots sensitive to light

Possess a Gastrovascular Cavity (GVC) and primitive organ systems for digestion and excretion

Do not have a circulatory or respiratory system but do take in O2 through their body surface (integumentary exchange)

Hermaphroditic : can reproduce sexually (do not self fertilize) or asexually by regeneration

Are motile and utilize an undulation form of motion Found in marine, freshwater and damp terrestrial

habitats

Free-living FlatwormsFree-living FlatwormsPlanaria : Planaria : Dugesia tigrinaDugesia tigrina

Freshwater, free-living flatworm Moves by beating cilia and gliding

on a film of mucus 3-12mm in size Have a single opening to their

stomachs in the middle of their bodies

Possesses two eyespots (ocelli) that are sensitive to light

Carnivorous (eat daphnia and midges)

Common to most parts of the world

Reproduce by asexual reproduction and capable of regeneration (see next slide)

Planaria RegenerationPlanaria Regeneration

Planarians will spontaneously detach the tail end of their bodies and each half will regenerate into a full size flatworm

Planarians can be cut either transversally (shown above) or dorsally and most will regenerate into a full size worm

Super Cool Fact: the smallest piece of planarian to ever regenerate in a lab into a new planarian was 1/279th of a planarian! That’s approximately 10,000 cells!

Parasitic FlatwormsParasitic FlatwormsThe pork tapeworm – The pork tapeworm – Taenia soliumTaenia solium

Infects pigs and humans Lives in the intestine of its host

and passes eggs through the feces Highly adapted to constant

internal environments Lacks sensory organs,

coordination for mobility and a digestive system (more room for reproductive structures!)

Have a modified epidermis “tegument” which protects against the digestive enzymes and the immune systems of the host

Can reach 7m in length in humans! Are flat and long which maximizes

absorption of nutrients from the host

The tapeworm “up close and personal….”The tapeworm “up close and personal….” The head end has a

scolex with four suckers (two seen here) that help it attach to the intestine of its host

The body is separated into sections called “proglottids” that house highly developed reproductive systems (darkened areas) capable of producing hundreds of thousands of eggs and sperm

Life cycle of the Pork TapewormLife cycle of the Pork Tapeworm

Super cool Flatworm FactSuper cool Flatworm Fact• the largest tapeworm ever reported the largest tapeworm ever reported

was in a sperm whale and was 30 was in a sperm whale and was 30 meters in length!meters in length!

Tapeworm Scolex