Phylum Platyhelminthes

Phylum PlatyhelminthesFlatworms

Introduction•# of species: 13,000•Size: wide range, from very small to very long/big•2 type of bodies:▫1) Slender and leaflike▫2) Long and ribbonlike

•2 types of symbiotic relationships▫1. Free living▫2. Parasites▫Adaptations: Organs that help them stick to host

Acoelomate• Lack a coelom or pseudocoelom

Characteristics

• Triploblastic – Organisms with three germ layers ▫1. Endoderm

Def – digestive system comes from this▫2. Ectoderm

Def – nervous system comes from this▫3. Mesoderm

Def – Muscular system and reproductive organs comes from this

Human development (germ layers)

Diploblastic vs. Triploblastic

Characteristics•Symmetry: Bilateral▫Description: True anterior and posterior end

•Body: Flattened •Internal area: One space (with all organs contained

within it)•Head region: Cephalization present▫This is when animals have a well defined head

region

Characteristics•Excretory system/Osmoregulatory▫Main cell type: Flame cell

Description: Bulb shaped

Function: Excretion of wastes Consist of: Large amount of cilia (hair-like

appendages), long canals that run the length of the body

Location: Along the length of body

Flame Cell

Characteristics•Digestive system: Incomplete (mouth, pharnyx

and intestine)•Nervous system▫Description: pair of ganglia (concentrations of

nervous tissue/cells)▫Longitudinal nerve cords▫Bilobed brain▫Ocelli - light sensitive eyespot▫Neurons – sensory, motor and association types

•Muscular system▫Description: layers of circular, diagonal and

longitudinal fibers beneath the epidermis•Epidermis▫Cellular or syncytial (nuclei not separated by cell

membrane)▫Some are ciliated▫Often described as “tegument” rather than a true

epidermis▫Unsure if this arrangement relates to parasitism

Characteristics

•Respiratory system▫NO real respiratory organs

•Circulatory system▫NO real circulatory organs

•Skeletal system▫NO skeletal system

Characteristics•Reproductive System▫Most are monoecious Def: have BOTH male/female reproductive

parts in the SAME individual▫Practice cross-fertilization▫Asexual reproduction by fission▫Regeneration of missing parts

Reproductive SystemHave complex reproductive systems - well developed gonads and accessory reproductive organs

Classification•Kingdom Animalia▫Phylum Platyhelminthes Class Turbellaria

Ex. Planarians Most are free-living (do not rely on host to live) Mostly marine/salt-water Body: soft, flattened carnivorous

Class TurbellariaProstheceraeus

Class TurbellariaDugesia (Ex: Planaria)

Classification•Kingdom Animalia▫Phylum Platyhelminthes

Class Trematoda Ex. Lung, liver and blood flukes Symbiotic relationship: parasitic (live in host and harm

the host) Body: soft, flattened Oral and ventral suckers with no hooks Cause Schistosomiasis▫Description: world’s second most common infectious

disease, causes severe diarrhea

Liver Fluke Life Cycle

Class TrematodaLiver and Blood Flukes

Classification•Kingdom Animalia▫Phylum Platyhelminthes

Class Cestoda Ex. Ribbon worms, tapeworms Symbiotic relationship: parasites OR free-living Body: flat, ribbon-like segmented body Digestion: No digestive tract so dependent on host’s

digestion Tegument covered in microthrix (similar to microvilli

which increases surface area)

Scolex •most specialized structure•Organ of attachment

Class CestodaRibbon Worms

Class CestodaTape Worms

Phylum Nematoda (Nemata)

Roundworms

Origin and Diversity• Location in world: Live everywhere! (oceans,

freshwater, soil, polar regions, tropical zones, mountains)

•Simplest organism to have complete digestive tract ( mouthanus)

•# of species: hundreds of thousands•Symbiotic relationship: free-living and parasitic▫Ex: Pinworms▫Pinworms: can affect crops, domestic animals and humans,

infect 30% of all US children

Characteristics•Symmetry: Bilateral •Unsegmented•Germ layers: Triploblastic (three layers)•Adults have a pseudocoelom ▫Def: closed fluid-filled space acting as a hydrostatic skeleton▫Description: tube-within-a-tube▫Function: aids in circulation and dispersal of nutrients and

movement of organism•Body wall: thickened cuticle▫Description: Hardened protective covering

•Muscle layers: mostly longitudinal

Characteristics•Digestive system▫Complete digestive system▫“Tube within a tube” arrangement▫Food comes in through mouth, leaves through anus

•Circulatory system▫NO true circulatory system/organs▫Hydrostatic skeleton – aids in moving materials

•Respiratory system▫NO true respiratory system/organs

Characteristics• Excretory System▫ Contain a cloaca▫ A cavity that receives excretory and reproductive systems

productsNervous System▫ Cerebral ganglia (nerve ring)▫ Nerve ring is connected anterior and posterior nerves▫ Contain many sensory organs (cilia, bristles, eyespots)

• Reproductive System▫Contain gonads▫Sexes usually separate▫Males are smaller than females

Classification•Kingdom Animalia ▫Phylum Nematoda

•Examples: Pinworm, filarial worms, Ascaris, hookworms

•Can be parasitic▫Cause: Elephantiasis, inflammation of limbs, death, hearing

loss, intestinal irritation/diarrhea

Trichinella spiralis

Ingestion of infected muscle

Taenia soliumPork tapeworm

Trichuris trichiura “whipworm”

Ascaris lumbricoides

Intestinal Roundworm

Dirofilaria immitis

Dracunculus medinensis

Phylum MolluscaMollusks

Origin and Diversity•# of species: 100,000•Classified by shell type, foot structure and

internal body organization•Mollusca, means “soft animal”▫From the Latin word Mollis which means soft

Characteristics•Development▫Torsion – twisting of the body

Causes the mantle to rest over the head Allows for body to face the incoming current (of water), so that they

can stay attached to rock surface

•Symmetry: Bilateral▫Usually have definite head region

•Bodies: Soft▫Some have a protective shell (snail)▫Others may have 2 shells (clams) OR internal shell

(octopus)

Characteristics•Mantle▫Soft outer tissue layer▫Contained on DORSAL body wall▫Secretes a protective shell

•Mantle Cavity▫Forms between the mantle and other body tissues▫Holds respiratory organs (gills OR lungs)

•Muscular Foot▫Used for locomotion

Characteristics•Visceral Mass/ Coelom▫Contains most of mollusk’s internal organs

Includes: heart, gonads, stomach, kidneys•Circulatory System▫Open circulatory system

Blood flows freely over body tissues Blood is enclosed in vessels in some places

▫Vessels are open ended▫Heart has three chambers

Characteristics•Digestive System▫Digestive tract has two openings▫Contains a rasping organ called radula▫Anus empties into mantle

•Respiratory System▫Gas exchange may occur in gills, lungs, mantle or body

surface•Reproductive System▫Most have separate sexes▫All reproduce sexually▫ Internal fertilization: Squid, some snails▫External fertilization: Clams, oysters

Characteristics•Nervous System▫Some have simple system▫Contain sensory organs

Touch, smell, taste, vision▫Eyes are highly developed▫Some contain ganglia: centralized nerve ring

Others have pairs of ganglia ▫Octopus have very complex nervous systems

Characteristics•Movement▫May slide (snail, slug)▫Bury foot and use as a shovel (clams)▫Expel water quickly (squid, octopus)▫Sessile (don’t move)

•Shell▫Made of calcium carbonate

Fossilizes easily Explains rich fossil record

Classification•Kingdom Animalia▫Phylum Mollusca Class Polyplacophora

Marine organisms▫Found on hard sea bottoms/rocky coasts▫Can withstand strong waves▫How? By attaching its strong “foot” to rocks

Breathe? Gills along the side of body Eat? Use? Radula to scrape algae off rocks Some are predatory (hunt others for food) Other: Little use to humans (some can be eaten)

Class Polyplacophora

• Ex. Chitons

Classification•Kingdom Animalia▫Phylum Mollusca

Class Gastropoda Ex. Snails, slugs Body: Coiled in shape Head: Well developed Feeding: Use radula # of species: ▫over 40,000

Class Gastropoda

Classification•Kingdom Animalia▫Phylum Mollusca Class Bivalvia

# of species: 15, 000 Includes: Clams, oysters # of shells: two (Bi = two) Feeding: Filter feeders

Class Bivalvia

Classification•Kingdom Animalia▫Phylum Mollusca Class Cephalopoda

Includes: Squid, octopus Shell: Reduced or absent Head:▫Contains well developed eyes▫Contains arms and tentacles

Ganglia▫Centralized (form a brain)

Class Cephalopoda