Phylum
Platyhelminthes
Flatworms
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
Diploblastic vs. Triploblastic
• 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)
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 System
Have 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
Turbellaria
Prostheceraeus
Class Turbellaria
Dugesia (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 Trematoda
Liver 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 Cestoda
Ribbon Worms
Class Cestoda
Tape 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
( mouthanus)
• # 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
products
Nervous 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 solium
Pork tapeworm
Trichuris trichiura
“whipworm”
Ascaris lumbricoides
Intestinal
Roundworm
Dirofilaria immitis
Dracunculus medinensis
Phylum
Mollusca
Mollusks
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