Flatworms and Roundworms
Porifera
Ctenophora
Eumetazoa
Hemichordata
Echinodermata
invertebrates
Chordata
Platyhelminthes
Rotifera
Ectoprocta
Brachiopoda
Mollusca
Annelida
Ecdysozoa
Nematoda
Arthropoda
protostomes
Lophotrochozoa
•Bilateral at some point
•Usually cephalized
•Triploblastic development
Acoela
Deuterostomia
True Tissues
Cnidaria
Bilateria
Single
common
animal
ancestor
Metazoa
ANCESTRAL
PROTIST
Terms of location (for bilateral organsims)
FLATWORMS (phylum platyhelminthes)
• Flattened body plan
– Puts all cells close to ext. env. or GVC
– No need for respiratory or circulatory systems
– Gas exchange across ext. surface and gastrodermis
•
•
•
•
Free living
Parasitic forms
Aceolomates (no body cavity)
Most belong to Rhabditophora
Digestive System
• Gastrovascular Cavity—incomplete digestive
system
• Highly branched (diverticula)
• Functions
– Digestive chamber
• most digestion occurs extracellularly
– distributes nutrients
Excretory System & Water Balance
•
•
•
•
Protonephridia
flame bulbs  internal  external env. through pores
In freshwater species for maintaining water balance
Some parasitic flatworms are isotonic with host and
protonephridia eliminate nitrogenous waste
• Interstitial fluid  cap cell of flame bulb 
eliminated via ducts and pores
• Nervous System:
– Dual ventral nerve cords
– “brain of ganglia”
CNS
• Reproduction;
– Mostly cross fertilizing hermaphrodites
– Some parasitic forms are dioecious
Planaria
free living Rabditophora
•
•
•
•
FREE LIVING RABDITOPHORA
predators and scavengers
move w/ ventral cilia & mucus
Sense Organs & NS
– Photoreceptors (eyes)
– Lateral flaps (auricles) that are chemoreceptor's
Trematodes
• Intermediate and final (ultimate) host
– Blood flukes (schistosoma), liver flukes
• epicuticle of proteins and lipids instead of epidermis
– digestion by the digestive enzyme in hosts
Schistosoma:
unique among trematodes; are dioecious with distinct sexual dimorphism
Large male that surrounds female
Female is enclosed within the males gynacophoric canal for entire life of worms where they
reproduce sexually.
Figure 33.11
Male
Human
host
Female
1 mm
Mature flukes
Motile
larva
Ciliated
larva
Snail host
Tapeworms
•
•
•
•
•
Mostly inside vertebrates
Scollex for attachment
No GVC; direct absorption of nutrients
Proglottids = reproductive segments
Reproduction is usually sexual between proglottids of
adjacent individuals
Tapeworms
Roundworms (phylum Nematoda)
Bilateria-protostoma-ecdysozoa
•
•
•
•
Cyclinderical shaped bodies that taper to tips at both ends
Psuedocoel
Usually dioecious
Free living in soil, fresh, and salt water
– decomposers: important ecological role as decomposers
• Many important parasitic forms
– Parasitize crop plants
– Parasitize humans (~50 species)
• e.g., trhinella spiralis—trichinoisis
– Parasitize non-human animals
– Parasitic forms manipulate host cells
BODY COVERING
• Cuticle (collagen based) that must be shed
– Ecdysis/molting
GAS AND WASTE EXCAHNGE
• Directly across body wall (gas & nitrogenous
wastes)
• Some species w/ glands to excrete salt
No circulatory system
• Nutrients transported by fluid in psuedocoel.
Digestive System
• Complete digestive tract (alimentary canal)
• Continuous feeding
• Specialized regions/organs
– Mouth, sucking pharynx, intestines, rectum, anus
– Contents propelled by body movements
Nervous system
• 4 nerve cords + “brain” of neuron cluster
surrounding pharynx.
• ventral nerve largest
Muscles:
• Longitudinal muscles only
• Psuedocoel acts as a hydrostatic skeleton
chistosomiasis, also known as bilharzia, snail fever,
nd Katayama fever
chistosomiasis affects almost 210 million people
worldwide,[5] and an estimated 12,000[6] to 200,000 people
ie from it a year.[7] The disease is most commonly found
n Africa, as well as Asia and South America.[3] Around 700
million people, in more than 70 countries, live in areas
where the disease is common.[7][8] Schistosomiasis is second
nly tomalaria, as a parasitic disease with the greatest
conomic impact.[9] It is classified as a neglected tropical
isease.[10]