Phylum Platyhelminthes and Friends

1
Phylum Platyhelminthes and Friends

• Characteristics
• Acoelomate
• Bilateral
• Sense organs on head
• Triploblastic (3 germ layers)
• Protostomes

2
Platyhelminthes

• Characteristics
• Mesodermal parenchyma
• 1 mm to many meters
• Some free-living some parasitic (may have
  several hosts)

3
4 Classes

• Turbellaria
• Trematoda
• Monogenea
• Cestoda

4
Form and Function

• Turbellarians
• Ciliated epidermal cells (some syncytial)
• Basement membrane
• Muscle fibers
• Rhabdites
• Dual-gland adhesive organs
• Parenchyma

5
Form and Function, cont.

• Non-turbellarians (Neodermata)
• No cilia
• Tegument

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Nutrition/Digestion

• Cestodes
• No digestive system
• Adsorb nutrients from host

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Nutrition/Digestion, cont.

• Othersmouth, pharynx, intestine
• Planaria
• Carnivores
• Rhabdites secrete mucous
• Extends proboscis
• Monogeneans Trematodes
• Feed on host cells, debris, body fluids

8
Excretion/Osmoregulation

• Protonephridia with flame cells
• Ions and molecules resorbed as needed
• Most metabolic wastes removed by diffusion
• Canal and bladder systems vary among classes

9
Nervous System

• Subepidermal nerve plexus (net) or
• Net plus nerve cords under muscle layer
• Neuron types
• Sensory
• Motor
• Association

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Sense Organs

• Cephalization aids locomotion
• Ocelli (eyespots)
• Tactile cells
• Chemoreceptive cells
• Statocysts in some
• Rheoreceptors (water currents)

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Reproduction/Regeneration

• Fission
• Sexual reproduction
• Most monoecious
• Cross-fertilize
• Most egg yolk produced by vitellaria
• Eggs (with yolk) attached to plants
• Most direct metamorphosis
• Parasitic larvae ciliated or hatch after being
  eaten

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Class Turbellaria

• Most free-living, carnivorous
• 5 mm to 50 cm
• Locomotion
• Ciliated epithelium
• Rhabdites (slime track)
• Regeneration
• Polarity retained

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2 Orders

• Orders determined based on form of gut and
  pharynx
• Tricladida
• Simple (3 branches) or no gut
• Simple pharynx when present
• Polycladida
• Highly branched gut
• Folded pharynx

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Class Trematoda

• Parasitic flukes
• Most endoparasites of vertebrates
• Adaptations
• Penetration glands
• Produce cysts
• Suckers
• Increased reproductive capacity
• Poorly developed sense organs

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Subclass Digenea

• Mollusc (first intermediate host)
• Vertebrate (definitive host)
• Serious parasites of humans and domestic animals
• Examples
• Liver fluke
• Blood fluke
• Lung fluke

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Sheep Liver Fluke

• Fasciola hepatica
• Life cycle
• Eggs
• Miracidia hatch, penetrate snails
• Sporocysts
• Rediae
• Cercaria encyst on vegetation
• Sheep eat
• Young fluke

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Human Liver Fluke

• Clonorchis sinensis
• China, Japan, Southeast Asia
• Also infects cats, dogs, pigs
• 10-20 mm

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Clonorchis Life Cycle

• Eggs to miracidia to snails to sporocysts to
  rediae to cercaria to bore and encyst in fish
  (Cyprinidae)
• Mammals eat raw fish, young flukes to liver

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Clonorchis Life Cycle
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Blood Flukes

• Schistosoma
• 200 million people infected
• Africa, South America, West Indies, Middle and
  Far East
• Dioecious
• Schistosome dermatitis
• Swimmers itch

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Schistosoma Life Cycle
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Lung Flukes

• Paragonimus westermani
• Humans, pigs, rodents
• Life cycle
• Eggs coughed up, swallowed, eliminated in feces
• Miricidia to snail to sporocysts to rediae to
  cercariae
• Freshwater crabs eat
• Humans eat raw

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Class Monogenea

• Most external parasites of fish
• Some in bladders of frogs, turtles
• Posterior attachment organ with hooks, suckers,
  clamps (opisthaptor)
• Monoecious

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Monogenean Life Cycle

• Egg
• Ciliated larva (oncomiracidium) with posterior
  hooks
• Attaches to host

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Class Cestoda

• Tapeworms
• Segmented shape (proglottids)
• Monoecious
• Scolex (head portion with suckers, hooks
• 2 hosts adult parasitic in vertebrate digestive
  tract

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Subclass Eucestoda

• Chain of proglottids (strobila) arises from
  germinative zone
• 1000 species, including
• Beef tapeworm
• Pork tapeworm
• Fish tapeworm
• Unolocular hydatid

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Beef Tapeworm

• Taenia saginata
• Adult in alimentary canal of humans
• Juvenile in cattle tissue
• 10 m long, 2000 proglottids
• Life cycle
• Proglottid passes, cattle eat shelled larvae,
  muscle cysts, humans eat rare beef, intestinal
  cysticercus

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Taenia Life Cycle
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Pork Tapeworm

• Taenia solium
• Adult in small intestine of humans
• Juvenile in pig muscles
• Scolex with suckers and hooks on rostellum
• Cysticerci in organs
• In eyes or brainblindness, death

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Fish Tapeworm

• Diphyllobothrium latum
• Adult in intestines of humans, dogs, cats, etc.
• Juvenile in crustaceans, fish
• 20 m
• Humans eat raw fish

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Unilocular Hydatid

• Echinococcus granulosus
• Adult in canines
• Juvenile in mammals
• Intermediate hosthuman
• Juvenile hydatid cyst (grows up to 20 years)

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Phylum Nemertea

• Ribbon worms (most less than 20 cm)
• Characteristics
• 650 species
• Simplest animal with blood-vascular system (but
  no heart) and one-way alimentary canal
• Eversible proboscis grasps prey
• Most marine, free-living

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Nemertean characteristics, cont.

• Most dioecious
• Ciliated epidermis
• Carnivorous
• Respiration through body surface
• Brain, sense organs, longitudinal nerves
• Tail can regenerate new proboscis

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Phylum Gnathostomulida

• Jaw worms (1 mm)
• Characteristics
• 80 species
• Commonly found in sediment
• No pseudocoel, circulatory system, or anus
• Ciliated epidermis
• Males, females, or hermaphrodites
• Some features similar to rotifers

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Phylogeny

• From theorized planuloid ancestor
• Sessile, radial branch (cnidarians)
• Creeping, bilateral branch (flatworms)
• Cephalization
• Turbellarians
• Ciliated epithelium, mucous glands
• Trematodes, monogeneans, cestodes
• Nonciliated, syncytial tegument, muscle

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Adaptive Radiation

• Parasitic body shape, metabolism
• Ribbon worms evolved for predatory niche
• Jaw worms evolved for low oxygen, marine
  environments