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Order Acoela (Flatworms)
- Bilateral symmetry
- Cephalization: Differentiation of head
- Neural ganglia: cluster of nerves at the back of the head (functions as brain)
- Less developed in sedentary animals
- Triploblastic
- Mostly marine worms
- Acoelmates: do not have a body cavity
- Flat
- Very minimal cephalization
- Do not have:
- Brain
- Anus
- Gut cavity
- Uses endocellular digestion: food is digested in vacuoles
- New phylogeny suggests Acoela is sister to Deuterostomia
- Clade Lophotrochozoa
- 18 Phyla
- Simple to complex worms
- Lophophore: feeding structure
- Trochozoa: larval stage
Phylum Platyhelminthes
- Flatworms
- Acoelmates
- No fluid filled cavity
- Just solid tissue
- Triploblastic
- Breathe using diffusion
- No specialized circulatory or gas-exchange system
- Thin skin
- Not a high surface area to volume ratio
- Incomplete digestive tract
- Has mouth and gut, but no anus
Class Turbelleria
- Free living flatworms
- Marine and predatory
- Epidermis covered in cilia
- Pair of ventral nerve cords
- Pair of ganglia
- No anus
- Food that is not digested is ejected from the mouth
Class Cestoidea
- Mostly parasites
- Endoparasites: Parasitize another organisms digestive system
- Mostly vertebrate hosts
- Invertebrates are intermediate hosts
- No digestive system
- Scolex: Suckers / hooks that hold onto hosts gut
Tapeworms
- Proglottids: long chain of units devoted to reproduction
- New ones produced near scolex
- Filled with eggs
- Also absorbes nutrients
- Creates many
- These fall off to infect other hosts
- Complex life cycle
- Needs 2 types of host to complete
- Intermediate Host (IH)
- Usually invertebrate
- Consumes the eggs
- Eggs hatch into larvae which encyst: attach themselves inside host
- Parasite goes through asexual reproduction
- Definitive Host (DH)
- Usually vertebrate
- Eats the IH
- Larvae develop into adult tapeworm inside DH
- Parasite goes through sexual reproduction
- Tapeworms in humans
- Comes from
- Undercooked pork and beef
- Raw fish
- Can cause blockage and nutritional deficiencies
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Class Trematoda
- "Flukes" with 2 large suckers
- Blood flukes (Schistosomia)
- Causes "Swimmers Itch"
- Have complex life cycles
Practice: Flatworms
Which of the following are true about flatworms? (select all that apply)
Practice: Tapeworms
Fill in the blanks.
Tapeworms often require 2 types of hosts. First they need a __________________ host followed by a _________________ host.
Mark Yourself Question
- Grab a piece of paper and try this problem yourself.
- When you're done, check the "I have answered this question" box below.
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