Unsegmented Worms

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Unsegmented Worms

• Phylum Platyhelminthes

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Advantage of Being Flat

• Surface area to volume ratio is important for
  organisms.
• many substances enter and leave through body
  surface.
• Faster absorption and release of wastes

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I. Unsegmented worms

• A. Worms that are not
• divided into sections
• externally internally
• B. Eg.
• 1. Phylum Platyhelminthes
• aka flatworms
• 2. Phylum Nematoda
• aka Roundworms

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Phylum Platyhelminthes the Flatworms
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C. What is a coelom?

• fluid-filled
• body cavity
• between
• body wall
• digestive tract

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Kinds of coelom

• Acoelomate no coelom
• i.e. body cavity is
• NOT fluid filled

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Kinds of coelom
2. Pseudocoelomate Fluid filled body
cavity BUT No mesentary or
peritoneum
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Kinds of coelom
3. Eucoelomate True coelom w/ mesentary
(holds gut in place) peritoneum
(mesodermal lining of body cavity
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The Coelom or Body Cavity Advances
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D. Phylum Platyhelminthes

• 1. Class Turbellaria planarians
• 2. Class Trematoda flukes
• 3. Class Cestoda tapeworms

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D. Phylum Platyhelminthes

• Also Acoelomate
• Phylum Nemertea ribbon worms
• Phylum Gnathostomulida-
• jaw worms

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E. General Info re Flatworms

• 1. platy flat
• helminth worm
• 2. Body structure
• a. Size range 1 mm ------?
• many meters (Cestoda)
• b. Shape flattened dorso-ventrally
• c. Only several cell layers thick

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E. General Info re Flatworms
? Cells fill body cavity (not fluid)
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F. Level of Organization

• organ system

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G. Symmetry

• bilateral
• (has forward movement cephalization)

I m a little bilateral animal too!
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H. Habitat

• aquatic (freshwater
• or marine)
• moist soil
• endoparasites of vertebrates

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I. Feeding - Class Turbellaria

• Planarians-
• mostly
• free-living
• carnivore
• or
• scavengers

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I. Feeding - Class Turbellaria

• Incomplete digestive tract one opening (no
  anus)
• Mouth on ventral side
• Protrusible pharynx
• Gastrovascular cavity (GVC)
• Intestine very branched
• Enzymes digest food

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I. Feeding - Class Trematoda

• Parasitic flukes
• endoparasites
• of
• vertebrates
• need only
• minimal
• digestive tract
• E.g. Human Liver fluke

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I. Feeding Class Cestoda

• tapeworms
• Endo-parasites
• Scolex w/ hooks suckers
• NO need for dig. tract
• absorbs nutrients from gut of host

scolex
suckers
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J. Respiration

• - via diffusion
• (only a few cell layers thick)

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K. Internal transport

• via diffusion

Marine flatworm
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L. Excretion via diffusion

• EXCEPTION planarians have
• flame cells ( w/ flagella
• that help move waste to
• excretory pores, then out of the body

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M. Response (Nervous system)

• Primitive brain anterior ganglia
• ganglion cluster of nerve
  cells
• 2. Two Longitudinal nerves (the length of the
  body)
• 3. Ladder-like cross-bridges of nerves

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M. Response (Nervous system)
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M. Response (Nervous system)

• 4. Sense organs (flatworms)
• a. Ocelli eyespots / photodetectors
• b. Auricles -
• contain chemoreceptors (chemicals)
• thigmoreceptors (touch)
• c. Statocysts balance
• d. Rheoreceptors sense
• direction of water current

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Nervous System and Sense Organs

• Have a Nerve-net.
• Most have more complex system.
• Cerebral ganglion primitive brain coordinates
  impulses.
• Ladder system carries impulses throughout body
• Many sense organs present
• Eyespots
• Chemoreceptors, touch sensors and rheoreceptors
  (sense direction) also common

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N. Locomotion

• - Planaria
• use cilia,
• slime,
• circular and
• longitudinal muscles
• to GLIDE
• Trematoda, Cestoda little motion

cilia
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O. Reproduction

• 1. Asexual Regeneration (Planaria only)
• 2. Sexual
• a. pattern monoecious (hermaphrodites)
• b. cross- fertilization (swap sperm)

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Reproduction in Free-living Flatwormssuch as
Planarians

• May reproduce sexually or asexually
• Asexual
• Binary fission split in two
• Sexual
• Both sexes present in same flatworm
  (hermaphrodites).
• Fertilization internal, eggs produced
• Embryos emerge as juveniles resembling adults.

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Reproduction in theTapeworm!

• Lack digestive system
• Sucker and hooks on anterior end for attachment
• Neck produces new segments
• Called proglottids
• Each proglottid contains male and female gonads
• Reproductive output high
• Many proglottids per worm
• Many eggs per proglottid

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Tapeworm - Life Cycle
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Flukes -- Life Cycle of a Liver Fluke
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P. Ecological Roles

• 1. Scavengers/ predators recycle nutrients to
  ecosystem (Class Turbellaria)
• 2. Prey for fish birds (Class Turbellaria)
• 3. Endo-parasites (cause disease)
• (Class Trematoda Class Cestoda)