Phylum Platyhelminthes: The Flatworms

1
Phylum Platyhelminthes The Flatworms

• Planarians
• Flukes
• Tapeworms

2
General Characteristics

• Bilateral symmetry ( allows for quicker movement)
• Cephalization (sense organs concentrated at the
  head or anterior end) with ladder-type nervous
  system that allows them to locate food and
  respond to stimuli in environment
• Not segmented
• Incomplete digestive tract
• Acoelomate
• Free-living and parasitic species
• Parasite lives off another living thing called a
  host.

3
General Characteristics

• Triploblastic (3 germ layers)
• Leaf-like or ribbon-like
• 1mm to 20m in length
• 20,000 species
• Marine, freshwater, damp terrestrial habitats

4
General Characteristics

• Carnivores - tiny aquatic animals
• Scavengers - recently dead organisms
• Parasites - live off other organisms
• Feed off of blood, tissue fluids, pieces of cells
  (things already digested by host)
• No true body cavity (gastrovascular)
• No extensive organ development
• No circulatory system no blood

5
Anatomy

• Integumentary- Rhabdites and one cell layer
  epidermis in Turbellaria and usually ciliated
  body covering called tegument in other classes.
  Materials pass easily into/out of bodies via
  diffusion.
• Skeletal - none hydrostatic
• Muscle - longitudinal, transverse, and circular
  muscles are present.
• Digestive - incomplete with intracellular and
  extracellular digestion no system in Cestoda.
  One opening.

6
Anatomy

• Excretory - protonephredia and flame cells, or
  excretory tubes in Cestoda that filter and remove
  excess water from body wastes.
• Respiratory - no system, diffusion
• Circulatory - none, diffusion.
• Nervous - anterior ganglia (groups of nerve cells
  considered to be a primitive brain), ventral
  ladder-like system that is two nerve cords.
  Photoreceptors, chemoreceptors, statocysts,
  rheoreceptors.

7
Anatomy

• Endocrine - hormones produced by nervous system
• Reproductive - Sexual or asexual. Most
  hermaphrodites reproducing sexually
• Pairs exchange sperm eggs laid in clusters and
  ciliated larva hatch within a few weeks
• Well developed reproductive organs, mostly
  internal fertilization.
• Two of the parasitic classes have complex life
  cycles
• Flatworms reproduce asexually more commonly by
  fission regeneration.

8
CLASSES
9
Taxonomy

• Class Turbellaria (tur-bell-er-e-a)
• Dugesia
• Class Monogenea (mon-o-gin-e-a)
• No representatives
• Class Trematoda (trim-a-toe-da)
• Clonorchis, Fasciola, Schistosoma
• Class Cestoda (ces-toe-da)
• Taenia, Dipylidium Echinococcus

10
Class Turbellaria

• Planaria -Free-living (nonparasitic) flatworms
  with soft flattened bodies covered with ciliated
  epidermis which has special secreting cells
  called rabdites that secrete slime to glide on.

Dugesia
11
Planaria

• Head with two large eyespots called ocelli to
  sense light changes and flaps called auricles at
  each side to detect chemicals
• Dense clusters of nervous tissue form a simple
  brain, and a pair of nerve cords connect brain
  with small nerves

12
Planarians

• Most are marine benthic
• Some freshwater
• Some in moist temperate tropical land
• Marine can be colorful
• 3,000 species 12 orders
• Little economic importance (labs aquiriums)
• Planarians are the best known members of class
  Turbellaria
• Moves using muscles that enable it to twist
  turn and cilia on ventral surface to crawl on a
  slime track

13
Planaria

• Gastrovascular cavity is highly branched
• Mouth is on the ventral surface
• When it feeds, a muscular tube called the pharynx
  projects through the mouth pulls food in
• Digestion begins with enzymes secreted onto food
  before sucked into intestine by pharynx
• Intestines may have lateral branches for more
  surface area.

14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
Class Trematoda

• Parasitic flukes
• Flukes have oral and ventral suckers, no hooks,
  they are parasites with complex life cycles, body
  with without cilia. Larva stages unique.
  Examples
• Clonorchis
• Fasciola
• Schistosoma

18
Class Trematoda

• Most are leaf-like shape
• Has a body covering, called tegument, without
  cilia
• Produce various forms of larvae including
  metacercariae which are juvenile flukes that
  develop into adults
• Most affect blood or internal organs of hosts
• Hermaphrodites

19
Schistosoma

• Blood Flukes
• Cerceria usually infect by burrowing through skin.

20
Schistosoma

• Parasites that live in a host
• Female spends most of her time in a groove
  running length of the body of the larger male -
  allows them to copulate frequently
• Both have suckers that attach to insides of blood
  vessels near hosts intestines
• In humans, cause schistosomiasis (blood fluke
  disease)
• Severe, long-lasting
• Causes severe abdominal pain, anemia, dysentery

21
Schistosoma

• Complex life cycle including reproduction in more
  than one host
• Blood flukes living in human host reproduce
  sexually. Fertilized eggs pass out in feces.
• Ciliated larva hatch
• Larva enter snails or other host.
• Asexual reproduction in snail occurs.
• Different larvae are produced that can infect
  humans.
• A person becomes infected when larvae penetrate
  skin.

22
Blood Fluke Life Cycle
23
(No Transcript)
24
Clonorchis

• Human liver fluke - has two intermediate or
  secondary host snail and fish.

25
(No Transcript)
26
Clonorchis

• Liver fluke in humans
• 10 to 20 mm long
• Obtained by eating metacercarial infected fish
• Heavy infection may cause cirrhosis of liver and
  death
• Diagnosed via fecal examination
• Thoroughly cook fish to prevent
• Some control of snail populations also used

27
(No Transcript)
28
Fasciola

• Sheep liver fluke

29
Fasciola life cycle
30
Class Cestoda

• Tapeworms
• Taenia

31
Tapeworms

• Parasitic
• Adults inhabit digestive tracts of vertebrate
  animals
• Intermediate host invertebrates
• Very long, ribbonlike body with repeated units
  (segments) called proglottids
• Absolutely no digestive tract - lives in
  digestive tract of host so absorb nutrients via
  body surface

32
Tapeworm Anatomy
33
Tapeworms

• Head (scolex) is smallest part - armed with
  suckers and teeth that grasp host
• Behind head is long ribbon of repeated units
  filled with both male and female reproductive
  structures (proglottids)
• Full of ripe eggs, those at posterior end break
  off pass out of hosts body in feces

34
(No Transcript)
35
Taenia
Proglotid
36
Tapeworms

• Complex life cycle - usually one than 1 host
• Most benefit from predator-prey relationships of
  hosts
• Sheep (prey) is infected by eating contaminated
  grass
• Larval tapeworms develop in host
• Coyote (predator) becomes infected when eats prey
• Adult tapeworms develop in predators intestine

37
Tapeworms

• Several kinds infect humans
• Taeniarhynchus by eating larvae infected raw beef

38
(No Transcript)
39
(No Transcript)