Phylum Platyhelminthes

1
Phylum Platyhelminthes
Flatworms
Monogenian
Flukes
Tapeworms
2
Phylum Platyhelminthes

• The phylum consists of four classes
• Turbellaria (flatworm)
• Trematoda (fluke)
• Cestoda (tapeworm)
• Monogenian

3
Reproduction

• Almost all are simultaneous hermaphrodites
• Parasitic species (flukes and tapeworms) have
  complex lifecycles, with various hosts and
  several different larval stages
• Incredible powers of regeneration

4
Nervous System

• Free-living species usually have a well-developed
  sensory system
• Parasites generally have less elaborate systems.

WHY?
5
Taxonomic Summary

• Phylum Platyhelminthes (Flatworms)
• Class Turbellaria
• Class Cestoda
• Class Trematoda
• Class Monogeneans

6
Class Turbellaria

• Most are freeliving, benthic, tiny and
  inconspicuous
• Primarily marine and freshwater, many
  interstitial
• 4,500 species

Free-living Flatworm
7
Flatworm Body Plans

• bilateral symmetry
• Acoelomate
• triploblastic

8
Digestion

• Mouth is usually located at the anterior end or
  mid-body on ventral surface
• Some species also have a protrusible pharynx that
  captures food and transfers it into the mouth
• Can be carnivores or scavenge on dead animals and
  detritus

9
Digestion

• Mouth is usually located at the anterior end or
  mid-body on ventral surface

9
10
Feeding Habits

• Some species also have a protrusible pharynx that
  captures food and transfers it into the mouth
• Can be carnivores or scavenge on dead animals and
  detritus

11
Feeding Habits
12
Excretion

• Excretory system
• Contains flame bulbs

12
13
Nervous System

• Posses several nerve cords with a centralized
  ganglia (brain)

14
Reproduction

• Reproduction occurs with the reciprocal exchange
  of sperm
• Fertilized eggs are released and usually develop
  directly into flatworms
• Muller's larva

15
Mating Reproduction

• Chemosensory to find mate
• Hermaphroditic

16
Regeneration

• Many species posses remarkable powers of
  regeneration and repair wounds

17
Camouflage
flatworm
nudibranch
18

• Toxins

• Staurosporine
• Tetrodoxin

19
HawaiianFlatworms
Class Turbellaria
20
Hawaiian Flatworms
Pseudoceros cf. rubroanus
Pseudoceros ferrugineus
Planocera cf. oligoglena
Pseudoceros dimidiatus
Pseudobiceros sp.
Class Turbellaria
21
Class Cestoda (Tapeworms)

• Defining characteristics
• Scolex
• Proglottids

22
Proglottids

• Proglottids
• Each animal can be 3,000 4,000 per animal
• Amazing reproductive output
• Each may contain several ovaries and 1,000
  distinct testes

23
Problems of a parasitic existence

• Reproduce within the definitive host
• Get fertilized eggs out of the host
• Contact a new and appropriate host
• Obtain entrance into the host
• Locate the appropriate environment within the
  host
• Maintain position within the host
• Withstand an often anaerobic environment
• Avoid digestion or attack by the hosts immune
  system
• Avoid killing the host, at least until
  reproduction is completed

24
Class Trematoda (Flukes)

• All are external and internal parasites of other
  animals
• Leech-like bodies with a sucker at each end
• Have a gut and well-developed reproductive
  system, never segmented

25
Trematoda Lifecycles

• The lifecycle is complex with up to 4 different
  hosts and several larval types

26
Trematodes of Concern
27

•