1. ZOO 115 Invertebrate Zoology
Phylum Platyhelminthes

2. Classes Turbellaria Mongenea Trematoda Cestoda Free-living flatworms
Mongenetic flukes - parasitic
Trematoda
Flukes- parasitic
Cestoda
Tapeworms- parasitic

3. Phylum Platyhelminthes
© David Luquet
/gecko.gc.maricopa.edu/~lsola/bio182/labreview/
Ed T. Schmidtmann, USDA/ARS.

4. Phylum Platyhelminthes
About 20,000 sp.
Substrate crawlers in both marine and freshwater
Mostly small and soft-bodied
Lack a circulatory system
Diffusion limited
Controversy about phylogeny

5. Platyhelminthes Class Turbellaria
Virtually all are aquatic with most being marine
Most are bottom dwellers but there are some pelagic forms

6. Body Outer-layer is a ciliated epidermis
Skeleton – weblike sheet of actin filaments
Secrete Rhabdites
Thought to be important in locomotion, cocoon development and predator repellant

7. Body Gland cells Mesenchyme – Hydraulic action on larger organisms
zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg
Gland cells
Gland cells
zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg
Mesenchyme – Hydraulic action on larger organisms
Parenchyma – connective tissue compartment between body wall, musculature and gut.
Neoblasts - wound repair and regeneration
Chromatophores may be present and under control by brain.

8. Nervous system Bilaterial or Ring like brain Longitudinal nerves
Nerve net

9. Nervous system - sensory
Chemoreceptors over entire body
Cilia mechanoreceptors
Ocelli
Some have statocysts in the head region

10. Musculature Also have diagonal muscles – not shown
Longitudinal muscles
zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg
Dorsoventral muscles
Circular muscles

11. How do they move? Ciliary creeping Muscular creeping Swimming
Peristalsis
Twisting, turning, extension and retraction
Somersaulting

12. Complete Bilateral gut
zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg
Gut

13. Feeding and digestion Food swallowed by pharynx or
Sense prey using chemreceptors and mechanoreceptors
Capture prey
Wrapping themselves around prey
Entangling it in slime
Pinning prey with adhesive glands
Some have toxic mucus
Some use penis
Most are carnivores and scavengers
Some Aoela have zooxanthellae
Proteolytic enzymes are injected into prey and pharynx is used to pump liquified contents.
Gut types
Acoela – syncytial mass enclosed by membrane
Simple unbranched sac
Multiple lateral branches
Gland cells in gut supply additional enzymes.
Digestive cells phagocytize remainder

14. Excretion

15. Reproduction
Regeneration
Clonal Reproduction – longitudinal fission

16. Reproduction Sexual Reproduction Most hermaphrodites
Most copulation and internal fertilization
Male
1 or more pairs of testis
Ducts, storage area
Penis – may have stylet
Female
I or more pairs of ovaries
Copulatory bursa (vagina), seminal receptacle, uterus

17. Reproduction Development
Some freshwater species produce summer and winter eggs
Usually egg->blastula->gastrula->juvenile->adult
Marine polyclads produce planktonic larvae
Generation time: days
Life span: days

18. Platyhelminthes – Dueling Penises
Wounds
Penis