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ZOO 115 Invertebrate Zoology
Phylum Platyhelminthes
Classes
Turbellaria Free-living flatworms
Mongenea Mongenetic flukes - parasitic
Trematoda Flukes- parasitic
Cestoda Tapeworms- parasitic
Phylum Platyhelminthes
© David Luquet
/gecko.gc.maricopa.edu/~lsola/bio182/labreview/
/gecko.gc.maricopa.edu/~lsola/bio182/labreview/
www.pbs.org/kcet/shapeoflife/imganim//gecko.gc.maricopa.edu/~lsola/bio182/labreview/
Ed T. Schmidtmann, USDA/ARS.
www.islandream.com/wakatobi/flatworm02.jpg
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
PlatyhelminthesClass Turbellaria
Virtually all are aquatic with most being marine
Most are bottom dwellers but there are some pelagic forms
www.seafriends.org.nz/enviro/habitat/f017217t.jpg
Body
Skeleton – weblike sheet of actin filaments
Outer-layer is a ciliated epidermis
Secrete Rhabdites Thought to be important in
locomotion, cocoon development and predator repellant
Body
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.
zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg
zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg
Gland cells
Gland cells
Nervous system
Bilaterial or Ring like brain Longitudinal nerves
Nerve net
Nervous system - sensory
Ocelli Some have statocysts in the head region
Chemoreceptors over entire body
Cilia mechanoreceptors
Musculature
zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg
Longitudinal muscles
Circular muscles
Dorsoventral muscles
Also have diagonal muscles – not shown
How do they move?
Ciliary creeping Muscular creeping Swimming Peristalsis Twisting, turning, extension and retraction Somersaulting
Complete Bilateral gut
www.emc.maricopa.edu/faculty/farabee/BIOBK/flatworm.gifwww.emc.maricopa.edu/faculty/farabee/BIOBK/flatworm.gif
zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg
Gut
Most are carnivores and scavengers Some Aoela have zooxanthellae
Feeding and digestion
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
Food swallowed by pharynx or
www.emc.maricopa.edu/faculty/farabee/BIOBK/flatworm.gif
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
Excretion
www.lifesci.utexas.edu/faculty/sjasper/images/protonephridia.jpg
Reproduction
Regeneration Clonal Reproduction – longitudinal fission
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
Reproduction
Development Some freshwater species produce summer
and winter eggs Usually egg->blastula->gastrula->juvenile-
>adult Marine polyclads produce planktonic larvae
Generation time: 16-75 days Life span: 65-140 days
Platyhelminthes – Dueling Penises
Penis
Wounds
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