ZOO 115 Invertebrate Zoology

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ZOO 115 Invertebrate Zoology

• Phylum Platyhelminthes

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Classes

• Turbellaria
• Free-living flatworms
• Mongenea
• Mongenetic flukes - parasitic
• Trematoda
• Flukes- parasitic
• Cestoda
• Tapeworms- parasitic

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Phylum Platyhelminthes
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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

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PlatyhelminthesClass Turbellaria

• Virtually all are aquatic with most being marine
• Most are bottom dwellers but there are some
  pelagic forms

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Body

• Skeleton weblike sheet of actin filaments

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Body
Gland cells

• 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.

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Nervous system
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Nervous system - sensory
Chemoreceptors over entire body
Cilia mechanoreceptors
Some have statocysts in the head region
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Musculature
Also have diagonal muscles not shown
Longitudinal muscles
Dorsoventral muscles
Circular muscles
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How do they move?

• Ciliary creeping
• Muscular creeping
• Swimming
• Peristalsis
• Twisting, turning, extension and retraction
• Somersaulting

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Complete Bilateral gut
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Feeding and digestion

• Most are carnivores and scavengers
• Some Aoela have zooxanthellae

• 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

• 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

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Excretion
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Reproduction

• Regeneration
• Clonal Reproduction longitudinal fission

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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

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Reproduction

• Development
• Some freshwater species produce summer and winter
  eggs
• Usually egg-gtblastula-gtgastrula-gtjuvenile-gtadult
• Marine polyclads produce planktonic larvae
• Generation time 16-75 days
• Life span 65-140 days

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Platyhelminthes Dueling Penises