-
Platyhelminthes: Symmetry
Bilateral
-
Platyhelminthes: # Germ Layers
- 3 (acoelomate, true organs, no body cavity)
- have ecto, meso, endoderm
- evolution of mesoderm important because it produces muscle tissue
- trues organs with solid mass of mesodermal parenchyma cells surround organs
-
Platyhelminthes: Metamerism
some internal
-
Platyhelminthes: Coelom
none
-
Platyhelminthes: Skeletal System
- none but have...
- hydraulic skeleton - gastrovascular fluid
- longitudinal and circular muscles
-
Platyhelminthes: Cephalization
- Some (eyespots, brain)
- cephalization: nervous system concentrated towards one end of organism => becomes head region
-
Platyhelminthes: Nervous System
- nerve ladder, eyespots
- organized like a ladder w/ two lateral cords connected by transverse cords
- some cephalization w/ sensory association
- motor neurons
- pigmented eyespots sensitivity to light but no imaging
-
Platyhelminthes: Digestive System
- pharynx leading to 3-branched GV cavity
- cestodes: none (absorb from host)
- GVC consists of mouth, pharynx, and 3 branched intestines
- extends through mouth during feeding and secretes digestive enzymes
- muscular contractions of pharynx pulls food into mouth
-
Platyhelminthes: Excretory System
- protonephridia w/ flame cells: regulate ion balance (osmoregulation)
- cilia line the blind ended tubes (protonephridia) that open to outside -> create negative pressure to pull fluid into tube -> expelled
- undigested food expelled out mouth
- nitrogenous waste diffuses into surrounding environmenta
-
Platyhelminthes: Reproductive cycle
- monoecious
- asexual, via regeneration when cut => budding in some
- sexual - most hermaphroditic with cross-fertilization
-
Platyhelminthes: Locomotion
- swimming via cillated ventral surface
- outer circular and inner longitudinal muscle contraction beneath epidermis
-
Platyhelminthes: Classes
- Turbellaria: free living (eg. Dugesia)
- Tremetoda: flukes (parasitic)
- Cestoda: tape worms (parasitic)
-
Platyhelminthes: Notes
- acoelomate and lack true body cavity (coelom)
- 80% parasitic
- 550 mya
-
Platyhelminthes: Body Layers
- Epidermis -> Circular muscle -> Longitudinal muscle -> Parenchyma -> (dorsalventral muscles) -> (testes and oviduct) -> (excretory canal/ protonephridia) -> 2x(gastrodermis->GVC) on each side
- Epithelium -> Pharyngeal sheath -> Pharyngeal cavity -> Epithelium -> Circular muscles -> Longitudinal muscle -> Gastrodermis -> Pharyngeal lumen
|
|