PLATYHELMINTHES

• Platyhelminthes Sometimes called “flatworms”
• Platyhelminthes may be free-living or parasites.
• Platyhelminthes' Body is bilaterally symmetrical with or without cilia.
• Platyhelminthes have Incomplete digestive system (do not have anus)
• Platyhelminthes are hermaphrodites
• Platyhelminthes respire by simple diffusion through the body surface.
• platyhelminthes reproduce sexually (internal fertilization) and asexually by regeneration.
• platyhelminthes have Acoelomate and triploblastic body
• Nervous System of Platyhelminthes:

  ❑ Have a centralized (nervous ladder-like) system consisting of a simple brain (cerebral ganglia) connected to longitudinal nerve cords.

  ❑ Allows to respond to stimuli and exhibit simple behaviors.
• Muscular Layer of Platyhelminthes:

  ❑ Beneath the epidermis lies a layer of muscles.

  ❑ Flatworms have both circular and longitudinal muscles that run along their body.

  ❑ These muscles allow flatworms to move in various ways, such as crawling, twisting, and contracting.
• Auricles – contains chemoreceptor to detect food.
• Eyespots (ocelli) - act as photoreceptors and are used to move away from light sources.
• Parenchyma - to pack the spaces between organs.
• Gastrovascular cavity – associated with digestion and the transport of nutrients.
• Flame cells (protonephridia) – specialized cells responsible for excretion and osmoregulation.
• Acetabulum - a specialized sucker for parasitic adaptation that responsible for the attachment on the host.
• Oral sucker - surrounds the mouth and is used to attach to the host.
• Mehlis’ gland (shell gland) – guiding the ova out towards the passage ending in the uterus of flatworms
• Nephridiopore - remove metabolic wastes and excess water from the body.
• Sexual Reproduction (Internal Fertilization)

  • Eggs are laid with or without a gel-like mass. A hard capsule called a cocoon encloses many turbellarian eggs.

  • The cocoons will attach to the substrate by a stalk and contain several embryos per capsule.
• Two kinds of capsules are laid.

  • Summer capsules hatch in two to three weeks, and immature animals emerge.

  • Autumn capsules have thick walls that can resist freezing and drying, and they hatch after overwintering