Overview
This lecture discusses the key features of flatworms like Planaria, focusing on their body symmetry, sensory structures, and feeding mechanism.
Bilateral Symmetry and Cephalization
- Flatworms like Planaria are the first animals to show bilateral symmetry.
- Cephalization refers to the concentration of sense organs in the head region.
Sensory Structures in Planaria
- Planaria have a pair of oceli, which are light-sensitive eyespots located near the center of the head.
- Lateral lobes extending from each side of the head contain chemosensory cells that detect chemicals in the environment.
Feeding Mechanism of Planaria
- Planaria feed using a protrusible (extendable) and muscular pharynx.
- Chemosensory cells on the lobes help Planaria locate food.
- By rhythmic contraction of the pharynx, Planaria pumps food into its gastrovascular cavity in a siphon-like manner.
Key Terms & Definitions
- Bilateral symmetry — body plan in which left and right sides are mirror images.
- Cephalization — concentration of sense organs and nervous tissue at the head.
- Oceli — simple, light-sensitive eye spots.
- Chemosensory cells — cells that detect chemical stimuli, aiding in finding food.
- Protrusible pharynx — extendable muscular tube used for feeding.
- Gastrovascular cavity — central digestive compartment in Planaria.
Action Items / Next Steps
- Review the structure and function of Planaria sensory and feeding organs.
- Learn the definitions of key terms related to flatworm biology.