1. 5.1 (a) (b) (c) Sea anemoneJelly fishHydra A B CD EFG50 mV 20 ms

2. 5.2 Helminthoida Helminthopsis Gyrolithes Cochlichnus Gordia Regular meandering without crossing Planolites Irregular meandering without crossing Spiraling Meandering sinusoidally Irregularly meandering and crossing Simple straight Second-order meanders First-order meanders Irregular Straight Early Cambrian Precambrian

3. 5.3 Water pik Siphon nerve Abdominal ganglion Genital nerve Pericardial nerve Branchial nerve Gill Siphon Stimulating and recording electrodes

4. 5.4 Siphon Mantle shelf Gill Int. II L22 L23 L16 Polysynaptic Monosynaptic SN1SN2SN3SN4SN5SN6SN7SN8 L7LDG1LDG2L9G1L9G2RDG

5. 5.5 (a) (b) (c) (d) (e) (f)

6. 5.6 Antenna tap Do-si-do Retreat Strike/Rip Meral spread No agonistic behavior Wresling

7. 5.7 Reflex Chain Motor neurons Stretch receptors contractedrelaxed Antagonist muscles Central Pattern Generator CNS CPG contractedrelaxed Antagonist muscles CNS

8. 5.8 MCPGs M M Buccal ganglion Cerebral ganglion Buccal mass Lip muscles

9. 5.9 600 Hz 200 Hz 400 Hz 600 Hz (1) (2) (3) (2) (4)(5) (6) (7) (8) (9) DS Habituation Trials Resting period

10. 5.10 DS

11. 5.11 Stimulus generator Time-date generator Video cassette recorder Petri plate holder Micromanipulator stand Microscope C. elegans Video monitor Antagonistic reflex systems mediate forward and backward locomotion in response to a tap stimulus. HeadTail Before habituation: ALM and AVM PLM AVM and ALM Backward motion PLM Forward motion (a) (b)

12. 5.12 Siphon Head SN IN L7 Gill

13. 5.13 Interneuron Serotonin and other neurotransmitters Axo-axonic synapse L7 Sensory neuron from siphon Membrane proteins Adenylate cyclase cAMP PKC PKA Closes K + channels Opens Ca ++ channels Mobilization of vescicles Spike broadening Short-term sensitization Dishabituation

14. 5.14

15. 5.15 Dolabrifera Bursatella Dolabella Aplysia Akera Bulla Increased excitability Spike broadening Loss of both: Increased excitability Spike broadening

16. 5.16 Body surface Body surface Body surface Effector Lower invertebrates Higher invertebrates Vertebrates PlasticExcitatory