Receptor Mediated Behavior (RMB)

    We first encountered RMB with P. Cnidaria.  There, we limited our discussion of it to only the simple behavior that hydras exhibit when ligands bind to specific receptors.  Actually, this is chemoreceptive mediated behavior - we just didn’t call it this at that time. Remember, the hydra are radially symmetrical and just “hang-out” in their environment and wait for stuff to come to it. No need for anything more than simple behaviors.
    With P. Platyhelminthes, we take RMB to a whole new level.  With flatworms, we have bilaterally symmetrical organism (with cephalization) that take an active part in their environment.  As such, they need to have a complex array of behaviors in response to external stimuli. Now we see a division of RMB into 3 specific types:

1. Chemoreceptive Mediated Behavior
2. Mechanoreceptive Mediated Behavior
3. Photoreceptive Mediated Behavior

    We did many experiments to show this as well.  For example, we poked them with a toothpick and observed their reaction.  These organisms were also able to LEARN.  Think about this for a second, in order to learn something you must be able to remember it.  Well, these organisms were able to remember a stimulus and modify their behavior.

Big Picture
Now with P. Platyhelminthes we see complex behavior with RMB that we first saw with P. Cnidaria – which, incidentally, is also an example of conservative evolution.