I'm trying to catch up with my backlog of research news (~600 unread messages) and what do you know, the first one is already worth blogging about! Researchers from the Brooklyn College in New York have tested classical conditioning in Nautilus. This was an interesting experiment, because Nautilus (which is a cephalopod like squid, cuttlefish and octopus) doesn't have the structures known to be important for forming memories in this group of animals. So in true Pavlovian fashion, they flashed a blue light into their tanks, just before they got fed. In the memory tests, they just flashed the light and observed the animals without food. Just like Pavlov's dogs which salivate after a tone was paired with food to the tone alone, Nautilus shows anticipation of the food by extending their tentacles to the blue light alone up to a day after conditioning.
Without a vertical lobe, these animals must use a different structure to store classical memories than other cephalopods. This result reinforces my opinion, that the minimum you need for a memory to form are two neurons and a synapse between them. Plasticity is probably a characteristic of all neurons. In this case, there ain't no such thing as a brain too small to learn.

Citation: R. Crook, J. Basil (2008). A biphasic memory curve in the chambered nautilus, Nautilus pompilius L. (Cephalopoda: Nautiloidea) Journal of Experimental Biology, 211 (12), 1992-1998 DOI: 10.1242/jeb.018531