Final answer:
Cephalopods possess the largest invertebrate brains, notable for complex behaviors and high intelligence among invertebrates, with brain-to-body ratios akin to some vertebrates.
Step-by-step explanation:
The class with the largest invertebrate brain is the Cephalopoda, which includes animals like squids, octopuses, and cuttlefish. These marine animals are known for their complex behaviors and high intelligence compared to other invertebrates. Their brains are the most developed among invertebrates and exhibit sophistication in various functions such as problem-solving, navigation, and communication. Interestingly, the brain-to-body ratio of some cephalopods is comparable to that of some vertebrates.
These creatures have a highly developed nervous system and possess the ability to solve complex problems and exhibit learning behavior.