The cephalopod known for high intelligence and problem-solving is the octopus. Octopuses can learn to distinguish shapes and patterns, solve maze-like tasks, and retain both short-term and long-term memories.
Their intelligence is especially striking because it evolved independently from the intelligence of vertebrates. Much of an octopus’s nervous system is distributed through its arms, allowing each arm to process sensory information while the animal explores, manipulates objects, and searches for food.
Octopuses have also demonstrated flexible behavior outside laboratory tests. They can open jars, escape from aquarium enclosures, and use discarded coconut shells as portable shelters. The veined octopus’s shell-carrying behavior is one of the clearest examples of tool use among invertebrates.
Cuttlefish and squid are also capable cephalopods, and nautiluses are living cephalopods too, but the octopus is the standard answer to this broad trivia question. “Intelligent” describes observed learning and problem-solving, not human-like language or reasoning.