Octopus arms are really feet with a variety of uses

“Why do octopuses have eight arms?” asked a young patron from the Arlington Heights Memorial Library.

Octopuses are mysterious. For example, they belong to the shell-covered mollusk phylum, but have no shell like their clam cousins. Instead, they keep predators away with a blast of ink, paralyzing venom and a complex camouflage response.

When trying to blend in with surrounding sand or rock features, octopuses switch on color-changing cells to create beautiful color variation, sometimes iridescent. Some have papillae that change the smoothness of their skin so arms develop a rough coral-like texture, another tactic to distract predators.

Mostly they're the strong silent types, enjoying their independence, living solo in rock crevices near the seafloor. Some are tiny, such as the octopus Wolfi at less than an inch in length, and some are very large, such as the giant Pacific octopus, with an arm span of up to 14 feet.

Octopuses haven't changed much in 165 million years. The few existing fossils look pretty familiar — an oversized head, giant eyes, a mantle and eight arms loaded with suckers. One ancient octopus species had a fin.

Because they don't have an outer shell or bone structure, octopus fossils are very rare. Surprisingly, there's one from Illinois, a 296-million-year-old octopus fossil found in Illinois' Mazon Creek that is now at the Field Museum.

“Head foot” is what cephalopod means — cephalopod being the family that octopuses, squid and cuttlefish belong to. Fanning out from the octopus's head are eight feet — what we call arms. A spokesperson from the National Aquarium in Baltimore explains the amazing functionality.

“The octopus uses its eight sucker-lined arms in a variety of different ways. Most of the octopus's neurons — cells that carry messages through the body — are in this creature's arms. This allows the octopus to use its eight arms to taste, feel and control basic movements without using its brain.

“Because the arms are doing some of the thinking for themselves, the octopus can multi-task and effortlessly explore its environment by crawling on the ocean floor with its eight arms.”

For all its complex characteristics, the octopus has only three parts — the head, mantle and arms. Maybe it's no mystery that as far as invertebrates go, octopuses are the smartest. Their advanced brains connect to a complex nervous system with acute vision, learning and memory capacity.

The mantle, atop its head, wraps the organs, including three hearts, in a band of protective muscles.

Playful, curious, elegant, octopuses are fascinating ocean dwellers. According to the National Aquarium, “Octopuses are the ultimate masters of disguise. Guests enjoy watching this otherworldly creature shift colors and textures while gliding effortlessly through its exhibit.”