What Do Octopuses & Squids Have That Other Mollusks Do Not Have?

Basic Structure

• In squid and octopi, the basic mollusk shape of a muscular head-foot and a fleshy body mass containing the organs has become something more elaborate. These creatures have eight strong arms, sometimes called tentacles, that some cephalopods use for swimming. Squid have two additional, more delicate arms. Octopi in particular can use their arms to manipulate objects, even opening jars. Their arms are sensitive to form and texture, an asset in murky ocean waters. Their good sense of touch lets the animals know whether something is a food item or a danger.

Suckers

• Another visible adaptation of octopi and squid is the presence of suckers on their arms. These suckers allow them to manipulate food, extract items from crevices and open armored prey, such as clams. Suckers also assist with locomotion, such as enabling octopi to climb.

Excellent Vision

• Octopi and squid have excellent vision, unlike other mollusks such as snails, which have simple eyes. Octopi and squid can see colors and forms at a level roughly equivalent to our own. The squid's sophisticated eyes enable them to communicate with light -- they possess light-emitting cells -- color and body language.

Complex Brains

• Cephalopods have a brain-to-body ratio that's larger than reptiles and comparable to mammals. The brain-to-body ratio provides a rough indication of intelligence. Other mollusks, such as slugs, have brains that are quite small and simple. Octopi and squid have complex ones. Unlike most invertebrates, cephalopods sleep. Sleep is something linked to consciousness and mostly seen in mammals and birds. Preliminary studies suggest that some cephalopods also enter a state similar to the rapid-eye movement, or dreaming, state of mammals. Octopi also are known to use tools to solve problems, both in the wild and under test conditions.