Differences Between an Octopus & a Squid

Differences in Appearance

• There are several key differences between the appearance of octopuses and squid. Squid are generally more streamlined than octopuses. They feature a triangular head that is longer and less rounded than the bulbous head of the octopus. Squid also have two fins located on their heads. Both animals have eight arms; however, squid also possess two tentacles. These tentacles are longer than their arms and are used to capture and hold prey. While species of both animals can be as small as 1 centimeter, squid range to as large as 20 meters. Octopuses, on the other hand, generally don't grow larger than 5 meters.

Differences in Anatomy

• Several differences in anatomy exist between octopuses and squid. Unlike other cephalopods, octopuses have absolutely no external or internal shell or skeleton. This enables them to squeeze their bodies through the tiniest of openings. In contrast, the squid has a stiff, internal shell, called a pen, which functions much like a flexible backbone. Another anatomical difference is the type of suckers on their arms. The arms of octopuses are equipped with two rows of smooth suckers. However, the squids' arms are equipped with suckers that feature hooked, or saw-like, outer rings.

Differences in Habitat

• The habitats of octopuses and squid are very different. Octopuses live entirely on the seafloor. They live in dens, exiting to catch their prey. On the other hand, squid live their lives swimming in the open water, maintaining no permanent housing or shelter. This difference extends to the reproduction activities of the two animals. The female octopus will deposit her eggs on the roof of her den, remaining there to protect and care for them until they are ready to hatch. The female squid will, instead, attach her eggs to strands of seaweed or seafloor objects.

Differences in Lifestyle

• There are some very distinct differences between the lifestyles of octopuses and squid. Octopuses are solitary creatures, living out their short lives (six months to five years) entirely on their own. However, squid often live in large communities, or schools. Octopuses are considered the most intelligent of all the invertebrates, displaying more curiosity, playfulness and problem-solving behavior than squid. Another difference between the octopus and squid lies in their choice of prey. As seafloor-dwelling creatures, octopuses primarily feed on crustaceans and other seafloor-dwelling creatures, including crabs, crayfish and mollusks. As ocean swimmers, squid feed primarily on fish and shrimp.