Cephalopods are a class of marine mollusks including the octopus, cuttlefish and squid. The name cephalopod means "head-foot" because they have limbs attached to their head, and these mollusks are well-known for their arms and tentacles. And while all cephalopods have arms, not all cephalopods have tentacles.
Tentacles are long, flexible organs found on invertebrate animals. They are important for feeding, sensing and grasping. Tentacles are longer than arms, are retractable and have a flattened tip that is covered in suckers.
Arms are similar to tentacles, but still distinctly different. Arms are covered with suckers that help with grasping food items. In addition, these arms are useful to attach to surfaces while resting.
The names may seem interchangeable, but when it comes to cephalopods, there’s a difference between arms and tentacles. An easy way to spot the difference is that arms have suckers along their entire length, while tentacles only have suckers at the tip.
This means that octopuses have eight arms and no tentacles, while other cephalopods—such as cuttlefish and squids—have eight arms and two tentacles.
Learn more about our eight-armed cephalopod, the giant Pacific octopus, here!