Understanding Octopuses: Context, Terminology, and Common Misconceptions

Octopuses fascinate many people — yet there is often confusion about what exactly they are.

Are they “fish”?
What is the difference between an octopus and a “Krake”?
And what do terms like octopus, squid, or cuttlefish actually mean?

This article brings clarity.

1. Octopuses Are Mollusks — But Highly Complex Ones

Octopuses belong to the phylum Mollusca (mollusks).

That may come as a surprise, because this group also includes:

• snails

• clams and other bivalves

And yet, biologically, they are all part of the same phylum.

👉 Within the mollusks, octopuses belong to the class Cephalopoda — a highly developed group characterized by:

• complex nervous systems

• highly developed sensory organs

• an active predatory lifestyle

Their scientific classification:

• Phylum: Mollusca (mollusks)

• Class: Cephalopoda (cephalopods)

• Order: Octopoda

👉 “Octopoda” literally means “eight-footed.” This order includes all animals commonly known as octopuses.

2. Octopus vs. “Krake” — Is There a Difference?

In short: No — they refer to the same animal.

• “Octopus” is the more scientific and internationally used term, derived from the Greek word “októpus”

• “Krake” is the common German term

👉 Both terms refer to animals belonging to the order Octopoda.

Why are there two terms?

In German, “Krake” is sometimes used somewhat loosely — occasionally even for other cephalopods.
“Oktopus” is more precise and is therefore used more frequently in scientific contexts.

3. Their Relatives: What Else Belongs to the Cephalopods?

The class Cephalopoda includes several groups that are often confused in everyday language.

Here are the most important ones:

🐙 Octopus (Oktopus / Krake)

• 8 arms

• no internal shell

• usually solitary

• highly flexible and intelligent

👉 Example: the common octopus (Octopus vulgaris), as shown in the image on the right:

By Diego Delso, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=118447006

🦑 Squid (squid in the narrower sense / calamari)

• 10 appendages (8 arms + 2 longer tentacles)

• elongated body

• often fast swimmers

• frequently live in groups

They are often confused with octopuses, but their body structure is distinctly different.

👉 Example: the European squid (Loligo vulgaris), as shown in the image on the left.

© Hans Hillewaert

Common squid from the Belgian continental shelf. Picture taken in the lab on board of the RV Belgica, of a live specimen to preserve colour and structure of chromophores. Mantle: length= 138 mm, width= 39 mm.

🦑 Cuttlefish

• also have 10 appendages

• possess an internal calcareous shell (the “cuttlebone”)

• can display extremely complex changes in color and patterns

• are also considered highly intelligent

👉 Example: the giant cuttlefish (Sepia apama), an endangered species, as shown in the image on the right.

Richard Ling from NSW, Australia - Australian Giant Cuttlefish

An Australian Giant Cuttlefish (Sepia apama). Fairy Bower, Manly, NSW

4. Why This Distinction Matters

At first glance, these animals may appear similar.
But biologically and behaviorally, there are important differences:

Octopuses, squid, and cuttlefish differ in several characteristics. Octopuses have eight arms, are usually solitary, and have a soft, highly flexible body without a shell. Squid, on the other hand, have ten appendages, are often social, and move particularly quickly through the water thanks to their streamlined bodies. Cuttlefish also have ten appendages, display both social and solitary behaviors, and have a more compact body. Unlike octopuses and squid, they also have an internal shell.

👉 Particularly important:

Octopuses are not “typical” livestock — nor are they what we would traditionally think of as “squid.”

Their:

• solitary lifestyle

• high intelligence

• flexible body structure

make them unique — and particularly difficult to reconcile with intensive farming systems.

5. An Unusual Branch of Life

What makes octopuses particularly fascinating:

They are an example of the convergent evolution of intelligence.

This means:

• Their complex abilities evolved independently of those found in vertebrates

• Their nervous system functions in a completely different way from ours

And yet they demonstrate:

• problem-solving behavior

• memory

• individuality

👉 This makes them one of the most fascinating groups of animals — and one that we still do not fully understand.

Conclusion

Octopuses are:

• mollusks — but highly developed ones

• part of the cephalopods — a unique group of animals

• biologically distinct from squid and cuttlefish

• and exceptionally complex among invertebrates

And perhaps that is the key point:

When an animal is so different from us — yet at the same time so similar to us in its behavior — we should take an especially close look at how we treat it.