An octopus typically has eight arms; a squid usually has eight arms plus two feeding tentacles. The suckers, body outline and fins provide further clues.
The difference at a glance
An octopus typically has eight arms. A squid usually has eight arms plus two longer feeding tentacles, with suckers concentrated on enlarged clubs at their tips. The familiar long, finned squid outline is another clue, but fins and habitat are not universal dividing lines: some octopuses have fins, and some squid live close to the seabed. [1] [2] [3] [4]
Both animals are cephalopod molluscs, not fish. This guide compares their usual body plans and then checks the exceptions that make an identification shortcut unreliable. [1]
| Feature | Octopus | Squid |
|---|---|---|
| Usual appendage plan | Eight arms | Eight arms plus two feeding tentacles [1] [4] |
| Where the suckers are | Along the arms | Along the arms; the extra tentacles have smooth shafts and sucker-bearing clubs [1] |
| Internal shell | Much more reduced; no comparable long squid pen | A reduced internal shell called a pen or feather [1] |
| Fins | Absent from many familiar forms, but present in finned octopuses | Present in the common squid and bigfin squid examples [2] [3] [4] |
| A useful example | Flapjack octopus: a finned, web-armed deep-sea form | Common squid: a long, cylindrical species found around UK coasts [2] [4] |
| Shared classification | A cephalopod mollusc | Also a cephalopod mollusc [1] |
Calling every appendage a “tentacle” hides the most useful distinction. In this comparison, an arm bears suckers along its length. A squid’s two specialised feeding tentacles instead have long shafts leading to expanded, sucker-bearing clubs. In many squid, the tentacles reach out to catch prey and the arms then hold it. [1]
The usual squid plan therefore totals ten appendages: eight arms + two tentacles. It does not mean ten identical arms. A photograph may hide the long pair behind the shorter arms or outside the frame, so counting only what is visible can be misleading.
The common squid (Loligo vulgaris) is found around UK coasts. It has an elongated, cylindrical body, with two fins at the end opposite the head and arms. Its eight arms and two longer prey-catching tentacles give a concrete example of the usual squid arrangement. [4]
A fin is not proof of “squid”. The flapjack octopus has stubby fins and webbed arms, and can use both when swimming. Nor does “near the seabed” prove “octopus”: the bigfin squid is often observed hovering close to the bottom. These examples show why a typical outline or lifestyle must not become an absolute identification rule. [2] [3]
Imagine View A shows a cephalopod with eight appendage tips visible, while its head end is partly hidden. The defensible result is not enough evidence: a squid’s additional tentacles might be out of sight. Do not add invisible structures to a record, but do not treat a cropped photograph as a complete count either.
View B shows eight shorter sucker-bearing arms and two much longer appendages ending in clear clubs. That combination supports a typical squid identification. If the animal also has the slender body and rear fins of the common squid example, the observations agree; they still do not identify every squid to species. [1] [4]
No. Eight visible tips are not necessarily a complete count. Look for the squid’s additional feeding pair and check whether the head and appendages are fully in view. [1] [4]
No. The flapjack octopus is a finned octopus. Fins help describe a body plan but cannot decide this comparison on their own. [2]
No. Bigfin squid are often seen near the bottom too. A place in the water column is supporting context, not a substitute for the animal’s structures. [3]
No. They are molluscs belonging to the cephalopod group, which also includes cuttlefish and nautiluses. [1]
No. A squid’s pen is a reduced internal shell. The octopus shell is much more reduced, so “soft-bodied” should not replace a careful description of each animal. [1]
Sources checked on 16 October 2026. The worked examples and exercises were written for this article.
AI tools assisted with drafting and the featured editorial illustration. The illustration is not a photograph, a measured diagram or evidence of an actual test.
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