A Squid Has Three Hearts and Blue Blood
A squid is a marine mollusc with ten arms. Its anatomy differs from ours in several fundamental ways.
A squid is a marine mollusc with a long body, eight arms and two longer tentacles. Its biology is genuinely alien: squid have three hearts, two pumping blood through the gills and one through the body, and their blood is blue because it uses copper-based haemocyanin instead of iron-based haemoglobin. That carries oxygen better in cold, low-oxygen water. The colossal squid has the largest eyes of any known animal, roughly the size of dinner plates.
- A ten-armed mollusc. *A giant squid.*
- Calamari — squid as food. *Fried calamari.*
- Cephalopod — the group. *Cephalopods.*
- Haemocyanin — blue blood pigment. *Haemocyanin.*
- Uncertain origin. *From the 1600s.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | squid | A squid. |
| Plural | squid / squids | Squid. |
| Food | calamari | Calamari. |
| Group | cephalopod | A cephalopod. |
| Greek | kephale | Head. |
- The squid vanished in a cloud of ink.Behaviour.
- Squid have three hearts.Anatomy.
- Their blood is copper-based.Biology.
Squid anatomy
- Three hearts — two for the gills, one for the body
- Blue blood — haemocyanin uses copper rather than iron
- Eight arms and two tentacles — octopuses have eight arms only
- Jet propulsion — water forced through a funnel
- Chromatophores — pigment cells that change colour in an instant
Of uncertain origin, recorded from the 1600s, possibly a variant of *squirt*.
Why is squid blood blue?
It uses haemocyanin, a copper-based oxygen carrier, rather than iron-based haemoglobin. Copper compounds are blue.
What is the difference between a squid and an octopus?
Squid have eight arms plus two longer tentacles and an internal stiffening pen; octopuses have eight arms and no shell at all.