Q 01/05

To which class of molluscs do octopuses belong, along with squid, cuttlefish and nautiluses?

A) Gastropoda

B) Cephalopoda

C) Polyplacophora

D) Bivalvia

Answer · why

B) Cephalopoda

The order Octopoda holds around 300 species.

Q 02/05

How many hearts does an octopus have?

A) One

B) Two

C) Three

D) Four

Answer · why

C) Three

One main heart pumps blood round the body; two branchial hearts push it through the gills, and the main one stops when the animal swims.

Q 03/05

Octopus blood is blue because it carries oxygen with which copper-rich protein?

A) Haemoglobin

B) Myoglobin

C) Ferritin

D) Haemocyanin

Answer · why

D) Haemocyanin

It works better than haemoglobin in cold, low-oxygen water, but is so viscous that blood pressure can top 75 mmHg.

Q 04/05

Roughly how many neurons does an octopus have, about the same as a dog?

A) About 5 million

B) Over 500 million

C) About 50 million

D) About 5 billion

Answer · why

B) Over 500 million

One part sits in a cartilaginous capsule around the brain; the rest is spread through the arms, which act with some independence.

Q 05/05

What fraction of an octopus's neurons are located in its arms rather than its brain?

A) One-tenth

B) Two-thirds

C) Nine-tenths

D) One-quarter

Answer · why

B) Two-thirds

A severed arm can still move and respond to stimuli.