Biology
How many hearts does an octopus have?
An octopus has three hearts and blue, copper-based blood. About two-thirds of its neurons are in its arms, which can act semi-independently.
Source: Hochner (2012), Current Biology.
Context
Three. Two pump blood through the gills and one sends it round the body. The blood is blue because it carries oxygen with a copper-based molecule instead of iron-based haemoglobin.
About two-thirds of an octopus's neurons are in its arms rather than its head. The arms can act semi-independently, which Hochner describes in a 2012 review.
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