The octopus (order Octopoda) is famous for its eight magnificent tentacles- but a lesser known fact is that they also have 3 hearts! One of these hearts, called the “systemic heart”, is in the center of the body and pumps oxygenated bloods to everywhere except the gills. The other two hearts are the “branchial” hearts, which pump blood through the gills. The reason the octopus has such a unique cardiac system, is because their blood contains hemocyanin (compared to humans which have hemoglobin). This oxygen-carrier is less efficient at carrying oxygen than hemoglobin, thus necessitating the extra hearts to move oxygen across the body.

Art by Kelsey Wood (instagram: @kelseywood.art)

[Edited by Isabelle McDonald-Gilmartin]

Reference:

Wells, M. J. (1978). Octopus, Physiology and Behaviour of an Advanced Invertebrate. Springer Science+Business Media. ISBN 978-94-017-2470-8.