Origin & Natural History
The common name, blue-ringed octopus, was given due to the bright blue rings that appear on the octopus
Cladogram
The cladogram above is based on three distinct fossil clades that are entirely extinct: Endoceratoidea, Actinoceratoidea, and Bactritoidea. All memebers of these clades were squid-like, but had straight external shells called orthocones. Octopoda is also included in the cladogram.