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Cuttlefish, squid and octopus are the three groups of coleoid cephalopods, famous for their large brain size and potential cognitive capability approaching that of small mammals. The brain layout and neural network complexity in all three were initially highlighted by Cajal and later JZ Young and colleagues. Recently, our work has sought to bring back to earth the thinking and hypotheses regarding the brains and behavioural boundaries of the cephalopods. Using new methods in high-resolution magnetic resonance imaging (16.4Tesla MRI), brain image analyses and other ‘basic’ anatomical techniques, combined with ecologically-informed comparisons, we have made many novel findings at the neuroanatomical level. Suggested links can also be made through behaviour, ecology, and life mode. Firstly, coastal cephalopods encounter different selection pressures, may be nocturnal or diurnal (e.g. octopus and cuttlefish) and mostly solitary (octopus) or partially social (e.g. cuttlefish and squid). These different ecologies and behavioural needs have driven remarkable differentiation of the optic lobe (vision), inferior frontal lobe (chemotactile) and vertical lobe (learning and memory). A comparison of the MRI-based cephalopod connectome, along with neural trace ground-truthing, shows that the diurnal octopus and cuttlefish have developed additional circuits in their vision and colouration systems related to their camouflage tactics in the bright reef habitats they dwell in. Moreover, our recent studies uncover previously-unknown features of sexual dimorphism in the octopus brain. The male brain continuously grows throughout its life, reaching its maximal size at the reproductive stage. Conversely, the growth rate of the female brain slows down while the gonad starts developing. Notably, the rapid shrinking of the female brain (a senescence-like event) is identified during reproduction and the extended duty in brooding. These new insights link the octopus brain fluctuations (rapid growth and decay) along with the heterogeneity of the optic and brachial lobes to ecological niches and its semelparous life, feeding hypotheses around evolutionary history and providing a timely, new-technology update to older literature. By assessing how the sex-biased neuroarchitecture changes in gross neuroanatomy and the associated neural networks, we shall recognise octopuses as a novel model for rethinking neural plasticity and their advanced cognitive capability. This gives a firm base to prompt a non-anthropomorphic interpretation of cephalopod comparative cognitive and behavioural abilities.