Sentience in cephalopod molluscs: an updated assessment

This article evaluates the evidence for sentience - the capacity to have feelings - in cephalopod molluscs: octopus, cuttlefish, squid, and nautilus. Our framework includes eight criteria, covering both whether the animal's nervous system could support sentience and whether their behaviour indicates sentience. There is strong evidence of sentience in octopuses and cuttlefish, which are assessed with very high or high confidence in meeting six of eight criteria. There is also substantial evidence for squid (very high or high confidence in five of eight criteria). By contrast, whether nautiluses are sentient remains unknown (high confidence in only one of eight criteria), since this group of cephalopods have attracted little research. This reflects a general pattern: cases where a taxon did not satisfy a criterion were invariably due to insufficient evidence, rather than evidence that the criterion was not met. In no cases were we confident that a taxon failed a criterion. We explore the nuances of evidence for sentience, examining both neural and behavioural markers, drawing from and updating our previous review (Birch et al., 2021), and shedding light on the implications for ethical treatment and welfare within this class of animals while also revealing areas where further research is needed.