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 might support sentience and whether their behaviour indicates sentience. There is very strong evidence of sentience in octopuses, which satisfy seven of the eight criteria. There is less evidence for cuttlefish and squid (4/8 criteria), although this is still substantial evidence. By contrast, whether nautiluses are sentient remains unknown (1/8 criteria), since this group of cephalopods have attracted little research. This reflects a general pattern: when criteria were not satisfied, this invariably reflected a lack of positive evidence. In no cases were we confident that a taxon failed a criterion. In our review, we explore the nuances of evidence for sentience, examining both neural and behavioural markers. This paper draws from and updates our review (Birch et al., 2021), shedding light on the implications for ethical treatment and welfare within this class of animals while also revealing areas where further research is needed