Visual cognition in deep - sea cephalopods : what we don ’ t know and why we don ’ t know it

A quick glance at the recent cephalopod literature, or even at the chapters of this book, tells us that when we talk about cephalopod cognition we are really considering cognition in a handful of genera. There can be no argument that studies of these animals have led to remarkable results that have challenged the traditional view of invertebrate intelligence. Yet when we consider that less than 10 species of cephalopod are commonly seen as the focus of behavioral studies, let alone in studies specifically about cognition, it becomes apparent that claims regarding the cognitive capabilities of cephalopods are generalizations drawn from work on a handful of genera. The majority of the 800 or so described species of cephalopod do not share the neritic and near-shore benthic habitats of the taxa with which we are most familiar; virtually unknown in terms of their behaviour and ecology, these species inhabit a different world in the deep, dark waters of the open ocean (Figure 10.1). In this chapter, we introduce and discuss the neglected cephalopods of the deep sea, many of which are not so distantly related to the species with which we are familiar, but whose existence in the deep sea has little in common with the complex reefs and nearshore habitats associated with taxa such as Octopus and Sepia. What effect might these differences in ecology have on the cognitive abilities of deep-sea cephalopods compared with their shallow water relatives? Chapter 9 of this volume (by Zylinski & Osorio) explored what we can deduce about cuttlefish visual cognition from the body patterns they use for camouflage. In this chapter we revisit the theme of making inferences about visual perceptive and cognitive abilities via body patterning in the handful of epipelagic and mesopelagic species that have been studied to date. Prior to that, we consider how the cognitive needs of these animals might differ from those of near-shore or shallow benthic environments. We explore what is known about the potential for visual cognition in deep-sea cephalopods and discuss why we know so little. Readers might find this chapter heavier on natural history and observation than the others in this book, but we hope that it will serve as a reminder that most cephalopods are essentially unknown beyond their descriptions.