One of the most distinctive and defining features of coleoid cephalopods—squid, cuttlefish and octopus—is their inking behavior. Their ink, which is blackened by melanin, but also contains other constituents, has been used by humans in various ways for millennia. This review summarizes our current knowledge of cephalopod ink. Topics include: (1) the production of ink, including the functional organization of the ink sac and funnel organ that produce it; (2) the chemical components of ink, with a focus on the best known of these—melanin and the biochemical pathways involved in its production; (3) the neuroecology of the use of ink in predator-prey interactions by cephalopods in their natural environment; and (4) the use of cephalopod ink by humans, including in the development of drugs for biomedical applications and other chemicals for industrial and other commercial applications. As is hopefully evident from this review, much is known about cephalopod ink and inking, yet more striking is how little we know. Towards closing that gap, future directions in research on cephalopod inking are suggested.

Inking by marine molluscs such as sea hares, cuttlefish, squid, and octopuses is a striking behavior that is ideal for neuroecological explorations. While inking is generally thought to be used in active defense against predators, experimental evidence for this view is either scant or lacks mechanistic explanations. Does ink act through the visual or chemical modality? If inking is a chemical defense, how does it function and how does it affect the chemosensory systems of predators? Does it facilitate escape not only by acting directly on predators but also by being an alarm signal for conspecifics? This review examines these issues, within a broader context of passive and active chemical defensive secretions. It focuses on recent work on mechanisms of defense by inking in sea hares (Aplysia) and extends what we have learned about sea hares to other molluscs including the cephalopods.

A complex nervous system enables spiny lobsters to have a rich behavioural repertoire. The present paper discusses the ways in which the sensory systems of the Caribbean spiny lobster, Panulirus argus , particularly its chemosensory systems, are involved in feeding behaviour. It addresses the neural mechanisms of three aspects of their food-finding ability: detection, identification, and discrimination of natural food odours; the effect of learning on responses to food odours; the mechanisms by which spiny lobsters orient to odours from a distance under natural flow conditions. It demonstrates that the olfactory organ of spiny lobsters might use acrossneuron response patterns in discriminating odour quality; that the hedonic value of food can be modified by experience, including associative and nonassociative conditioning; that spiny lobsters can readily orient to distant odour sources; and that both chemo- and mechanosensory antennular input are important in this behaviour. Either aesthetasc or nonaesthetasc chemosensory pathways can be used in identifying odour quality, mediating learned behaviours, and permitting orientation to the source of distant odours. Studying the neuroethology of feeding behaviour helps us understand how spiny lobsters are adapted to living in complex and variable environments.

This review covers recent research on how marine invertebrates use chemical cues to find and select food.