Can cephalopods vomit? Hypothesis based on a review of circumstantial evidence and preliminary experimental observations.

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English. In representative species of all vertebrate classes, the oral ejection of upper digestive tractcontents by vomiting or regurgitation is used to void food contaminated with toxins orcontaining indigestible material not voidable in the feces. Vomiting or regurgitation has beenreported in a number of invertebrate marine species (Exaiptasia diaphana, Cancer productus,and Pleurobranchaea californica), prompting consideration of whether cephalopods havethis capability. This “hypothesis and theory” paper reviews four lines of supporting evidence:(1) the mollusk P. californica sharing some digestive tract morphological and innervationsimilarities with Octopus vulgaris is able to vomit or regurgitate with the mechanisms wellcharacterized, providing an example of motor program switching; (2) a rationale for vomitingor regurgitation in cephalopods based upon the potential requirement to void indigestiblematerial, which may cause damage and ejection of toxin contaminated food; (3) anecdotalreports (including from the literature) of vomiting- or regurgitation-like behavior in severalspecies of cephalopod (Sepia officinalis, Sepioteuthis sepioidea, O. vulgaris, and Enteroctopusdofleini); and (4) anatomical and physiological studies indicating that ejection of gastric/cropcontents via the buccal cavity is a theoretical possibility by retroperistalsis in the upperdigestive tract (esophagus, crop, and stomach). We have not identified any publicationsrefuting our hypothesis, so a balanced review is not possible. Overall, the evidence presentedis circumstantial, so experiments adapting current methodology (e.g., research communitysurvey, in vitro studies of motility, and analysis of indigestible gut contents and feces) aredescribed to obtain additional evidence to either support or refute our hypothesis.We recognize the possibility that further research may not support the hypothesis; therefore,we consider how cephalopods may protect themselves against ingestion of toxic food byexternal chemodetection prior to ingestion and digestive gland detoxification post-ingestion.Reviewing the evidence for the hypothesis has identified a number of gaps in knowledgeof the anatomy (e.g., the presence of sphincters) and physiology (e.g., the fate of indigestiblefood residues, pH of digestive secretions, sensory innervation, and digestive glanddetoxification mechanisms) of the digestive tract as well as a paucity of recent studies onthe role of epithelial chemoreceptors in prey identification and food intake.