Initial stages of food ingestion bySepia officinalis(Mollusca: Cephalopoda)

Wear patterns of radular teeth in Loligo vulgaris (Cephalopoda; Mollusca) are related to their structure and mechanical properties

Radular teeth have to cope with wear, when interacting with ingesta. In some molluscan taxa, wear-coping mechanisms, related to the incorporation of high contents of iron or silica, have been previously determined. For most species, particularly for those which possess radulae without such incorporations, wear-coping mechanisms are understudied. In the present study, we documented and characterized the wear on radular teeth in the model species Loligo vulgaris (Cephalopoda). By applying a range of methods, the elementary composition and mechanical properties of the teeth were described, to gain insight into mechanisms for coping with abrasion. It was found that the tooth regions that are prone to wear are harder and stiffer. Additionally, the surfaces interacting with the ingesta possessed a thin coating with high contents of silicon, probably reducing abrasion. The here presented data may serve as an example of systematic study of radular wear, in order to understand the relationship between the structure of radular teeth and their properties.

Can Cephalopods Vomit? Hypothesis Based on a Review of Circumstantial Evidence and Preliminary Experimental Observations

In representative species of all vertebrate classes, the oral ejection of upper digestive tract contents by vomiting or regurgitation is used to void food contaminated with toxins or containing indigestible material not voidable in the feces. Vomiting or regurgitation has been reported in a number of invertebrate marine species (Exaiptasia diaphana, Cancer productus, and Pleurobranchaea californica), prompting consideration of whether cephalopods have this capability. This "hypothesis and theory" paper reviews four lines of supporting evidence: (1) the mollusk P. californica sharing some digestive tract morphological and innervation similarities with Octopus vulgaris is able to vomit or regurgitate with the mechanisms well characterized, providing an example of motor program switching; (2) a rationale for vomiting or regurgitation in cephalopods based upon the potential requirement to void indigestible material, which may cause damage and ejection of toxin contaminated food; (3) anecdotal reports (including from the literature) of vomiting- or regurgitation-like behavior in several species of cephalopod (Sepia officinalis, Sepioteuthis sepioidea, O. vulgaris, and Enteroctopus dofleini); and (4) anatomical and physiological studies indicating that ejection of gastric/crop contents via the buccal cavity is a theoretical possibility by retroperistalsis in the upper digestive tract (esophagus, crop, and stomach). We have not identified any publications refuting our hypothesis, so a balanced review is not possible. Overall, the evidence presented is circumstantial, so experiments adapting current methodology (e.g., research community survey, in vitro studies of motility, and analysis of indigestible gut contents and feces) are described 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 by external chemodetection prior to ingestion and digestive gland detoxification post-ingestion. Reviewing the evidence for the hypothesis has identified a number of gaps in knowledge of the anatomy (e.g., the presence of sphincters) and physiology (e.g., the fate of indigestible food residues, pH of digestive secretions, sensory innervation, and digestive gland detoxification mechanisms) of the digestive tract as well as a paucity of recent studies on the role of epithelial chemoreceptors in prey identification and food intake.

Effect of early feeding experience on subsequent prey preference by cuttlefish,Sepia officinalis

Food preferences were investigated in cuttlefish during the first 3 months' posthatching, using choice tests between crabs, shrimps, and young fish. The results showed that without previous feeding experience, cuttlefish preferred shrimps on Day 3. This suggests an innate food preference; however, it was possible to induce a preference for an originally nonpreferred prey item in 3-day-old and naïve cuttlefish, demonstrating the flexibility of this initial behavioral preference in response to previous individual experience. This preference suggests a learning process involving a form of long-term memory, demonstrated for the first time in juvenile cuttlefish. Until Day 30, juvenile cuttlefish fed exclusively shrimps chose shrimps. This preference probably depends on their previous feeding experience. Finally, it appears that from Day 60, cuttlefish reared on the same restricted diet have a tendency to switch their preference to novel prey items, which diversify their diet.

The radular apparatus of cephalopods

This paper describes the ontogeny, breakdown and absorption of the radular teeth of cephalopods and, for the first time, considers the function of the ‘bolsters’ or radular support muscles.

The radular ribbon, which bears many regularly arranged transverse rows of teeth one behind the other, lies in a radular canal that emerges from the radular sac. Here the radular teeth are formed by a set of elongate cells with microvilli, the odontoblasts. These are organized into two layers, the outer producing the radular membrane and the bases of the teeth, the inner producing the cusps. The odontoblasts also secrete the hyaline shield and the teeth on the lateral buccal palps, when these are present. At the front end of the radular ribbon the teeth become worn in feeding and are replaced from behind by new ones formed continuously in the radular sac, so that the whole ribbon moves forward during ontogeny. Removal of the old teeth is achieved by cells in the radular organs; these cells, which are formed from modified odontoblasts (‘odontoclasts’), dissolve the teeth and membranes and absorb them. There is a subradular organ in all cephalopods. InOctopus vulgaris, which bores into mollusc shells and crustacean carapaces, it is especially well–developed and there is also a supraradular organ.

A characteristic feature of the cephalopod radular apparatus is the pair of large radular support muscles or ‘bolsters’. Their function seems never to have been investigated, but experiments reported here show that when they elongate, the radular teeth become erect at the bending plane and splayed, presumably enhancing their ability to rake food particles into the pharynx. The bolsters ofOctopusfunction as muscular hydrostats: because their volume is fixed, contraction of their powerful transverse muscles causes them to elongate. In decapods and in nautiloids each bolster contains a ‘support rod’ of semi–fluid material, as well as massive transverse musculature. This rod may elongate to erect the radular teeth. At the extreme front end of the bolsters inOctopusthere are many nerve fibres that may constitute a receptor organ signalling the movements of the radula against hard material. Such nerves are absent from decapods and from octopods that do not bore holes.

The buccal mass ofNautilusis massive, with heavily calcified tips to the beaks and a wide radular ribbon, with 13 rather than nine elements in each row. Nevertheless all the usual coleoid features are present in the radular apparatus and the teeth are formed and broken down in the same way. However,Nautilushas a unique structure, the radular appendage. This comprises a papillate mass extending over the palate in the mid–line and forming paired lateral masses that are in part secretory. The organ is attached to the front of the radula by muscles and connective tissue. Its function is unknown.