Abstract
The octopus sucker represents a fascinating natural system performing adhesion on different terrains and substrates. Octopuses use suckers to anchor the body to the substrate or to grasp, investigate and manipulate objects, just to mention a few of their functions. Our study focuses on the morphology and adhesion mechanism of suckers in Octopus vulgaris. We use three different techniques (MRI, ultrasonography, and histology) and a 3D reconstruction approach to contribute knowledge on both morphology and functionality of the sucker structure in O. vulgaris. The results of our investigation are two-fold. First, we observe some morphological differences with respect to the octopus species previously studied (i.e., Octopus joubini, Octopus maya, Octopus bimaculoides/bimaculatus and Eledone cirrosa). In particular, in O. vulgaris the acetabular chamber, that is a hollow spherical cavity in other octopuses, shows an ellipsoidal cavity which roof has an important protuberance with surface roughness. Second, based on our findings, we propose a hypothesis on the sucker adhesion mechanism in O. vulgaris. We hypothesize that the process of continuous adhesion is achieved by sealing the orifice between acetabulum and infundibulum portions via the acetabular protuberance. We suggest this to take place while the infundibular part achieves a completely flat shape; and, by sustaining adhesion through preservation of sucker configuration. In vivo ultrasonographic recordings support our proposed adhesion model by showing the sucker in action. Such an underlying physical mechanism offers innovative potential cues for developing bioinspired artificial adhesion systems. Furthermore, we think that it could possibly represent a useful approach in order to investigate any potential difference in the ecology and in the performance of adhesion by different species.
Highlights
Octopuses use their suckers to perform a remarkable variety of functions [1], such as, anchoring the body to the substrate, grasping, manipulating and investigating objects [2].Despite several studies on this topic, spanning more than 100 years, many questions relating the function of the sucker remain unclear
Morphology of the Octopus vulgaris Suckers Results on the morphology of the Octopus vulgaris suckers, obtained by using histology, showed that the acetabulum is similar to an ellipsoid, which appeared flattened at the poles (Figure 2A)
This particular morphology was determined by means of Magnetic Resonance Imaging (MRI) and 3D reconstructions of O. vulgaris suckers (Figure 4 and Video S1)
Summary
Octopuses use their suckers to perform a remarkable variety of functions [1], such as, anchoring the body to the substrate, grasping, manipulating and investigating objects [2].Despite several studies on this topic, spanning more than 100 years, many questions relating the function of the sucker remain unclear. A detailed description of the anatomy of suckers on several different octopus species (namely Octopus joubini, Octopus maya, Octopus bimaculoides/bimaculatus and Eledone cirrosa) was reported by Kier and Smith [14,15]. In these studies no particular anatomical differences were found using histology and cinematography, with the exception of a different location of muscles bundles in Eledone cirrosa. The external surface of the infundibulum is covered by the chitinous cuticle or sucker lining, which is periodically shed and continuously renewed [1,3,11,18]. The ridges are organized in mammelliforme structures, composed of micrometer elementary units, called denticles
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