Cryo‐scanning electron microscopy investigation of the Octopus Vulgaris arm structures for the design of an octopus‐like arm artefact

Abstract

Octopus vulgaris is a cephalopod of the Octopodidae family. It has four pairs of arms and two rows of suckers which perform many functions, including bending and elongation. For this reason the octopus was chosen as model to develop a new generation of soft-body robots. In order to explain some of the fine structures of the octopus arm in relation to its specific ability, we examined the external and internal structures of O. vulgaris arms in a frozen-hydrated state using cryo-scanning electron microscopy. The arms showed skin with a very complex design that is useful to elongation, and a pore pattern distribution on their surface which is functional to cutaneous oxygen uptake. The analysis of freeze-fractured frozen-hydrated arm samples allowed us to describe the developmental differences in the relative proportion of the areas of axial nerve cord, intrinsic and extrinsic musculature, in relation to the growth of the arms and of the increase in functional capability. In the suckers, we analyzed the shedding mechanisms in the outer part of the infundibulum and described the outer and inner characteristics of the denticles, showing in detail their pore system, which is fundamental for their ability to explore the environment. These results are discussed by considering their possible application in the design of new octopus-like artefacts, which will be able to take advantage of some of these ultrastructure characteristics and achieve advanced bioinspired functionalities.

<strong></strong>Convergent Evolution of Attachment Mechanisms in Aquatic Animals

“…Lastly, returning to the group of animals that symbolises biological suction attachment, many coleoid species possess microstructures called cuticular pegs on their suckers (Fig. 5J-L) (Nixon and Dilly 1977;Salcedo-Vargas 1995;Schmidtberg 1999;Minnocci et al 2015). Cuticular pegs, similarly to the arthropod cuticle, are made of chitin-protein complexes and may also be stiff structures (Hunt and Nixon 1981;Accogli et al 2017).…”

“…Researchers have hypothesized that they may increase friction when in contact with the surface and could also help to maximize attachment strength by transmitting low internal pressures throughout the disc (Kier and Smith 1990). High mechanical wear from contacting and increasing friction may be why the lining of the infundibulum is periodically shed (Kier and Smith 1990;Minnocci et al 2015). Further research is needed to reveal the material properties of these cuticular pegs and how they generate additional friction during coleoid suction attachment.…”

Diffusion MRI Connections in the Octopus Brain

“…Following the pioneering work of Young [ 22 ], a large number of anatomical and physiological studies of the octopus and related coleoid cephalopods have been undertaken. In addition to detailed histological studies [ 8 , 12 , 15 , 16 , 23 - 36 ], other efforts have utilized computed tomography [ 37 , 38 ], electron microscopy [ 39 , 40 ], positron emission tomography [ 41 ], fluorescent dye labeling of neuronal connections [ 42 - 44 ] and magnetic resonance imaging [ 45 - 48 ].…”

“…Thus, the octopus is a compelling system for comparison with mammals due to its ancient origin and great anatomical differences combined with fascinating similarities in problem solving skills, learning and memory [11,21] Following the pioneering work of Young [22], a large number of anatomical and physiological studies of the octopus and related coleoid cephalopods have been undertaken. In addition to detailed histological studies [8,12,15,16,[23][24][25][26][27][28][29][30][31][32][33][34][35][36], other efforts have utilized computed tomography [37,38], electron microscopy [39,40], positron emission tomography [41], fluorescent dye labeling of neuronal connections [42][43][44] and magnetic resonance imaging [45][46][47][48].…”