Suction adhesion in the gliding joint of a cephalopod [RESEARCH ARTICLE]

Andrew M. Smith, Scott M. LaValva, Matthew M. Loiacono, and Joseph T. Thompson We have discovered features of the nuchal joint in the squid, Doryteuthis pealeii, that are unique compared with moveable joints in other animals. The joint's function is unclear but it allows the head to glide toward and away from the mantle. The head glides along the joint with ease yet disarticulating the joint perpendicular to the axis of movement requires considerable force. After disarticulation, the joint components can be repositioned and full function restored immediately. Thus, an unknown attachment mechanism prevents the joint from being disarticulated yet permits gliding. We show that the joint was formed by the articulation of the nuchal cartilage and a heretofore-undescribed organ that we named the nuchal ‘joint pad’. The joint pad is composed predominantly of muscle, connective tissue and cartilage organized into two distinct regions: a ventral cartilaginous layer and a dorsal muscular layer. Disarticulating the nuchal joint at a displacement rate of 5 mm s–1 required 1.5 times greater stress (i.e. force per unit area) than at 1 mm s–1. The force required to disarticulate the joint increased with nuchal cartilage area0.91 and with nuchal cartilage length1.88. The stress required to shear the nuchal joint was nearly three orders of magnitude lower than that required to disarticulate the joint. Stimulation of the joint pad dorso-ventral...
Source: Journal of Experimental Biology - Category: Biology Authors: Tags: RESEARCH ARTICLE Source Type: research
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