Squid dances: an ethogram of postures and actions of Sepioteuthis sepioidea squid with a muscular hydrostatic system

A taxonomy of the movement possibilities for any species, within the constraints of its neural and skeletal systems, should be one of the foundations of the study of its behaviour. Caribbean reef squid, Sepioteuthis sepioidea, appear to have many degrees of freedom in their movement as they live in a three-dimensional habitat and have no fixed skeleton but rather a muscular hydrostatic one. Within this apparent lack of constraints, there are regularities and patterns of common occurrences that allow this article to describe an ethogram of the movements, postures and positions of squid. Squid have a combination of bent, spread and twisted maintained postures of the eight arms and two tentacles that enhance camouflage. Their body arm posture combinations are actively maintained in the water but also influenced by gravity. Positions related to conspecifics are stereotyped and important for communication. For locomotion, squid use a well-coordinated dual fin jet locomotion system. This motor system uses tonic postures for camouflage and maintains body position in courtship, though squid seldom touch. The interdependence of movement control by different units is seen in fins and jet propulsion, and bilateral symmetry is maintained even for the eight arms. It is argued that the repertoire is well adapted for a soft-bodied animal in its three-dimensional, open but near-shore demersal habitat.