Functional morphology of ventral tail bending and prehensile abilities of the seahorse,Hippocampus kuda

Abstract

Unlike most teleosts, the seahorse (genus Hippocampus) is able to bend its tail ventrally, uses its tail in a postural role as a grasping and holding appendage, and possesses heavy body plates instead of scales. To investigate seahorse axial bending mechanisms and the role of plating in those mechanisms, observations were made on seahorses curling their tails ventrally and holding a support and components of the mechanical system used for axial bending, including dermal plates, vertebrae, and axial muscles, were examined. Anatomical modifications involved in ventral tail bending include hypertrophy of the ventral region of the hypaxial muscle, ventrolateral attachment of the myomeres to plates, and modification of the infracarinalis posterior muscles so that they act in axial bending rather than in fin movement as has previously been hypothesized (Harder, '75) for other fishes. Modifications for prehension include the presence of fibers histochemically characterized as tonic in the median ventral muscles (the modified infracarinalis muscle) and in portions of the myomeres. Dermal plates are an important part of the force transmission system used in seahorse tail bending. They transmit forces from the hypaxial myomeres to bend the tail both laterally and ventrally. This study expands our understanding of axial bending in fishes by examining extreme modifications of the musculoskeletal system associated with the evolution of unique functional capabilities within teleosts. © 1996 Wiley-Liss, Inc.