Meeting Abstract
Fish fin rays (lepidotrichia) are typically composed of paired and segmented structures (hemitrichia) that help support and change the shape of the fins to affect water flow. Yet, marine fish that are members of the family Priontinae (sea-robins) have specialized pectoral fin rays that are separated from the pectoral fin and used like limbs to walk along the seafloor. While previous kinematic studies have supported the use of these specialized fin rays as walking appendages, there is little information on how the morphology of the “walking-rays” and associated muscles facilitate underwater walking. Here we examine the musculoskeletal anatomy and flexibility of the walking-rays and pectoral fin rays in two species of sea robin, Prionotus evolans and P. carolinus using gross dissection, microCT, and materials testing. Our main goals were to determine what structural modifications may be present in the walking rays that would promote the use of these flexible chain-link rays as supportive structures capable of propelling the fish forward along the seafloor. Our results revealed enlarged processes for muscle attachment and novel S-shaped bone segments forming the dorsal hemitrich of the walking rays. The three-point bending tests of the walking fin rays revealed a significant reduction in flexibility when bent dorsally or rostrocaudally. This increased rigidity rostrocaudally may support the ray once it is depressed into the seafloor and enters the propulsive phase. The novel S-shape segments of the hemitrichs may also promote the directional rigidity of the walking rays of sea-robins. These novel features, which are also used for prey detection, may have allowed these benthic fish to conserve energy while foraging on the seafloor. Furthermore, the features of the ray morphology may be applicable in robotics or the development new lightweight prosthetics.
