Biological Department, College of Mathematics and Sciences, Westfield State University, 577 Western Avenue, Westfield, MA 01086, USA
Biological Department, College of Mathematics and Sciences, Westfield State University, 577 Western Avenue, Westfield, MA 01086, USA.
J Exp Biol. 2020 Sep 28;223(Pt 18):jeb227140. doi: 10.1242/jeb.227140.
Fish fin rays (lepidotrichia) are typically composed of paired and segmented flexible structures (hemitrichia) that help support and change the shape of the fins to affect water flow. Yet, marine ray-finned fish that are members of the family Priontinae (sea-robins) have specialized pectoral fin rays that are separated from the fin and used as limbs to walk along the seafloor. While previous kinematic studies have demonstrated the use of these specialized fin rays as walking appendages, there is little information on how the morphology of the 'walking rays' and associated musculature facilitate underwater walking. Here, we examine the musculoskeletal anatomy of the walking and pectoral fin rays in the striped sea-robin and compare the mechanical properties of the rays with those of the smaller northern sea-robin We aimed to determine what structural modifications in the walking rays allow them to function as a supportive limb. We found enlarged processes for muscle attachment, bone extensions that brace the hemitrich articulations, and reduced flexibility and increased second moment of area along the rostro-caudal bending axis in the rays used for walking. This novel limb design may have promoted the benthic foraging behavior exhibited by these species by uncoupling locomotion and feeding.
鱼鳍的鳍条通常由成对的、分段的柔韧结构（半鳍条）组成，这些结构有助于支撑和改变鳍的形状，以影响水流。然而，属于 Priontinae 科（海鲂）的海洋软骨鱼具有专门的胸鳍鳍条，这些鳍条与鳍分离，用作在海底行走的附肢。虽然之前的运动学研究已经证明了这些专门的鳍条可以用作行走的附肢，但关于“行走鳍条”的形态以及相关肌肉组织如何促进水下行走的信息却很少。在这里，我们检查了条纹海鲂行走和胸鳍鳍条的肌肉骨骼解剖结构，并比较了行走鳍条和较小的北方海鲂的机械性能。我们旨在确定行走鳍条的哪些结构修改使其能够作为支撑肢发挥作用。我们发现，用于行走的鳍条上的肌肉附着处有增大的突起、支撑半鳍关节的骨延伸、以及沿头尾部弯曲轴的柔韧性降低和第二转动惯量增加。这种新的附肢设计可能通过解耦运动和进食，促进了这些物种的底栖觅食行为。
