A hydrodynamic antenna: novel lateral line system in the tail of myliobatid stingrays

Eagle rays, cownose rays and manta rays (order Myliobatiformes) have a slender tail that can be longer than the animal's body length, but its function and structure are unknown. Using histology, immunohistochemistry and three-dimensional imaging with micro-computed tomography scans, we describe the anatomy and function of the tail in Rhinoptera bonasus, the cownose ray. The tail is an extension of the vertebral column with unique morphological specializations. Along the tail behind the barb, vertebral centra are absent and neural and haemal arches fuse to form a solid mineralized structure that we describe for the first time and term caudal synarcual, which imparts passive stiffness to the tail, reducing bending. Two lateral line canals connected to an extensive tubule network extend along both sides of the tail. Tubules branch from the lateral line canal toward the dorsal and ventral tail surfaces, opening to the surrounding water via pores. A continuous neuromast is located within each lateral line canal, maintaining an uninterrupted structure along the entire tail. The complex lateral line mechanosensory system in the tail of R. bonasus supports the hypothesis that the tail functions like a hydrodynamic sensory antenna and may play an important role in their behavioural and functional ecology.