Meeting Abstract
79.3 Sunday, Jan. 6 A filtration mechanism for large vertebrate suspension feeders: fluid flow and filter anatomy in the devil rays (Mantas and Mobulas) PAIG-TRAN, EWM*; SUMMERS, AP; U Washington; U Washington mpaig@uw.edu
The gross anatomy and microstructure of the filter pad in the 11 species of devil rays are unusual with respect to other filter-feeding elasmobranch fishes. We used a combination of anatomical descriptions, scanning electron microscopy (SEM), histology, and modeling to describe the anatomy and filtration mechanisms in the mobulids rays. The filter pads are chevron-shaped, rigid, cartilaginous structures composed of repeating filter lobes located on the anterior (toward the incoming flow) and posterior (toward the esophagus) surfaces of the epibranchial and ceratobranchial arches. The ultrastructure of the leaf-like, ascending filter lobes varies between species; however, most are keratinous and can be either smooth or covered in micro-cilia, and some include the presence of denticles. The shape and surface of the terminal filtering lobes are distinct in each species and can be used as a tool for species identification. The epithelium has a high density of mucosal cells which we propose serves as a mechanism for sticky sieve filtration. Fluid flow in the mobulid rays is unusual; instead of following a relatively straight trajectory through the buccopharyngeal cavity as in other suspension feeding fishes, it diverges 90° from the incoming flow to pass through the branchial filter pores. Food particles within the incoming water contact the filter lobes via inertial impaction and remain attached to the filter through sticky sieve filtration. The deviation of the streamline results in a modified form of cross-flow filtration where large shearing forces tangential to the surface of the filter pad create a self-cleaning mechanism for the filter lobe and concentrate filtered particles near the esophagus. This is similar to our results from physical models of filter-feeding fishes we quantified multiple mechanisms of filtration working together during a filtering event.
