Filter feeding in the mysid crustacean Limnomysis benedeni: Evidence of the maxillary pump and the ventral filtration current

Although the first study on filter feeding in mysids was published almost a hundred years ago, our knowledge on the mechanism is still uncertain mainly due to the inherent difficulty of observing live specimens undisturbed, especially in pelagic species. In this study, we aimed at clarifying the issue using a species more amenable for live observations, the successful Ponto-Caspian invader Limnomysis benedeni. Based on slow-motion video recordings of specimens resting on the wall of the aquarium, we were able to demonstrate that the filtration currents are generated synergistically by the maxillae, the thoracic exopods, and possibly also by the epipods of the first thoracopods and the oostegites in adult females. We could confirm the previously questioned existence of a forwardly directed ventral current between the two rows of thoracopods; however, food particles can approach the mouth from a relatively wide angle. The rows of bristled setae on the proximal lobe of the maxillae can be regarded as the main filters present in most mysids. The studied species also bears accessory filtering setae on the basis of the second thoracopods indicating specialization for filter feeding. It is also likely that some even more specialized pelagic species with bristled setae on their thoracic endopods can use their 'feeding basket' for filtering. Clarifying the filtering mechanism represents a major contribution to our understanding of the func-tional morphology in mysids which might serve as a basis for further studies (e.g., comparisons of filter mesh sizes).