A complete understanding of the feeding structures is fundamental in order to study how animals survive. Some birds use long and protrusible tongues as the main tool to collect their central caloric source (e.g. woodpeckers and nectarivores). Hummingbirds are the oldest and most diverse clade of nectarivorous vertebrates, being a perfect subject to study tongue specializations. Their tongue functions to intraorally transport arthropods through their long bills and enables them to exploit the nectarivorous niche by collecting small amounts of liquid, therefore it is of vital importance to study its anatomy and structure at various scales. I focused on the portions of the hummingbird tongue that have been shown to be key for understanding their feeding mechanisms. I used histology, transmission and scanning electron microscopy, microCT, and ex-vivo experiments in order to advance the comprehension of the morphology and functioning of the hummingbird feeding apparatus. I found that hummingbird tongues are composed mainly of thin cornified epithelium, lack papillae, and completely fill the internal cast of the rostral oropharyngeal cavity. Understanding this puzzle-piece match between bill and tongue will be essential for the study of intraoral transport of nectar. Likewise, I found that the structural composition and tissue architecture of the tongue groove walls provide the rostral portion of the tongue with elastic properties that are central to the study of tongue-nectar interactions during the feeding process. Detailed studies on hummingbirds set the basis for comparisons with other nectar-feeding birds and contribute to comprehend the natural solutions to collecting liquids in the most efficient way possible. PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2986v1 | CC BY 4.0 Open Access | rec Abstract 12 A complete understanding of the feeding structures is fundamental in order to study how 13 animals survive. Some birds use long and protrusible tongues as the main tool to collect their 14 central caloric source (e.g. woodpeckers and nectarivores). Hummingbirds are the oldest and 15 most diverse clade of nectarivorous vertebrates, being a perfect subject to study tongue 16 specializations. Their tongue functions to intraorally transport arthropods through their long bills 17 and enables them to exploit the nectarivorous niche by collecting small amounts of liquid, 18 therefore it is of vital importance to study its anatomy and structure at various scales. I focused 19 on the portions of the hummingbird tongue that have been shown to be key for understanding 20 their feeding mechanisms. I used histology, transmission and scanning electron microscopy, 21 microCT, and ex-vivo experiments in order to advance the comprehension of the morphology and 22 functioning of the hummingbird feeding apparatus. I found that hummingbird tongues are 23 composed mainly of thin cornified epithelium, lack papillae, and completely fill the internal cast 24 of the rostral oropharyngeal cavity. Understanding this puzzle-pie...

The ultrastructure of the digestive system of tardigrades was already described in some species, but it has never been studied in relationship to diet.

The purpose of the work is to analyze the possibilities of implementing the principles of closed-loop economics in the fisheries industry of the Russian Federation, including for achieving national goals.Methods: A SWOT analysis was carried out to assess the waste management situation in the specified industry and to identify the prerequisites for the introduction of the principles of the closed-cycle economy. Monographic, comparative and descriptive methods are used for analyzing of information sources.Novelty: the identification of opportunities and threats for the formation of closed cycles of circulation of raw materials and waste in fisheries systems are the novelty elements of the presented research.Results: the necessity of transition from a linear economy to a closed-loop economy in the analyzed industry  in the light of achieving the national goals of the Russian Federation is revealed, the necessary steps for this are shown. The conclusion is made about the significance of such a transition for the Russian Federation.The results of the study are of practical significance both for biologists, managers, economists, and for the business community.

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