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Tonguefish on the seabed. Tonguefish (family Cynoglossidae) are often found mainly in brackish water, such as where rivers flow into the sea, but a few species are found in deep sea floors. They are thought to mimic toxic flatworms, both in the way they are marked and how they crawl across the bottom. They are distinguished by the presence of a long hook on the snout overhanging the mouth, and the absence of pectoral fins. Photographed in the Lembeh Strait, Sulawesi, Indonesia. (KEYSTONE/SCIENCE PHOTO LIBRARY/MATTHEW OLDFIELD)