: an order or other division of Choanichthyes including a number of fossil fishes known from the Devonian and later formations and three surviving genera, Neoceratodus, Protopterus, and Lepidosiren, comprising aberrant fishes that have overlapping cycloid scales and dermal fin rays, a largely cartilaginous skeleton with a persistent notochord, an autostylic skull, paired fins of the archipterygial type, gills covered by an operculum, and in addition a lung or pair of lungs communicating with the ventral side of the esophagus by a short tube
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Merriam-Webster unabridged
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