Certain fish of deep levels are equipped with relatively huge mouths and jaws and remarkably distensible stomachs, for example Saccopharynx, Eurypharynx (Figure 4.12c and d) and Gigantura. The jaws are often the only well-developed parts of the skeletal and muscular systems, and their swimming movements must be sluggish. In zones of darkness and scarce food it is evidently important to be able to take very large mouthfuls on the infrequent occasions when prey is found. These deep-level fish are mostly quite small, seldom more than about 10 cm in length. There is insufficient food within the water column to support many large bathypelagic species, but on the deep sea floor aggregation of food provides sufficient for a more numerous population of larger, bottom-feeding animals. Some of the macrurid fish at 5000-6000 m grow to over 1 m in length.
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