Antarctic krill, Euphausia superba, makes up the great majority of the crabeater seal's diet. True crabs are essentially absent from the pack-ice waters it hunts in, so the name describes something the animal does not do. The German Krabbenfresser and the loose historical use of crab-like for small crustaceans are the usual explanations offered.
The teeth are the point of interest. Each post-canine tooth carries several sharp accessory cusps, and when the jaws close the upper and lower rows interlock into a fine grid. The seal takes in krill-laden water, closes the jaws and expels the water through the gaps in that grid.
Crabeater seals are also very numerous. Population estimates commonly cited run into the millions, sometimes quoted as high as fifteen million, but these rest on extrapolations from aerial and ship-based surveys of a vast, patchy and largely inaccessible ice zone, and the true figure is genuinely uncertain.