The harbor seal (Phoca vitulina) is the most widely occurring phocid seal in the world. In the United States, it is found on both the east and west coasts. Their size varies fairly widely across their distribution with the smallest animals weighing around 80-90kg (N. Gulf of Alaska) and the largest animals weighing up to about 170kg (Aleutian Islands). Coloration patterns can also vary between individuals within a population such that they can appear light with dark spots or dark with lighter spots, though often times it is difficult to tell the difference within a population. There is also sexual dimorphism present in this species with males being generally larger than females. You can further explore the normal anatomy of the harbor seal below. Note that many images in the normal anatomy section also feature the Northern Elephant Seal, another phocid species.
As noted in the porpoise and in the sea lion anatomy areas, the musculoskeletal system consists of the muscles, bones, ligaments, and tendons, and teeth! In marine mammals, one of the first noticeable differences during a necropsy is the dark red color of the muscles compared with terrestrial animals. This color is especially distinctive in phocids, especially the deep divers such as elephant seals, because like all marine mammals, they store a significant portion of their oxygen supply for diving on myoglobin in the muscle.
The digestive system of marine mammals consists of the mouth, esophagus, stomach, small and large intestine, colon, and rectum. Accessory organs are also critical for digestive function including the liver and pancreas. Like other marine mammals, phocids swallow their fish whole. The fish travel down the esophagus to the stomach. Phocids like otariids, have a single stomach (in contrast with cetaceans) and it is lined with thick ridges (rugae) which helps with the grinding function of the food.
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