Briefly formulate the features of the external structure of pinnipeds, allowing them to lead a semi-aquatic lifestyle.

The representatives of pinnipeds have many characteristics that help these organisms lead such a lifestyle that they spend part of the time on land and the other part in water. The most prominent first difference is the presence of modified limbs in pinnipeds – they are much shorter than the usual ones and their modification is associated with the reorientation of the function for which they are used – movement not on land, but in water. They are called flippers – they replace fins. The second difference is the streamlined body shape, which helps to swim easily and without hindrance. They also secrete a large fat reserve, which helps to retain heat and reduce heat transfer to a minimum.