Final answer:
The epidermis is the skin layer that provides a watertight, protective seal for the body. It consists of keratinocytes which form a waterproof barrier of keratin.
Step-by-step explanation:
The layer of the skin that forms a watertight, protective seal for the body is the epidermis. The epidermis is the outermost layer of the skin and is key to the skin's role as a barrier. It consists mainly of cells called keratinocytes, which form a protective, waterproof layer of keratin.
The epidermis is relatively thin and lacks blood vessels, obtaining nutrients by diffusion from the blood vessels in the underlying dermis. Despite its thinness, it is crucial for protecting the body against water loss and pathogen invasion. This protection is enhanced by additional layers such as the dermis and the subcutaneous tissue, but the initial and primary barrier is the epidermis.