Compare physical feature of freshwater and marine cetaceans. speculate how those physical differences might provide advantages to survival in freshwater versus marine environments.

Marine mammals can be classified as animal that lives partially or wholly on coastal waters or oceans from survival while fish can be classified as a cold blooded gill bearing, egg producing species. However, whales survive by the development of echolacation, modified lungs, thick layers of blubber and lager arteries  among other things to ensure their prosperity and survival.

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.