6. If the ancestral form for a particular lineage was aquatic and used gills for respiration, what changes would you expect to see in a terrestrial descendant?

They now had lungs to support the function of extracting the right amount of oxygen,O₂ from the free air as there is an abundance of oxygen in the atomic form inside the atmosphere. The organisms required hind and fore limbs for the process of locomotion, how ever some of them crawl over the land for movement.A more hard and brittle form of covering or skin was formed by the organisms to save themselves from too much heat and other factors.

Explanation:

There are a number of living beings which have evolved from the aquatic form of life. Mainly, the reptiles and some of the amphibians are termed to have evolved from the aquatic form of life, as they developed there characteristic to cope with the factors that were being faced on lands. Many of the living being which were once fish now had the lungs to extract the right amount of oxygen, O₂ from the free air. As gills were not suitable for the organisms to have in order to have a life on land and thus they were termed as terrestrial organisms.

The answer is lymph sinuses.