Write short notes based upon the information known to you.
Connecting link: Connecting link refers to plant and organisms which show characteristics related to two different groups. For example, Peripatus is considered a connecting link between annelida and arthropoda. It has characteristics like segmented body, thin cuticle and parapodia-like organs which are similar to annelids. It also shows tracheal respiration and open circulatory system which is similar to arthropods. Another example is duck billed platypus which is a connecting link between reptiles and mammals as it lays eggs like reptiles and has mammary glands like mammals.