In Ascomycetes, a round or oval fruiting body without any external opening which encloses the asci is identified as:

Explanation

In Ascomycetes, a Cleistothecium is a round or oval fruiting body that is completely enclosed, meaning it lacks any external opening. This structure houses the asci, where the spores are formed. Other types of fruiting bodies, such as Apothecia and perithecia, have openings that allow spores to be released, which distinguishes them from Cleistothecia. A Pseudothecium, although similar in appearance to a Perithecium, differs in its internal structure and development. Understanding these differences helps in identifying the correct type of fruiting body described in the question.