When the entire body of a bacterium is covered by flagella, such a bacterium is called:

Explanation

Bacteria are classified based on the arrangement of their flagella, which affects their motility. Peritrichous bacteria have flagella all over their surface, enabling them to move in various directions efficiently. This is in contrast to atrichous bacteria, which lack flagella entirely and are non-motile. Lophotrichous and amphitrichous bacteria have flagella localized to specific areas, either in bundles at one end or at both ends, respectively. Thus, the correct answer is D: Peritrichous.