Final answer:
Fungi producing mycelium are called filamentous fungi. Mycelium consists of a network of hyphae, which are prominent in multicellular fungal organisms, in contrast to yeasts that are unicellular.
Step-by-step explanation:
Fungi that produce mycelium are known as filamentous fungi. Mycelium is the term used to describe a network of hyphae, which are the thread-like filaments that make up the body of the fungus. Most multicellular fungi go through a vegetative stage where they form this complex network. While yeasts are a type of fungus, they are unicellular and do not form mycelium. Thus, the correct answer is 'a. Filamentous fungi'.
It's important to note that some molds are also composed of multicellular structures that produce hyphae, which collectively form a mycelium. These organisms are critical to the decomposition process in nature and have been utilized for various benefits in healthcare, such as the production of antibiotics like penicillin.