The mycelium of multicellular fungi is linear and branched. They are composed of slender and linear hyphae or filaments. Hyphae join together to form mycelium. Mycelium may be septate or septate or non-septate. Mycelium which has septa or walls is called septate. Penicillium and Agaricus are acinocytic. The mycelium that does not have septa or walls is called sinocytic mycelium. Cells of sinusocytic mycelium contain multiple nuclei. This is called sinusitis. Mucor and Saprolegnia are acinocytic.