Fungi are eukaryotic, heterotrophic organisms characterized by filamentous structures called hyphae, which form a network known as mycelium. They reproduce both sexually and asexually, lack chlorophyll, and obtain nutrients through absorptive nutrition. Fungal somatic structures can be modified for various purposes, including nutrient acquisition and survival in adverse conditions, with specialized structures such as rhizomorphs, sclerotia, and haustoria serving distinct functions.