The fungal group Zygomycota is most frequently encountered as common bread molds, although both freshwater and marine species exist. Most of these live on decaying plant and animal matter found on the substrate. Aquatic species are primarily found in sediments or on algae, but some species are also free floating. A few are found attached to aquatic animals or on decaying leaves. Some are parasites of plants, insects, or small soil animals, while others cause serious infections in humans and domestic animals. They are usually recognized by their profuse, rapidly growing hyphae, but some exhibit a unicellular, yeast-like form of growth. Asexual reproduction is by means of spores produced in sporangia borne on the hyphae. Zygotmycota get their name from the production of thick walled sexual structures called zygosporangia which can remain dormant for long periods.