Zygomycetes

The zygomycetes (Phylum Zygomycota) comprise about 1,060 species, including common bread molds, as well as both freshwater and marine species. Most have profuse, rapidly growing hyphae, but some are unicellular and yeast-like. 
  

Phylum Zygomycota

Zygomycetes carry out asexual reproduction by means of spores produced in sporangia that are borne on the hyphae. They also produce thick-walled sexual structures called zygosporangia (singular zygosporangium), which can remain dormant for long periods. These sporangia, produced by various zygomycetes, have a series of forms that predate the evolution of the conidia seen in the later group, ascomycetes.
 

                  Zygosporangium of Rhizopus Zygosporangium 

Many zygomycetes produce multiple sporangiospores inside a single sporangium. Some have multiple small sporangia that contain only a few sporangiospores, or even a single one. This single structure is very similar to the conidium produced by ascomycetes.    

Sporangium

The evolution from sporangiospore to conidia is the main difference between the two groups.

Most species of zygomycetes live in soil, or on decaying plant and animal matter. Aquatic species are primarily found in sediments or algae, but some species are free-floating or attached to aquatic animals or decaying leaves. 

Some are parasites of plants, insects, or small soil animals, while others are symbiotic with plants. Still, others cause serious infections in humans and domestic animals.

Black bread mold (Rhizopus stolonifer) is a typical example of a zygomycete. It spreads over the surface of bread and other food sources (often soft fruits, such as bananas, tomatoes and grapes). It sends hyphae inside the food to absorb nutrients. In its asexual phase, it develops bulbous black sporangia at the tips of upright hyphae, each containing hundreds of haploid spores.
   

Rhizopus stolonifer

As in most zygomycetes, asexual reproduction is the most common form of reproduction. Sexual reproduction in Rhizopus stolonifera, as in other zygomycetes, occurs during adverse environmental conditions, and when haploid hyphae of different mating types come together. 

Plasmogamy occurs, followed by karyogamy, producing a thick-walled, diploid zygosporangium that is environmentally resistant and metabolically inert. When the environment becomes favorable, the zygosporangia germinate, undergo meiosis, and produce and release haploid spores.

Black bread mold simply releases its spores, but some zygomycetes disperse their spores very precisely. Pilobolus, a fungus that grows on animal feces, bends its sporangiophores towards light with the help of a light-sensitive pigment, and then "fires" them with an explosive squirt of high-pressure cytoplasm. 
    

Polibolus

Sporangia can be launched as far as two meters, placing them far away from the feces and, hopefully, on vegetation that will be eaten by a herbivore. The sporangium passes through the digestive tract without germinating and is eventually deposited elsewhere with feces. 

Different mechanisms for forcible spore discharge have evolved among some zygomycetes.