Zygomycotina Class Zygomycetes
This phylum contains two classes, the class Zygomycetes and the class Trichomycetes (parasites or commensals inside the guts of living arthropods)
Zygomycetes which we will touch upon are mostly coencytic ( hyphae with no septations) though species exist which are septate.
The more than 900 species are primarily terrestrial. Generally they feed on decaying plant and animal matter (substrates of starch & sugar), though this group does contain symbiotic members as well as parasitic forms.
The gametangia arise from hyphae of a single mycelium in homothallic species, or from different but sexually compatible mycelia in heterothallic species. Zygosporangia usually develop thick walls, and act as resting spores.
Below, study the life
cycle of Rhizopus ( known as bread mold), a very common zygomycete
which most of you have noticed growing on bread exposed to air.
Sexual cycle of Rhizopus: When 2 genetically different hyphae meet, swellings form and are eventually cut off from the hyphae by a septation.After fusion, the wall between them dissolves. Nuclei from the 2 strains unite to form diploid nuclei. Any unmatched nuclei disintegrate. This multinucleate cell forms the zygote which remains for several months as the zygospore. It is heavily walled.
After a few months, 1+ filaments grow out of the zygospore to form a sporangium, into which haploid nucei migrate. Each nucleus is surrounded by a wall to form a spore.
Below is the asexual cycle - what logically happens here?
The following image is from :
We will only view one order Mucorales 13 families, 56 genera, 300 species. This order includes all the common saprobic zygomycetes. Here belong the ubiquitous bread mold Rhizopus stolonifer shown above, and the equally common genus Mucor. Perhaps one of the most entertaining genus is Pilobus..
It is coprophilous (dung-feeding) and grows very rapidly, one of the first fungi to fruit in the extended succession that occurs on dung and has an explosive dispersal mechanism.
Underneath the black apical sporangium is a lens-like vesicle, with a light-sensitive `retina' at its base that regulates the growth of the sporangiophore, aiming it towards any light source.
Osmotically active compounds cause pressure in the sporangiophore and the subsporangial vesicle to build up until it is more than 100 pounds per square inch (7 kilograms per square centimetre). This eventually causes the vesicle to explode, hurling the black sporangium away to a distance of up to 2 metres, directly toward the light. The mucilaginous contents of the subsporangial vesicle go with the sporangium, and glue it to whatever it lands on.