ZYGOMYCETES
They have thick walled resting spores called zygospores formed by gametangial coupulation and do not have motile zoospores at any stage of life cycle . Therefore they are also called conjugating fungi .
One of the order under zygomycetes is mucorales . It includes Mucor , Rhizopus etc .
Rhizopus
Class - Zygomycetes
Order - Mucorales
Family - Mucoraceae
Genus - Rhizopus
Rhizopus has branched , filamentous and coenocytic mycelium . Hyphae are stolons , rhizoids and sporangiophores . Asexual reproduction takes place by non-motile sporangiospores ( aplanospores ) and chlamydospores . Sporangium is divided into peripheral cytoplasm and central sterile columella . Peripheral cytoplasm divide to form sporangiospores .
Most of the species of Rhizopus are heterothallic . Sexual reproduction takes place by isogametangial coupulation . Progametangia develops into club shaped isogametangia and suspensor . After gametangial coupulation zygospore is formed . Zygosore contains many diploid nuclei formed by fusion between nuclei of two opposite strains . Unfused nuclei degenerate . Zygospore enlarges , secretes several layers around themself and becomes thick walled . After a long resting period zygospore germinates to form a zygosporangium on sporangiophore . Dipoid nuclei in zygosporangium divide to form haploid meiospores . If coupulation does not take place zygospore develops into azygospore .
Mucor
Mucor has same classification as Rhizopus . Mucor are commonly called pin mould or black mould . They cause mucoromycosis ( a disease of lung and brain ) in domestic animals as well as in humans . In anaerobic liquid cultures especially in the presence of CO2 the hyphae break to form yeast like bodies . This condition is called torula stage . It is a reversible condition . If the O2 is made available it reverts to filamentous stage . A. F. Blakeslee studied the phenomenon of heterothallism in Mucor . Heterothallic species requires two different strains for sexual reproduction .
Differences between Rhizopus and Mucor
1. Mycelium is differentiated ( stolons , rhizoids and sporangiophores ) in Rhizopus but undifferentiated in Mucor .
2. Food material is absorbed by rhizoids in Rhizopus and by entire mycelial surface in Mucor .
3. Sporangiophores occurs in tuft in Rhizopus and singly in Mucor .