Classification is changing rapidly and unstable with

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Classification is changing rapidly and unstable with yet inclusive ORDERS but Protosteliales, Dictyosteliales and Acrasiales are popular in literature. They occur mostly in moist on organic matter, humus, cultivated lands and forests. Characteristics that separate this class from other groups in the division myxomycota include: (i) Trophic or somatic phase is commonly amoeboid or myxoamoeba
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Continuation (ii) Aggregation of myxoamoebae to form Pseudoplasmodium which depending on the suitability of environmental condition progresses to form sorocarp/sporocarp (sporangium), (iii) Do not produce swarm or flagellated cells, except the genus Pocheina rosea. (iv) Sporangial wall contains cellulose (v) Reproduces both sexually and asexually
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Continuation Stages in the life-cycle of Acrasids are as follows: (i) Haploid spores released from the sorocarp germinates to form myxoamobae, (ii) During unfavorable condition of drought and food, each myxoamoebae encyst or form microcyst. (iii) Microcyst is capable of germinating on return of mositure back to myxoamoebae (iv) Myxoamoebae in reation to a chemical stimulus (acrasin) aggragates to form a pseudoplasmodium which develops to form a sorocarp and a stalk. (v) Sexual process is Fig.9: Schematic representation of the life-cycle of cellular slime mold – Acrasis rosea
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Continuation The dictyostelids cellular slime mold is classified in the Division Myxomycota and the ORDER Dictyosteliales. They exhibit a slightly advance reproductive process that included plasmogamy and karyogamy or sexual reproduction. The feeding phase structurally differs from the acrasid slime mould in being filose (acutely pointed) at one end and uroid (globose) at the other. The reproductive stages in the Dictyosteliales is as Folows: (i) Spores released from the sporocarp germinates to produce myxoamoebae
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Continuation (ii ) After feeding, the myxoamoebae may reproduce asexually by binary fission to produce 2 daughter amaeboid cells. (iii) Like the acrasid, encystment in members of this group triggered by starvation, drought and poisonous chemical signals like ammonia, hydrogen sulphide, etc. (iii) The myxoamoeba can form microcyst which germinates on return of favorable conditions to form myxoamoebae. (iv) Sexual process is initiated by the fusion (plasmogamy) of compatible myxoamoebae to form a zygote which thickens into a macrocyst. (v) This large diploid macrocyst attracts and aggregate with single myxoamoebae, forms a common wall. (vi) Following aggregation is nuclei fusion within the giant cell, cannibalistic feeding by the giant cell, meiosis, and the formation of a secondary wall of cellulose. Macrocyst germinates to form haploid amoebae. (vii) Note that protostelids also forms pseudoplasmodium in a process that does not involve mitosis and meiosis. This slug- like structure compact and forms fructification and columella
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Continuation Fig. 10 : Schematic representation of the life cycle of protostelids ( Dictyostelium discoidium )
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CLASS - Myxomycetes Members of this CLASS – Myxomycetes are
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  • Fall '19
  • Spore, Slime mold, multinucleate sporangia

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