This document provides an overview of Myxomycotina (slime molds). It discusses that they are fungus-like organisms characterized by an amoeboid vegetative phase without cell walls. The document outlines the key characteristics and life cycles of the four classes: Acrasiomycetes, Hydromyxomycetes, Myxomycetes, and Plasmodiophoromycetes. It also briefly discusses their economic importance in nutrient cycling and use in laboratory studies due to their protoplasm without cell walls.

1. Myxomycotina: General account
Vaishali S.Patil
Professor, Department of Botany
Shri Shivaji College of Arts, Commerce & Science
Akola

2. Introduction-
1.The Myxomycota or slime molds, are fungus-like organisms.
2.They are characterised by the absence of cell wall from their
amoeboid,’ animal-like vegetative or assimilatory phase.
3.The amoeboid assimilatory phase may consist of a free-
living multinucleate mass of protoplasm called a plasmodium
or simple uninucleate amoeboid cells, the myxamoebae (sing,
myxamoeba) often aggregating into a pseudoplasmodium or
amoeboid cells interconnected by slime filaments giving rise
to a structure known as net plasmodium or filoplasmodium.
4.They exhibit characteristic of both animals and plants.
5.The true slime molds are mostly saprophytic(formation of

3. fructifications) with a few parasitic ones.(absence of development of
fructifications, the plasmodium is converted into masses of spores).
6. All the true slime molds produce flagellated cells, the swarm cells.
7. The formation swarm cells is absent in the cellular slime molds. In the
cellular slime molds fructifications are developed from the
pseudoplasmodia.
8. In the net slime molds each cell is converted into a mucilaginous
sporocyte in which spores are developed.
9.The spores escape as biflagellate zoospores which after swimming for
some time, lose their flagella become surrounded by delicate envelope
and give rise to new net plasmodium.
10. They are found on moist dead wood, rotting logs, damp soil, leaf
mold, moist sawdust, bark of trees, decaying fleshy fungi, or other

4. organic matter. They often spend most of their lives within the
substrate and emerge only when about to produce sporangia.
Following periods of rainy weather they may occur on leaves
of grasses or other plants on lawns.
moist dead wood rotting logs damp soil, leaf mold,
moist sawdust bark of trees decaying fleshy fungi
on leaves of grasses or
other plants on lawns.
Other organic matter

5. Phylogeny-
•Macbride (1899) believed that the slime molds are fungi.
• Karling (1944) suggested that the slime molds are closely related to
Protozoa than to fungi.
•Martin (1932, 1960-61) has pointed out that if the algal origin of fungi
is accepted, then the slime molds are not fungi; but if the fungi have been
descended from colourless flagellates, the slime molds can well be
regarded as fungi.
• Sparrow (1958) proposed that the parasitic slime molds be regarded as
a separate Class the Plasmodiophoromycetes.
•Talbot (1971), Webster (1983), and others grouped all the four classes of
slime molds under the Division Myxomycota close to fungi.
•Bonner considers the Acrasiomycetes to have had their origin from the
free-living amoebae of the soil.

6. Classification- Kingdom Fungi
Division Myxomycota
(Plasmodium or pseudoplasmodium present) Eumycota
Classes
Acrasiomycetes Hydromyxomycetes Myxomycetes Plasmodiophoromycetes
(Amoeboid
cells
aggregating
into a
pseudoplasmo
dium)
(Amoeboid cells
spindle-shaped to oval
interconnected by
slime filaments
forming a net
commonly known as
‘net plasmodium’ or
‘filo-plasmodium’)
(Free-having
plasmodium bearing
haploid or diploid
nuclei, Plasmodium
non-parasitic,
fructification present.)
Plasmodium
parasitic,
fructification
lacking

7. A. Class: Acrasiomycetes:
Acrasiomycetes are commonly known as cellular
or amoeboid slime molds, and are found
profusely in the upper layer of humus in
deciduousforests and also in cultivated lands.
The characteristic features are:
1. Somatic phase commonly consists of amoeboid
cells or myxamoebae.
2. Myxamoebae aggregate to form a pseudoplasmodium, which develops fruit body.
3. Lack of flagellated cells, except in Pocheina rosea.
4. Spore wall contains cellulose.
5. Fruit bodies may be sorocarps (in Dictyostelium) or sporocarp (in Protostelium).
Raper (1973) divided the class into 3 subclasses: Protostelidae, Acrasidae and
Dictyostelidae.
Later, Olive (1975) raised the rank subclasses into classes as Protosteliomycetes,
Acrasiomycetes and Dictyosteliomycetes.
Reproduction- When resources such as water or food become limiting, the amoeba
will release pheromones such as acrasin to aggregate amoebal cells in preparation for
movement as a large (thousands of cells) grex or pseudopod. When in the grex, the
amoeboids reproduce, resulting in fruit-like structures called spores, which develop
into unicellular molds of the same species.

8. B. Class: Hydromyxomycetes:
The thallus forms net plasmodium or filoplasmodium. They are commonly aquatic
and saprobic, but rarely parasitic.
The characteristic features are:
1.The thallus consists of uninucleate spindle shaped cells, forming extensive
filaments.
2. The filaments are tubular and form net-like structure, the net-plasmodium or
filoplas- modium.
3. Reproduction by cyst formation, zoospore formation or by congregation.
The class consists of two orders Hydro- myxales and Labyrinthulales. But
Hawksworth et al. (1983) excluded Hydromyxales from fungi and included it in
Protozoans. The members of Labyrinthulales are parasitic on higher plants and also
on marine algae. Labyrinthula macrocystis is a very common species, found as parasite
on Zostera marina, the eel-grass.

9. Class-Myxomycetes /true slime molds /slime molds/ slime fungi /Mycetozoa. /
plasmodial slime molds (Fig. 4.10).
They are commonly found in damp places, especially on old wood and other
decomposing plant parts. T. Panckow in 1654 was the first to discover the
Myxomycetes.
The characteristic features are:
1. The vegetative body is a free-living plasmodium.
2. They feed on yeast cells, protozoa, fungal spores and other substances.
3. Reproduction takes place by asexual and sexual means. The reproductive process
is plantlike producing spores with definite cell walls.
4. Asexual reproduction takes place by fragmentation of plasmodium or binary
fission in myxamoebae.
5.Sexual reproduction takes place by fusion between flagellated zoospores or
myxamoeba to form zygote, from which multinucleate plasmodium develops by
mitotic divisions. They develop different types of fructification. These are
sporangium, aethalium and plasmodiocarp (Fig. 4.11D-G). Meiosis takes place
during spore formation in the fructification.
Alexopoulos (1973) divided the class Myxomycetes into three subclasses: Ceratio-
myxomycetidae, Myxogastromycetidae and Stemonitomycetidae.

13. D. Class: Plasmodiophoromycetes:
This group is commonly known as endo- parasitic slime molds. They are obligate
parasites, grow on algae, aquatic fungi and higher plants (commonly in the roots).
The characteristic features are:
1. Members of this class are obligate (i.e., biotrophic) parasites of fresh water algae,
aquatic fungi and higher plants (commonly in the roots).
2. Somatic body consists of a naked holocarpic plasmodium.
3. Plasmodia are of two types in their life cycle: sporangiogenous plasmodium
(form sporangia) and cytogenous plasmodium (gives rise to cysts i.e., resting
spores).
4. Zoospores biflagellate, having unequal flagella of whiplash type, situated in
opposite direction, the shorter one in anterior and longer one in posterior side.
The class consists of a single order Plasmodiophorales with a single family Plasmo-
diophoraceae. The class consists of 16 genera and 45 species. Some like
Plasmodiophora brassicae causes club-root of crucifer; Spongospora subterranea
causes powdery scab of potato.

14. Sexual reproduction-
•The myxamoebae or swarm cells , behave as gametes and as such take part in the
sexual reproduction.
•Fusion may take place between the two swarm cells or two myxamoebae or between a
swarm cell and a myxamoeba resulting in the formation of a zygote, when plasmogamy
is followed by karyogamy.
•Fusion between the two swarm cells or between a swarm cell and a myxamoeba leads
to the development of a flagellated zygote which sheds its flagella and becomes
amoeboid.
• The zygote formed in any one of the processes grows, along with which the diploid
nucleus also divides mitotically giving rise to a multinucleate amoeboid structure, the
plasmodium.
•According to some, karyogamy takes place during zygote formation. To them, the
plasmodium represents the diplophase in the life history of a myxomycete and meiosis
takes place during the formation of spores in the fructification (fruit body).Whereas,
others are of opinion that karyogamy takes place just before meiosis during the
development of spores in the fructification and as such the plasmodium is in the
dikaryophasic condition.

15. Life cycle-
•The spores on germination produce one to four swarm cells or
myxamoebae.
•The swarm cells or myxamoebae behave as gametes. They fuse in pairs,
plasmogamy is followed by karyogamy. The zygote so formed grows
accompanied with repeated mitotic division of the diploid zygotic
nucleus resulting in the development of a plasmodium.
•Many zygotes may also coalesce to produce a plasmodium.
• A mature plasmodium thickens and gives rise to the fructification of
varied nature.
• During the development of the fructification (fruiting body) and spore
formation the diploid nuclei divide reductionally. Each haploid nucleus
with a portion of cytoplasm enveloped by a thick wall develops into a
spore.
•The spores vary greatly in colour and characteristics of the wall which
are of taxonomic importance.(Figure 327).

17. Economic Importance of Myxomycota:
1.They have been the subject of intensive laboratory studies.
2. They contribute to the carbon and nitrogen cycles by
using various organic matter including bacteria as food.
3. They provide a large amount of protoplasm free from
cell walls which has been used as an ideal medium to solve
variety of fundamental problems of biochemists,
biophysicists, mycologists and even the geneticists.