1. MYXOMYCETES AND
ZYGOMYCETES
Marilen M. Parungao
Biology 112 Laboratory

2. MYXOMYCETES: WHY STUDY THEM
HERE?
• Members of this division are commonly
referred to as slime molds.
• Classified as Pro8sts: since they form
amoeboid cells
• Regarded as Fungi: because they produce
spores that are borne in sporangia

3. MYXOMYCETES
Some Important Terms
*** all images in the next set of slides are from Google images

4. PLASMODIUM
• A naked mul8nucleate
mass of protoplasm
that moves and feeds in
an amoeboid fashion
• Formed aDer numerous
mito8c division of the
zygote

5. MYXAMOEBA
• An amoeboid cell released by the
spore upon germina8on
• May con8nue to proliferate for an
indefinite period of 8me if there is
available nutrient and the
environment remains favorable
• 2 func8ons: ingest food or func8on
as gametes during during
reproduc8on

6. SWARM CELLS
• When free water is
available, myxamoebae can
become flagellated and
swim through the water
• During condi8ons
unfavorable for
myxamoebae growth, the
cells may round up and
form the resistant microcyst
stage

7. SCLEROTIA
• A hard res8ng body resistant
to unfavorable condi8ons
• When condi8ons become
unfavorable, a plasmodium
can become dormant forming
a resistant stages
• Actually composed of smaller
units called macrocysts

8. PHYSARUM TYPICAL LIFE CYCLE

9. FRUTING BODIES
• Frui8ng bodies may
either be carrying
spores externally or
internally
• Exospores: Example
Cera%omyxa
– Columnar, branched
structures bears the
spores externally

10. FRUITING STRUCTURE TYPE 1:
PLASMODIOCARP
• An elongated, curved or
branched, vein‐like frui8ng
structure
• Example: Hemitrichia
serpula
– The spores and capilli8um of
this sporangium type retains
the shape of the plasmodial
stage

11. FRUTING STRUCTURE TYPE 2:
SPORANGIUM
• Sac‐like structure
• Example: Physarum and Dydmium
• the fragile, outer layer of the
sporangium is the peridium which
may be persistent or degenerate
by the 8me the sporangium is
ready to disperse its spores

12. OTHER GENERA FORMING
SPORANGIUM
Arcyria and Stemoni@s

13. FRUITING STRUCTURE TYPE 3:
AETHALIUM
• aethalium resembles a
sessile sporangium but is
much larger and generally
cushioned
– Believed to be fused
sporangium
• Example:
– Lycogala = pseudocapilli8um
without any dis8nc8ve
ornamenta8on and spores
– Fuligo = produces the largest
known aethalium

14. VARIATIONS IN CAPILLITIUM
MORPHOLOGY
Example: Trichia favoginea, capilli8um ornamented
with annular rings
Example: Hemitrichia serpula, capilli8um
unbranched. Composed of strands of elaters. Elaters
ornamented with double spirals, each coming from
opposite direc8ons
Example: Lycogala epidendrum, Capilli8um (actually
pseudocapilli8um) without any dis8nc8ve
ornamenta8on and spores

15. ACRASIN
• Chemotac8c chemicals that act as
pheromones in aggrega8on of amoebae in
cellular slime molds
• One of the earliest iden8fied acrasins: cyclic
AMP or cAMP
– Dictyostelium discoideum
– exhibits a complex swirling‐pulsa8ng spiral paUern
when forming a pseudoplasmodium

16. ZYGOMYCOTA
“the saprobes, faculta@ve parasites
and air contaminants”

17. IMPORTANT TERMS
• ZYGOSPORE
– A res8ng spore that
results from the fusion
of 2 gametangia
• ZYGOSPORANGIUM
– A sporangium containing
a zygospore
• ZYGOPHORE
– A special hypha capable
of developing into a
progametangium

18. DIMORPHIC GROWTH
• Producing two
morphologically‐dis8nct
types of zoospores (yeast
form or mycelial form)
• Usually the yeast type occurs
internally and the mycelial
type occurs externally (with
excep8ons)

19. MUCOR
Mucor versus Rhizopus

20. PHYCOMYCES

21. ABSIDIA

22. PILOBOLUS
• Unique spore dispersal
mechanism
• “shot‐gun fungi”

23. SPORE DISPERSAL
• Ini8al result to phototrophic response of the
sporangiophore and later its elonga8on
• Steps:
– Sporangiophore bends towards the light
(sporangial vesicle act as lens)
– Subsporangial vesicle has high turgor pressure,
upon rupture will eject the sporangium towards
the source of light

24. hUp://www.chlorofilms.org/index.php/crpVideo/display/videoid/51

25. DIFFERENCES BETWEEN ORDERS
• ORDER MUCORALES
– They have a well developed mycelia that is generally aseptate.
Whenever septa will be present, they lack spores with specialized
plugs
• ORDER DIMARGARITALES
– They are monotypic unlike the Mucorales, they are haustorial
mycoparasites
• ORDER KICKXELLALES
– Produces single‐spores merosporangia, usually from structures called
pseudophialides that are borne on specialized septate or aseptate
fer8le branches called sporocladia
• ORDER ENDOGONALES
– Their sporocarps contain only zygospores and sporangia are unknown

26. DIFFERENCES BETWEEN ORDERS
• ORDER GLOMALES
– They are referred to as VAM fungi or vesicular‐arbuscular
mycorrizae or endomycorrhizae. This group may be found
in 70% of all plant families
• ORDER ENTOMOPHTHORALES
– This group includes the insect pathogens
• ORDER ZOOPAGALES
– The Zoopagales comprises the fungal group with
interac8ons that involve a variety of small animals and
other fungi, although mycoparasi8c species may also be
observed

27. FORMATION OF ZYGOSPORE

28. NEXT MEETING: ASCOMYCETES