tella persicaria(E.D. Eddy) Hesselt. (Powell
et al. 1981 ).
c) Yeast Cells
Anaerobic formation of yeast cells has been
described inMucor rouxiiby Bartnicki-Garcia
( 1978 ).InC. recurvatusand species ofBenja-
miniellaandMycotypha, yeast cells are pro-
duced aerobically when the spores germinate
on the surface of a nutrient-rich culture
medium[Fig.8.4(39)] (Benny and Benjamin
1976 ; Benny et al. 1985 ). Changes in cell wall
chemistry (carbohydrates, hexosamine, pro-
tein, lipids, fatty acids, ash) were noted as the
yeast cells passed through an intermediate
phase and, finally, to vegetative hyphae in
Benjaminiella poitrasii(R.K. Benj.) von Arx
(Cole et al. 1980 ).
- Meiospores
a) Zygospores
Zygospores are formed as a result of the copu-
lation between two or, rarely, three, usually
differentiated, gametangia.The stages in zygo-
spore formation are illustrated forSyzygites
megalocarpusby Fuller ( 1978 ) and O’Donnell
( 1979 ) and as part of a life cycle ofR. stolonifer
by Alexopoulos et al. ( 1995 ). Ultrastructural
studies of zygospore formation are demon-
strated usingR. stolonifer(isogamous, hetero-
thallic) andZygohynchus heterogamus(Vuill.)
Vuill. (heterogamous, homothallic) (Edelmann
and Komparens 1995 ; Ho and Chen 1998 ).
The zygospore is thick-walled and hyaline
and usually contains a single globule, and only
one is formed in each zygosporangium. The
characteristics of the “zygospore” noted in
species descriptions are really the color and
ornamentation of the zygosporangial wall
(Schipper et al. 1975 ). The zygosporangium
formed by species of Mucorales can be smooth
to variously ornamentated and pigmented
[Fig.8.4(35)]. The zygosporangia can be dark
brown or black and opaque, lighter brown and
translucent, or light brown and transparent;
these light brown spores can have either an
undulate or smooth wall. These zygospores, all
found in Mucorales, have opposed suspensors
[Fig. 8.4(35)] and are formed aerially. The
zygospore when released is hyaline and thick-
walled and usually contains a single yellow
globule when mature [Fig.8.4(36)]. The “zygo-
spore” conforms to the internal shape of the
zygosporangium and the remnants of the sus-
pensors (Benny and Schipper 1992 ).
Other zygospores produce apposed suspen-
sors that are often entwined or bear protuber-
ances. These zygospores are usually produced at
or below the surface of the substrate. Members
of Endogonales [Fig. 8.4(29)], Mortierellales
[Fig.8.3(27)], Zoopagales [Fig.8.5(45, 46, 48)],
and some families of Mucorales (Choanephor-
aceae, Mucoraceae, Phycomycetaceae, Pilobola-
ceae) have zygospores with apposed suspensors
(Benjamin 1959 , 1966 , 1979 ,1985b; Degawa and
Tokumasu 1998 ; Fuller 1978 ; Kuhlman 1972 ;
Thaxter 1922 ). Dimargaritales and Kickxellales
produce hyaline, globose zygospores in the sub-
strate and have two or even three undifferenti-
ated suspensors [Fig. 8.2(20, 21)] (Benjamin
1959 ; Kurihara et al. 2004 ).
Meiospore formation requires the presence
of two compatible hyphae (denoted by+and)
in heterothallic species, whereas only a single
hyphal type is required for homothallic taxa.
The majority of Mucorales members are het-
erothallic (Feofilova 2006 ; Schipper and Stal-
pers 1980 ), but in the remaining orders, where
sexual reproduction is known, the species are
homothallic.In Mucorales, zygospore forma-
tion is by light-induced biosynthesis ofb-car-
otene to the hormone trisporic acid, which
initiates the conversion of vegetative hyphae
to zygophores; intermediate molecules act like
pheromones (Corrochano and Garre 2010 ;
Schimek and Wo ̈stemeyer 2006 , 2009 ).b) Azygospores
Azygospores are parthenogenetically formed
zygospores. These structures look like zygos-
pores, but they are formed on only a single
suspensor. Azygospores have been reported in
many of the orders in which zygospores are
produced (Benjamin and Mehrotra 1963 ; Gin-
man and Young 1989 ).Zygomycetous Fungi: Phylum Entomophthoromycota and Subphyla Kickxellomycotina,... 229