garitales but not in culture (Benjamin 1959 ;
Vuillemin 1904 ).
c) Harpellales
The members of Harpellales [Fig.8.2(17, 18)]
are found in the mid- or hindgut of immature
aquatic insects usually collected from fast-
flowing streams, but they may also be found in
ponds and other still waters. The thalli are sep-
tate and are attached to the lining of the host’s
gut by a noncellular holdfast. Asexual reproduc-
tion is by unispored sporangia [trichospores
(Fig.8.2(17, 18))] that usually bear one or more
long, basal appendages. Zygospores [Fig.8.2
(17)], where known, are more or less conical,
biconical, or long-cylindrical and coiled.
Two families are recognized: Harpellaceae
is reserved for those taxa with unbranched
thalli, whereas Legeriomycetaceae contains
only fungi that are branched.The shape of
the trichospore and whether or not it bears a
basal collar, the number of appendages, and the
nature of the holdfast are all important charac-
ters in identifying a genus in Harpellales. The
genera of Harpellales are listed in Table8.1[see
Benny ( 2012 ) for the literature on the majority
of the genera].
Zygospores are variously shaped (types
according to Moss et al. 1975 ): the biconical
zygospore types (I–III) are in the following
position in relation to the zygosporophore: (1)
perpendicular or type I (Allantomyces,Boja-
myces,Harpella,Genistelloides,Klastostachys,
Simuliomyces,Spartiella,Stipella); (2) oblique
or type II (Austrosmittium, Capniomyces
[Fig.8.2(17)], Legeriomyces,Glotzia, Grami-
nella, Harpellomyces, Laculus, Legerioides,
Legeriomyces, Legeriosimilis, Sinotrichium,
Smittium,Tectimyces,Trichozygospora,Zancu-
domyces); (3) parallel or type III (Genistellos-
pora,Pennella); or (4) pointed with a round
base and attached to the zygosporophore at
the base or type IV (Carouxella,Dacryodio-
myces, Lancisporomyces, Plecopteromyces,
Zygopolaris). The ultrastructure of selected har-
pellalean zygospores is illustrated by Moss and
Lichtwardt ( 1977 ). A fifth type of zygospore
formation has been reported inOrphella; these
zygospores are elongate-cylindrical and coiled
or basally coiled and then straight medially to
distally (Valle and Santamaria 2005 ). Zygos-
pores are unknown in the remaining genera of
Harpellales.
In many taxa the upper portion of the wall
of the generative cell may remain with the tri-
chospore as a collar. The trichospore and gen-
erative cell remain intact inCarouxella, and
dehiscence is the result of thallus separation.
InOrphella(Lichtwardt et al. 1991 ) the trichos-
pore, generative cell, and a sterile terminal cell
remain attached and form a dehiscent complex
reproductive unit. In a few taxa, trichospores
are produced from germinating blackfly ovar-
ian cysts that may infect blackfly larvae, poten-
tially adding infectious propagules to the life
cycle (Labeyrie et al. 1996 ); zygospores were
observed later (Rizzo and Pang 2005 ). White
et al. (2006a) used sequence data on blackfly
larvae to identify the cyst inducing Harpellales.
Horn (1989a, 1990 ) showed that extrusion
(germination in some authors) of Smittium
trichospores occurs only after passage through
the gut of a mosquito larva. This process
occurs in two parts: in phase I the concentra-
tion of potassium is relatively high (40 mM)
and the pH is 10 (environment of larval mid-
gut), and in phase II the pH is ca. 7 (6–8)
(condition in the larval hindgut). Extrusion
of trichospores occur after exposure of
15 min or less to each phase. Holdfast forma-
tion of Zancudomyces culisetae (Lichtw.) Y.
Wang, Tretter, Lichtw. & M.M. White (as
Smittium culisetaeLichtw.) andS. culicisMan-
ier occur after phase II, but spore extrusion
takes place after phase I (S. culicis) or phase II
(Z. culisetae,asS. culisetae). An ultrastructural
study of trichospore extrusion and holdfast
formation in the aforementioned Smittium
spp. showed canals and an interwall layer at
both ends of the spore. Spore bodies, struc-
tures that hold the initial holdfast material,
accumulate at the apical end of the trichospore
after phase I. Holdfast formation occurs dur-
ing phase II in 10 s or less. Spore bodies are
randomly dispersed in the trichospore cyto-
plasm before it is exposed to the phase I envi-
ronment (Horn1989b). Additional papers on
trichospore ultrastructure have been published
(Moss and Lichtwardt 1976 ; Sato 2002 ).Zygomycetous Fungi: Phylum Entomophthoromycota and Subphyla Kickxellomycotina,... 231