Introduction to Fungi, Third Edition

70 STRAMINIPILA: MINOR FUNGAL PHYLA
Fig 4.4 Organization of the straminipilous flagellum.
(a) Postulated attachment of TTHs to the microtubule
doublets1and 5 of the axoneme as seen in transverse section
(after Dick, 2001a). (b) Longitudinal arrangement of TTHs
along the axoneme of a straminipilous flagellum.Only one row
of TTHs is drawn.TheTTHs are thought to be arranged in an
alternating fashion as regards the orientation of long and
short fibres in adjacent TTHs. b redrawn from Dick (1990a).
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straminipilous fungi, the straminipilous flagellum
always seems to point towards the direction
of movement, and Dick (1990a, 2001a) has
advanced a theory to explain how movement
can be generated from a sinusoidal wave starting
at the flagellar base, likening the straminipilous
flagellum to ‘a rowing eight with fixed oars and
a flexible keel’ (Fig. 4.4b; Dick, 2001a). An anterior
straminipilous flagellum therefore pulls the
spore through the water, whereas a backwardly
directed whiplash flagellum pushes the spore.
The construction of the straminipilous flagellum
is so elaborate that it is most unlikely to
have arisen more than once during evolution
(Dick, 2001a). The presence of a straminipilous
flagellum, whether or not accompanied by
another, smooth flagellum, therefore indicates
membership in the Straminipila.
4.3 Hyphochytriomycota
This group, formerly called Hyphochytridiomycetes
probably due to the perpetuation of
Fig 4.5 Schematic drawing of a L.S. of a zoospore of the
hyphochytrid Hyphochytrium catenoides.The elongated shape
of the zoospore and of the nucleus (N) is maintained by a
system of ‘rootlets’consisting of parallel bundles of
microtobules (thick lines).The straminipilous flagellum arises
from a kinetosome (Kin). A second, non-functional
kinetosome (NFK) is interpreted as the base of a whiplash
flagellum lost in the course of evolution from a heterokont
ancestor. Mitochondria (Mit),TTH-containing vesicles (TV),
a Golgi stack (G), ER, ribosomes (Rib), a large basal lipid
droplet (LD) and microbodies (MB) are also visible. Some
organelles of unknown function, e.g. electron-opaque bodies
and osmiophilic bodies, have been omitted from the
original for improved clarity. Redrawn and modified from
Cooney et al. (1985).
a typographical error (see Dick, 1983), is a very
small phylum currently comprising 23 species in
6 genera (Kirk et al., 2001). The Hyphochytriomycota
(colloquially called hyphochytrids) are