Introduction to Fungi, Third Edition

24 INTRODUCTION
Fig1.17 Zoospore types found in fungi, diagrammatic and not to scale.The arrow indicates the direction of movement of the
zoospore. (a) Posteriorly uniflagellate (opisthokont) zoospore with a flagellum of the whiplash type found in many Chytridiomycota.
(b) Posteriorly multiflagellate zoospore with numerous (up to16) whiplash flagella which occur in certain anaerobic rumen-inhabiting
Chytridiomycota (Neocallimastigales). (c) Zoospore with unequal (anisokont) whiplash flagella characteristic of the Myxomycota
and the Plasmodiophoromycota. (d) Anteriorly uniflagellate zoospore with a flagellum of the tinsel type, the axoneme being clothed
with rows of mastigonemes, typical of the Hyphochytriomycota. (e,f) Biflagellate zoospores with heterokont flagella, one of the
whiplash and the other of the tinsel type, which are found in different groups of the Oomycota. For more details turn to the
different fungal groups.
flagellation is termed opisthokont (Gr. opisthen ¼
behind, at the back; kontos ¼ a pole). Detailed
descriptions of the fine structure of chytridiomycete
zoospores are given on p. 129.
2. Biflagellate zoospores with two whiplash
flagella of unequal length are called anisokont
(Fig. 1.17c) and are found in some Myxomycota
and the Plasmodiophoromycota, both now
classified among the Protozoa (see Chapters 2
and 3).
3. Anteriorly uniflagellate zoospores with
a flagellum of the tinsel type are characteristic
of the Hyphochytriomycota (Chapter 4). The
axoneme sheath of the tinsel or straminipilous
flagellum (Lat. stramen ¼ straw; pilus ¼ hair) is
adorned by two rows of fine hairs (Fig. 1.17d).
These are called tripartite tubular hairs or
mastigonemes (Gr. mastigion ¼ a small whip;
nema ¼ a thread). Rhythmic sinusoidal beating of
the tinsel type flagellum pulls the zoospore
along, in contrast to the pushing action of
whiplash flagellum. Details of the fine structure
of this type of zoospore are given in Fig. 4.5.
4. Biflagellate zoospores with anteriorly or
laterally attached flagella, one of which is of
the whiplash type and the other of the tinsel
type (Figs. 1.17e,f), are characteristic of the
Oomycota (Chapter 5). Zoospores with the two
different kinds of flagellum are heterokont.
Where the two types of flagellum are attached
anteriorly, as in the first-released zoospores of
Saprolegnia, their propulsive actions tend to
work against each other and the zoospore is
a very poor swimmer (Fig. 1.17e). However,
the secondary zoospore (termed the principal
zoospore) in Saprolegnia and in many other
Oomycota has laterally attached flagella, with
the tinsel-type (pulling action) flagellum pointing
forwards and the whiplash-type (pushing
action) flagellum directed backwards and possibly
acting as a rudder, jointly providing much
more effective propulsion (Fig. 1.17f).
1.4.2 Sporangiospores
In the Zygomycota, and especially in the
Mucorales (see p. 180), the asexual spores are
contained in globose sporangia (Fig. 1.18) or
cylindrical merosporangia. Because they are
non-motile, the spores are sometimes termed
aplanospores (Gr. a ¼ not, planos ¼ roaming).