common in marine habitats. Other species thrive in freshwater environments. Bicosoecida reproduce only through asexual binary division.
Opalinida
23 are parasites or, more probably, commensals
in the digestive tract of metazoans, mainly frogs and toads.
They are large (500 μm or more) and flattened. The cells
have multiple nuclei (two to several hundred). The
undulipodiums are numerous and short, which makes
Opalinida resemble ciliates. Nutrition is saprotroph.
Labyrinthulobionta
24 (¼labyrinthulomycetes, Labyrinthulomycota, Labyrinthulea, slime nets) belong to the
polyphyletic group formerly called “fungi” (customary
meaning). They produce within their host a network of
tubes, which serve as tracks for the cells to glide along.
They live in marine or estuarine environment. They are
saprotrophic or parasites. The saprotrophic species play
an important role in the degradation of dead leaves of
Magnoliophyta, especially in the mangroves. Heterotrophic
pico-stramenopiles (1 μm in diameter), close to Labyrinthulobionta, are very abundant within the mucus of Fungia
(corals, metazoans); their role (mutualistic symbionts?) is
not known (Kramarsky-Winter et al. 2006).
7.9.2 Oobionta
Oobionta
25 (¼Oomycetes, Oomycota) are part of the polyphyletic set previously called “fungi” (customary meaning).
The fusion of the Oobionta with the Chromobionta and the
split from Fungi (modern meaning), on the basis of
cytological and biochemical characteristics, was proposed
early (Mereschkowsky 1910; Cavalier-Smith 1981), well
before molecular phylogenies confirmed their position
within the kingdom Stramenopiles. Present-day Oobionta
are all heterotrophic, but the sequencing of the genome of
Phytophthora showed that their ancestors were photosynthetic; they had acquired photosynthesis through secondary
endosymbiosis with a Rhodobionta; they have in fact
hundreds of genes possibly inherited from Rhodobionta
and Cyanobacteria (Tyler et al. 2006). We know about
500 species of Oobionta, mainly belonging to Saprolegniales
and Perososporales (Molds 2009).
Oobionta are characterized by their coenocytic-type
vegetative apparatus with numerous scattered nuclei in a
single cytoplasm. Their cell wall is mainly composed of
cellulose (β 1,4 polymer of glucose, with hydrogen bonds
between molecules). The main reserve polysaccharide is
chrysolaminarin (β 1,3 polymer of glucose with a number
of β 1,6 bonds). Unlike other eukaryotes, Oobionta do not
synthesize sterols and must obtain them from their environment; the loss of this metabolism is secondary (Tyler
et al. 2006). Their mitochondria have tubular cristae, a
characteristic common to all Stramenopiles and even to
Chromalveolata (Beakes 1989). The nuclear membrane
does not disappear during mitosis (designated “closed mitosis”). Reproductive cells are mobile due to two unequal
undulipodiums, one being covered by tripartite mastigonemes, while the other is smooth and usually longer than
the first (Barr and De ´saulniers 1989).
Asexual reproduction is often the only one known.
It occurs by means of conidia equipped with two
undulipodiums. In Saprolegnia, primary conidia with terminal undulipodiums encyst (conidial cysts) and germinate into
secondary conidia that yield again multinucleate vegetative
stage cells (Fig. 7.40a, e). The life cycle is monogenetic; the
single, diploid (diplophase) generation can be interpreted as
a sporogen or as a gametogen; meiosis occurs in male and
female sporocysts, spores functioning as gametes; gametes
are not spread and male gametes are not materialized;
the male nucleus reaches the female nucleus through a
siphon (siphonogamy). The zygote that has two apical
undulipodiums, encysts (carpoconidian cyst) and then
germinates, yielding a carpoconidium with two lateral
undulipodiums that in turn yield the multinucleated vegetative stage (Fig. 7.40 a and f–h).
Oobionta are always heterotrophic, sometimes
saprotrophic but mostly parasites. Peronosporales generally
live in open habitats; they are in particular parasites of
nematodes, of vertebrates (Metazoa), and Magnoliophyta
(Archaeplastida). Phytophthora infestans, a parasite of
potato, is famous for causing the Irish potato famine in the
nineteenth century, which resulted in more than one million
deaths and forced more than two million Irish to migrate
(Gray 1995). Plasmopara viticola, the downy mildew of
vine, is an introduced species from North America that
destroyed European vineyards between 1878 and 1883,
until a treatment with copper sulfate was discovered
(Chadefaud 1978). Pythium insidiosum can be transmitted
to dogs and horses (that are not its normal hosts); these
diseases are called pythioses. Finally, a number of
Peronosporales (Pythium, Maullinia, etc.) parasitize marine
Rhodobionta and Chromobionta. The Saprolegniales are
aquatic. They parasitize in particular teleosts, nematodes,
rotifers, and crustaceans (Metazoa); they are thus a problem
in fish farms. Ectrogella eurychasmoides is a parasite of
23 The name of Opalinida is derived from their opalescent appearance
when illuminated with sunlight.
24 The name of Labyrinthulobionta is derived from Labyrinthula, a
diminutive of the Latin Labyrinthus (labyrinth) and the ancient Greek
biont (living thing).
25 Oobionta: From the Greek “oon”, egg. The name refers to the female
gametes, that are rounded, large, and non motile, that ancient writers
named ‘eggs’.
230
C.-F. Boudouresque
Opalinida
23 are parasites or, more probably, commensals
in the digestive tract of metazoans, mainly frogs and toads.
They are large (500 μm or more) and flattened. The cells
have multiple nuclei (two to several hundred). The
undulipodiums are numerous and short, which makes
Opalinida resemble ciliates. Nutrition is saprotroph.
Labyrinthulobionta
24 (¼labyrinthulomycetes, Labyrinthulomycota, Labyrinthulea, slime nets) belong to the
polyphyletic group formerly called “fungi” (customary
meaning). They produce within their host a network of
tubes, which serve as tracks for the cells to glide along.
They live in marine or estuarine environment. They are
saprotrophic or parasites. The saprotrophic species play
an important role in the degradation of dead leaves of
Magnoliophyta, especially in the mangroves. Heterotrophic
pico-stramenopiles (1 μm in diameter), close to Labyrinthulobionta, are very abundant within the mucus of Fungia
(corals, metazoans); their role (mutualistic symbionts?) is
not known (Kramarsky-Winter et al. 2006).
7.9.2 Oobionta
Oobionta
25 (¼Oomycetes, Oomycota) are part of the polyphyletic set previously called “fungi” (customary meaning).
The fusion of the Oobionta with the Chromobionta and the
split from Fungi (modern meaning), on the basis of
cytological and biochemical characteristics, was proposed
early (Mereschkowsky 1910; Cavalier-Smith 1981), well
before molecular phylogenies confirmed their position
within the kingdom Stramenopiles. Present-day Oobionta
are all heterotrophic, but the sequencing of the genome of
Phytophthora showed that their ancestors were photosynthetic; they had acquired photosynthesis through secondary
endosymbiosis with a Rhodobionta; they have in fact
hundreds of genes possibly inherited from Rhodobionta
and Cyanobacteria (Tyler et al. 2006). We know about
500 species of Oobionta, mainly belonging to Saprolegniales
and Perososporales (Molds 2009).
Oobionta are characterized by their coenocytic-type
vegetative apparatus with numerous scattered nuclei in a
single cytoplasm. Their cell wall is mainly composed of
cellulose (β 1,4 polymer of glucose, with hydrogen bonds
between molecules). The main reserve polysaccharide is
chrysolaminarin (β 1,3 polymer of glucose with a number
of β 1,6 bonds). Unlike other eukaryotes, Oobionta do not
synthesize sterols and must obtain them from their environment; the loss of this metabolism is secondary (Tyler
et al. 2006). Their mitochondria have tubular cristae, a
characteristic common to all Stramenopiles and even to
Chromalveolata (Beakes 1989). The nuclear membrane
does not disappear during mitosis (designated “closed mitosis”). Reproductive cells are mobile due to two unequal
undulipodiums, one being covered by tripartite mastigonemes, while the other is smooth and usually longer than
the first (Barr and De ´saulniers 1989).
Asexual reproduction is often the only one known.
It occurs by means of conidia equipped with two
undulipodiums. In Saprolegnia, primary conidia with terminal undulipodiums encyst (conidial cysts) and germinate into
secondary conidia that yield again multinucleate vegetative
stage cells (Fig. 7.40a, e). The life cycle is monogenetic; the
single, diploid (diplophase) generation can be interpreted as
a sporogen or as a gametogen; meiosis occurs in male and
female sporocysts, spores functioning as gametes; gametes
are not spread and male gametes are not materialized;
the male nucleus reaches the female nucleus through a
siphon (siphonogamy). The zygote that has two apical
undulipodiums, encysts (carpoconidian cyst) and then
germinates, yielding a carpoconidium with two lateral
undulipodiums that in turn yield the multinucleated vegetative stage (Fig. 7.40 a and f–h).
Oobionta are always heterotrophic, sometimes
saprotrophic but mostly parasites. Peronosporales generally
live in open habitats; they are in particular parasites of
nematodes, of vertebrates (Metazoa), and Magnoliophyta
(Archaeplastida). Phytophthora infestans, a parasite of
potato, is famous for causing the Irish potato famine in the
nineteenth century, which resulted in more than one million
deaths and forced more than two million Irish to migrate
(Gray 1995). Plasmopara viticola, the downy mildew of
vine, is an introduced species from North America that
destroyed European vineyards between 1878 and 1883,
until a treatment with copper sulfate was discovered
(Chadefaud 1978). Pythium insidiosum can be transmitted
to dogs and horses (that are not its normal hosts); these
diseases are called pythioses. Finally, a number of
Peronosporales (Pythium, Maullinia, etc.) parasitize marine
Rhodobionta and Chromobionta. The Saprolegniales are
aquatic. They parasitize in particular teleosts, nematodes,
rotifers, and crustaceans (Metazoa); they are thus a problem
in fish farms. Ectrogella eurychasmoides is a parasite of
23 The name of Opalinida is derived from their opalescent appearance
when illuminated with sunlight.
24 The name of Labyrinthulobionta is derived from Labyrinthula, a
diminutive of the Latin Labyrinthus (labyrinth) and the ancient Greek
biont (living thing).
25 Oobionta: From the Greek “oon”, egg. The name refers to the female
gametes, that are rounded, large, and non motile, that ancient writers
named ‘eggs’.
230
C.-F. Boudouresque