eukaryotic ribosomes, and floridean starch are present. The
nucleomorph is the remnant of the nucleus of the
Rhodobionta cell that is at the origin of the chloroplast, via
secondary endosymbiosis. In contrast with the other taxa
(Chromalveolata) which acquired photosynthesis from
endosymbiosis with a Rhodobionta, the Rhodobionta
nucleus has been preserved, but has lost most of its genes
(Bhattacharya et al. 2003; Tanifuji et al. 2011). The
thylakoids contain chlorophylls a and c2 (Jeffrey 1989). In
addition, they have preserved phycobilins (phycocyanin or
phycoerythrin); however, unlike cyanobacteria, Glaucocystobionta and Rhodobionta, phycobilins are not localized
within phycobilisomes, granules located on the thylakoid
(Figs. 7.13 and 7.15), but within the thylakoid lumen
(Fig. 7.49). The alloxanthin is a xanthophyll specific to
Cryptophyta; its presence in the Dinobionta Dinophysis
norvegica is due to a tertiary endosymbiosis with a
Cryptophyta (Meyer-Harms and Pollehne 1998). The
thylakoids are stacked into two-thylakoid lamellae, an
uncommon feature in eukaryotes, which Cryptophyta only
share with Chlorarachnobionta (cf. Sect. 7.6.3).
Cryptophyta have two undulipodiums, of identical
length or not, inserted into a vestibular groove (a sort of
cytostome) or in the vicinity of this groove. These
undulipodiums are covered with bipartite mastigonemes:
a cylindrical hollow section and a terminal very thin hair;
compared to the tripartite mastigonemes of Chromobionta,
the basal section is missing. One of the undulipodiums has
two rows of mastigonemes, the other a single one
(Fig. 7.49; Leadbeater 1989). The undulipodial root
system comprises a rhizostyle which originates near
the kinetosome, is longitudinally elongated, and has
6–10 microtubules (de Reviers 2003). The trichocysts
(ejectisomes) are of a particular type, different from those
of Alveolata and Stramenopiles. The “corps de Maupas” is
a large vesicular structure, specific to Cryptophyta, whose
main function could be that of disposing of unwanted
cytoplasmic structures by digestion.
In Cryptophyta, asexual reproduction is by binary fission.
The sexual reproduction is unknown in most species. It is
known in Proteomonas sulcata, whose life cycle is digenetic
and diphasic (haplo-diplophasic), with slightly heteromorphic generations (de Reviers 2003).
Most species of Cryptophyta are photosynthetic, but
some have secondarily lost photosynthesis; some of these
have retained a remnant chloroplast (Chilomonas), others
not (Goniomonas). Cryptophyta live in both marine and
freshwater plankton, more rarely in the intersticial water of
soils and beach sand. In the marine ultra-phytoplankton
(<5 μm), Cryptophyta are one of the three dominant taxa
(with Haptobionta and Chrysophyceae) (McDonald et al.
2007).
Several unicellular taxa seem to be related to
Cryptophyta, on the basis of molecular phylogenies.
Katablepharida are the sister-group of Cryptophyta (Burki
et al. 2012). They live in marine and freshwater habitats;
they lack chloroplasts and are therefore heterotrophic,
though some species are kleptoplastic (Okamoto and Inouye
2005). The Picobiliphyta (¼Biliphyta) are a recently discovered taxon, present and sometimes abundant in the
nanoplankton (2–6 μm in length) of all the seas of the
world, while still poorly known. As Cryptophyta, they have
phycobilins and a nucleomorph (Not et al. 2007; Cuvelier
et al. 2008). Picobiliphyta have been considered as autotrophic organisms; there is, however a strong question mark
over this hypothesis: they are more likely heterotrophic than
autotrophic (Kim et al. 2011a).
7.12 Kingdom Discicristates
7.12.1 General Remarks
The Discicristates
33 are often met with Excavates within a
single kingdom, which seems to be monophyletic (Simpson
2003; Hampl et al. 2009). Discicristates are characterized,
from a cytological point of view, by their mitochondria
whose cristae are flattened at the ends, like ping-pong
rackets. Discicritates encompass in particular Euglenobionta
(Euglenoidea, Kinetoplastida, and Pseudociliata), Percolobionta, and Acrasiobionta (¼Heterolobosa).
Percolobionta (¼Percolozoa) are unicellular organisms
which are either in the form of amoeba (e.g., Vahlkampfia
and Pseudovahlkampfia), or in the form of a cell with
undulipodiums (e.g., Percolomonas, Lyromonas, and
Psalteriomonas), but can also alternate amoeboid forms
(when the environment is nutritionally rich) and cells
with undulipodiums (when fast moving is a priority). The
“brain-eating amoeba” Naegleria fowleri, a Percolobionta,
infects humans by entering the body through the nose,
which occurs when people go swimming in warm freshwater places.
Acrasiobionta
(¼Acrasiomycota,
Acrasiomycetes,
Acrasidae) are sometimes included within Percolobionta,
or alternatively placed in their vicinity (Heterolobosa).
They occur only in the amoeboid stage.
33 Discicritates, from the Latin discus (disk) and crista (crest). This
name refers to the mitochondrial cristae which resemble ping-pong
rackets.
7 Taxonomy and Phylogeny of Unicellular Eukaryotes
239
nucleomorph is the remnant of the nucleus of the
Rhodobionta cell that is at the origin of the chloroplast, via
secondary endosymbiosis. In contrast with the other taxa
(Chromalveolata) which acquired photosynthesis from
endosymbiosis with a Rhodobionta, the Rhodobionta
nucleus has been preserved, but has lost most of its genes
(Bhattacharya et al. 2003; Tanifuji et al. 2011). The
thylakoids contain chlorophylls a and c2 (Jeffrey 1989). In
addition, they have preserved phycobilins (phycocyanin or
phycoerythrin); however, unlike cyanobacteria, Glaucocystobionta and Rhodobionta, phycobilins are not localized
within phycobilisomes, granules located on the thylakoid
(Figs. 7.13 and 7.15), but within the thylakoid lumen
(Fig. 7.49). The alloxanthin is a xanthophyll specific to
Cryptophyta; its presence in the Dinobionta Dinophysis
norvegica is due to a tertiary endosymbiosis with a
Cryptophyta (Meyer-Harms and Pollehne 1998). The
thylakoids are stacked into two-thylakoid lamellae, an
uncommon feature in eukaryotes, which Cryptophyta only
share with Chlorarachnobionta (cf. Sect. 7.6.3).
Cryptophyta have two undulipodiums, of identical
length or not, inserted into a vestibular groove (a sort of
cytostome) or in the vicinity of this groove. These
undulipodiums are covered with bipartite mastigonemes:
a cylindrical hollow section and a terminal very thin hair;
compared to the tripartite mastigonemes of Chromobionta,
the basal section is missing. One of the undulipodiums has
two rows of mastigonemes, the other a single one
(Fig. 7.49; Leadbeater 1989). The undulipodial root
system comprises a rhizostyle which originates near
the kinetosome, is longitudinally elongated, and has
6–10 microtubules (de Reviers 2003). The trichocysts
(ejectisomes) are of a particular type, different from those
of Alveolata and Stramenopiles. The “corps de Maupas” is
a large vesicular structure, specific to Cryptophyta, whose
main function could be that of disposing of unwanted
cytoplasmic structures by digestion.
In Cryptophyta, asexual reproduction is by binary fission.
The sexual reproduction is unknown in most species. It is
known in Proteomonas sulcata, whose life cycle is digenetic
and diphasic (haplo-diplophasic), with slightly heteromorphic generations (de Reviers 2003).
Most species of Cryptophyta are photosynthetic, but
some have secondarily lost photosynthesis; some of these
have retained a remnant chloroplast (Chilomonas), others
not (Goniomonas). Cryptophyta live in both marine and
freshwater plankton, more rarely in the intersticial water of
soils and beach sand. In the marine ultra-phytoplankton
(<5 μm), Cryptophyta are one of the three dominant taxa
(with Haptobionta and Chrysophyceae) (McDonald et al.
2007).
Several unicellular taxa seem to be related to
Cryptophyta, on the basis of molecular phylogenies.
Katablepharida are the sister-group of Cryptophyta (Burki
et al. 2012). They live in marine and freshwater habitats;
they lack chloroplasts and are therefore heterotrophic,
though some species are kleptoplastic (Okamoto and Inouye
2005). The Picobiliphyta (¼Biliphyta) are a recently discovered taxon, present and sometimes abundant in the
nanoplankton (2–6 μm in length) of all the seas of the
world, while still poorly known. As Cryptophyta, they have
phycobilins and a nucleomorph (Not et al. 2007; Cuvelier
et al. 2008). Picobiliphyta have been considered as autotrophic organisms; there is, however a strong question mark
over this hypothesis: they are more likely heterotrophic than
autotrophic (Kim et al. 2011a).
7.12 Kingdom Discicristates
7.12.1 General Remarks
The Discicristates
33 are often met with Excavates within a
single kingdom, which seems to be monophyletic (Simpson
2003; Hampl et al. 2009). Discicristates are characterized,
from a cytological point of view, by their mitochondria
whose cristae are flattened at the ends, like ping-pong
rackets. Discicritates encompass in particular Euglenobionta
(Euglenoidea, Kinetoplastida, and Pseudociliata), Percolobionta, and Acrasiobionta (¼Heterolobosa).
Percolobionta (¼Percolozoa) are unicellular organisms
which are either in the form of amoeba (e.g., Vahlkampfia
and Pseudovahlkampfia), or in the form of a cell with
undulipodiums (e.g., Percolomonas, Lyromonas, and
Psalteriomonas), but can also alternate amoeboid forms
(when the environment is nutritionally rich) and cells
with undulipodiums (when fast moving is a priority). The
“brain-eating amoeba” Naegleria fowleri, a Percolobionta,
infects humans by entering the body through the nose,
which occurs when people go swimming in warm freshwater places.
Acrasiobionta
(¼Acrasiomycota,
Acrasiomycetes,
Acrasidae) are sometimes included within Percolobionta,
or alternatively placed in their vicinity (Heterolobosa).
They occur only in the amoeboid stage.
33 Discicritates, from the Latin discus (disk) and crista (crest). This
name refers to the mitochondrial cristae which resemble ping-pong
rackets.
7 Taxonomy and Phylogeny of Unicellular Eukaryotes
239