Morphologically similar K-body vesicles
have now been widely found in the zoospores
of basal oomycetes (Fig.3.16h, l–r), such as
Eurychasma(Sekimoto et al.2008a) and both
freshwater and marineOlpidiopsisspp. (Bort-
nick et al. 1985 ; Sekimoto et al. 2007 ). This is
another feature that links the basal clades
directly with the saprolegniomycete line. The
Rhipidialean genusSapromycesalso hasK-bod-
ies(Gotelli and Hanson 1987 ) rather than smal-
ler, more widely dispersedvsv, typical of the
peronosporomycete line. This again points to
this orders showing intermediate characteris-
tics between the main classes and at the plesio-
morphy of the K-bodies. The gene encoding the
protein secreted by thevsv fractioninPh. cin-
namomihas been cloned and shown to contain
athrombospondin-1 repeat, which is a motif
associated with adhesins in the malarial para-
site Plasmodium and animals (Robold and
Hardham 2005 ).
The second cortical vesicle fraction is more
abundant and widely distributed within both
hyphochytrid (Cooney et al. 1985 ;Fullerand
Reichle 1965 ) and oomycete zoospores (Beakes
1983 , 1987 ; Dick 2001) and are the source of
spines that might decorate encysted spores
(Fig.3.8j, r, s). In oomycetes they were first
described inSaprolegniaasbar bodies(Beakes
1987 ), and homologous vesicles, which have a
structured periphery and hollow core (which
contains any spines), have been described
throughout most of the early-diverging genera,
includingEurychasma(Sekimoto et al. 2008),
Haptoglossa(Beakes and Glockling 1998 , 2000 ),
severalOlpidiopsisspp. (Bortnick et al. 1986;
Sekimoto et al. 2009 ), andHaliphthoros(Overton
et al. 1983 ; Sekimoto 2008 ). In the Saprolegnia-
ceae, genera with eccentric oospores, such as
Dictyuchus, have secondary cysts decorated by
broad tapered spines (Fig.3.11j) (Beakes 1987 ),
whereas those with centric or subcentric oos-
pores, such as the genusSaprolegnia,typically
have fine bifurcated boat-hook spines
(Fig.3.11r, s)(Beakes 1983 ; Hallett and Dick
1986 ; Burr and Beakes 1994 ;Beakesetal. 1995 ).
In contrast, in most Peronosporomycetes, the
homologous peripheral dorsal small vesicle
(dsv) fraction has homogenous contents and is
often morphologically indistinguishable from the
ventral vesicle fraction. Although similar in
appearance tovsv,thedsvfraction has different
immunological properties and upon discharge
forms the initial coat that protects the encysting
zoospores (Beakes et al. 1995 ;RoboldandHard-
ham 2004 ;Hardham 2005 ). Now that many dis-
crete subclades have been identified in large and
complex taxa such asPythiumandPhytophthora,
it might be worthwhile to carry out a detailed
comparative ultrastructural examination of
their zoospores to see whether any structural
features can be associated with particular clades,
as has been so successfully done for chytrids (see
Powell and Letcher 2014 ).B. Life Histories and Sexual Cycle
CharacteristicsMost stramenopiles arediploid organismsthat
undergo gametic meiosis (Dick 2001; Sims et al.
2006 ), although triploid and tetraploid forms
have been reported inPhytophthora (Tooley
and Therrien 1987 ). However, knowledge of
the precise timing of meiosis and plasmogamy
in osmotrophic stramenopiles outside of
Oomycota is sparse. Although the morphologi-
cal changes that accompany the life cycles of
different thraustochytrid genera are now well
documented (Fig.3.2), the stages where meiosis
and karyogamy take place have still not been
established. In labyrinthulids, evidence of mei-
osis is supported by the finding of synaptone-
mal complexes in nuclei in thalli that are
forming zoospores (Perkins and Amon 1969 ;
Porter 1990 ), but where syngamy takes place is
still not known. In the Hyphochytriomycota s.
str. it is not known where meiosis and karyog-
amy take place (Fuller 1990 , 2001 ). The only
documented occurrence of karyogamy is
described inAnisolpidium ectocarpii[Karling
1943 ; Johnson 1957 ; summarized by Karling
( 1981 )], which we now suspect may belong in
the oomycete clade. In this genus, two naked
endobiotic thalli, arising from two adjacent
cysts (Fig.3.4l, m), immediately fuse to produce
a zygote (Fig.3.4o, p). This fused nucleus imme-
diately undergoes meiosis (Fig. 3.4p), which
gives rise to presumably haploid zoospores
(Fig. 3.4q). In oomycetes a common feature80 G.W. Beakes et al.