LSU rRNA trees (Fig.3.5),Haptoglossaseems to
share a common ancestor withEurychasma,
although with long branch separation
(Fig.3.5b). There are few obvious features that
these two genera share, which is why we have
chosen to keep them in separate orders.Hap-
toglossa is also unusual amongst early-
diverging genera in that it is predominantly a
terrestrial genus, althoughH. heterosporahas
been reported to infect marine nematodes
(Newell et al. 1977 ). The isolates ofHaptoglossa
that have so far been sequenced cluster in two
or three clades (Hakariya et al. 2007 , 2009 ),
suggesting new genera will almost certainly
need to be defined.
- Olpidiopsidales s. lat.
The ~Olpidiopsidales as defined here encom-
pass a number of relatively poorly studied
groups of families [~Olpidiopsidaceae
(Fig.3.7m–r), PontismataceaeandSirolpidia-
ceae(Tables3.3and3.5)] consisting of rather
small holocarpic species that had traditionally
been placed in the Lagenidiales (Karling 1981 ).
Dick (2001a) considered these families to be
incertae sedis(Table3.4). They are a fairly
diverse assemblage of parasites of algae, proto-
zoans, and other oomycetes that have been
documented in detail by Karling ( 1981 ). A
number cause economically significant losses
of commercially cultivated seaweeds, such as
Olpidium porphyrae(Sekimoto et al.2008b),
the causal agent of “red rot” disease of nori,
andPeterseniaspp., which cause “green rot”
disease ofChrondrus crispus(Craigie and Cor-
rea 1996 ) and the “wasting disease” of dulse,
Palmaria palmata(Pueschel and van der Meer
1985 ). Most have simple spherical or ovoid
thalli that fill their infected host cells and pro-
duce one or more tube-like discharge tubes
(Fig. 3.7o) to permit zoospore escape
(Fig.3.7r). The type species,Olpidium sapro-
legniae(Fig.3.7m–q), parasitizes Saprolegnio-
mycete water moulds (Karling 1981 ) and shows
the typical characteristics of the genus.
Encysted zoospores produce a fine germ tube
that releases an unwalledplasmodiuminto the
host cytoplasm (Fig.3.7m, n). This ultimately
develops into a small flask-shaped walled thal-
lus, with a prominent discharge tube (Fig.3.7o).
Sexual reproductionhas been described inO.
saprolegniaeand closely related freshwater taxa
and results in the formation of spiny resting
spores (Fig. 3.7p) (Karling 1981 ; Sparrow
1960 , 1976 ). The adjacent thalli (Fig.3.7q) that
conjugate have been interpreted as antheridia
and oogonia and the resting spores that result
as oospores (Martin and Miller 1986 ).
To date, combined morphological, ultra-
structural, and molecular sequence data have
been published for just two species in the
~Olpidiopsidaceae: O. porphyrae (Sekimoto
et al. 2008c) and O. bostrychiae (Sekimoto
et al. 2009 ), both of which infect red seaweeds
(PorphyraandBostrychia). Both diverge after
the Eurychasma and Haptoglossa clades
(Fig.3.5a), but they do not form a monophy-
letic clade. Similarly, unpublished sequence
data also show that the freshwater oomycete
parasitic species fall into one or more clades
that are close to, but separate from, the marine
species (Inaba and Sekimoto, in preparation).
This indicates thatOlpidiopsisas currently con-
stituted is a paraphyletic genus (Fig.3.6) and
will require substantial revision. It is assumed
the Sirolpidiaceae and Pontismataceae, which
include genera such asPetersenia,Pontisma,
andSirolpidium(Table3.5), are likely to be
closely related to the Olpidiopsidales clades
(Dick 2001a). However, until there is
greater taxon sampling, we retain all in the
~Olpidiosidales s. lat. for the time being
(Fig.3.6, Table3.5).
- Haliphthorales
The order “Haliphthorales” is an exclusively
marine order consisting of a small number of
genera belonging to a single family, the
Haliphthoraceae, which also was originally
placed in the Lagenidiales (Table3.3) (Sparrow
1973c). The family currently contains three
genera,Haliphthoros(Fig.3.7s–u),Halioticida
(Fig.3.7v, w) (Hatai 2012 ; Maurosa et al. 2009 ),
andHalocrusticida(syn.Halodaphnea) (Dick
1998 ) (Fig.3.7x) (Sekimoto et al. 2007 ; Hatai
2012 ). The family was transferred by Dick
Systematics of the Straminipila: Labyrinthulomycota, Hyphochytriomycota, and Oomycota 57