Systematics and Evolution, Part A The Mycota

whereas some genera, such asUlkenia, have a
free-living amoeboid stage (Figs.3.2and3.3h,
j). Thraustochytrids can be recovered in large
numbers from marine sediments, including the
deep sea (Bongiorni 2012 ). Labyrinthulids are
prevalent living on or within seaweeds and sea
grasses, and there is increasing evidence that
they can live as commensals or mutualists in
plants and in other organisms, such as amoebae
(Dykova et al. 2008 ) and mollusc tissues (Aze-
vedo and Corral 1997 ). Thraustochytrids are
also parasites of marine animals, such asMer-
cenaria(quahog clam; Bower 1987 ) and cepha-
lopods (Jones and O’Dor 1983 ; Polglase 1980 ).
A new labyrinthulid species (Labyrinthula ter-
restris) (Craven et al. 2005 ; Olsen 2007 ) has
been identified as a causal agent of a serious
blight disease of irrigated turf grasses (Douhan
et al. 2009 ). Many isolates of the morphologi-
cally simpleDiplophrys-like protists (Table3.1),

and intercalated environmental sequences, are

well represented from freshwater habitats

(Anderson and Cavalier-Smith 2012 ), confirm-

ing that members of this lineage are much more

widespread in terrestrial ecosystems than pre-

viously thought.

Labyrinthulomycetes have traditionally

been divided into two families, theLabyrinthu-

laceae and the Thraustochytriaceae (Dick

2001a; Honda et al. 1999 ; Porter 1990 ) within a

single order, the Labyrinthulales(or Labyr-

inthulida). The former are characterized by

their spindle-shaped thalli, which are enrobed

in an ectoplasmic track-like networkalong

which the cells freely migrate (Fig.3.3a). The

latter form ovoid or spherical thalli, which,

except in the genusAlthornia(Karling 1981 ;

Porter 1990 ), are associated with a fine network

of rhizoid-likeectoplasmic threads(Fig.3.3c–i),

which act both as anchoring and feeding struc-

Table 3.1Taxonomic classification of Labyrinthulomycota/Labyrinthulea (Anderson and Cavalier-Smith 2012 )

Kingdom: Straminipila
{Heterokonta}a
Phylum: {BIGYRA Subphylum:
Sagenista}
Class: LABYRINTHULOMYCOTAb
{Labyrinthulea}
Order:Thraustochytridiales
{Thraustochytrida}
Family: Thraustochytridiacae
{Thraustochytriidae}

Aurantiochytriumc,Botryochytrium,Diplophrys,Parietichytrium,QPZ
Quahog parasite,Schizochytrium,Sicyoidochytrium,
Thraustochytrium,Ulkenia
Family: Oblongochytridiaceae
{Oblongochytriidae}

Oblongichytrium

Family: Althornidiaceae
{Althorniidae}

Althornia

Family: Diplophryidaceae
{Diplophryidae}

Diplophrys

{Superfamily: Amphifiloidea}
Family: Amphifilaceae
{Amphifilidae}

Amphifilad

{Family: Sorodiplophryidae} Sorodiplophyrs
Order: Labyrinthulales
{Labyrinthulida}
Family: Labyrinthulaceae
{Labyrinthulidae}

Labyrinthula

Family: Aplanochytridiaceae
{Aplanochytriiadae}

Aplanochytrium

aNames in { } are protistan nomenclatural equivalents used by Anderson and Cavalier-Smith ( 2012 )
bPorter ( 1990 ) used this name for the Phylum level rank
cGenera in bold have published sequences
dThis monotypic genus is the species formerly described by Dykstra and Porter asDiplophrys marina( 1984 )

44 G.W. Beakes et al.