Systematics and Evolution, Part A The Mycota

B. Generalized Structure of Motile Cells
of Blastocladiomycota

Surveys of ultrastructural characters in motile
cells of the Chytridiomycetes have found four
basic patterns of side body complexes ormicro-
body–lipid globule complexes (MLCs)
corresponding to the various orders of posteri-
orly uniflagellate fungi (Lange and Olson 1979 ;
Powell 1978 ). The MLC of the Blastocladiales
(type 4) was distinguished as an ordered
arrangement of one or more mitochondria,
microbodies, and lipid globules located along
one side of an axially arranged nucleus and
nuclear cap and enclosed by a backing mem-
brane. Molecular phylogenetic studies provided
most of the evidence by which Blastocladiales
was raised to phylum status (James et al.
2006b); however, the formal description of phy-
lum Blastocladiomycota was based largely on
ultrastructural details. In the following account
ultrastructural characters defining the phylum
are discussed along with characters believed to
be of systematic and phylogenetic importance

in distinguishing major clades, subclades, and

component genera.

1. Axial Assembly

The remarkable homogeneity of the nucleus,

nuclear cap, and associated structures is

revealed in drawings and photographs of motile

cells of representatives of major clades of Blas-

tocladiomycota, including a zoospore of B.

emersonii(Fig.7.7a, b), a zoospore ofAllomyces

macrogynus(Fig.7.8a, b), a meiospore ofCoe-

lomomyces punctatus (Fig.7.9), and a meios-

pore ofPhysoderma maydis(Fig.7.10). The

flagellated cells of all known members of Blas-

tocladiomycota are characterized by a linear

arrangement of organelles (axial assembly)

consisting of a posterior flagellum with

contained axoneme, functional kinetosome,

nucleus with contained nucleolus, and anterior

nuclear cap. The flagellum has the nine-plus-

two arrangement typical of microtubules and

narrows distally to a short whiplash portion. At

the point where the flagellum joins the spore

F

K

N

M

M

V

B

G

P R Mb

N

K

Nkc

ab

Fig. 7.7(a,b)Blastocladiella emersonii. Interpretive
drawings of zoospore showing ultrastructural details
based primarily on several studies (Cantino and Trues-
dell 1970 ; Lessie and Lovett 1968 ; Reichle and Fuller
1967 ; Shaw and Cantino 1969 ). (a) Median longitudinal
section through zoospore. (b) Detail of kinetosomal
region and side body complex.Nnucleus;Nunucleo-

lus;Ncnuclear cap;Fflagellum;Kfunctional kineto-

some, Nkc nonkinetosomal centriole, P prop, R

rhizoplast,Mmitochondrion,Mbmicrobody,Llipid

globule,Bbacking membrane,Ggamma body,Tcyto-

plasmic microtubule,Vvacuole,open arrow, amor-

phous perikinetosomal material

Blastocladiomycota 193