Diplomastigomycotina

Sub-division: Diplomastigomycotina:- Flagellated cells bear two different types of flagella whiplash type as well as tinsel type. It includes 1 class -

Oomycetes:- 

> Most of the members are aquatic but some grow on the soil and the others attack the shoots of terrestrial plants.

> The primitive forms are unicellular, whereas the advanced forms have a well-developed branched, filamentous, and coenocytic mycelium.

> The cell wall is mainly composed of cellulose-β-glucan and chitin is altogether absent.

> A sexual reproduction takes place by means of pyriform or reniform biflagellate zoospores, which are devoid of cell wall. In pyriform zoospores, the flagella are attached anteriorly and in reniform laterally. One flagellum is of whiplash type and the other of tinsel type.

> In primitive aquatic form, zoosporangia are not well differentiated from somatic hyphae, whereas in advanced forms distinct zoosprangia are found.

> Some forms also produce non-motile asexual spores, known as conidia.

> Most of the Oomycetes are eucarpic, but the members of the order Lagenidiales are holocarpic.

> The sexual reproduction is of oogamous type. The male and female sex organs are known as antheridia and oogonia, respectively. The sex organs are either terminal or intercalary.

> It is now established that meiosis in Oomycetes takes place within the diploid nuclei of gametangia (antheridia and oogonia) hence is called gametangial-meiosis. That is, zygotic meiosis is absent. As a result, the vegetative thallus is diploid.

> The gametes are non-flagellate. The fusion of gametes results in the formation of thick-walled oospores.

> Oomycets show interesting parallel changes in their biology and morphology, which are closely connected with their phylogeny.

> Classification:-

4 Orders:-

a. Laginidiales:-

Family:- Lagenidiaceae

Eg.- Lagenidium, Lagenisma, Myzocytium

b. Saprolegnials:-

Family:- Saprolegniaceae

Eg.- Saprolegnia, Leptolegnia, Geolegnia, Brevilegnia, Aphanomyces, Achlya, Isoachlya, Dictyuchus, Pythiopsis, Thraustotheca

c. Leptomitales:-

2 Families:-

i. Leptomitaceae:- Eg.- Leptomitus, Apodachlya

ii. Rhipidiaceae:- Eg.- Aqualinderella, Rhipidium, Apodachlyella

d. Peronosporales:-

4 Families:-

i. Pythiaceae:- Eg.- Pythium, Phytophthora

ii. Peronosporaceae:- Eg.- Peronospora, Sclerospora, Plasmopara, Basidiophora, Bremia

iii. Peronophythoraceae:- Eg.- Peronophythora

iv. Albuginaceae:- Eg.- Albugo