Classification of Protozoa

Protozoa is classified by many based on different characters of protozoa but the classification of Protozoa is complicated and difficult. The classification followed here is based on Hyman's classification.

Phylum Protozoa is divided into two subphyla:

I. Subphylum: Plasmodroma

The Locomotory organelles are pseudopodia and flagella Nucleus is single or many but all are one kind Asexual reproduction is by binary and multiple fissions. Sexual reproduction is by complete fusion of gametes. The sub-phylum is classified into three classes and classification is based on the locomotor organelles.

• Class I: Mastigophora
• Class II: Rhizopoda
• Class III: Sporozoa

Class I: Mastigophora (or) Flagellata:

1. The body is covered by pellicle or cuticle.
2. The Locomotory organelle is flagellum. Flagella are one to many.
3. In fresh water forms contractile vacuole is present associated with accessory vacuoles
4. In many eye-spot or stigma is present.
5. Asexual reproduction is by longitudinal binary fission.
6. They may be free living or parasitic. This class is divided into ten orders.

Order 1: Chrysomonadina:

The mouth and gullet are absent Flagella one or two. Chromatophores either one or two. and the body is covered by thin pellicle.

E.g: Chrysamoeba.

Order 2: Cryptomonadina:

The gullet is present and reaches up to the middle of body. Flagella one or two, chromatophores two, or absent pellicle is firm.

E.g: Cryptomonas.

Order 3: Dinoflageilata:

Two flagella are almost of equal size. Chromatophores are green, brown or yellow. Body is enclosed in a thick and rigid shell of cellulose. A few forms are luminescent. E.g: Noctiluca, Ceratium.

Order 4: Chioromonadina:

Gullet is present but transverse groove is absent. Flagella are two. Chromato-phores are numerous. Body covering is thick cuticle and usually amoeboid.

E.g: Coelomonas.

Order 5: Euglenoidina or Euglenida:

Cytostome and cytopharynx are present, Flagellum is single. Chromato-phores are numerous or absent.

Order 6: Phytomonadina (or) Volvocales:

Gullet is absent. Flagella are one or two or four or rarely more. Body is enclosed in the rigid cellulose covering. Chromatophores are green or brown.

E.g: Chlamydomonas & Volvox.

Order 7: Protomonadina:

Flagella are one, two or rarely more. Mouth is absent and nutrition is holozoic in free living and saprozoic or saprophytic in parasitic forms. They are colourless.

E.g: Trypanasoma & Leishmania.

Order 8: Polymastigina:

Flagella are 3 to 8 or more, Mouth is present. Harmless and intestinal parasites are included.

E.g: Trichomonas, Giardia.

Order 9: Hypertnastigina:

Numerous flagella, arranged in one or more tufts. Mouth is absent. Food ingestion is by pseudopodia. Parasites in the intestine of termites and cockroaches.

E.g: LophomonasTrichonympha.

Order 10: Rhizomastigina (or) Pantostomatida:

Locomotory organelles are both flagella and pseudopodia.

Class II: Rhizopoda or Sarcodina:

1. They do not show definite shape.
2. Muscle parasites of invertebrates and spores with spore cases.
3. E.g: Haplosporidium.

II. Subphylum: Ciliophora or (Infusoria):

1. The locomotory organs are cilia.
2. There are two types of nuclei, mega and micronucleus.
3. Sexual reproduction is by conjugation.
4. Asexual reproduction is by binary fission and by budding.
5. Class - I Ciliata:
   • Cilia persist throughout life.
     • (a) Sub-class Protociliata:
       • Cilia are all equal and uniform, cytostome is absent. Two nuclei are present. Nuclear dimorphism is seen Reproduction is by syngamy.
       • E.g: Opalina.
     • (b) Sub-class Euciliata
       • Cilia are of different sizes. Cytostome is usually present. Two nuclei are present. Sexual reproduction is by conjugation.

Order 1: Holotricha:

Ciliation of body is uniform.

Order 2: Spirotricha:

Cilia is not uniform, adoral zone of membranelle are present around cytostome.

E.g: Balantidium.

Order 3: Peritricha:

Cilia reduced to one or more girdles, gullet with undulating membrane. E.g: Vorticella.

Order 4: Chonotricha:

Adoral zone of membranellae arranged clock-wise. E.g: Spirochona.

Class III: Suctoria:

Adults sedentary and without cilia which are present only in young stages. E.g: Epelota, Acineta.