PROTOZOA CLASSIFICATION:
CLASSIFICATION OF PROTOZOA
Protozoa are unicellular organisms that are widely diverse in their modes of locomotion, reproduction, and habitat. The classification of Protozoa is based on various criteria, such as their structure, mode of movement, and method of reproduction. The classification of Protozoa is complex, but Hyman’s classification system is one of the most widely accepted methods in the scientific community. This article aims to provide an in-depth understanding of the classification of Protozoa, its subphyla, and the major classes within each subphylum.
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:
- Sub-phylum Plasmodroma
- Sub-phylum Ciliophora (Infusoria)
These subphyla are further subdivided into classes based on specific features such as the type of locomotory organelles, presence of nuclei, and reproduction methods. Let's explore each subphylum and its associated classes.
Sub-phylum Plasmodroma : Locomotory Organelles
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.
The Sub-phylum Plasmodroma is defined by protozoa that primarily use pseudopodia (false feet) and flagella for movement. These protozoa may have one or more nuclei, but they all share a similar structural organization. Asexual reproduction occurs via binary fission or multiple fission, while sexual reproduction takes place through the fusion of gametes.
Class 1 : 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 '10' orders.
Subdivisions of Mastigophora:
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.
Ex : 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.
Ex : 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. Ex : 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.
Ex : 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.
Ex : 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.
Ex : Trypanasoma & Leishmania.
Order 8: Polymastigina:
Flagella are 3 to 8 or more, Mouth is present. Harmless and intestinal parasites are included.
Ex: 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.
Ex :LophomonasTrichonympha.
Order 10 : Rhizomastigina (or) Pantostomatida :
Locomotory organelles are both flagella and pseudopodia.
Order 11 : Rhizopoda or Sarcodina :
1. They do not show definite shape.
Muscle parasites of invertebrates and spores with spore cases.
Ex : Haplosporidium
Class II: Rhizopoda (or Sarcodina) :
- Locomotory organelle: Pseudopodia
- Reproduction: Asexual reproduction by binary fission
- Characteristics: Amoeboid cells with an irregular shape
- Example organisms: Haplosporidium
Class III: Sporozoa
- Locomotory organelle: No cilia or flagella, but specialized spores for movement.
- Reproduction: Primarily through spore formation.
- Example organisms: Plasmodium (causes malaria)
Subphylum - II Ciliophora or (Infusoria) :
The Sub-phylum Ciliophora, also called Infusoria, is characterized by the presence of cilia, which are short, hair-like structures used for locomotion and feeding. Protozoa in this group have two types of nuclei: a macronucleus and a micronucleus. Reproduction occurs both sexually (via conjugation) and asexually (via binary fission).
1) The locomotory organs are cilia.
2) There are 2 types of nuclei, mega and micronucleus.
3) Sexual reproduction is by conjugation.
4) Asexual reproduction is by binary fission and by budding.
Class - 1 Ciliata :
Cilia persist throughout life. Sub-class a Protociliata :
Cilia are all equal and uniform, cytostome is absent. 2 nuclei are present. Nuclear dimorphism is seen Reproduction is by syngamy.
Ex : Opalina
Sub-class b Euciliata
Cilia are of different sizes. Cytostome is usually present. Two nuclei are present. Sexual reproduction is by conjugation.
- Sub-class a: Protociliata: Cilia are uniform in size, cytostome absent.
Example: Opalina - Sub-class b: Euciliata: Cilia are of varying sizes, cytostome present.
Example: Balantidium
Order 1 : Holotricha :
Ciliation of body is uniform.
Order 2 Spirotricha :
Cilia is not uniform, adoral zone of membranelle are present around cytostome.
Ex ; Balantidium
Order 3 Peritricha :
Cilia reduced to one or more girdles, gullet with undulating membrane. Ex : Vorticella
Order 4 : Chonotricha :
Adoral zone of membranellae arranged clock-wise. Ex : Spirochona
Class II Suctoria :
Adults sedentary and without cilia which are present only in young stages. Ex : Epelota, Acineta.
Summary of Protozoan Classification
Protozoa are classified based on several distinguishing characteristics, including their mode of movement, reproduction, and structural features. By categorizing protozoa into subphyla, classes, and orders, researchers can better understand their biological functions and ecological roles. From the flagellates in Mastigophora to the ciliates in Ciliophora, the classification system offers a framework for studying these fascinating organisms.
Protozoan classification remains a complex yet essential area of research for understanding the diversity and function of unicellular organisms. By following systems like Hyman’s classification, scientists can categorize protozoa into their respective subphyla and classes, opening up new possibilities for studying their behavior, role in diseases, and potential therapeutic applications.