Paramecium | Classification, Structure, Examples, Introduction

Hello friends, today we will know step by step about what is Paramecium. so let’s start.

Introduction to Paramecium

Paramecium is a phylum ciliate animal and is placed in the subphylum Ciliophora of the phylum Protozoa. The characteristic of ciliate animals is the cilia present in them which are in the form of a moving organ.

Two types of nuclei are found in all ciliate animals, which are called Macronucleus and Micronucleus.

Hence, it shows nuclear dimorphism. The number of micronuclei may be one or more in different species.

For example, P. caudatum possesses single, large and well-organized micronuclei. P. aurelia has two micronuclei. Whereas P. multimicronucleatum possesses many micronuclei.

The genus Paramecium is a phenotypic ciliate with 10 known species. P. bursaria is green due to the presence of the symbiotic algae Zoochlorella.

Where is Found Paramecium?

Paramecium is found in ponds, lakes, and rivers. It is found in large numbers along with decaying organic matter in freshwater bodies.

What is a Paramecium
Image credit – Wikimedia commons

Classification of Paramecium –

Paramecium caudatum

Class  Ciliata
What is a Paramecium?

Structure of Paramecium –

Paramecium size and shape –

Paramecium is a one-celled microorganism. Its size is different in different species. The size of Paramecium caudatum is 170 – 290 µm, and the size of P. aurelia is 120–250 µm. Paramecium is an elongated, slipper-shaped animal. Commonly it is also called a slipper animalcule.

Their body is asymmetric with a flattened oval or ventral and distal or dorsal surface with a convex face. The anterior end of the paramecium is rounded and the posterior end is thick and conical.

The structure of Paramecium is quite complex due to few developed organs. The following main parts can be described below.


The body of Paramecium is surrounded by a thin, strong, and flexible thin membrane called a pellicle. It gives a definite form of the body of the organism. The pellicle is divided into a polygonal or truncated pit with a raised margin.

A cilium emerges from the center of each pectoral region, and from the polygonal regions a regular series of similar cavities, follicular, and cilia emerge. The anterior and posterior margins of the pectoral region bear the pores of trichocysts.

The pellicle is made up of three membranes. There is an outer membrane or surface membrane with cilia around the membrane. The alveoli are packed tightly under the outer membrane.

They are mostly in flat form. The outer and inner membranes of the alveoli form the inner and middle membranes of the pellicle.

Paramecium Cilia –

Cilia are like hairs. It covers the entire body surface of Paramecium uniformly. It comes out from the center of the alveoli. The cilia of some ends which are long are called Caudal Tuft. Except these, all others are of the same size.

Ultrastructure of cilia –

Each cilium is composed of a liquid matrix and is surrounded on all sides by a membranous covering. With the outer membrane of the pellicle, there is a continuous membranous covering. Within the matrix are nine peripheral longitudinal fibers and two central longitudinal fibers.

Each filament is made up of two sub-filaments. One of which has a double row of short sides running in the same direction. The central filament is single and is attached to an inner membranous sac. Between the central and peripheral fibers are 9 very sensitive accessory or radial fibers.

Oral groove –

In Paramecium, there is a clear, shallow facial groove on the ventral surface. The oral groove has a long oblique and a conical funnel-shaped pit at the back, which is called the vestibule.

The vestibule leads into the oral cavity, a wide tubular passage. It opens into a wide cytopharynx through an oval cytostome. The cytopharynx forms a food vacuole at its adjacent end.

The cilia in the oral groove show variation in size and arrangement. The cilia in the oral groove show variation in size and arrangement. They form the following structures.

Endocrine membrane –

Special cilia in the oral cavity join together in a crescent-shaped manner to form the endocrine membrane. It runs transversely and is located at the junction of the vestibule and the oral cavity.


Here two panniculus are located in the left wall of the oral cavity. Each has four rows of cilia. The dorsal panniculus is long and crosses the right wall into the cytostome.

It ends at the right wall of the cytopharynx. The ventral panniculus is short and ends at the cytostome. The cilia of the dorsal and ventral panniculus beat in opposite directions.


It is also formed by four rows of cilia. It runs along the dorsal wall of the oral cavity, passes to the right near the cytostome, and ends near the end of the dorsal panniculus.

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