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 typical Sleet and is included in the subphylum Ciliophora. is characterised by the presence of cilia and locomotor organelles. All ciliates possess two types of nuclei macronucleus and micronucleus.

Thus they show nuclear dimorphism Number of micronuclei may be one or more in different species. P.  caudatum has a single large and compact micronucleus.P. Aurelia has micronuclei while P. multi-micronucleatum has many micronuclei.

Genus Paramecium is a typical ciliate with 10 known species. P.  bursaria is green due to the presence of the symbiotic Algae Zoochlorellae.

Where is Found Paramecium?

Paramecium is found in freshwater Ponds pools, stream lakes, and rivers. It is found in abundance in stagnant water bodies with decaying organic matter.

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 in the unicellular microscopic organism. Its size varies in different species being  170 microns –  290 microns in Paramecium caudatum and 120-  250 Microns in Paramecium aurelia.

Paramecium ( GrParamekos or parameces, oolong + L, Caudata, tail) Is an elongated slipper-shaped animal and is commonly referred to as a sleeper animalcule.

The body is asymmetrical with flat oral or ventral and a convex aboral or dorsal surface. The anterior end is rounded and the posterior is thick and cone-shaped.

The structure is more complicated due to the development of certain organisations and can be described under the following heads.


The body is covered by a thin, firm but elastic pellicle. It gives a  definite body form to the organism. The pellicle is divided into polygonal or hexagonal depressions with raised margins. 

A single cilium project out from the centre of each hexagonal area. The polygonal area corresponds to two regular series of cavities, the  Alveoli, from which cilia emerge. 

The anterior and posterior margins of hexagonal areas bear the openings of trichocysts.

Pellicle Consists of three membranes. The outer or surface membrane is continuous with the membrane surrounding the cilia. Beneath The outer membrane is closely packed alveoli.

These are greatly flattened. The outer and inner membranes of the alveoli this Form the middle and inner membranes of the pellicle.

Paramecium Cilia –

The entire body surface is covered by a uniform covering of hair-like protoplasmic processes. They emerge from the centre of the alveoli.  all are of equal size except For a few at the extreme posterior end which is longer and forms the caudal tuft.

Ultrastructure of cilia –

Each cilium consists of a fluid matrix Surrounded by a membrane sheath.  The membrane sheath is continuous with the outer membrane of the Pellicle.  within the matrix are nine peripheral longitudinal fibres and two Central longitudinal fibres.

Each fibre is formed of two fibres one of Which carries a double row of Short  Arms all running in the same direction. The central fibres are single and are enclosed with an inner membranous sheath. 9 very delicate accessory or radial fibrils lie between the central and peripheral fibres.

Oral groove –

In Paramecium, there is a  broad shallow oral groove on the ventral surface. The oral Groove Extent and equally backward into a Conical funnel-shaped depression called a vestibule. The vestibule leads into a tubular and passes the buccal cavity.

It opens into a wide cytopharynx through an oval l cytostome. The cytopharynx forms a food vacuole at its proximal end.

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

Endoral membrane –

Special cilia in the buccal cavity fuse in a crescentic manner to form an oral membrane. It runs transversely and lies at the junction of the vestibule and the buccal cavity.


There are two peniculi located in the left wall of the buccal cavity. Each consists of four rows of cilia. The dorsal panniculus is longer and crosses over to the right wall at the cytostome. It terminates on the right wall of the cytopharynx.

The ventral panniculus is short and ends at the cytostome. The cilia of the dorsal and ventral peniculi beat in opposite directions.


 It is also formed of four rows of cilia. It runs along the dorsal wall of the buccal cavity, crosses over to right near the cytostome, and ends near the termination of the dorsal peniculus.

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