Phylum – Protozoa (Acellular or unicellular)
Subphylum – Sarcomastigophora (Flagella or pseudopodia or both present)
Superclass – Mastigophora (One or more flagella present)
Class – Phytomastigophorea (Chloroplasts present)
Order – Euglenoidida (Flagella arise from the bottom of a pit called reservoir, many
chloroplasts, gullet present.)
Genus – Euglena
Habits and Habitat
It is a free living flagellate. It is found in great numbers in stagnant freshwater pond, ditches, etc., containing nitrogenous organic matter like urine and faeces of animals. Under favourable environmental conditions it multiplies rapidly and forms green scum on the water surface (like algal blooms). E. viridis, E. agilis, E.fusiformis and E. orientalis are common Indian species.
1. Size and shape It is small (60 microns in length), spindle-shaped.
2. Pellicle The shape of the body ismaintained by a thin, flexible and
strong covering, the pellicle orthc periplast. The pellicle shows spiral or parallel striations, called myonemes.
3. Anterior end (Reservoir and flagellum) Its anterior enu has a flask-shaped invagination. The
body of the flask is callcd reservoir, the neck of the flask forms gullet or cytopharynx, and the opening is called the cell mouth or cytostome.
From the bottom of the reservoir arises one long and one very short flagellum. Each flagellum originates from a tiny granule, the blepharoplast, located in the cytoplasm. The long flagellum contains a lateral swelling, the para flagellar body. It acts as a photoreceptor. The animal moves with the help of long flagellum only. The short flagellum does not come out of the reservoir.
The cytoplasm is divisible into two zones- a clear, dense, outer or peripheral zone or the ectoplasm, and a fluid like, granular central zone or the endoplasm. Endoplasm contains the following :
(a) Nucleus : A single, large, spherical or oval nucleus lies usually in the middle or towards the posterior end of the boay. It contains several nucleoli and chromosomes.
(b) Contractile vacuole : A large contractile vacuole is found close to the reservoir. It discharges its watery contents into the reservoir. It remains surrounded by several minute, accessory contractile vacuoles.
(c) Stigma: Near the reservoir and opposite to contractile vacuole, there is a small discoid red or orange-red body, the stigma or the eye-spot. It is composcd-ofoil droplets and red pigment, the carotenoid. It forms a cover or shield over the light sensitive paraflagcllar body.
(d) Chloroplasts or chromatophores : There ate a large number oi elongated rod-like bodies called chloroplasts or chromatophores. These radiate from a ccntral body and form a star-shaped structure. The central body or the pyrenoid is formed of proteins. It remains surrounded by a number of small granules of paramylon (a polysapcharide). It is the reserve food of Euglena and is formed by the products of photosynthesis. The chloroplasts contain chlorophyll a and b and carotene.
(e) In addition, the cytoplasm contains Golgi bodies, endoplasmic reticulum, mitochondria and ribosomes etc.