IAS Gyan

Daily News Analysis


30th May, 2023 Environment

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  • Researchers at the Pune-based Agharkar Research Institute (ARI) have discovered a new species of single-cell algae, known as diatoms, from the northern Western Ghats — and named it after a veteran geo-archaeologist from the city, the late Professor S N Rajaguru.

S N Rajaguru was a former faculty member of Deccan College and known for his attempts to link biological and archaeological remains during excavations. It was through Rajaguru’s extensive studies that researchers today have a clear time-frame of India’s paleo-environment. He retired in 1994 as Joint Director of Deccan College, and passed away in December 2022.

About the new species

  • The new species named Gomphonema rajaguruii was found in a semi-aquatic environment along the wet walls in Maharashtra's popular hill station Mahabaleshwar in Satara district.
  • Gomphonema rajaguruii is unique because it shows the characteristics of two genus — Gomphonema and Gomphoneis.
  • This is a freshwater diatom species.
  • Diatoms showcasing such dual characteristics are very rare.
  • Diatoms can be found in freshwater and brackish water, and are commonly traced in lakes, rivers, streams, rivulets and the sea.
  • Similar to plants and trees that produce oxygen during the process called photosynthesis, diatoms, too, supply oxygen to the atmosphere.

About Diatom

  • A diatom is a unicellular eukaryotic alga characterized by having a siliceous covering and a symmetrical body.
  • Diatoms are mostly aquatic, being found in fresh, brackish, and saltwater. Some are found in moist places, such as soil.
  • Diatoms comprise the taxonomic phylum Bacillariophyta.
  • They may be solitary or in colonies. When in colonies, they form various shapes, e.g. ribbons, zigzags, stars, or fans.

Classification of Diatoms

  • The phylum Bacillariophyta includes the diatoms. The taxonomic classes of diatoms under Bacillariophyta are as follows:
    • Coscinodiscophyceae (centric diatoms)
    • Fragilariophyceae (araphids, i.e. pennate diatoms without a raphe)
    • Bacillariophyceae (raphids, pennate diatoms with a raphe)

General Characteristics


  • Diatoms are a major group of microscopic algae and are among the most common types of phytoplankton.
  • Diatoms are unicellular.
  • The cell size may range from 2 to 200 micrometers. They may live singly or in colonies.


  • A characteristic feature of diatom cells is that they are encased within a unique cell wall made of silica (i.e. hydrated silicon dioxide).
  • The siliceous cell wall is called a frustule. 


  • Diatom cell has two distinct halves: the hypotheca (the slightly smaller theca) and the epitheca (the slightly larger theca.


  • Diatoms have yellowish-brown to olive-brown chloroplasts due to the predominance of carotenoids (fucoxanthin), and xanthophylls. Their chloroplasts are four-membraned.


  • Most diatoms are photosynthetic whereas a few of them are heterotrophs.

Food reserve

  • Their carbohydrate reserve is chrysolaminarin. They also store lipids.

Lacking flagella

  • Diatoms do not have flagella except for the male gametes of centric diatoms that have smooth flagella.


  • Diatoms reproduce asexually by binary fission.


  • Diatoms are able to stay suspended through various mechanisms. 


  • Diatoms are referred to as the jewels of the sea because of their structural coloration. They are major oxygen producers on Earth. They generate about 20% oxygen annually.


Q) Which of the following statements with reference to Diatoms is/are correct?

1. All diatoms are photosynthetic.

2. Diatoms are referred to as the jewels of the sea.

3. A diatom is a unicellular eukaryotic alga.

  1. 1 and 2
  2. 2 and 3
  3. 1 and 3
  4. 1, 2 and 3

Correct Answer: b