Diatom: Definition, Classification, and Examples

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Diatom Definition

A diatom is a single-celled eukaryotic alga with a siliceous coating and symmetrical shape. Diatoms are typically found in freshwater, brackish water, and saltwater. They belong to the Bacillariophyceae taxonomic family. They can live alone or in groups. They produce diverse forms in colonies, such as ribbons, zigzags, stars, or fans.

Etymology: The word diatom comes from the Ancient Greek words diá, which means “through,” and témnein, which means “to cut.” Bacillariophyte is a synonym for bacillariophyte.

Diatom Classification

The diatoms belong to the Bacillariophyta phylum. Diatoms are classified into the following taxonomic groups under Bacillariophyta:

1. Coscinodiscophyceae is a phylum of the Coscinodiscophyceae family (centric diatoms)

2. Fragilariophyceae is a phylum of the family Fragilariophyceae (araphids, i.e. pennate diatoms without a raphe) 3.Bacillariophyceae (Bacillariophyceae) (raphids, pennate diatoms with a raphe).

Bacillariophyceae are pennate bacillariophytes that belong to the Bacillariophyceae taxonomic family. All diatoms were previously classified as part of the Phylum Chrysophyta. Bacillariophyceae was later classified as a class under the Phylum Heterokontophyta by van den Hoek et al. in 1995.

However, more current taxonomic categorization considers this class to be a group of pennate or featherlike diatoms, rather than all diatoms, as previous classifications did, and it is classified as belonging to the Phylum Bacillariophyta. Ongoing research and investigations on these species, however, may result in future taxonomic revisions.

General Characteristics of Diatom

i. Unicellularity

Diatoms are a kind of phytoplankton that consists of a large variety of tiny algae. Diatoms are single-celled organisms. Cells can be anything from 2 and 200 micrometres in size. They can live alone or in groups.

ii. Frustule

The fact that diatom cells are enclosed in a distinct silica cell wall is a distinguishing trait (i.e. hydrated silicon dioxide). Frustule is the name for the siliceous cell wall. These walls come in a variety of shapes and sizes, some of which are extremely lovely and ornate, but they all have two symmetrical sides with a split in the middle, hence the group name.

Centric diatoms have radial symmetry and are referred to as such. Pennate diatoms are frequently observed to have bilateral symmetry. Frustules are produced when silica is deposited on the cell wall. The polymerization of silicic acid monomers inside the cell results in the formation of silica.

iii. Thecae

The hypotheca (the smaller of the two parts of a diatom cell) and the epitheca (the bigger of the two halves) are the two halves of a diatom cell (the slightly larger theca). These two thecae frequently cross. The cingulum is a girdle that links the two sides of the cell.

Each daughter cell obtains one of the two halves during cell division and then develops the other half, only smaller. As cell division proceeds, progeny cells get smaller and smaller until the progeny cell ceases to divide and forms an auxospore that can expand in size.

iv. Pigments

Because chlorophyll (a and c), carotenoids (fucoxanthin), and xanthophylls predominate, diatoms have yellowish-brown to olive-brown chloroplasts. They have four-membraned chloroplasts.

v. Nutrition

The majority of diatoms are photosynthetic, although a few are heterotrophs.

vi. Food Reserve

Chrysolaminarin is their carbohydrate reserve. Lipids are also stored in them.

vii. Lacking Flagella

Except for the male gametes of centric diatoms, which contain smooth flagella, diatoms lack flagella.

viii. Reproduction

Binary fission is used by diatoms to reproduce asexually. The offspring cells that inherit the parent cell’s bigger theca will have a cell size similar to that of the parent. The other offspring cell with the smaller theca of the parent cell, on the other hand, will be smaller.

As a result, the cell size may decrease with subsequent binary fissions. The development of auxospores and sexual reproduction would aid in the restoration of the diatom population’s cell size.

ix. Bouyancy

Diatoms are able to maintain their suspension through a variety of methods. To slow their sinking pace, some of them create spines and chains. Ionic pumps also aid in bouyancy control.

x. Ecology

Because of their structural colouring, diatoms are known as the “jewels of the sea.” They are the world’s largest generators of oxygen. They produce roughly 20% of the oxygen in the atmosphere each year.

Through their shell, they are also a significant source of silicon. Due to the presence of a cyanobacterial endosymbiont in diatoms, some species are capable of nitrogen fixation.

Diatomaceous earth, also known as diatomite, is a diatom shell collection found in the earth’s crust. It’s made up of diatoms that have been petrified. It serves a variety of functions in the industry. It’s utilised in water filtration and as a mild abrasive, for example.

Diatom Examples

Pinnularia is a mucilaginous diatom with an elongated, elliptical shape. The genus Pinnulariaceae is a member of the Pinnulariaceae family, order Naviculales, and class Bacillariophyceae.

Navicula is a genus of the Naviculaceae family, order Naviculales, and class Bacillariophyceae. The name (Latin navicula, meaning “little ship”) comes from the appearance of species of this genus, which resembles a boat. It is this genus that creates almost a quarter of the oxygen on the planet.

Members of this genus are particularly important keystone species because they provide food for a variety of aquatic organisms. In marine environments, Chaetoceros is one of the biggest genera of planktonic diatoms. It is a member of the Chaetocerotaceae family and the Coscinodiscophyceae class.

Bacillaria is a genus of the Bacillariaceae family, Bacillariales order, and Bacillariophyceae class. The cells of this genus are elongated. They move past each other to build colonies that are piled on top of each other.

Diatom Citations
  • Diatom mediated heavy metal remediation: A review. Bioresour Technol . 2020 Jun;305:123068.
  • Research advances in forensic diatom testing. Forensic Sci Res . 2020 Mar 23;5(2):98-105.
  • Diatom isoprenoids: Advances and biotechnological potential. Biotechnol Adv . 2019 Dec;37(8):107417.
  • A Review of Diatom Lipid Droplets. Biology (Basel) . 2020 Feb 21;9(2):38.
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