We are surrounded by a lot of living and non living creatures. Living creatures are the ones that are made up of cells and need food, air and water to survive and are of different shapes and sizes. They can be unicellular or multi cellular. They are capable of responding to changes and have the ability to move from one place to another. No living creature is immortal and someday or the other every living creature have to die. Moreover, living creatures have the ability to reproduce either directly or indirectly. Living creatures thus possess following characteristics such as they can breathe or respire and have to feed and excrete, have the capability to move, reproduce and grow and are sensitive to changes around them and have the potential to adapt themselves according to those changes. Living creatures can be of different sizes ranging from a few micrometers to thousands of meters. This article gives us the list of the smallest living creatures as per the size that can be found on earth.
10. SEA URCHIN – ECHINOCYAMUS SCABER (6 mm)
Sea urchins belong to the class of Echinoidea and are the species that live in oceans at the depth of around 5000 meters. They are very tiny animals that are globular in shape and possess a spiny and round shell. They exist in many colors such as green, blue, red, purple, olive and shades of brown. There exists around 950 species of sea urchins of varying sizes having a shell ranging from 3 to 10 cm. Their movement is very slow and they usually feed on algae. They may sometimes also be called as hedgehogs. The smallest sea urchin that is found is Echinocyamus scaber which possess a shell of only 6 mm in size. This sea urchin is the tenth smallest living creature that is found on earth.
9. STARFISH – PATIRIELLA PARVIVIPARA (5 mm)
Starfish which is sometimes also known as sea stars belongs to the class of Asteroidea. They are found in oceans all over the world, usually at the depth of around 6000 meters or more. Their shape is like that of a star having a circular disc at the centre with five arms surrounding it. Some star fishes possess more than five arms. They are found in many colors such as red, blue, orange, brown or grey. They have the ability to regenerate their arms and can reproduce in both ways be it sexually or asexually. They feed on a specific prey and thus are also known as opportunistic feeders. Their life cycle is considered to be a complex one. There exist many star fishes having various sizes but the smallest among them is Patiriella Parvivipara which is 5mm in size. It is usually found in South Australia on granite rocks. Patiriella Parvivipara is usually yellow – orange in color.
8. SEA CUCUMBER – PSAMMOTHURIA GANAPATII (4 mm)
Sea cucumbers are marine animals that belong to the glass of Holothuroidea. They possess an elongated body that resembles like that of leather and contains a single and branched sex gland. They are found in oceans all over the world and mostly in the Asia Pacific region. They are even consumed by humans and may even be cultivated. They send hormone signals to communicate with each other. They are found in varying sizes ranging from 10 to 30 centimeters in length but the smallest among these is Psammothuria ganapatii which is 4mm in length and is usually found on the coast of India between sand grains.
7. BEETLES – SCYDOSELLA MUSAWASENSISIS (300 μm)
Beetles are classified under insects and have two pair of wings. Beetles can survive in almost all kind of environment except that in marine and cold regions. They have the ability to feed on any kind of diet be it flesh, waste, fungi, plants and many more. There are around forty thousand species of beetles that can be found all over the world having varying sizes. The smallest beetle that exists is Scydosella musawasensis which is of Nanosellini tribe and is 300 micrometer in length. Scydosella musawasensisis is the smallest non parasitic beetle that can be found across the world.
6. ERIOPHYIDAE (125 to 250 μm)
Eriophyidae is a plant parasite which causes damage to the plant tissues. There are around 36 hundred species of Eriophyidae and many more are still yet to be discovered. They are usually yellow, pink or purple in color and have two leg pairs. They resemble worms and usually spread their population with the help of wind. Though they are plant parasites, but some of them are also used to control invasive plant and weeds. They are found in different sizes ranging from 125 to 250 micrometer.
5. CRUSTACEAN – STYGOTANTULUS STOCKI (94 μm)
Crustaceans are free living animals that may be either aquatic or terrestrial or parasitic. There are around 67 thousand species of crustaceans of varying sizes. They form an important part of the food chain and are also consumed by the humans. Stygotantulus stocki is the smallest species of crustaceans that belongs to the Tantulocarida which is a specialized group of parasitic crustaceans. Tantulocarida consists of 33 species and the smallest among them is Stygotantulus stocki which is only 94 micrometer in length.
4. EUKARYOTES (0.8 μm)
Eukaryotes are those organisms that are enclosed within a membrane. Eukaryotes include many types of plants, fungi, animals and unicellular organisms. They have the ability to reproduce either with the help of mitosis or meiosis. They exist in many different sizes and shapes but the smallest among them is Prasinophytes which is a type of green algae with the size of 0.8 micrometer of a single cell. It is a free living organism which is mostly found in marine waters.
3. NANOARCHAEUM (400 nm)
Nanoarchaeum equitans is a microbe which has a diameter of around 400 nm. Specific conditions which are required for the growth of Nanoarchaeum equitans are an environment with a pH of 6 having saline concentration of approximately 2 percent. It requires a high temperature for its growth, which is usually close to the boiling temperature of water. For survival, it has to stay in contact with the host living creature. It has the genes which are required for replication and repair but it lacks the ones which are required for synthesis of cofactors, amino acids, lipids and nucleotides. They possess a circular structure and have an extra layer to provide protection to the cell. Because of their small size of 400 nm they are considered as the third smallest living creatures that are found on earth.
2. MYCOPLASMA GENITALIUM (200 – 300 nm)
Mycoplasma Genitalium is considered as the second smallest organism that have the ability to grow and reproduce. It is basically a parasitic bacterium which is found in respiratory tracts. It may lead to genital diseases and is usually transmitted between partners as a result of unprotected sexual intercourse. It is possible to cure the disease caused by Mycoplasma Genitalium with the help of antibiotics. It have been seen that Mycoplasma Genitalium have 470 coding regions, DNA pairs, energy metabolism, cellular transport, genes and all other things that are necessary to sustain life. Mycoplasma Genitalium may be of different sizes ranging from 200 to 300 nm.
1. NANOBES (20 nm)
Nanobes is one tenth of the size of bacteria and are considered as the smallest of the tiniest form of life that exists on earth. Earlier it was controversial whether nanobes are living or nonliving organisms since scientists earlier have only found mineral-crystalline structures in nanobes rather than any type of life. But due to recent advancements in technology, it has been claimed that nanobes are living organisms as they contains DNA and have the capability to reproduce. They are only 20 nanometre in size which is really small to contain any bio chemicals which helps to sustain life and reproduce, so for nanobes to reproduce and grow, an unconventional way has to be there which nanobes possess. It is still in argument whether nanobes are individual living creatures or parts of larger living organisms.