What is Earthworm?

Earthworms are tiny invertebrate organisms that live in the soil, as they are susceptible to pH, waterlogging, compaction, rotation, tillage, and organic matter, which are considered good biological indicators of soil health. The numbers and distribution of Earthworms in a field indicate what is happening under the surface. In nearly all types of soils in the world, Earthworms are present wherever the conditions are suitable according to them, i.e. the moisture and organic content are sufficient to support them.


Classification of Earthworms

The scientific name for Earthworms is Lumbricina. 


There are more than 1,800 species of the Oligochaeta class of terrestrial worms present in the world. The most common species of Earthworm found in the environment is Lumbricus terrestris. 


Currently, according to the species name database, there are over 6,000 terrestrial Earthworm species and just about 150 species are widely distributed around the world, out of a total of around 6,000 species. These are Earthworms, either peregrine or cosmopolitan in nature.

  • Few of the common Earthworm species are listed below. The name in the bracket is an Earthworm scientific name.

  • Redhead Worm (Lumbricus rubellus)

  • Common Earthworm (Lumbricus terrestris)

  • Green Worm (Allolobophora chlorotica)

  • European Nightcrawler (Eisenia hortensis)

  • Brandling Worm (Eisenia fetida)

  • Giant Gippsland Earthworm (Megascolides australis)

  • Kentucky Earthworm (Komarekiona eatoni)

  • Oregon Giant Earthworm (Driloleirus macelfreshi)

  • Louisiana Mud Worm (Lutodrilus multivesiculatus)

  • Washington Giant Earthworm (Driloleirus americanus)

  • Gray Worm (Aporrectodea calignosa)

  • African Nightcrawler (Eudrilus eugeniae)

  • Composting Worm (Perionyx excavatus)

Morphology of Earthworm

Earthworms are extremely important for the environment and there is an essential need to preserve and understand the Earthworms. Some key details about the shape and size of an Earthworm are:

  • Earthworms are generally broad, small, cylindrically elongated with points at the front, blunt behind, and thickest slightly behind the anterior end.

  • They are Bilaterally symmetrical.

  • The presence of a dark median line of a dorsal blood vessel that runs just below the skin in the body is indicated by the dorsal surface of the body.

  • The presence of genital openings and papillae in the anterior sections of the body marks the ventral surface.

  • Size varies from species to species and from people to people of the same species.

  • A mature Earthworm has a length of around 150 mm and a width of 3 to 5 mm.

Earthworm Anatomy

Some key features about the anatomy of an Earthworm are given below:

  • The mouth is a crescentic anterior aperture. On the ventral line, it is located just below the prostomium. Surrounded by the peristomium or buccal segment of the 1st segment of the body.

  • The exit of the alimentary canal is anus which is a vertical slit-like aperture at the posterior terminus. Undigested wastes are removed from it.

  • The Earthworm is a hermaphrodite, but in the same individuals, male and female generative openings are found.

  • There are 4 pairs of small ventrolateral spermathecal pores which lie intersegmental between the grooves of 5/6, 6/7, 7/8, and 8/9 segments.

  • A large number of very minute nephridiopores are present. They are scattered all over the body except for the first two segments. These pores are apertures of the integumentary nephridia, through which metabolic wastes of the body are removed.

  • Dorsal pores of minute apertures of coelomic chambers are present behind the 12th segment which is located mid-dorsally, one in each intersegmental groove, except the last groove. Through these pores, coelom communicates with the exterior.

  • Earthworms have no eyes, but they have specialized photosensitive cells, called light cells of Hess. These photoreceptor cells have a microvilli-filled central intracellular cavity.

  • The brains of Earthworms are made up of a pair of pear-shaped cerebral ganglia. These are found in the third segment of the dorsal side of the food canal, in a groove between the buccal cavity and the pharynx.

  • Earthworms have a dual circulatory system in which food, waste, and respiratory gases are carried both by the coelomic fluid and a closed circulatory system.

  • The excretory system includes a pair of nephridia in every section, except for the first three and the last ones. Integumentary, septal, and pharyngeal are the three forms of nephridia.

  • Earthworms do not have any separate breathing organs. Gases are exchanged through the wet skin and capillaries, where the haemoglobin dissolved in the blood plasma takes up oxygen and releases carbon dioxide. Water can also be transferred through the skin through active transport, as well as salts.

  • The musculature (a combined effect of contraction and relaxation of both the muscle layer) of the body wall and seta and the hydrostatic pressure produced by the coelomic fluid is involved in Earthworm movements. For forward locomotion, the increase in the hydrostatic pressure of the anterior segments of the body (usually 9 segments) is responsible. 

Types of Earthworms

There are three types of Earthworms and all these three can be defined by the part of the ecosystem that the worms primarily inhabit. These are:

  • Epigeic Earthworms 

  • Endogeic Earthworms 

  • Anecic Earthworms 

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FAQs (Frequently Asked Questions)

1. What is an Earthworm?

An earthworm is a terrestrial invertebrate belonging to the Annelida phylum. They exhibit a body plan of tube-within-a-tube, are segmented externally with sufficient internal segmentation, and typically have setae on all segments.

2. What are the Types of Earthworm?

There are three main types of earthworms.

  • Epigeic earthworms

  • Endogeic earthworms

  • Anecic earthworms

3. What are the uses of earthworms?

The Earthworms allow copious amounts of air and water that get into the soil to increase its fertility. They break down the organic matter into nutrients that can be used by plants, including leaves and grass. They also leave behind castings while feeding, which are also a very useful form of fertilizer. Earthworms act like free aid to the farm and hence are extremely important to farming. With the rising trend of organic farming and people willing to pay more money for farm products that are grown organically, the importance of earthworms is going to increase.

4. How am I Supposed to Know Which End of an Earthworm is Which?

Find the earthworm's anterior (front) end by finding the fleshy bump, called the prostomium, over its mouth. There is a small opening in the posterior (back) end where solid waste is removed, called the anus. Many tiny segments make up the length of the worm, each divided by a thin wall called a septum.

5. What are Anecic earthworms?

In the Greek language, the word “Anecic” means ‘out of the earth’, because these worms live below the ground and they come to the surface of the soil for their food. These worms are those that vertically burrow in the mineral layers of the soil. The structure of their burrow is very comprehensive and can be as wide as one inch. In the form of organic matter, such as fallen leaves, these worms gather food from above ground and drag it back to the ground. 

6. What is the earthworm habitat?

It has been observed that some earthworms prefer mud, such that the mud that is found along the shores of lakes and swamps, the habitat of the earthworm is mostly in moist land. The earthworms can be found in the soil of the backyards, as well as near the bodies of fresh and saltwater. Most earthworms live in the topsoil but some dwell deeper in the soil. In tropical regions, some earthworms can also be found in tree branches.

7. What are the benefits of earthworms?

The Earthworms mainly feed on decomposing organic matter such as leaves and dead plant roots. These nutrients are concentrated in the digestive system of the worm and are released into the soil as the excreted earthworms cast back into the soil. These casts are highly nutrient-rich, especially nitrogen and phosphorus, and are often left in the burrows of the worms. So, The soil's surface under the burrows contains nutrients that are readily accessible to plant roots.

8. What are the environmental aspects of earthworms?

The Earthworms feed on the organic matter which decays and rots, and this process helps break down the materials, allowing microorganisms like bacteria and fungi to feed on them. Although it is nice for our soil and plants to keep the worm populations alive, we should also note that worms are an important source of food for many predators, such as birds, and hence play an important role in the food chain. Without flourishing worm populations to feed on, certain creatures will quickly decline, such as endangered land snails.

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