Introduction
Phylum Annelida is a very broad phylum belonging to the kingdom Animalia. The Annelids are found in aquatic as well as terrestrial environments. These are bilaterally symmetrical invertebrate organisms. Their segmented body distinguishes them from any other organism.
Characteristics of Annelida
The characteristics of the organisms present in the Phylum Annelida are as follows:
1.The Annelids are coelomate and triploblastic.
2.They exhibit organ system level organization.
3.Their body is segmented.
4.They respire through their body surface.
5.Nephridia are the excretory organs.
6.They have a well-developed circulatory and digestive system.
7.Their body contains haemoglobin, which gives them a red colour.
8.Regeneration is a very common characteristic of the Annelids.
9.Setae help them in movement.
10.Most of the Annelids are hermaphrodite, i.e., male and female organs are present in the same body. They reproduce both sexually and asexually. The others reproduce sexually.
Eg., Earthworms, and leeches.
Classification of Annelida
Following are the different classification of Annelida:
Polychaeta
Oligochaeta
Hirudinea
Archiannelida
1.Polychaeta
The body is elongated and divided into segments.
They are found in the marine environment.
These are true coelomates, bilaterally symmetrical worms.
They excrete through metanephridia and protonephridia.
Fertilization is external.
They have a well-developed nervous system.
The circulatory system is closed type.
They are hermaphrodites.
They might possess fin-like appendages called parapodia.
The organisms belonging to this group lack clitellum and are dioecious.
Eg., Nereis, Syllis.
2.Oligochaeta
They are mostly freshwater and terrestrial organisms.
The body is segmented metamerically.
Head, eyes and tentacles are not distinct.
They are hermaphrodites, but cross-fertilization takes place.
Fertilization is external.
Cocoon formation occurs.
Setae are segmented.
They do not possess parapodia but clitellum is present.
The organisms belonging to this class are monoecious.
They exhibit no free larval stage and the development takes place inside the cocoons.
Eg., Pheretima, Tubifex.
3.Hirudinea
Most commonly found in freshwater. Some are marine, terrestrial, and parasitic.
The body is segmented.
The tentacles, parapodia, and setae are not present.
The animals are monoecious.
The body is dorsoventrally or cylindrically flattened.
They have an anterior and posterior sucker on the ventral side.
The organisms lay eggs in cocoons.
There is no larval stage during the development of the organism.
The mouth is located ventrally in the anterior sucker, while the anus is present dorsally in the posterior sucker.
Fertilization is internal.
They are hermaphrodites.
Eg., Hirudinaria.
4.Archiannelida
They are found only in the marine environment.
The body is elongated without setae and parapodia.
They are unisexual or hermaphrodite.
Tentacles are present on the prostomium.
Eg., Dinophilus, Protodrilus
In conclusion, members of Phylum Annelida have bodies that are segmented, such as leeches and earthworms.
Earthworm (Lampito maruitii)
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 .
Life cycle of Earthworm (Lampito mauritii)
Lampito mauritii begins its life cycle, from the fertilized eggs. The eggs are held in a protective cocoon. These cocoons have an incubation period of about 14- 18 days after which they hatch to release juveniles.
The juveniles undergo changes into non-clitellate forms in phase – I after about 15 days, which then develops a clitellum, called the clitellate at the end of the growth phase – II taking 15 - 17 days to complete. During the reproductive stage, earthworms copulate, and later shed their cocoons in the soil after about 10 days. The life cycle of Lampito mauritii takes about 60 days to complete.
Earthworms are known as “friends of farmer” because they make burrows in the soil and make it porous which helps in respiration and penetration of developing plant roots. Vermiculture, vermicomposting, vermiwash and wormery are inter-linked and interdependent processes, collectively referred as Vermitech.
Lampito mauritti helps in recycling of dead and decayed plant material by feeding on them. Artificial rearing or cultivation of earthworms involves new technology for the betterment of human beings. This process is known as Vermiculture.
The process of producing compost using earthworms is called Vermicomposting. Vermiwash is a liquid manure or plant tonic obtained from earthworm. It is used as a foliar spray and helps to induce plant growth.
It is a collection of excretory products and mucus secretion of earthworms along with micronutrients from the soil organic molecules. Earthworms can be used for recycling of waste food, leaf, litter and biomass to prepare a good fertilizer in container known as wormery or wormbin. It makes superior compost than conventional composting methods. Earthworms are also used as bait in fishing.
Benefits of earthworms
By their activity in the soil, earthworms offer many benefits: increased nutrient availability, better drainage, and a more stable soil structure, all of which help improve farm productivity.
Improved nutrient availability
Worms feed on plant debris (dead roots, leaves, grasses, manure) and soil. Their digestive system concentrates the organic and mineral constituents in the food they eat, so their casts are richer in available nutrients than the soil around them. Nitrogen in the casts is readily available to plants. Worm bodies decompose rapidly, further contributing to the nitrogen content of soil.
New Zealand research shows that worm casts release four times more phosphorus than does surface soil. Worms often leave their nutrient-rich casts in their tunnels, providing a favourable environment for plant root growth. The tunnels also allow roots to penetrate deeper into the soil, where they can reach extra moisture and nutrients. Earthworm tunnelling can help incorporate surface applied lime and fertiliser into the soil.
Improved drainage
The extensive channelling and burrowing by earthworms loosens and aerates the soil and improves soil drainage. Soils with earthworms drain up to 10 times faster than soils without earthworms. In zero-till soils, where worm populations are high, water infiltration can be up to 6 times greater than in cultivated soils. Earthworm tunnels also act, under the influence of rain, irrigation and gravity, as passageways for lime and other material.
Improved soil structure
Earthworm casts cement soil particles together in water-stable aggregates. These are able to store moisture without dispersing. Research has shown that earthworms which leave their casts on the soil surface rebuild topsoil. In favourable conditions they can bring up about 50 t/ha annually, enough to form a layer 5 mm deep. One trial found worms built an 18-cm thick topsoil in 30 years.
Improved productivity
Research into earthworms in New Zealand and Tasmania found earthworms introduced to worm-free perennial pastures produced an initial increase of 70–80% in pasture growth, with a long-term 25% increase: this raised stock carrying capacity. Researchers also found that the most productive pastures in the worm trials had up to 7 million worms per hectare, weighing 2.4 tonnes. There was a close correlation between pasture productivity and total worm weight, with some 170 kg of worms for every tonne of annual dry matter production.
