Earthworm Classification (Taxonomy)

I doubt whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures. ~ Charles Darwin

Earthworm plays a major role in the proper functioning of the soil ecosystem. It acts as scavenger and helps in recycling of dead and decayed plant material by feeding on them. Earthworm increases the soil fertility and is often referred to as a farmer's friend. It burrows the soil and ingests soil particles coming on its way. Both these processes aerate the soil and help in mixing the soil particles between the upper and underlying layer. Earthworm is found all over the world in any type of soil, except waterlogged and sandy soils. Let's discuss in brief about the taxonomic classification and characteristics of earthworm.

Earthworm Classification (Taxonomy)
Though all species of earthworm are classified in the same class and order, they do not belong to the same family. To be precise, there are five families, each classified based on the specific characteristics and the area of distribution. The five earthworm families are Lumbricidae (North America, Europe and Asia), Moniligastridae (Asia and Africa), Megascolecidae (Asia, Australia, Africa and America), Glossoscolecidae (America and Africa) and Eudrilidae (Africa). Following is the classification of common earthworm (scientific name Lumbricus terrestris).

Kingdom: Animalia
Earthworms are eukaryotic, multicellular organisms. They have the ability to move and depend on dead plant materials and microorganisms for food.

Phylum: Annelida
Earthworms are segmented, each segment is separated by a septum. They have multiple segments; those belonging to a species possess organs in same segments. In some species of annelids, septa are less defined or absent.

Class: Clitellata
Earthworms have clitellum, a type of collar that secretes clitella or cocoon during reproduction. The head of earthworm is less developed than other annelid species.

Subclass: Oligochaeta
Earthworms have setae or bristles on the body, which helps them to attach to the surface during movement. They lack lateral appendages or parapodia, which is a characteristic feature of the subclass polychaeta.

Order: Haplotaxida
All species of earthworms are categorized under Haplotaxida, which is one of the two orders of Oligochaeta.

Family: Lumbricidae
Lumbricidae is one of the largest earthworm family. About 33 species of earthworms are identified under this family.

Genus: Lumbricus

Species: terrestris

Earthworm Characteristics
The earthworm resembles a cylindrical tube, with average length of about 25 cm. Its body is divided into various segments in which vital organs are present in particular segments. The skin is covered by a moist mucous layer that serves the main purpose for respiration (exchange of air). Earthworm does not have any locomotory organ; it moves by means of muscle contraction and relaxation.

Earthworm feeds on dead plant materials and organic matter of the soil. The ingested food is broken down into finer particles in the gizzard portion. The fine food particles are acted upon by various enzymes for digestion process. Useful nutrients are absorbed and indigested soil and other particles are passed out as worm casts. Studies have revealed the presence of useful soil microorganisms in earthworm casts. Common predators of earthworm include birds and other small mammals.

Earthworm is hermaphrodite, meaning both male and female sex organs are present in the same body. However, reproduction takes place via cross fertilization. The eggs are enclosed in egg case or cocoon; juvenile earthworm resembles an adult worm, except the lack of sex organs. It attains sexual maturity within 2 - 3 months after hatching. One amazing characteristic feature of earthworm is the ability to regenerate small segments. The lifespan of earthworm varies depending upon the species; the common earthworm can live up to 6 years in captivity.