Scientific Name of Earthworm: Morphology, Anatomy & Classification

Scientific Name of Earthworm is Lumbricina. An earthworm is a phylum Annelida terrestrial invertebrate. They have a tube-within-a-tube body plan, external and internal segmentation, and setae on all segments. They can be found anywhere there is soil, water, and temperature. 

• There are over 1,800 different species of Oligochaeta terrestrial worms in the world. 
• Lumbricus Terrestris is the most common species of Earthworm found in the environment. 
• There are currently over 6,000 terrestrial Earthworm species, with only about 150 of them being widely distributed around the world. 
• They can be either peregrine or cosmopolitan Earthworms.

Key terms: Earthworm, Morphology, Segments, Species, Tube, Worm, Lumbricina

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Morphology of Earthworm

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An adult earthworm can range in size from 10 mm long and 1 mm wide to 3 m long and more than 25 mm wide, but the normal Lumbricus Terrestris grows to about 360 mm long.

• The earthworm's basic shape is a cylindrical tube-in-a-tube divided into a series of sections that compartmentalize the body from front to back. Concerning the clitellum, the body is separated into three sections: preclitellar, clitellar, and postclitellar.
• Furrows delineate the segments on the body; dorsal pores and nephridiopores exert a fluid that lubricates and safeguards the worm's surface, letting it breathe.
• Both ends of the body are tapered, with the tail end being the blunter of the two. 
• Earthworms are blind and deaf, but they are sensitive to light and vibrations.

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Anatomy of Earthworm

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The body wall of the earthworm is covered externally with a thin non-cellular cuticle. Underneath this cuticle, a layer of the epidermis is sheathed, followed by two muscle layers and coelomic epithelium (inner layer). The epithelium comprises a single layer of glandular columnar epithelium.

Nervous System

The brain of earthworms is made up of a pair of pear-shaped cerebral ganglia. It is found in the third segment of the alimentary canal, on the dorsal side, between the buccal cavity and the pharynx. 

Circulatory System

Earthworms have a dual circulatory system that transports food, waste, and respiratory gases via coelomic fluid and a confined circulatory system. 

The closed circulatory system consists of five main blood vessels:

• Dorsal vessel (top), above the digestive tract
• Ventral vessel (bottom), below the digestive tract
• Sub-neural vessel, under the ventral nerve cord
• Two lateral neural vessels, on either side of the nerve cord.

Respiratory System

Earthworms lack separate breathing organs. Gases are exchanged via the wet skin and capillaries, in which haemoglobin dissolved in blood plasma absorbs oxygen and emits carbon dioxide. Water and salts can also be transported through the skin via active transport.

Also Read: Respiration in Cockroach and Earthworm

Sensory System

Although earthworms lack eyes, they have specialised sensory receptors that allow them to detect changes in their environment. They react to stimuli perfectly thanks to specialised sensory organs. The earthworm's sensory system is located in the anterior portion of the body. Earthworms are immensely sensitive to mechanical sound waves.

Digestive System

The earthworm's gut is a straight tube that runs from the worm's mouth to its anus. 

• It is divided into an alimentary canal and affiliated glands that are embedded in the alimentary canal's wall. 
• The alimentary canal in an earthworm includes a mouth, buccal cavity, pharynx, esophagus, crop, gizzard, and intestine.

Reproductive System 

Earthworms are hermaphrodites(bisexual) which means they have both male and female reproductive organs. Segments 9 to 15 contain sexual organs. Earthworms contain 1 or 2 pairs of testes within sacs. 

• The male pores contain 2 or 4 pairs of seminal vesicles that produce, store, and release sperm. 
• Segment 13 ovaries and oviducts release eggs through female pores in segment 14, while segment 15 expels sperm. 
• One or more pairs of spermathecae (internal sacs that acquire and store sperm from the other worm during mating) are available in segments 9 and 10 (based on the species). 
• As an outcome, segment 15 of one worm exudes sperm into segments 9 and 10 along with its mate's storage vesicles.

Excretory System

Nephridium is a network of coiled tubules that monitor and control the volume and composition of body fluids, serving as the excretory organ in earthworms. Except for the first three and last segments of the excretory system, each segment contains a pair of nephridia. Nephridia are classified into three types: integumentary, septal, and pharyngeal.

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Previous Year Questions

• During an injury nasal septum gets damaged and for its recovery which cartilage is preferred?...(NEET 2001)
• Haversian canals occur in...(NEET 1989)
• Histamine secreting cells are found in...(NEET 1989)
• Which of the following features is not present in Periplaneta americana?...(NEET 2016)
• Protein present in cartilage is...(NEET 1997)
• If the head of cockroach is removed, It may live for few days because..(NEET 2020)
• An epithelial tissue which has thin flat cells, arranged edge to edge so as to appear like closely packed tiles, is found to be present at...(NEET 1994)
• Areolar connective tissue joins…(NEET 2006)
• Basement membrane is made up of...(NEET 1997)
• Characteristics of smooth muscle fibres are....(NEET 1992)

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Things to remember

• Earthworms move underground using waves of muscular contractions that alternately reduce and elongate the body. The shortened part is held in place by tiny clawlike fibres set across its segmented length.
• Earthworms can regenerate lost segments however, this ability varies by species and is dependent on the extent of the injury.
• Earthworms are born small but fully formed, with the exception of their sex structures, which develop in 60 to 90 days. They grow to full size in about a year. According to scientists, the average lifespan in the field is four to eight years.
• Earthworm is the standard term for the largest Oligochaeta members. They were in the order of Opisthopora in classical systems. The earthworm is also known as the dew-worm, rainworm, nightcrawler, and angleworm.