Morphology of Earthworm (External features of Earthworm) - Class 11

Earthworm: Introduction, Systematic Position, Habitat and Habit -CLASS 11

Earthworm: Economic importance

Earthworms are of  great economic importance to man.

Beneficial aspects:

i.          In Agriculture: They are regularly ploughing and manuring the soil. Their habit of burrowing and swallowing soil makes soil loose, aerated and porous. Their worm castings make soil fertile. Thus, they are regarded as friends of farmer.

ii.        As bait: They are used as bait for fishing.

Earthworm: Reproduction

Earthworms reproduce sexually. Asexual reproduction is absent. However some power of regeneration is present. Though they are hermaphrodite, cross-fertilization takes place in them due to protandrous condition ( A condition  in which male gametes mature  earlier than female gametes in hermaphrodite organisms) . It is preceded by copulation and cocoon formation.

Copulation

It takes place during rainy seasons, generally at night or early morning and lasts for about one hour. During it, two earthworms come in contact of each other by their ventral surface facing anterior end towards opposite direction in such a way  that male genital pore of each earthworm lie against a pair of spermethecal pores of other. The male genital apertures are raised into papillae, which are inserted successively from behind to forward into the spermethecal pores of other earthworm and discharge the spermatic and prostatic fluid with sperms, which are stored in spermetheca.

After this exchange of sperms, the two earthworms separate.

Cocoon formation and fertilization

            Cocoon formation begins after copulation. During it, clitellum produces a type of viscous and gelatinous substance forming a broad membranous band around the 

Earthworm: Reproductive System

Earthworms are hermaphrodite i.e. monoecious, an individual with both male and female reproductive organs.   

Male Reproductive Organs

The male reproductive organs are testes, testis sacs, seminal vesicles, spermiducal funnel, vasa defferentia, prostate glands and accessory glands.

·        Testes: Two pairs of testes, each pair ventrally beneath alimentary canal of 10^th and 11^th segment are present. Testes remain enclosed inside the testis sac of respective segments. Each testis is white coloured structure with narrow base and 4-6 digitate projections. The base remains attached with the under surface of roof of testis sac. Inside the digitate projections a number of round structures are present called as spermatogonia. These spermatogonia undergo the process of spermatogenesis to form sperms.

            The testis are found well-developed in young earthworms while remains degenerated in adult earthworm.

Earthworm: Excretory System

Nephridia are excretory organells of earthworm. Nephridium is coiled tubular and glandular structure. A typical nephridium consists of nephrostome, body and terminal duct. In some nephridia nephrostome is lost. The terminal duct may opens inside body or out side body. If terminal duct opens outside body, nephridium is called as exonephric. If opens inside body, nephridium is called as enteronephric.

In earthworm, three tyes of neohridia are present:- septal nephridia, pharyngeal nephridia and integumentary nephridia.

Earthworm: Nervous System

It is well developed and consists of central nervous system, peripheral nervous system and sympathetic nervous system.

Central nervous system:-   It consists of nerve ring and ventral nerve cord.

Earthworm: Digestive system

The digestive system of Earthworm consists of alimentary canal which is a straight tubular structure of varying diameter. It is complete as it has both mouth and anus. It remains differentiated in to following parts: mouth, buccal chamber, pharynx, oesophagus, gizzard, stomach, intestine and anus.

Earthwom: Coelom and coelomic fluid

The space between body wall and alimentary canal is called as coelom or body cavity.

It remains lined on both side by coelomic epithelium derived from mesoderm so it is true coelom or schizocoel. The coelom is not continuous and remains differentiated into a number of small chambers called as coelomic chambers by plate like structures called as septa. Each septum arises from inner region of inter segmental groove of body wall and extends up to wall of alimentary canal. Each septum consists of interwoven muscle fibers covered on both side by coelomic epithelium. The first septum lies between fourth and fifth segment and is thin and membranous. Next five septa are thick and muscular. These septa lie obliquely in between body wall and alimentary canal while 

Earthworm: Morphoogy

The morphology or external features are explained under following headings,

i)                   Shape & size:- Body is elongated, cylindrical with bilateral symmetry. The anterior end is pointed while posterior end is blunt. The widest part of body is present behind anterior end and measures about 150 mm in length and (3-5) mm in width.

       

Earthworm: Systematic position, Habit and Habitat

Systematic Position:

Phylum:-  Annelida

Class:-  Oligochaeta

Order:- Opisthopora

Genus:-  Pheretima

Species:-  posthuma

Common name:- Earthworm

Habit and Habitat:

Earthworm lives inside burrows in moist soil surfaces. They make their burrows