MORPHOLOGY AND ANATOMY IN EARTHWORM

Earthworm:-

·         It is reddish brown in colour, terrestrial, Invertebrate and inhabiting in the upper layer of moist soil.

·         Some common Indian earthworms are pheretima and Lumbricus.

Morphology:-

·         Its body is cylindrical and segmented with more than 100 segments.

·         Its dorsal part is marked by their dark median mid dorsal line and ventral with presence of genital pore.

·         Its whole body is divisible into three parts-

1)      Preclitellar Part (1-13^th segment)

2)      Clitellar Part (14,15&16 segment)

3)      Postclitellar Part (17- Last segment)

·         Its first segment is poses mouth and Prostomium. The Prostomium helps in crawling and in covering of mouth.

·         There are four pair of spermathecal aperture are present at the ventro-lateral side on 5^th-9^th segments.

·         There are a single female genital pore is present at the mid-ventral line of 14^th segment.

·         At maturity, the 14^th to 16^th segments are covered with a prominent dark band of glandular tissues called clitellum.

·         A pair of male genital pores present on the ventro-lateral side of 18^th segment.

·         There are several nephridiophores are opens at each segments except 1^st,clitellum and last segments.

                            

Fig- Earthworm (a) Dorsal view, (b) Ventral view, (c) Lateral view showing mouth.

Anatomy:-                                                                                       

·         Externally it is covered with cuticle> Epidermis (columnar containing secretary gland cells i.e. glandular epithelium) > Two muscular layer (circular and longitudinal)> Innermost layer is coelomic epithelium.

·         Alimentary canal straight starts from mouth to last anus.

·         Mouth opens into buccal cavity (1-3 segments)> Pharynx> Oesophagus (small narrow tube at 5-7 segments)> muscular gizzard (Helps in grinding of soil 8^th-9^th)> Stomach (having calciferous gland which neutralise the humic acid at 9-14^th)> intestine (15^th -26^th here, median fold of dorsal wall called typhlosole at 23^rd-25^th help in absorption and at 26^th segment present a pair of projection called intestinal caecum)> Last anus.

Fig- Alimentary canal of earthworm.

Ø Pheretima:-

1)      Blood Vascular Tissue:-

·         It consists of blood vessels, capillaries and hearts.

·         It is a unidirectional and has closed blood vessels.

·         Smaller blood vessels supply the gut, nerve chord and blood vessels.

·         There are blood glands are present on the 4^th,5^th&6^th which produce blood cells and haemoglobin.

·         Blood cells are phagocytic in nature i.e. lack specialised breathing organ. Respiratory exchange occurs through moist body surface and blood stream.

Fig- Circulatory System of earthworm (Closed)

2)      Excretory system:-

·         Its excretory organ is nephridia which help in regulation of fluid and wastes.

·         It is of three types.

                                                        I.            Septal Nephridia:- It is the present on the both side of the integument septa from 15^th- last. It is the largest and well developed nephridia and its counting is 80-100 in each septum. It opens into the intestine.

                                                      II.            Integumentary nephridia:- It is attach to the body wall from 3^rd-Last. It is smaller than septal nephridia. It opens outside the on the body surface.

                                                    III.            Pharyngeal nephridia:- It is present on the 4^th,5^th and 6^th segments. It is almost similar to the septal nephridia. Its 4^th&5^th segment opens into the Pharynx at 4^th segment as well as 6^th segment into the buccal cavity at 2^nd segment.

Fig- Excretory System in the earthworm.

3)      Nervous System:-

·         Its nervous system is represented by ganglion of ganglia.

·         It is arranged in segment wise and consists of three parts.

                                                        I.            Central Nervous system:-

·         It consists of nerve ring + ventral nerve chord.

·          A nerve ring consists of Cerebral Ganglia + Circumpharyngeal Connectives + subpharyngeal ganglion.

ü  A pair of closely attach, pear-shaped supra-pharyngeal ganglia forming brain. Brain is situated dorsally at the 3^rd segment between the buccal cavity and pharynx.

ü  A thick, sought Circumpharyngeal connective is jointed with supra-pharyngeal ganglia and post pharyngeal ganglia laterally. It acts as a defending.

ü  A subpharyngeal ganglia are situated ventrally just below the pharynx in 4^th segment.

·         Ventral Nerve Chord arises from sub-pharyngeal ganglia to the posterior end in mid-ventral line just posterior to the body. In its joining each segment having a ganglion. Ventral Nerve Chord is looks like a single but actually it is double (two chords) and its ganglion also has a pair of ganglia forms double ventral nerve chord.

                                                      II.            Peripheral Nervous System:-

·         The nerves which arises from different parts of central nerves system, called peripheral nervous system.

                                                    III.            Sympathetic Nervous system:-

·         It consists of nerve plexus present in the epidermis of alimentary canal.

Fig-Nervous System in earthworm dorsal and lateral view

4)      Sensory System:-

·         It has light and touch sensory organs but not have eye as a sensory organ.

·         It also have chemoreceptor which reacts on chemical stimuli.

·         These all sense organs are located on the anterior parts of worm.

5)      Reproductive System:-

·         It is hermaphrodite i.e. bisexual in nature.

·         About Male genital organ-

ü  At the 6^th -9^th segment the four spermathecae are present (one pair in each segment). It store spermatozoa during copulation.

ü  At 10^th-11^th segment there are two pair of testis are present and there vasa differentia runs up to the 18^th segment.

ü  At 17^th and 19^th segment there are two pair of accessory glands are present i.e. one at each.

ü  At 18^th segment the prostate gland and vasa differentia jointed and open to the ventral side called male genital pore.

 

·         About Female genital organ-

ü  At the inter-segmental septum of 12^th-13^th segment, there are there are one pair of ovaries are present.

ü  At beneath the each ovary an ovarian funnel is present which along with oviduct opens outside as a single female general pore on the 14^th segment.

Fig-Reproductive System in Earthworm.

6)      Process after the maturation:-

·         At maturity, two worms come close together and mate as opposite gonadal openings to exchange packet of sperms called spermatophores.

·         After exchanging the spermatophores, egg cells along with nutritive fluid goes into the cocoons. Here fertilization occurs and after this cocoons splits off the worm and goes in or on the soil then further development occurs.

·         After about three weeks, each cocoons produce about 2-20 baby worms. Generally four worms produced.

·         Its development is direct development i.e. no larva stage are formed’

Importance of earthworm:-

·         Earthworm is popularly known as the “friends of farmer” because it helps in respiration and penetration of the development of roots through borrows.

·         The process of increase in fertility of soil through the earthworm called vermicomposting

·         They are also used as the bait in the game fishing.