Worm eats the soil it goes on eating the soil progressive downwards the organic content are digested and absorbed in the gut,while the residual soil is discharged by its anus at the opening of the burrow as castings-WORM CASTING
•Earthworm is a reddish brownterrestrial invertebrate that inhabits theupper layer of the moist soil.•During day time, they live in burrowsmade by boring and swallowing thesoil. In the gardens, they can be tracedby their faecal deposits known as wormcastings.•The common Indian earthworms arePheretima and Lumbricus.
MorphologyEarthworms have long cylindrical body. The body isdivided into more than hundred short segments whichare similar (metameres about 100-120 in number).Dorsal Surface: The dorsal surface of the body ismarked by a dark median mid dorsal line (dorsal bloodvessel) along the longitudinal axis of the body.Ventral Surface: The ventral surface is distinguishedby the presence of genital openings (pores).
•Segments: Anterior end consists of themouth and the prostomium, a lobe which servesas a covering for the mouth and as a wedge toforce open cracks in the soil into which theearthworm may crawl.•The prostomium is sensory in function. The firstbody segment is called the peristomium (buccalsegment) which contains the mouth.• In a mature worm, segments 14-16 are coveredby a prominent dark band of glandular tissuecalled clitellum.•Thus the body is divisible into three prominentregions – preclitellar, clitellar and postclitellarsegment.
Genital Openings:• Four pairs of spermathecal apertures are situated onthe ventro-lateral sides of the intersegmental grooves,i.e., 5th -9th segments.• A single female genital pore is present in the mid-ventral line of --14th segment.• A pair of male genital pores are present on theventro-lateral sides of the-- 18th segment.•17 and 19 the segment -genital papillaeLocomotion: In each body segment, except the first,last and clitellum, there are rows of S-shaped setae,embedded in the epidermal pits in the middle of eachsegment. Setae can be extended or retracted. Theirprincipal role is in locomotion
HOW DO EARTHWORMS REPRODUCE?This matter is as complex as it is interesting, so put your mind in low gear and hold on... Heres a drawing to help you keep oriented:First of all, not every earthworm segment bears sex organs. Counting from thefront, the worms male sex cells lie in segments 10 and 11. From here thesperm pass through sperm ducts to two male genital openings on the bottomof segment 15. On segments 9 and 10 there are two minuscule sacs calledsperm receptacles, or pores, where, during earthworm sex, sperm aredeposited. However, this is not where eggs are produced. The egg-producingovaries reside in segment 13, from which eggs are released through the femalepores into egg sacs in segment 14. Finally, theres a rubbery, arm-band-likething covering the worms body from segments 31 or 32 to 37, and this is calledthe clitellum.
Anatomy•Body Wall: The body wall of the earthworm iscovered externally by a thin non-cellular cuticle belowwhich is the epidermis, two muscle layers (circular andlongitudinal) and an innermost coelomic epithelium. Theepidermis is made up of a single layer of columnarepithelial cells which contain secretory gland cells.•alimentary Canal: The alimentary canal is astraight tube and runs between first to last segment of thebody. A terminal mouth opens into the buccal cavity (1-3segments) which leads into muscular pharynx. A smallnarrow tube, oesophagus (5-7 segments), continues into amuscular gizzard (8-9 segments). It helps in grinding thesoil particles and decaying leaves, etc. The stomachextends from 9-14 segments.
•The food of the earthworm is decaying leaves andorganic matter mixed with soil. Calciferous glands,present in the stomach, neutralise the humic acid presentin humus. Intestine starts from the 15th segmentonwards and continues till the last segment. A pair ofshort and conical intestinal caecae project from theintestine on the 26th segment. The characteristic featureof the intestine between 26-35 segments is the presenceof internal median fold of dorsal wall called typhlosole.This increases the effective area of absorption in theintestine.•The alimentary canal opens to the exterior by a smallrounded aperture called anus. The ingested organic richsoil passes through the digestive tract where digestiveenzymes breakdown complex food into smallerabsorbable units. These simpler molecules are absorbedthrough intestinal membranes and are utilised.
•Blood Vascular System:• Pheretima exhibits a closed type of blood vascular system,consisting of blood vessels, capillaries and heart. Due to closed circulatory system, blood is confined to theheart and blood vessels. Contractions keep blood circulatingin one direction.• Smaller blood vessels supply the gut, nerve cord, and thebody wall. Blood glands are present on the 4th, 5th and 6thsegments.•They produce blood cells and haemoglobin which isdissolved in blood plasma.Blood cells are phagocytic innature.• Earthworms lack specialised breathing devices. Respiratoryexchange occurs through moist body surface into their bloodstream
Excretory System: The excretory organs occur assegmentally arranged coiled tubules callednephridia (sing.: nephridium).They are of three types: (i) septal nephridia, present on both the sides ofintersegmental septa of segment 15 to the last thatopen into intestine,(ii) integumentary nephridia, attached to lining ofthe body wall of segment 3 to the last that open onthe body surface and(iii) pharyngeal nephridia, present as three pairedtufts in the 4th, 5th and 6th segments.
Nervous System: Nervous system is basicallyrepresented by ganglia arranged segment wise on theventral paired nerve cord. The nerve cord in the anteriorregion (3rd and 4th segments) bifurcates, laterallyencircling the pharynx and joins the cerebral gangliadorsally to form a nerve ring. The cerebral gangliaalongwith other nerves in the ring integrate sensory inputas well as command muscular responses of the body.Sensory System: Sensory system does not have eyes butdoes possess light and touch sensitive organs (receptorcells) to distinguish the light intensities and to feel thevibrations in the ground. Worms have specialisedchemoreceptors (taste receptors) which react to chemicalstimuli. These sense organs are located on the anteriorpart of the worm.
REPRODUCTIVE SYSTEMVASA DEFFEREN SEMINALOVARIAN OVARY S VESICLESFUNNEL TESTI S
Reproductive System: Earthworm is hermaphrodite(bisexual), i.e., testes and ovaries are present in the sameindividual. There are two pairs of testes present in the 10thand 11th segments. Their vasa deferentia run up to the 18thsegment where they join the prostatic duct. Two pairs ofaccessory glands are present one pair each in the 17th and19th segments. The common prostrate and spermatic duct(vary differential) opens to the exterior by a pair of male genitalpores on the ventro-lateral side of the 18th segment. Fourpairs of spermathecae are located in 6th-9th segments (onepair in each segment).They receive and store spermatozoa during copulation. Onepair of ovaries is attached at the inter-segmental septum of the12th and 13th segments. Ovarian funnels are present beneaththe ovaries which continue into oviduct, join together and openon the ventral side as a single median female genital pore onthe 14th segment
•Fertilization & Development: A mutual exchange of spermoccurs between two worms during mating.• One worm has to find another worm and they mate juxtaposingopposite gonadal openings exchanging packets of sperms calledspermatophores.•Mature sperm and egg cells and nutritive fluid are deposited incocoons produced by the gland cells of clitellum.•Fertilisation and development occur within the cocoons which aredeposited in soil.•the ova (eggs) are fertilised by tholds the worm embryos.•After about 3 weeks, each cocoon produces two to twenty babyworms with an average of four.• Earthworms development is direct, i.e., there is no larva formed.
Economic Importance:• Earthworms are known as ‘friends of farmers’because they make burrows in the soil and make itporous which helps in respiration and penetration ofthe developing plant roots.• The process of increasing fertility of soil by theearthworms is called vermicomposting. They arealso used as bait in game fishing.