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Earthworm

morphology of animals

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Earthworm

  1. 1. EARTHWORM dr.aarif
  2. 2. EARTHWORM - Earthworm is a reddish brown terrestrial invertebrate that inhabits the upper layer of the moist soil. - During day time, they live in burrows made by boring and swallowing the soil. - In the gardens, they can be traced by their faecal deposits known as worm castings. - The common Indian earthworms are Pheretima and Lumbricus.
  3. 3. EARTHWORM : Morphology - Earthworms have long cylindrical body. - The body is divided into more than hundred short segments which are similar (metameres about 100-120 in number). - The dorsal surface of the body is marked by a dark median mid dorsal line (dorsal blood vessel) along the longitudinal axis of the body. - The ventral surface is distinguished by the presence of genital openings (pores). - Anterior end consists of the mouth and the prostomium, a lobe which serves as a covering for the mouth and as a wedge to force open cracks in the soil into which the earthworm may crawl. - The prostomium is sensory in function.
  4. 4. EARTHWORM : Morphology CLITELLUM : - The first body segment is called the peristomium (buccal segment) which contains the mouth. - In a mature worm, segments 14-16 are covered by a prominent dark band of glandular tissue called clitellum. It secretes mucus and albumen for the formation of cocoon or egg capsule. - Thus the body is divisible into three prominent regions – preclitellar, clitellar and postclitellar segments SETAE : - 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 each segment. - Setae can be extended or retracted. - Their principal role is in locomotion
  5. 5. EARTHWORM : Morphology APERTURES : - Four pairs of spermathecal apertures are situated on the 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 the ventro-lateral sides of the 18th segment. - Numerous minute pores called nephridiopores open on the surface of the body
  6. 6. EARTHWORM : Digestive System ALIMENTARY CANAL FEATURES & FUNCTIONS 1. MOUTH Terminal opening in peristomium overhung by prostomium 2. BUCCAL CAVITY extends from 1st to 3rd segment 3. PHARYNX Small pear shaped sac from middle of 3rd segment to end of 4th segment 4. OESOPHAGUS narrow tubular structure from 5th to the 7th segment 5. GIZZARD Prominent, oval, hard and thick walled muscular organ in segment 8th and 9th. It grinds the food with the help of thick muscles and cuticle 6. STOMACH Short narrow and tubular structure from 9th to the 14th segment. Highly vascular and glandular walls. The chalky secretion of the calciferous glands neutralise the humic acid in the humus 7. INTESTINE Intestine starts from the 15th segment onwards and continues till the last segment. A pair of short and conical intestinal caecae project from the intestine on the 26th segment. The characteristic feature of the intestine between 26-35 segments is the presence of internal median fold of dorsal wall called typhlosole. This increases the effective area of absorption in the intestine. 8. ANUS The alimentary canal opens to the exterior by a small rounded aperture called anus
  7. 7. EARTHWORM : Circulatory 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 the heart and blood vessels. - Heart : 4 pairs of tubular hearts, 7th and 9th segment : lateral hearts whereas 12th and 13th segment : lateral oesophageal hearts - Anterior Loops : Thin walled ,non pulsatile loop like broad vessels without valves in 10th and 11th segment - Blood Vessels : Weel organised vessels which run along the body of earthworm i) Dorsal blood vessel : largest blood vessel of the body running mid dorsally above the alimentary canal from one end of the body to the other. It has valves and receives blood from various parts of the body ii) Ventral blood vessel : Also extends from end to end but it does not have valves. It is the main distributing vessel.
  8. 8. EARTHWORM : Circulatory System - Blood Glands : In segments 4th, 5th, and 6th lying above the pharyngeal mass are small red coloured follicular bodies called as blood glands. They produce blood corpuscles and haemoglobin. - Blood : made up of colourless plasma and blood cells. The respiratory pigment,haemoglobin is present in the plasma and helps in transport of oxygen. The only type of blood cell is the leucocyte and hence is phagocytic in nature.
  9. 9. EARTHWORM : Excretory System NEPHRIDIA FEATURES & FUNCTIONS 1. Pharyngeal three paired tufts in the 4th, 5th and 6th segments 2. Integumentary attached to lining of the body wall of segment 3 to the last that open on the body surface 3. Septal present on both the sides of intersegmental septa of segment 15 to the last that open into intestine - These different types of nephridia are basically similar in structure - Nephridia regulate the volume and composition of the body fluids. - A nephridium starts out as a funnel that collects excess fluid from coelomic chamber. - The funnel connects with a tubular part of the nephridium which delivers the wastes through a pore to the surface in the body wall into the digestive tube.
  10. 10. EARTHWORM : Nervous System All the activities of the earthworm are under the control of the nervous system. The Nervous System is made up of an Anterior Nerve ring and Posterior Nerve cord Nervous system is basically represented by ganglia arranged segment wise on the ventral paired nerve cord. Nervous System Features and Functions Nerve ring & Nerve cord - The nerve cord in the anterior region (3rd and 4th segments) bifurcates, laterally encircling the pharynx and joins the cerebral ganglia dorsally to form a nerve ring. - The cerebral ganglia along with other nerves in the ring integrate sensory input as well as command muscular responses of the body
  11. 11. EARTHWORM : Reproductive System
  12. 12. EARTHWORM : Male Reproductive System FEATURES & FUNCTIONS Testis sacs There are two pairs of testis sacs in the 10th and 11th segments. Each sac encloses a testis and a spermiducal funnel Testis - There are two pairs of testes in 10th and 11th segments. - Each testis arises from the anterior wall of each testis sac. - Immature spermatozoa produced by the testes first enter testis sacs and then make their way into seminal vesicle where they undergo further development to become mature sperms. Seminal Vesicle There are two pairs of seminal vesicles in 10th and 11th segments Spermiducal funnel - There are two pairs of spermiducal funnels one in 10th segment and the other in 11th segment. - Each spermiducal funnel leads into a fine tube, the vas deferens. Vasa deferentia - There are present two pairs of vasa deferentia. Each spermiducal funnel leads into a vasa deferens. - Vasa deferentia of each side run very close to each other upto the 18th segment. In 18th segment, both the vasa deferentia of each side are joined to the prostate duct coming from the prostate gland. - Two vasa deferentia ducts and one prostate duct of each side are enclosed in a common thick muscular sheath called the common prostate and spermatic duct. They open to the outside separately into male genital aperture.
  13. 13. EARTHWORM : Male Reproductive System FEATURES & FUNCTIONS Prostate - A pair of large prostate glands are present in earthworm. - These glands are situated on either side of the intestine and extend from the 16th to the 21st segment. - They produce a secretion, which serves as a medium for transfer of sperms Accessory glands - There are two pairs of whitish glandular masses situated internally in 17th and 19th segments. - The secretion of these glands is supposed to help in keeping the two worms close together during copulation
  14. 14. EARTHWORM : Female Reproductive System FEATURES & FUNCTIONS Ovaries There is a pair of white minute masses of the ovaries attached to the posterior surface of the septum present between the 12th and 13th segments. They produce ova. Oviducts - They are two short tubes each lying immediately behind the respective ovary. - The two ovarian tubes converge to meet in the body wall and open to outside by a female genital aperture on mid-ventral side of the 14th segment. - The mature ova liberated by each ovary are received by the oviducts and are finally passed outside into the cocoon through a female genital aperture Spermathecae - There are present four pairs of spermathecae which lie in the 6th, 7th 8th and 9th segments. - They open to outside through the spermathecal pores situated ventro-laterally in the successive grooves separating the above mentioned segments. They store the sperms received from another earthworm during copulation
  15. 15. EARTHWORM : Fertilization - A mutual exchange of sperm occurs between two worms during mating. - One worm has to find another worm and they mate juxtaposing opposite gonadal openings exchanging packets of sperms called spermatophores. - Mature sperm and egg cells and nutritive fluid are deposited in cocoons produced by the gland cells of clitellum. - Fertilisation and development occur within the cocoons which are deposited in soil. - The ova (eggs) are fertilised by the sperm cells within the cocoon which then slips off the worm and is deposited in or on the soil. - The cocoon holds the worm embryos. After about 3 weeks, each cocoon produces two to twenty baby worms with an average of four. Earthworms development is direct, i.e., there is no larva formed.

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