When the longitudinal muscle fibres contract, then earthworm becomes shorter and its diameter increases. The nervous system of earthworm is well developed and consists of a pair of cerebral ganglia forming the brain situated in the third segment above the pharynx. Some of the anterior seg­ments bear superficial furrows and may appear to be subdivided, but these are merely external subdivisions. From the peri-pharyngeal or circum-pharyngeal connectives, 2 or 3 pairs of nerves arise. Image Source: ExpertsMind. The wall of the stomach is highly glandular, vascular and thrown into internal folds. All the nerves present in earthworm are of mixed type as they contain both afferent and efferent nerve fibres and adjustors (association neurons). From cerebral ganglia, 8-10 nerves arise and supply to prostomium, buccal chamber, and pharynx. The soft and naked body is made up of distinct segments or metameres separated from each other by inter-segmental ring-like grooves or annuli. 4.6 REPRODUCTIVE SYSTEM 4.7 NERVOUS SYSTEM AND SENSORY ORGANS 4.8 ECONOMIC IMPORTANCE . All nerves arise from CNS and supply to various parts of body. It prefers to live in burrow during daytime and at night and rainy season they come out of their shelter. Excretory System 11. The dorsal wall of the pharynx is lobulated and richly vascular. However, in median and sub-median fibers, the impulse is conducted postero-anteriorly. The thinning and elongation of the body gradually spread to more poste­rior segments. Three pairs of nerves arise from the sub-pharyangeal ganglia to supply the 2nd, 3rd and 4th segment. Pheretima is a terrestrial earthworm, liv­ing in burrows made in moist soil. Conservation of water 3. From the sub-pharyngeal ganglia, 3 pairs of the nerve arise supply to 2 nd, 3 rd, and 4 th segments. When an earth­worm starts to crawl, the first few segments become thinner and longer. The body is made up of a series of 100-120 similar segments. Enteronephric nephridial system of Pheretima is an adaptation for 1. The body of each cell gives out numerous bulging’s. Autonomic nervous system (ANS) of earthworm: ANS of Pheretima posthuma possess sympathetic nervous system only with extensive nerve plexus that are connected to the nerves from circum-pharyngeal connectives. 1.94). Nerve ring is an oblique ring around the pharynx in 3. It starts after copulation when ovaries mature. For instance, when a hot object is touched, its temperature is conveyed quickly to the central nervous system and the response is an immediate reflex of removing the hand, through the action of skeletal muscles. Introduction to Pheretima 2. The first body segment is called peristomium (Greek : peri, around; stoma, mouth) which bears the mouth aperture on the ven­tral surface. Reproductive System. Nerve cells are mainly present in ventral and lateral sides of the nerve cord. Before the food is taken in, they are moistened by mucus secreted from the pharyngeal bulb. Conservation of urea 2. The anterior end is more pointed than the posterior end. The buccal cavity leads into the pharynx lying in seg­ments 3rd and 4th, and is internally marked off from the buccal chamber by a dorsal transverse groove. Digestive System. The body of earthworm is elongated, narrow and cylindrical (Fig. Pharynx is pear-shaped and its wall is thick and muscular. Sensory fibers start in the epidermis from sensory cells or receptor organs and end in fine branches in the ventral nerve cord. Eight to ten nerves arise from the cerebral ganglia to supply the prostomium, buccal chamber and pharynx. 2. The large majority of the axon bundles called nerves are considered to belong to the PNS, even when the cell bodies of the neurons to which they belong reside within the brain or spinal cord. In dry weather The coelom opens to the exterior by dorsal pores and nephridiopores. The dorsal pores lie as minute openings along the mid-dorsal line, one pore in each inter-segmental groove behind the 12th segment onwards, excepting the last one. Below the cuticle is the epidermis which is single layered. It is extensive, but not continuous and is divided into a number of compart­ments by transverse partitions running between the body wall and the alimentary canal. Pharyngeal nephridia 2. Shape - Bilaterally symmetrical animal. 2 pairs of nerves arise from the circumpharyngeal connectives supply 1 st segment and buccal cavity. In lateral giant fibers, impulse is conducted antero-posteriorly. Although earthworms lack eyes they have specialized receptor cells to recognize the changes around them. 11. A fourth layer in the form of cuticle is present only in the buccal cavity (thin layer) and in the gizzard (thick layer). The below mentioned article provides an overview on Pheretima (Earthworm):- 1. 1.97). Elimination of faeces 40. organ of ingestion of food. Nerve fibers are mainly present in dorsal and middle portion of nerve cord. Peripheral nervous system. 1.96). This external segmentation corresponds to internal segmentation and is referred to as metameric segmentation. From the cerebral ganglia/brain, 8-10 pairs of nerves arise. Nervous system – consists of paired ganglia connected by lateral nerves to a double ventral nerve cord. The locomotory organs of earthworm are the setae. Insoluble and unabsorbed remains of food along with the ingested soil are pushed out through the anus. These are elongated cells, each having a broad, fan-like process attached to a narrow nucleated body. 1.99A). Disclaimer Copyright, Zoology Notes | Exclusive Notes on Zoology for Students, Anatomy of Neanthes (Sandworm): With Diagram | Phylum Annelida, Phylum Annelida and Its Classification | Coelomates | Zoology, Study Notes on Fasciola Hepatica | Platyhelminthes. Morphology. The region next to the stomach is the intestine, which is a long, wide and thin- walled tube, extending from the 15th to the last segment, up to the anus. Of first and second body segments as … peripheral nervous system ( PNS ) to regenerate segments if skin. 0-03 mm in length and 0-03 mm in breadth natural tillers of land an enclosed in a common sheath accidentally. In damp, moist, humus-rich soil of lawns, gardens etc of much practice earthworms. Peri-Pharyngeal connective to complete the ring coelomic compartment separa­ted from each other by inter-segmental grooves. 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