{"id":758,"date":"2018-01-18T19:58:53","date_gmt":"2018-01-18T19:58:53","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/chapter\/phylum-nematoda\/"},"modified":"2024-04-26T21:33:31","modified_gmt":"2024-04-26T21:33:31","slug":"phylum-nematoda","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/chapter\/phylum-nematoda\/","title":{"raw":"Phylum Nematoda","rendered":"Phylum Nematoda"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Describe the features of animals classified in phylum Nematoda<\/li>\r\n<\/ul>\r\n<\/div>\r\nThe Nematoda, like most other animal phyla, are triploblastic and possess an embryonic mesoderm that is sandwiched between the ectoderm and endoderm. They are also bilaterally symmetrical, meaning that a longitudinal section will divide them into right and left sides that are symmetrical. Furthermore, the nematodes, or roundworms, possess a pseudocoelom and consist of both free-living and parasitic forms.\r\n\r\nIt has been said that were all the non-nematode matter of the biosphere removed, there would remain a shadow of the former world in the form of nematodes.[footnote]Stoll, N. R., \u201cThis wormy world. 1947,\u201d <em>Journal of Parasitology<\/em> 85(3) (1999): 392\u201396.[\/footnote]\u00a0Phylum\u00a0<strong>Nematoda<\/strong>\u00a0includes more than 28,000 species with an estimated 16,000 being parasitic in nature. The name Nematoda is derived from the Greek word \u201cNemos,\u201d which means \u201cthread\u201d and includes roundworms. Nematodes are present in all habitats with a large number of individuals of each species present in each. The free-living nematode,\u00a0<em>Caenorhabditis elegans<\/em>\u00a0has been extensively used as a model system in laboratories all over the world.\r\n<h2>Morphology<\/h2>\r\nIn contrast with flatworms, nematodes show a tubular morphology and circular cross-section. These animals are pseudocoelomates and show the presence of a complete digestive system with a distinct mouth and anus. This is in contrast with the cnidarians, where only one opening is present (an incomplete digestive system).\r\n\r\nThe cuticle of Nematodes is rich in collagen and a carbohydrate-protein polymer called chitin, and forms an external \u201cskeleton\u201d outside the epidermis. The cuticle also lines many of the organs internally, including the pharynx and rectum. The epidermis can be either a single layer of cells or a syncytium, which is a multinucleated cell formed from the fusion of uninucleated cells.\r\n\r\nThe overall morphology of these worms is cylindrical, as seen in\u00a0Figure\u00a01. The head is radially symmetrical. A mouth opening is present at the anterior end with three or six lips as well as teeth in some species in the form of cuticle extensions. Some nematodes may present other external modifications like rings, head shields, or warts. Rings, however, do not reflect true internal body segmentation. The mouth leads to a muscular pharynx and intestine, which leads to a rectum and anal opening at the posterior end. The muscles of nematodes differ from those of most animals: They have a longitudinal layer only, which accounts for the whip-like motion of their movement.\r\n\r\n[caption id=\"attachment_2447\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-2447\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2840\/2018\/01\/18195852\/Figure_28_04_01-1024x367.jpg\" alt=\"Photo a shows a worm-shaped nematode next to a capsule-shaped nematode egg. The illustration in part b shows a cross-section of a nematode, which has a mouth at one end and an anus at the other. The mouth connects to a pharynx, then to an intestine. A dorsal nerve runs along the top of the animal and joins ring-like head ganglia at the front end. Testes run alongside the intestine toward the back of the animal.\" width=\"1024\" height=\"367\" \/> Figure 1. Scanning electron micrograph shows (a) the soybean cyst nematode (<em>Heterodera glycines<\/em>) and a nematode egg. (b) A schematic representation shows the anatomy of a typical nematode. (credit a: modification of work by USDA ARS; scale-bar data from Matt Russell)[\/caption]\r\n<h2>Excretory System<\/h2>\r\nIn nematodes, specialized excretory systems are not well developed. Nitrogenous wastes may be lost by diffusion through the entire body or into the pseudocoelom (body cavity), where they are removed by specialized cells. Regulation of water and salt content of the body is achieved by renette glands, present under the pharynx in marine nematodes.\r\n<h2>Nervous System<\/h2>\r\nMost nematodes possess four longitudinal nerve cords that run along the length of the body in dorsal, ventral, and lateral positions. The ventral nerve cord is better developed than the dorsal or lateral cords. All nerve cords fuse at the anterior end, around the pharynx, to form head ganglia or the \u201cbrain\u201d of the worm (which take the form of a ring around the pharynx) as well as at the posterior end to form the tail ganglia. In\u00a0<em>C<\/em>.<em>\u00a0elegans<\/em>, the nervous system accounts for nearly one-third of the total number of cells in the animal.\r\n<h2>Reproduction<\/h2>\r\nNematodes employ a variety of reproductive strategies that range from monoecious to dioecious to parthenogenic, depending upon the species under consideration.\u00a0<em>C<\/em>.\u00a0<em>elegans<\/em>\u00a0is a monoecious species and shows development of ova contained in a uterus as well as sperm contained in the spermatheca. The uterus has an external opening known as the vulva. The female genital pore is near the middle of the body, whereas the male\u2019s is at the tip. Specialized structures at the tail of the male keep him in place while he deposits sperm with copulatory spicules. Fertilization is internal, and embryonic development starts very soon after fertilization. The embryo is released from the vulva during the gastrulation stage. The embryonic development stage lasts for 14 hours; development then continues through four successive larval stages with ecdysis between each stage\u2014L1, L2, L3, and L4\u2014ultimately leading to the development of a young male or female adult worm. Adverse environmental conditions like overcrowding and lack of food can result in the formation of an intermediate larval stage known as the dauer larva.\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/69032aff-4c14-418a-8510-b8804db37b4c\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Describe the features of animals classified in phylum Nematoda<\/li>\n<\/ul>\n<\/div>\n<p>The Nematoda, like most other animal phyla, are triploblastic and possess an embryonic mesoderm that is sandwiched between the ectoderm and endoderm. They are also bilaterally symmetrical, meaning that a longitudinal section will divide them into right and left sides that are symmetrical. Furthermore, the nematodes, or roundworms, possess a pseudocoelom and consist of both free-living and parasitic forms.<\/p>\n<p>It has been said that were all the non-nematode matter of the biosphere removed, there would remain a shadow of the former world in the form of nematodes.<a class=\"footnote\" title=\"Stoll, N. R., \u201cThis wormy world. 1947,\u201d Journal of Parasitology 85(3) (1999): 392\u201396.\" id=\"return-footnote-758-1\" href=\"#footnote-758-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a>\u00a0Phylum\u00a0<strong>Nematoda<\/strong>\u00a0includes more than 28,000 species with an estimated 16,000 being parasitic in nature. The name Nematoda is derived from the Greek word \u201cNemos,\u201d which means \u201cthread\u201d and includes roundworms. Nematodes are present in all habitats with a large number of individuals of each species present in each. The free-living nematode,\u00a0<em>Caenorhabditis elegans<\/em>\u00a0has been extensively used as a model system in laboratories all over the world.<\/p>\n<h2>Morphology<\/h2>\n<p>In contrast with flatworms, nematodes show a tubular morphology and circular cross-section. These animals are pseudocoelomates and show the presence of a complete digestive system with a distinct mouth and anus. This is in contrast with the cnidarians, where only one opening is present (an incomplete digestive system).<\/p>\n<p>The cuticle of Nematodes is rich in collagen and a carbohydrate-protein polymer called chitin, and forms an external \u201cskeleton\u201d outside the epidermis. The cuticle also lines many of the organs internally, including the pharynx and rectum. The epidermis can be either a single layer of cells or a syncytium, which is a multinucleated cell formed from the fusion of uninucleated cells.<\/p>\n<p>The overall morphology of these worms is cylindrical, as seen in\u00a0Figure\u00a01. The head is radially symmetrical. A mouth opening is present at the anterior end with three or six lips as well as teeth in some species in the form of cuticle extensions. Some nematodes may present other external modifications like rings, head shields, or warts. Rings, however, do not reflect true internal body segmentation. The mouth leads to a muscular pharynx and intestine, which leads to a rectum and anal opening at the posterior end. The muscles of nematodes differ from those of most animals: They have a longitudinal layer only, which accounts for the whip-like motion of their movement.<\/p>\n<div id=\"attachment_2447\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2447\" class=\"size-large wp-image-2447\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2840\/2018\/01\/18195852\/Figure_28_04_01-1024x367.jpg\" alt=\"Photo a shows a worm-shaped nematode next to a capsule-shaped nematode egg. The illustration in part b shows a cross-section of a nematode, which has a mouth at one end and an anus at the other. The mouth connects to a pharynx, then to an intestine. A dorsal nerve runs along the top of the animal and joins ring-like head ganglia at the front end. Testes run alongside the intestine toward the back of the animal.\" width=\"1024\" height=\"367\" \/><\/p>\n<p id=\"caption-attachment-2447\" class=\"wp-caption-text\">Figure 1. Scanning electron micrograph shows (a) the soybean cyst nematode (<em>Heterodera glycines<\/em>) and a nematode egg. (b) A schematic representation shows the anatomy of a typical nematode. (credit a: modification of work by USDA ARS; scale-bar data from Matt Russell)<\/p>\n<\/div>\n<h2>Excretory System<\/h2>\n<p>In nematodes, specialized excretory systems are not well developed. Nitrogenous wastes may be lost by diffusion through the entire body or into the pseudocoelom (body cavity), where they are removed by specialized cells. Regulation of water and salt content of the body is achieved by renette glands, present under the pharynx in marine nematodes.<\/p>\n<h2>Nervous System<\/h2>\n<p>Most nematodes possess four longitudinal nerve cords that run along the length of the body in dorsal, ventral, and lateral positions. The ventral nerve cord is better developed than the dorsal or lateral cords. All nerve cords fuse at the anterior end, around the pharynx, to form head ganglia or the \u201cbrain\u201d of the worm (which take the form of a ring around the pharynx) as well as at the posterior end to form the tail ganglia. In\u00a0<em>C<\/em>.<em>\u00a0elegans<\/em>, the nervous system accounts for nearly one-third of the total number of cells in the animal.<\/p>\n<h2>Reproduction<\/h2>\n<p>Nematodes employ a variety of reproductive strategies that range from monoecious to dioecious to parthenogenic, depending upon the species under consideration.\u00a0<em>C<\/em>.\u00a0<em>elegans<\/em>\u00a0is a monoecious species and shows development of ova contained in a uterus as well as sperm contained in the spermatheca. The uterus has an external opening known as the vulva. The female genital pore is near the middle of the body, whereas the male\u2019s is at the tip. Specialized structures at the tail of the male keep him in place while he deposits sperm with copulatory spicules. Fertilization is internal, and embryonic development starts very soon after fertilization. The embryo is released from the vulva during the gastrulation stage. The embryonic development stage lasts for 14 hours; development then continues through four successive larval stages with ecdysis between each stage\u2014L1, L2, L3, and L4\u2014ultimately leading to the development of a young male or female adult worm. Adverse environmental conditions like overcrowding and lack of food can result in the formation of an intermediate larval stage known as the dauer larva.<\/p>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_69032aff-4c14-418a-8510-b8804db37b4c\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/69032aff-4c14-418a-8510-b8804db37b4c?iframe_resize_id=assessment_practice_id_69032aff-4c14-418a-8510-b8804db37b4c\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-758\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology. <strong>Provided by<\/strong>: OpenStax CNX. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section><hr class=\"before-footnotes clear\" \/><div class=\"footnotes\"><ol><li id=\"footnote-758-1\">Stoll, N. R., \u201cThis wormy world. 1947,\u201d <em>Journal of Parasitology<\/em> 85(3) (1999): 392\u201396. <a href=\"#return-footnote-758-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":16,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology\",\"author\":\"\",\"organization\":\"OpenStax CNX\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\"}]","CANDELA_OUTCOMES_GUID":"3dce1991-0440-4b9c-93bb-be582d08dbc3, 0e60f01e-676d-4c47-a2f2-ed2663d1ce9f","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-758","chapter","type-chapter","status-publish","hentry"],"part":710,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapters\/758","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":5,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapters\/758\/revisions"}],"predecessor-version":[{"id":3039,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapters\/758\/revisions\/3039"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/parts\/710"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapters\/758\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/wp\/v2\/media?parent=758"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapter-type?post=758"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/wp\/v2\/contributor?post=758"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/wp\/v2\/license?post=758"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}