{"id":1826,"date":"2017-01-30T23:20:31","date_gmt":"2017-01-30T23:20:31","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&#038;p=1826"},"modified":"2024-04-25T19:05:11","modified_gmt":"2024-04-25T19:05:11","slug":"classifying-animals","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/classifying-animals\/","title":{"raw":"Classifying Animals","rendered":"Classifying Animals"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Identify key features scientists use to classify animals<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idp101075840\">Scientists have developed a classification scheme that categorizes all members of the animal kingdom, although there are exceptions to most \u201crules\u201d governing animal classification (Figure 1). Animals have been traditionally classified according to two characteristics: body plan and developmental pathway. The major feature of the body plan is its symmetry: how the body parts are distributed along the major body axis. Symmetrical animals can be divided into roughly equivalent halves along at least one axis. Developmental characteristics include the number of germ tissue layers formed during development, the origin of the mouth and anus, the presence or absence of an internal body cavity, and other features of embryological development, such as larval types or whether or not periods of growth are interspersed with molting.<\/p>\r\nThe Eumetazoa (\"true animals\") are divided into those with radial versus bilateral symmetry. Generally, the simpler and often nonmotile animals display radial symmetry, which allows them to explore their environment in all directions. Animals with radial symmetry are also generally characterized by the development of two embryological germ layers, the endoderm and ectoderm, whereas animals with bilateral symmetry are generally characterized by the development of a third embryologic germ layer, the mesoderm. Animals with three germ layers, called triploblasts, are further characterized by the presence or absence of an internal body cavity called a coelom. The presence of a coelom affords many advantages, and animals with a coelom may be termed true coelomates or pseudocoelomates, depending the extent to which mesoderm lines the body cavity. Coelomates are further divided into one of two groups called protostomes and deuterostomes, based on a number of developmental characteristics, including differences in zygote cleavage, the method of coelom formation, and the rigidity of the developmental fate of blastomeres.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"650\"]<img id=\"4\" class=\"\" src=\"https:\/\/openstax.org\/resources\/4ebbee6bb49de1c0f1127a10079e17599e5099ab\" alt=\"The phylogenetic tree of metazoans, or animals, branches into parazoans with no tissues and eumetazoans with specialized tissues. Parazoans include Porifera, or sponges. Eumetazoans branch into Radiata, diploblastic animals with radial symmetry, and Bilateria, triploblastic animals with bilateral symmetry. Radiata includes cnidarians and ctenophores (comb jellies). Bilateria branches into Acoela, which have no body cavity, and Protostomia and Deuterostomia, which possess a body cavity. Deuterostomes include chordates and echinoderms. Protostomia branches into Lophotrochozoa and Ecdysozoa. Ecdysozoa includes arthropods and nematodes, or roundworms. Lophotrochozoa includes Mollusca, Annelida, Brachopoda, Ectoprocta, Rotifera, and Platyhelminthes.\" width=\"650\" height=\"650\" data-media-type=\"image\/png\" \/> Figure 1. Animal phylogeny. The phylogenetic tree of animals is based on morphological, fossil, and genetic evidence. The Ctenophora and Porifera are both considered to be basal because of the absence of Hox genes in this group, but how they are related to the \u201cParahoxozoa\u201d (Placozoa + Eumetazoa) or to each other, continues to be a matter of debate.[\/caption]\r\n\r\n<div class=\"textbox exercises\">\r\n<h3>Practice\u00a0Question<\/h3>\r\nWhich of the following statements is false?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>Eumetazoans have specialized tissues and parazoans don\u2019t.<\/li>\r\n \t<li>Lophotrochozoa and Ecdysozoa are both Bilataria.<\/li>\r\n \t<li>Acoela and Cnidaria both possess radial symmetry.<\/li>\r\n \t<li>Arthropods are more closely related to nematodes than they are to annelids.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"692101\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"692101\"]Statement c is false.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/504a66d2-18a2-4f8f-b20d-a7313625c503\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Identify key features scientists use to classify animals<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idp101075840\">Scientists have developed a classification scheme that categorizes all members of the animal kingdom, although there are exceptions to most \u201crules\u201d governing animal classification (Figure 1). Animals have been traditionally classified according to two characteristics: body plan and developmental pathway. The major feature of the body plan is its symmetry: how the body parts are distributed along the major body axis. Symmetrical animals can be divided into roughly equivalent halves along at least one axis. Developmental characteristics include the number of germ tissue layers formed during development, the origin of the mouth and anus, the presence or absence of an internal body cavity, and other features of embryological development, such as larval types or whether or not periods of growth are interspersed with molting.<\/p>\n<p>The Eumetazoa (&#8220;true animals&#8221;) are divided into those with radial versus bilateral symmetry. Generally, the simpler and often nonmotile animals display radial symmetry, which allows them to explore their environment in all directions. Animals with radial symmetry are also generally characterized by the development of two embryological germ layers, the endoderm and ectoderm, whereas animals with bilateral symmetry are generally characterized by the development of a third embryologic germ layer, the mesoderm. Animals with three germ layers, called triploblasts, are further characterized by the presence or absence of an internal body cavity called a coelom. The presence of a coelom affords many advantages, and animals with a coelom may be termed true coelomates or pseudocoelomates, depending the extent to which mesoderm lines the body cavity. Coelomates are further divided into one of two groups called protostomes and deuterostomes, based on a number of developmental characteristics, including differences in zygote cleavage, the method of coelom formation, and the rigidity of the developmental fate of blastomeres.<\/p>\n<div style=\"width: 660px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" id=\"4\" class=\"\" src=\"https:\/\/openstax.org\/resources\/4ebbee6bb49de1c0f1127a10079e17599e5099ab\" alt=\"The phylogenetic tree of metazoans, or animals, branches into parazoans with no tissues and eumetazoans with specialized tissues. Parazoans include Porifera, or sponges. Eumetazoans branch into Radiata, diploblastic animals with radial symmetry, and Bilateria, triploblastic animals with bilateral symmetry. Radiata includes cnidarians and ctenophores (comb jellies). Bilateria branches into Acoela, which have no body cavity, and Protostomia and Deuterostomia, which possess a body cavity. Deuterostomes include chordates and echinoderms. Protostomia branches into Lophotrochozoa and Ecdysozoa. Ecdysozoa includes arthropods and nematodes, or roundworms. Lophotrochozoa includes Mollusca, Annelida, Brachopoda, Ectoprocta, Rotifera, and Platyhelminthes.\" width=\"650\" height=\"650\" data-media-type=\"image\/png\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 1. Animal phylogeny. The phylogenetic tree of animals is based on morphological, fossil, and genetic evidence. The Ctenophora and Porifera are both considered to be basal because of the absence of Hox genes in this group, but how they are related to the \u201cParahoxozoa\u201d (Placozoa + Eumetazoa) or to each other, continues to be a matter of debate.<\/p>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Practice\u00a0Question<\/h3>\n<p>Which of the following statements is false?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>Eumetazoans have specialized tissues and parazoans don\u2019t.<\/li>\n<li>Lophotrochozoa and Ecdysozoa are both Bilataria.<\/li>\n<li>Acoela and Cnidaria both possess radial symmetry.<\/li>\n<li>Arthropods are more closely related to nematodes than they are to annelids.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q692101\">Show Answer<\/span><\/p>\n<div id=\"q692101\" class=\"hidden-answer\" style=\"display: none\">Statement c is false.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_504a66d2-18a2-4f8f-b20d-a7313625c503\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/504a66d2-18a2-4f8f-b20d-a7313625c503?iframe_resize_id=assessment_practice_id_504a66d2-18a2-4f8f-b20d-a7313625c503\" 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-1826\">\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 2e. <strong>Provided by<\/strong>: OpenStax. <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>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":7,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"3e80555e-5dce-4599-8626-9aa9ce0448cc, 5ae78b77-c42e-4c8d-8e2e-7a9ced6fd4bc","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1826","chapter","type-chapter","status-publish","hentry"],"part":21,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/1826","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":13,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/1826\/revisions"}],"predecessor-version":[{"id":8413,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/1826\/revisions\/8413"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/21"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/1826\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=1826"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=1826"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=1826"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=1826"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}