{"id":807,"date":"2018-01-18T22:14:48","date_gmt":"2018-01-18T22:14:48","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/chapter\/invertebrate-chordates\/"},"modified":"2024-04-26T21:40:02","modified_gmt":"2024-04-26T21:40:02","slug":"invertebrate-chordates","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/chapter\/invertebrate-chordates\/","title":{"raw":"Invertebrate Chordates","rendered":"Invertebrate Chordates"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Discuss the invertebrate chordate lineages<\/li>\r\n<\/ul>\r\n<\/div>\r\nChordata also contains two clades of invertebrates: Urochordata and Cephalochordata. Members of these groups also possess the four distinctive features of chordates at some point during their development.\r\n<h2>Urochordata<\/h2>\r\nMembers of <b>Urochordata<\/b> are also known as <b>tunicates<\/b> (Figure 1). The name tunicate derives from the cellulose-like carbohydrate material, called the tunic, which covers the outer body of tunicates. Although adult tunicates are classified as chordates, they do not have a notochord, a dorsal hollow nerve cord, or a post-anal tail, although they do have pharyngeal slits. The larval form, however, possesses all four structures. Most tunicates are hermaphrodites. Tunicate larvae hatch from eggs inside the adult tunicate\u2019s body. After hatching, a tunicate larva swims for a few days until it finds a suitable surface on which it can attach, usually in a dark or shaded location. It then attaches via the head to the surface and undergoes metamorphosis into the adult form, at which point the notochord, nerve cord, and tail disappear.\r\n\r\n[caption id=\"attachment_2501\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-2501\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2840\/2018\/01\/18221443\/Figure_29_01_03abc-1024x298.jpg\" alt=\"Photo A shows tunicates, which are sponge-like in appearance and have holes along the surface. Illustration B shows the tunicate larval stage, which resembles a tadpole, with a post anal tail at the narrow end. A dorsal hollow nerve cord run along the upper back, and a notochord runs beneath the nerve cord. The digestive tract starts with a mouth at the front of the animal connected to a stomach. Above the stomach is the anus. The pharyngeal slits, which are located in between the stomach and mouth, are connected to an atrial opening at the top of the body. Illustration C shows an adult tunicate, which resembles a tree stump anchored to the bottom. Water enters through a mouth at the top of the body and passes through the pharyngeal slits, where it is filtered. Water then exits through another opening at the side of the body. A heart, stomach and gonad are tucked beneath the pharyngeal slit.\" width=\"1024\" height=\"298\" \/> Figure 1.\u00a0(a) This photograph shows a colony of the tunicate <em>Botrylloides violaceus<\/em>. (b) The larval stage of the tunicate possesses all of the features characteristic of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. (c) In the adult stage, the notochord, nerve cord, and tail disappear. (credit: modification of work by Dann Blackwood, USGS)[\/caption]\r\n\r\nMost tunicates live a sessile existence on the ocean floor and are suspension feeders. The primary foods of tunicates are plankton and detritus. Seawater enters the tunicate\u2019s body through its incurrent siphon. Suspended material is filtered out of this water by a mucous net (pharyngeal slits) and is passed into the intestine via the action of cilia. The anus empties into the excurrent siphon, which expels wastes and water. Tunicates are found in shallow ocean waters around the world.\r\n<h2>Cephalochordata<\/h2>\r\nMembers of <b>Cephalochordata<\/b> possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage (Figure 2). The notochord extends into the head, which gives the subphylum its name. Extinct members of this subphylum include\u00a0<em data-effect=\"italics\">Pikaia<\/em>, which is the oldest known cephalochordate. <em data-effect=\"italics\">Pikaia<\/em> fossils were recovered from the Burgess shales of Canada and dated to the middle of the Cambrian age, making them more than 500 million years old.\r\n\r\nExtant members of Cephalochordata are the <b>lancelets<\/b>, named for their blade-like shape. Lancelets are only a few centimeters long and are usually found buried in sand at the bottom of warm temperate and tropical seas. Like tunicates, they are suspension feeders.\r\n\r\n[caption id=\"attachment_2502\" align=\"aligncenter\" width=\"500\"]<img class=\"wp-image-2502\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2840\/2018\/01\/18221446\/Figure_29_01_04.jpg\" alt=\"The illustration shows a lancelet with a head protruding form the sand, and the rest of the body buried. On the head, tentacles surround the mouth. The mouth leads to a digestive tract. The anus is just before the post anal tail. The pharyngeal slits are next to the atrium, which empties into the atriopore. The body has segmented muscles running along it from top to bottom.\" width=\"500\" height=\"458\" \/> Figure 2.\u00a0The lancelet, like all cephalochordates, has a head. Adult lancelets retain the four key features of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Water from the mouth enters the pharyngeal slits, which filter out food particles. The filtered water then collects in the atrium and exits through the atriopore.[\/caption]\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/4657d4f7-b1c5-4195-a205-006f21020a58\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Discuss the invertebrate chordate lineages<\/li>\n<\/ul>\n<\/div>\n<p>Chordata also contains two clades of invertebrates: Urochordata and Cephalochordata. Members of these groups also possess the four distinctive features of chordates at some point during their development.<\/p>\n<h2>Urochordata<\/h2>\n<p>Members of <b>Urochordata<\/b> are also known as <b>tunicates<\/b> (Figure 1). The name tunicate derives from the cellulose-like carbohydrate material, called the tunic, which covers the outer body of tunicates. Although adult tunicates are classified as chordates, they do not have a notochord, a dorsal hollow nerve cord, or a post-anal tail, although they do have pharyngeal slits. The larval form, however, possesses all four structures. Most tunicates are hermaphrodites. Tunicate larvae hatch from eggs inside the adult tunicate\u2019s body. After hatching, a tunicate larva swims for a few days until it finds a suitable surface on which it can attach, usually in a dark or shaded location. It then attaches via the head to the surface and undergoes metamorphosis into the adult form, at which point the notochord, nerve cord, and tail disappear.<\/p>\n<div id=\"attachment_2501\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2501\" class=\"size-large wp-image-2501\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2840\/2018\/01\/18221443\/Figure_29_01_03abc-1024x298.jpg\" alt=\"Photo A shows tunicates, which are sponge-like in appearance and have holes along the surface. Illustration B shows the tunicate larval stage, which resembles a tadpole, with a post anal tail at the narrow end. A dorsal hollow nerve cord run along the upper back, and a notochord runs beneath the nerve cord. The digestive tract starts with a mouth at the front of the animal connected to a stomach. Above the stomach is the anus. The pharyngeal slits, which are located in between the stomach and mouth, are connected to an atrial opening at the top of the body. Illustration C shows an adult tunicate, which resembles a tree stump anchored to the bottom. Water enters through a mouth at the top of the body and passes through the pharyngeal slits, where it is filtered. Water then exits through another opening at the side of the body. A heart, stomach and gonad are tucked beneath the pharyngeal slit.\" width=\"1024\" height=\"298\" \/><\/p>\n<p id=\"caption-attachment-2501\" class=\"wp-caption-text\">Figure 1.\u00a0(a) This photograph shows a colony of the tunicate <em>Botrylloides violaceus<\/em>. (b) The larval stage of the tunicate possesses all of the features characteristic of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. (c) In the adult stage, the notochord, nerve cord, and tail disappear. (credit: modification of work by Dann Blackwood, USGS)<\/p>\n<\/div>\n<p>Most tunicates live a sessile existence on the ocean floor and are suspension feeders. The primary foods of tunicates are plankton and detritus. Seawater enters the tunicate\u2019s body through its incurrent siphon. Suspended material is filtered out of this water by a mucous net (pharyngeal slits) and is passed into the intestine via the action of cilia. The anus empties into the excurrent siphon, which expels wastes and water. Tunicates are found in shallow ocean waters around the world.<\/p>\n<h2>Cephalochordata<\/h2>\n<p>Members of <b>Cephalochordata<\/b> possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage (Figure 2). The notochord extends into the head, which gives the subphylum its name. Extinct members of this subphylum include\u00a0<em data-effect=\"italics\">Pikaia<\/em>, which is the oldest known cephalochordate. <em data-effect=\"italics\">Pikaia<\/em> fossils were recovered from the Burgess shales of Canada and dated to the middle of the Cambrian age, making them more than 500 million years old.<\/p>\n<p>Extant members of Cephalochordata are the <b>lancelets<\/b>, named for their blade-like shape. Lancelets are only a few centimeters long and are usually found buried in sand at the bottom of warm temperate and tropical seas. Like tunicates, they are suspension feeders.<\/p>\n<div id=\"attachment_2502\" style=\"width: 510px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2502\" class=\"wp-image-2502\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/2840\/2018\/01\/18221446\/Figure_29_01_04.jpg\" alt=\"The illustration shows a lancelet with a head protruding form the sand, and the rest of the body buried. On the head, tentacles surround the mouth. The mouth leads to a digestive tract. The anus is just before the post anal tail. The pharyngeal slits are next to the atrium, which empties into the atriopore. The body has segmented muscles running along it from top to bottom.\" width=\"500\" height=\"458\" \/><\/p>\n<p id=\"caption-attachment-2502\" class=\"wp-caption-text\">Figure 2.\u00a0The lancelet, like all cephalochordates, has a head. Adult lancelets retain the four key features of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Water from the mouth enters the pharyngeal slits, which filter out food particles. The filtered water then collects in the atrium and exits through the atriopore.<\/p>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_4657d4f7-b1c5-4195-a205-006f21020a58\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/4657d4f7-b1c5-4195-a205-006f21020a58?iframe_resize_id=assessment_practice_id_4657d4f7-b1c5-4195-a205-006f21020a58\" 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-807\">\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>","protected":false},"author":17,"menu_order":4,"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":"251b7e96-f6ea-40c7-a895-097c5a8049cc, cca60398-4b70-4347-8c2a-197ccd15d73b","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-807","chapter","type-chapter","status-publish","hentry"],"part":798,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapters\/807","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":4,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapters\/807\/revisions"}],"predecessor-version":[{"id":3048,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapters\/807\/revisions\/3048"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/parts\/798"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapters\/807\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/wp\/v2\/media?parent=807"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/pressbooks\/v2\/chapter-type?post=807"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/wp\/v2\/contributor?post=807"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-nmbiology2\/wp-json\/wp\/v2\/license?post=807"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}