ADW: Chaetognatha: INFORMATION

<!DOCTYPE html> <html xmlns:og="http://ogp.me/ns#" lang="en" xml:lang="en"> <head> <title>ADW: Chaetognatha: INFORMATION</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <link rel="canonical" href="https://animaldiversity.org/accounts/Chaetognatha/" /> <script type="text/javascript" src="//code.jquery.com/jquery-3.6.0.min.js"></script> <script type="text/javascript" src="//code.jquery.com/jquery-migrate-3.3.2.min.js"></script> <script type="text/javascript" src="/static/js/compat.js"></script> <link rel="shortcut icon" href="https://animaldiversity.org/favicon.ico" /> <link href="//fonts.googleapis.com/css?family=Gentium+Book+Basic:400,400italic,700,700italic" rel="stylesheet" type="text/css" /> <link href="//fonts.googleapis.com/css?family=PT+Sans:400,700,400italic,700italic" rel="stylesheet" type="text/css" /> <link rel="stylesheet" type="text/css" href="/static/bootstrap/css/bootstrap.css" /> <link rel="stylesheet" href="/static/css/pica.styles.css" /> <link rel="stylesheet" href="/static/css/pica.print.css" media="print" />  <link rel="stylesheet" type="text/css" href="/static/colorbox/colorbox.css" /> <meta property="og:url" content="https://animaldiversity.org/accounts/Chaetognatha/" /> <meta content="Chaetognatha (arrow worms)" property="og:title" /> <meta content="website" property="og:type" /> <meta content="Animal Diversity Web" property="og:site_name" /> <meta content="https://animaldiversity.org/collections/contributors/Grzimek_inverts/Chaetognatha/Sagitta_bipunctata/medium.jpg" property="og:image" /> <meta name="twitter:card" content="summary" /> <meta name="twitter:site" content="@AnimalDiversity" /> <meta name="twitter:title" content="Chaetognatha (arrow worms)" /> <meta name="twitter:description" content="Read about Chaetognatha (arrow worms) on the Animal Diversity Web." /> <meta name="twitter:image:src" content="https://animaldiversity.org/collections/contributors/Grzimek_inverts/Chaetognatha/Sagitta_bipunctata/medium.jpg" /> <meta name="twitter:image:height" content="480" /> <meta name="twitter:image:width" content="113" /> <meta name="twitter:url" content="https://animaldiversity.org/accounts/Chaetognatha/" /> <script type="text/javascript" src="/static/js/Hyphenator.js"></script> <link rel="stylesheet" href="/static/social-likes/social-likes_birman.css" /> <style> .social-likes { margin: 0; } .social-likes__widget { margin: 0; } </style>   </head> <body> <div id="outerwrap"> <div id="header" aria-role="header"> <h1> <a id="homelink" href="/">Animal Diversity Web</a> </h1> <div class="umlinks"> <div class="relative"> <a href="https://lsa.umich.edu/ummz/" id="ummzlink">University of Michigan Museum of Zoology</a> <a href="https://www.umich.edu/" id="umlink">University of Michigan</a> </div> </div> </div> <div id="wrap" class="gradient"> <div class="container-fluid"> <div class="row-fluid"> <div class="span2 sidebar left"> <ul class="nav nav-tabs nav-stacked" id="sitemap"> <li> <a href="/">Home</a> </li> <li> <a href="/about/">About Us</a> </li> <li> <a href="/animal_names/">About Animal Names</a> </li> <li> <a href="/teach/">Educational Resources</a> </li> <li> <a href="/collections/">Special Collections</a> </li> <li> <a href="/glossary/">Glossary</a> </li> <li> <a href="/accounts/Animalia/">Browse Animalia</a> </li> </ul> <h2 class="offscreen">More Information</h2> <div class="well"> <h3>Additional Information</h3> <ul class="unstyled"> <li> <a href="http://eol.org/search/?q=Chaetognatha&search=Go">Encyclopedia of Life</a> </li> </ul> </div> </div> <div class="span7_5 blahblahblah main" aria-role="main"> <h2 class="rank-unspecified">Chaetognatha<span class="vernacular-name">arrow worms</span></h2> <div class="social-likes" data-counters="no"> <div class="facebook" title="Share link on Facebook">Facebook</div> <div class="twitter" title="Share link on Twitter">Twitter</div> </div> <div class="snapshots" aria-hidden="true"> <ul> <li> <a href="/accounts/Chaetognatha/pictures/collections/contributors/Grzimek_inverts/Chaetognatha/Sagitta_bipunctata/"> <img alt=" " src="/collections/contributors/Grzimek_inverts/Chaetognatha/Sagitta_bipunctata/button.jpg" border="0" /> </a> </li> <li> <a href="/accounts/Chaetognatha/pictures/collections/contributors/Grzimek_inverts/Chaetognatha/Spadella_cephaloptera/"> <img alt=" " src="/collections/contributors/Grzimek_inverts/Chaetognatha/Spadella_cephaloptera/button.jpg" border="0" /> </a> </li> <li> <a href="/accounts/Chaetognatha/pictures/collections/contributors/Grzimek_inverts/Chaetognatha/Eukrohnia_fowleri/"> <img alt=" " src="/collections/contributors/Grzimek_inverts/Chaetognatha/Eukrohnia_fowleri/button.jpg" border="0" /> </a> </li> <li> <a href="/accounts/Chaetognatha/pictures/collections/contributors/Grzimek_inverts/Chaetognatha/Sagitta_setosa/"> <img alt=" " src="/collections/contributors/Grzimek_inverts/Chaetognatha/Sagitta_setosa/button.jpg" border="0" /> </a> </li> <li> <a href="/accounts/Chaetognatha/pictures/collections/contributors/Grzimek_inverts/Chaetognatha/Sagitta_enflata/"> <img alt=" " src="/collections/contributors/Grzimek_inverts/Chaetognatha/Sagitta_enflata/button.jpg" border="0" /> </a> </li> </ul> </div> <div class="byline">By Jeremy Wright</div> <nav class="contents"> <ul> <li> <a href="#diversity">Diversity</a> </li> <li> <a href="#geographic_range">Geographic Range</a> </li> <li> <a href="#habitat">Habitat</a> </li> <li> <a href="#taxonomic_history">Systematic and Taxonomic History</a> </li> <li> <a href="#physical_description">Physical Description</a> </li> <li> <a href="#development">Development</a> </li> <li> <a href="#reproduction">Reproduction</a> </li> </ul> <ul> <li> <a href="#lifespan_longevity">Lifespan/Longevity</a> </li> <li> <a href="#behavior">Behavior</a> </li> <li> <a href="#communication">Communication and Perception</a> </li> <li> <a href="#food_habits">Food Habits</a> </li> <li> <a href="#predation">Predation</a> </li> <li> <a href="#ecosystem_roles">Ecosystem Roles</a> </li> <li> <a href="#economic_importance_positive">Economic Importance for Humans: Positive</a> </li> </ul> <ul> <li> <a href="#economic_importance_negative">Economic Importance for Humans: Negative</a> </li> <li> <a href="#conservation_status">Conservation Status</a> </li> <li> <a href="#comments">Other Comments</a> </li> <li> <a href="#contributors">Contributors</a> </li> <li> <a href="#references">References</a> </li> </ul> </nav> <div class="inner-wrap"> <section class="hyphenate"> <h3 id="diversity">Diversity</h3> <p audience="advanced intermediate">The phylum <span class="taxon-link rank-unspecified">Chaetognatha</span>, also known as arrow worms, contains nearly 200 species of mostly planktonic, bilaterally symmetrical, coelomate, worm-like organisms. The phylum contains two orders, <span class="taxon-name">Phragmophora</span> and <span class="taxon-name">Aphragmophora</span>. The main difference between the two is the presence of ventral transverse muscle bands in <span class="taxon-name">Phragmophora</span>, which are absent in <span class="taxon-name">Aphragmophora</span>. Chaetognaths may be found in marine and some estuarine environments throughout the world. About a fifth of the total species are benthic, some living just above the deep ocean floor; these are often attached to the substrate by adhesive secretions. Chaetognaths may range from 1 mm to 12 cm in length and are typically transparent, although some deep-water species may be orange in color, and phragmophorids may be opaque, due to their musculature. The common name, arrow worms is derived from their streamlined appearance, with paired lateral fins and a single caudal (tail) fin, while their scientific name comes from the hooked set of jaws that protrude lateral to the mouth. These structures are used in prey capture, with chaetognaths feeding on a number of crustacean (mainly copepods) and fish (mainly larvae) species, which they track through daily vertical migrations in the water column (these migrations may also protect them from predators). Chaetognaths are hermaphroditic, and may undergo reciprocal, nonreciprocal, or self-fertilization. <span class="citations"> (<a href="#14EC8978-9AE7-11E2-AF6F-002500F14F28" class="citation">"Chaetognatha", 2012</a>; <a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#CF144861-9AEF-11E2-883B-002500F14F28" class="citation">Goto and Yoshida, 1985</a>; <a href="#76CC303A-9AE7-11E2-A112-002500F14F28" class="citation">Margulis and Chapman, 2010</a>; <a href="#AC9F6A9C-9AE7-11E2-AD9C-002500F14F28" class="citation">Shapiro, 2012</a>; <a href="#18471078-6F4B-11E3-A5F7-002500F14F28" class="citation">Zhang, 2011</a>)</span></p> </section> <section class="hyphenate"> <h3 id="geographic_range">Geographic Range</h3> <p audience="advanced intermediate">Chaetognaths may be found in marine and some estuarine environments throughout the world, including polar and tropical regions. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#76CC303A-9AE7-11E2-A112-002500F14F28" class="citation">Margulis and Chapman, 2010</a>; <a href="#AC9F6A9C-9AE7-11E2-AD9C-002500F14F28" class="citation">Shapiro, 2012</a>)</span></p> <ul class="keywords donthyphenate "> <li class="keywords-header">Biogeographic Regions</li> <li> <a class="gloss" href="#20020914235803">nearctic</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <a class="gloss" href="#20020915001330">palearctic</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <a class="gloss" href="#20020915001348">oriental</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <a class="gloss" href="#20020916134510">ethiopian</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <a class="gloss" href="#20020915000403">neotropical</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <a class="gloss" href="#20020916135737">australian</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <a class="gloss" href="#20020916135918">antarctica</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <a class="gloss" href="#20020917113601">arctic ocean</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <span>indian ocean</span> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <a class="gloss" href="#20020917114102">atlantic ocean</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <a class="gloss" href="#20020917114731">pacific ocean</a> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> <li> <span>mediterranean sea</span> <ul> <li> <a class="gloss" href="#20020904145365">native</a> </li> </ul> </li> </ul> <ul class="keywords donthyphenate last"> <li class="keywords-header">Other Geographic Terms</li> <li> <a class="gloss" href="#200304045530">holarctic</a> </li> <li> <a class="gloss" href="#20020904145620">cosmopolitan</a> </li> </ul> </section> <section class="hyphenate"> <h3 id="habitat">Habitat</h3> <p audience="advanced intermediate">Chaetognaths are mainly planktonic organisms in marine and estuarine environments. About a fifth of the total species are benthic, some living just above the deep ocean floor. They are often found in great numbers, particularly in mid-water and neritic waters, and may be found in rock pools or associated with certain oceanic currents. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#76CC303A-9AE7-11E2-A112-002500F14F28" class="citation">Margulis and Chapman, 2010</a>; <a href="#34AD5F1C-9AE7-11E2-92C0-002500F14F28" class="citation">Ramel, 2012</a>)</span></p> <ul class="keywords donthyphenate "> <li class="keywords-header">Habitat Regions</li> <li> <a class="gloss" href="#20020904145595">temperate</a> </li> <li> <a class="gloss" href="#20020904145598">tropical</a> </li> <li> <a class="gloss" href="#20020904145371">polar</a> </li> <li> <a class="gloss" href="#20020904145582">saltwater or marine</a> </li> </ul> <ul class="keywords donthyphenate "> <li class="keywords-header">Aquatic Biomes</li> <li> <a class="gloss" href="#20020904145836">pelagic</a> </li> <li> <a class="gloss" href="#20020904145431">benthic</a> </li> <li> <a class="gloss" href="#20020904145675">reef</a> </li> <li> <span>temporary pools</span> </li> <li> <a class="gloss" href="#20020904145825">coastal</a> </li> <li> <a class="gloss" href="#20020904145323">abyssal</a> </li> <li> <a class="gloss" href="#20020904145435">brackish water</a> </li> </ul> <ul class="keywords donthyphenate last"> <li class="keywords-header">Other Habitat Features</li> <li> <a class="gloss" href="#20020904145350">estuarine</a> </li> </ul> </section> <section class="hyphenate"> <h3 id="taxonomic_history">Systematic and Taxonomic History</h3> <p audience="advanced intermediate">Since first being recorded in 1775, chaetognaths have been classified many ways, including as <a class="taxon-link" href="/accounts/Mollusca/">molluscs</a>, <a class="taxon-link" href="/accounts/Arthropoda/">arthropods</a>, and <a class="taxon-link" href="/accounts/Nematoda/">nematodes</a>. They were elevated to their own phylum by the German zoologist Rudolf Leuckart in 1854, a decision which is supported by numerous morphological and embryological autapomorphies, indicated below. The monophyly of this phylum is widely accepted, and molecular phylogenetic analyses of 28S ribosomal DNA have supported the monophyly of its two constituent orders, <span class="taxon-name">Phragmophora</span> and <span class="taxon-name">Aphragmophora</span> (without the traditionally included family <a class="taxon-link rank-family" href="/accounts/Pterosagittidae/">Pterosagittidae</a>). <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#10EDF005-6F39-11E3-BD0F-002500F14F28" class="citation">Leuckart, 1854</a>; <a href="#DFD59BC5-6F36-11E3-9A78-002500F14F28" class="citation">Littlewood, et al., 2004</a>; <a href="#288FB202-6F3F-11E3-BC71-002500F14F28" class="citation">Papillon, et al., 2006</a>; <a href="#B22B0D19-6F3D-11E3-AF94-002500F14F28" class="citation">Telford and Holland, 1993</a>; <a href="#6F3160D1-6F3C-11E3-8D2D-002500F14F28" class="citation">Telford and Holland, 1997</a>)</span></p> <p audience="advanced intermediate">Chaetognaths were originally considered <a class="taxon-link" href="/accounts/Deuterostomia/">deuterostomes</a>, based on embryological observations. All molecular phylogenetic analyses performed thus far, however, strongly support the placement of <span class="taxon-link rank-unspecified">Chaetognatha</span> within <a class="taxon-link" href="/accounts/Protostomia/">protostome</a> animals. The precise phylogenetic placement of <span class="taxon-link rank-unspecified">Chaetognatha</span> within <span class="taxon-name">Protostomata</span> remains somewhat confused today, as molecular analyses have suggested <span class="taxon-link rank-unspecified">Chaetognatha</span> is a sister group to all other protostomes, <span class="taxon-name">Spiralia</span>, or phylum <span class="taxon-name">Priapulida</span> (within the superphylum <a class="taxon-link rank-unspecified" href="/accounts/Ecdysozoa/">Ecdysozoa</a>). Their potential identity as a basal sister group to such a large metazoan group makes further examination of their phylogenetic placement essential, as it has the potential to greatly contribute to our understanding of morphological and developmental characters found in some of the earliest bilaterian organisms. <span class="citations"> (<a href="#02EA6478-9AE9-11E2-B9DB-002500F14F28" class="citation">Brands, 2009</a>; <a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#26397E66-6F3A-11E3-BEC8-002500F14F28" class="citation">Dunn, et al., 2008</a>; <a href="#B65E0454-6F39-11E3-9725-002500F14F28" class="citation">Edgecombe, et al., 2011</a>; <a href="#BC638AF5-6F3A-11E3-9D44-002500F14F28" class="citation">Giribet, et al., 2007</a>; <a href="#BF4CD08A-6F3F-11E3-81DB-002500F14F28" class="citation">Helmkampf, et al., 2008</a>; <a href="#DFD59BC5-6F36-11E3-9A78-002500F14F28" class="citation">Littlewood, et al., 2004</a>; <a href="#44EDFEE6-6F3E-11E3-BA0A-002500F14F28" class="citation">Matus, et al., 2006</a>; <a href="#13F87CFA-6F41-11E3-BF3F-002500F14F28" class="citation">Papillon, et al., 2004</a>; <a href="#654D5BF0-6F41-11E3-9083-002500F14F28" class="citation">Paps, et al., 2009</a>)</span></p> <ul class="aside block-grid donthyphenate one-up"> <li> <dl> <dt>Synapomorphies</dt> <dd> <ul> <li>Their mesoderm and coelom form by enterocoely.</li> <li>Chaetognaths have chitinous retractable jaws.</li> <li>Chaetognaths have multilayered epithelium on their body.</li> <li>Chaetognaths have cephalic hoods.</li> <li>These animals have retrocerebral organs and ciliary loops whose function is unknown.</li> </ul> </dd> </dl> </li> </ul> </section> <section class="hyphenate"> <h3 id="physical_description">Physical Description</h3> <p audience="advanced intermediate">Chaetognaths range from 1 mm to 12 cm in length and are typically transparent, although some deep-water species may be orange in color (carotenoid pigmentation), and phragmophorids may be opaque, due to their musculature. They are bilaterally symmetrical and have long, streamlined bodies, which may be divided into head, trunk, and tail regions. They have paired lateral fins and a single tail fin. The mouth is located ventrally on the head, and is set into a vestibule; this structure is typically associated with grasping spines or hooks, located laterally to the mouth, as well as teeth, which are in located at the front of the mouth. Some species have serrated hooks and/or cuspidate teeth. A hood (anterolateral body wall fold) may be pulled over the head to enclose the vestibule. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#A3529A2B-9AE9-11E2-8AD5-002500F14F28" class="citation">Ghirardelli, 1968</a>; <a href="#76CC303A-9AE7-11E2-A112-002500F14F28" class="citation">Margulis and Chapman, 2010</a>; <a href="#AC9F6A9C-9AE7-11E2-AD9C-002500F14F28" class="citation">Shapiro, 2012</a>)</span></p> <p audience="advanced intermediate">Chaetognaths are covered in a thin, flexible cuticle on top of the epidermis. Epidermal cells are mainly squamous and have interlocking margins; they may be stratified. Epidermal cells covering the fins are elongated and the cells lining the vestibule are columnar rather than squamous. The cuticle is not continuous and, where it is not present, there are many secretory cells in the epidermis. There is a basement membrane present between the epidermis and body wall; the body wall is made up of four quadrants of dorsolateral and ventrolateral longitudinal muscles. The body cavities are most likely derived from enterocoelic cavities, which form during development. The body cavity has a tripartite arrangement, with a head cavity (protocoel, reduced in space by the cephalic musculature), and paired trunk and tail coeloms with dorsal and ventral longitudinal mesenteries, which correspond to the mesocoel and matcoel, respectively. Transverse septa separate the body regions. The body fluid has a variety of cells and cell-like structures, although their functions are largely unknown. The fluid-filled coeloms, body wall, basement membrane, and cuticle all provide support to the body. They do not have circulatory, respiratory, or excretory organs; gases are diffused across the body wall and fluid transport is via cilial action within the body cavities. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#76CC303A-9AE7-11E2-A112-002500F14F28" class="citation">Margulis and Chapman, 2010</a>; <a href="#AC9F6A9C-9AE7-11E2-AD9C-002500F14F28" class="citation">Shapiro, 2012</a>)</span></p> <p audience="advanced intermediate">A few species of deep sea chaetognaths, including <a class="taxon-link rank-species" href="/accounts/Eukrohnia_fowleri/">Eukrohnia fowleri</a> and <a class="taxon-link rank-species" href="/accounts/Caecosagitta_macrocephala/">Caecosagitta macrocephala</a>, are bioluminescent. <span class="citations"> (<a href="#9DB8140C-9AF4-11E2-8478-002500F14F28" class="citation">Thuesen, et al., 2010</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Other Physical Features</li> <li> <a class="gloss" href="#20020916131519">ectothermic</a> </li> <li> <a class="gloss" href="#20020916125902">heterothermic</a> </li> <li> <a class="gloss" href="#20020904145642">bilateral symmetry</a> </li> <li> <a class="gloss" href="#20020904145397">venomous</a> </li> </ul> </section> <section class="hyphenate"> <h3 id="development">Development</h3> <p audience="advanced intermediate">Chaetognaths are hermaphroditic. Cross-fertilization is most common, although some species will self-fertilize. Fertilization is typically internal and eggs may be released into the water, deposited on the sea floor or other substrate, or brooded in pouches near the tail. Cleavage is radial, holoblastic, and equal, leading to a coeloblastula. Development is direct and accomplished quickly, typically from zygote to juvenile within 48 hours. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#76CC303A-9AE7-11E2-A112-002500F14F28" class="citation">Margulis and Chapman, 2010</a>)</span></p> </section> <section class="hyphenate"> <h3 id="reproduction">Reproduction</h3> <p audience="advanced intermediate">Chaetognaths may undergo reciprocal, nonreciprocal, or self-fertilization. Some benthic species have been documented performing a mating "dance," with an individual depositing balls of sperm onto a mate. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#CF144861-9AEF-11E2-883B-002500F14F28" class="citation">Goto and Yoshida, 1985</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Mating System</li> <li> <a class="gloss" href="#20020904145483">polygynandrous (promiscuous)</a> </li> </ul> <p audience="advanced intermediate">Chaetognaths have paired ovaries located in their trunks and paired testes located in their tails. Sperm mature before eggs (which makes self-fertilization less likely), and are stored in coelomic cavities within the tail until they are released in clusters outside the body via a pair of seminal vesicles. Ovaries have oviducts, which lead to genital pores located near the trunk-tail junction. In populations of at least a few species, breeding occurs twice a year, and hatching occurs from April to June and late September to December (typically fewer hatchlings). <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#A3529A2B-9AE9-11E2-8AD5-002500F14F28" class="citation">Ghirardelli, 1968</a>; <a href="#34AD5F1C-9AE7-11E2-92C0-002500F14F28" class="citation">Ramel, 2012</a>; <a href="#B302A980-9AF1-11E2-A5C0-002500F14F28" class="citation">Zo, 1973</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Key Reproductive Features</li> <li> <a class="gloss" href="#20020904145554">iteroparous</a> </li> <li> <a class="gloss" href="#20020904145584">seasonal breeding</a> </li> <li> <span>simultaneous hermaphrodite</span> </li> <li> <a class="gloss" href="#20020904145786">sexual</a> </li> <li> <a class="gloss" href="#20020904145546">fertilization</a> <ul> <li> <a class="gloss" href="#20020904145427">internal</a> </li> </ul> </li> <li> <a class="gloss" href="#20020904145572">oviparous</a> </li> </ul> <p audience="advanced intermediate">Outside of a few species (such as members of genus <span rank="Genus" class="taxon-name rank-genus">Eukronhnia</span>) that brood their young until they are ready to swim, chaetognaths exhibit no parental investment beyond the production of gametes. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Parental Investment</li> <li> <a class="gloss" href="#20020904145746">female parental care</a> </li> <li> <span>pre-fertilization</span> <ul> <li> <span>provisioning</span> </li> </ul> </li> <li> <span>pre-hatching/birth</span> <ul> <li> <span>protecting</span> <ul> <li> <span>female</span> </li> </ul> </li> </ul> </li> </ul> </section> <section class="hyphenate"> <h3 id="lifespan_longevity">Lifespan/Longevity</h3> <p audience="advanced intermediate">Most cold water chaetognaths have a longer life expectancy than those in tropical waters, two years versus six weeks, respectively. <span class="citations"> (<a href="#5ECFF7E3-9AF3-11E2-8B77-002500F14F28" class="citation">"Arrow Worms — Phylum Chaetognatha", 2002</a>)</span></p> </section> <section class="hyphenate"> <h3 id="behavior">Behavior</h3> <p audience="advanced intermediate">Many species within this phylum are known to undergo daily vertical migrations, rising to the surface at night to follow prey and sinking during the day, which provides protection from predators. These worms have ammonia-filled vacuolated cells in their trunks, which help them to regulate their depth in the water column. Pelagic chaetognaths move by contracting the longitudinal muscles of their right and left sides alternately, creating forward, darting motions. Fins do not appear to aid in locomotion, instead acting as stabilizers. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#76CC303A-9AE7-11E2-A112-002500F14F28" class="citation">Margulis and Chapman, 2010</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Key Behaviors</li> <li> <a class="gloss" href="#20020914213156">natatorial</a> </li> <li> <a class="gloss" href="#20020904145414">diurnal</a> </li> <li> <a class="gloss" href="#20020904145503">nocturnal</a> </li> <li> <a class="gloss" href="#20020904145752">crepuscular</a> </li> <li> <a class="gloss" href="#20020904145472">motile</a> </li> <li> <a class="gloss" href="#20020904145585">sedentary</a> </li> <li> <a class="gloss" href="#20020904145381">solitary</a> </li> </ul> </section> <section class="hyphenate"> <h3 id="communication">Communication and Perception</h3> <p audience="advanced intermediate">Chaetognaths have a central nervous system with a large cerebral ganglion, dorsal to the pharynx. Additional ganglia, which serve muscles and sensory organs of the head, arise from this structure. They also have a pair of circumenteric connective nerves, emerging from the rear of the cerebral ganglion and extending (posterioventrally) to meet in a ventral ganglion in the epidermis of the trunk. This ganglion controls swimming motion and also gives rise to many pairs of nerves, which create a subepidermal nerve plexus. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>)</span></p> <p audience="advanced intermediate">Chaetognaths have a pair of compound eyes below the epidermis, on the head. They are made up of five inverted pigment-cup ocelli, one large ocellus directed laterally and four smaller ones directed medially; this gives these worms a nearly uninterrupted field of vision. Their eyes do not typically have lenses and likely do not form images, but are used for light reception and body orientation. The ocelli also contain ciliated receptor cells. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#A3529A2B-9AE9-11E2-8AD5-002500F14F28" class="citation">Ghirardelli, 1968</a>; <a href="#34AD5F1C-9AE7-11E2-92C0-002500F14F28" class="citation">Ramel, 2012</a>)</span></p> <p audience="advanced intermediate">Chaetognaths have a ciliary loop (corona ciliata) on the dorsal surface of the head-trunk juncture, made up of two rings of cilial cells that may be chemoreceptive and/or aid in sperm transfer. They are covered in patches of ciliary fans, which enhance the detection of vibrations in the water. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#A3529A2B-9AE9-11E2-8AD5-002500F14F28" class="citation">Ghirardelli, 1968</a>)</span></p> <ul class="keywords donthyphenate "> <li class="keywords-header">Communication Channels</li> <li> <a class="gloss" href="#20020904145694">visual</a> </li> <li> <a class="gloss" href="#20020904145500">tactile</a> </li> <li> <a class="gloss" href="#20020904145606">chemical</a> </li> </ul> <ul class="keywords donthyphenate "> <li class="keywords-header">Other Communication Modes</li> <li> <a class="gloss" href="#20020904145612">photic/bioluminescent</a> </li> </ul> <ul class="keywords donthyphenate last"> <li class="keywords-header">Perception Channels</li> <li> <a class="gloss" href="#20020904145694">visual</a> </li> <li> <a class="gloss" href="#20020904145500">tactile</a> </li> <li> <a class="gloss" href="#20020904145852">vibrations</a> </li> <li> <a class="gloss" href="#20020904145606">chemical</a> </li> </ul> </section> <section class="hyphenate"> <h3 id="food_habits">Food Habits</h3> <p audience="advanced intermediate">Chaetognaths are carnivorous predators, particularly of <span class="taxon-name">copepods</span>. They are also known to feed on other crustaceans and small fishes. Benthic species are typically ambush predators. They use adhesive secretions to affix themselves to substrate and extend their mouths and vestibules, as well as their associated hooks. When prey is detected by a worm (by the cilia on the body), the head darts forward and prey is captured, using the hooks. Prey is swallowed whole. Panktonic species dart forward in the water column to catch prey within reach, using their grasping spines to pull prey in. The majority of these worms inject their prey with a neurotoxin (tetrodotoxin); it has been hypothesized that chaetognaths have a commensal relationship with bacteria (from genus <span rank="Genus" class="taxon-name rank-genus">Vibro</span>) in their heads or guts, which actually produce the toxin. <span class="citations"> (<a href="#4DB9CDA1-9AE6-11E2-9F8A-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#76CC303A-9AE7-11E2-A112-002500F14F28" class="citation">Margulis and Chapman, 2010</a>; <a href="#34AD5F1C-9AE7-11E2-92C0-002500F14F28" class="citation">Ramel, 2012</a>; <a href="#AC9F6A9C-9AE7-11E2-AD9C-002500F14F28" class="citation">Shapiro, 2012</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Primary Diet</li> <li> <a class="gloss" href="#20020904145419">carnivore</a> <ul> <li> <a class="gloss" href="#20020904145838">piscivore</a> </li> <li> <span>eats non-insect arthropods</span> </li> </ul> </li> <li> <a class="gloss" href="#20020904145368">planktivore</a> </li> </ul> </section> <section class="hyphenate"> <h3 id="predation">Predation</h3> <p audience="advanced intermediate">Chaetognaths are prey to many larger organisms including fishes, whales, other marine invertebrates, and molluscs. <span class="citations"> (<a href="#AC9F6A9C-9AE7-11E2-AD9C-002500F14F28" class="citation">Shapiro, 2012</a>)</span></p> <ul class="aside block-grid donthyphenate one-up"> <li> <dl> <dt>Known Predators</dt> <dd> <ul> <li>Alewives (<a class="taxon-link rank-species" href="/accounts/Alosa_pseudoharengus/">Alosa pseudoharengus</a>)</li> <li>Atlantic herrings (<a class="taxon-link rank-species" href="/accounts/Clupea_harengus/">Clupea harengus</a>)</li> <li>anchovies (<a class="taxon-link rank-family" href="/accounts/Engraulidae/">Engraulidae</a> sp.)</li> <li>sea ravens (<a class="taxon-link rank-species" href="/accounts/Hemitripterus_americanus/">Hemitripterus americanus</a>)</li> <li>anglerfishes (<a class="taxon-link rank-species" href="/accounts/Lophius_americanus/">Lophius americanus</a>)</li> <li>silver hakes (<a class="taxon-link rank-species" href="/accounts/Merluccius_bilinearis/">Merluccius bilinearis</a>)</li> <li>pollack (<a class="taxon-link rank-species" href="/accounts/Pollachius_pollachius/">Pollachius pollachius</a>)</li> <li>mackerels (<a class="taxon-link rank-genus" href="/accounts/Scomber/">Scomber</a> sp.)</li> <li>window panes (<a class="taxon-link rank-species" href="/accounts/Scophthalmus_aquosus/">Scophthalmus aquosus</a>)</li> <li>red hakes (<a class="taxon-link rank-species" href="/accounts/Urophycis_chuss/">Urophycis chuss</a>)</li> <li>spotted codlings (<a class="taxon-link rank-species" href="/accounts/Urophycis_regia/">Urophycis regia</a>)</li> <li>white hakes (<a class="taxon-link rank-species" href="/accounts/Urophycis_tenuis/">Urophycis tenuis</a>)</li> <li>thorny skates (<a class="taxon-link rank-species" href="/accounts/Amblyraja_radiata/">Amblyraja radiata</a>)</li> <li>little skates (<a class="taxon-link rank-species" href="/accounts/Leucoraja_erinacea/">Leucoraja erinacea</a>)</li> <li>winter skates (<a class="taxon-link rank-species" href="/accounts/Leucoraja_ocellata/">Leucoraja ocellata</a>)</li> <li>toothed whales (<a class="taxon-link rank-suborder" href="/accounts/Odontoceti/">Odontoceti</a> species)</li> <li>arrow worms (<span class="taxon-link rank-unspecified">Chaetognatha</span> species)</li> <li>comb jellies (<a class="taxon-link rank-unspecified" href="/accounts/Ctenophora/">Ctenophora</a> species)</li> <li>mussels (<a class="taxon-link rank-species" href="/accounts/Actinonaias_ellipsiformis/">Actinonaias ellipsiformis</a>)</li> <li>Arctic astartes (<a class="taxon-link rank-species" href="/accounts/Astarte_arctica/">Astarte arctica</a>)</li> </ul> </dd> </dl> </li> </ul> </section> <section class="hyphenate"> <h3 id="ecosystem_roles">Ecosystem Roles</h3> <p audience="advanced intermediate">A number of tetrodotoxin producing bacteria have been isolated from the guts of chaetognaths; these are likely responsible for the production of the toxin used by the worms in prey capture. They may be hosts to parasitic <span class="taxon-name">digeneans</span>, <a class="taxon-link" href="/accounts/Nematoda/">nematodes</a>, and metacestodes; infections may be the result of the worm ingesting infested <span class="taxon-name">copepods</span>, which serve as intermediate hosts. In turn, they may pass these parasites on to their predators (particularly fishes). They may also serve as hosts to ectoparasites such as <span class="taxon-name">copepods</span> and <span class="taxon-name">dinoflagellates</span>. <span class="citations"> (<a href="#E059DB4C-9BA5-11E2-911B-002500F14F28" class="citation">DaPonte, et al., 2008</a>; <a href="#9B98E6D4-9BA9-11E2-AF08-002500F14F28" class="citation">McLean and Nielsen, 1989</a>; <a href="#B8E42C19-9BA3-11E2-8B79-002500F14F28" class="citation">Thuesen and Kogure, 1989</a>; <a href="#189FF5DC-9BAA-11E2-8CA8-002500F14F28" class="citation">Øresland, 1986</a>)</span></p> <div class="note"> <strong>Mutualist Species</strong> <br /> <ul> <li><span rank="Genus" class="taxon-name rank-genus">Vibrio</span> species</li> <li> <span rank="Species" class="taxon-name rank-species">Vibrio alginolyticus</span> </li> </ul> </div> <div class="note"> <strong>Commensal/Parasitic Species</strong> <br /> <ul> <li><span rank="Species" class="taxon-name rank-species">Hysterothylacium aduncum</span> (Order <a class="taxon-link rank-order" href="/accounts/Ascaridida/">Ascaridida</a>, Phylum <a class="taxon-link rank-phylum" href="/accounts/Nematoda/">Nematoda</a>)</li> <li><span rank="Species" class="taxon-name rank-species">Adolescaria progastrica</span> (Order <a class="taxon-link rank-order" href="/accounts/Plagiorchiida/">Plagiorchiida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><a class="taxon-link rank-genus" href="/accounts/Derogenes/">Derogenes</a> sp. (Order <a class="taxon-link rank-order" href="/accounts/Plagiorchiida/">Plagiorchiida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><a class="taxon-link rank-species" href="/accounts/Derogenes_varicus/">Derogenes varicus</a> (Order <a class="taxon-link rank-order" href="/accounts/Plagiorchiida/">Plagiorchiida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><a class="taxon-link rank-family" href="/accounts/Didymozoidae/">Didymozoidae</a> (Order <a class="taxon-link rank-order" href="/accounts/Plagiorchiida/">Plagiorchiida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><a class="taxon-link rank-species" href="/accounts/Ectenurus_virgulus/">Ectenurus virgulus</a> (Order <a class="taxon-link rank-order" href="/accounts/Plagiorchiida/">Plagiorchiida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><a class="taxon-link rank-species" href="/accounts/Hemiurus_levinseni/">Hemiurus levinseni</a> (Order <a class="taxon-link rank-order" href="/accounts/Plagiorchiida/">Plagiorchiida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><span rank="Species" class="taxon-name rank-species">Lepocreadiid metacercariae</span> (Order <a class="taxon-link rank-order" href="/accounts/Plagiorchiida/">Plagiorchiida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><a class="taxon-link rank-species" href="/accounts/Monascus_filiformis/">Monascus filiformis</a> (Order <a class="taxon-link rank-order" href="/accounts/Plagiorchiida/">Plagiorchiida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><a class="taxon-link rank-species" href="/accounts/Parahemiurus_merus/">Parahemiurus merus</a> (Order <a class="taxon-link rank-order" href="/accounts/Plagiorchiida/">Plagiorchiida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><a class="taxon-link rank-order" href="/accounts/Tetraphyllidea/">Tetraphyllidea</a> sp. (Class <a class="taxon-link rank-class" href="/accounts/Cestoda/">Cestoda</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Platyhelminthes/">Platyhelminthes</a>)</li> <li><span rank="Species" class="taxon-name rank-species">Microsetella norwegica</span> (Order <a class="taxon-link rank-order" href="/accounts/Harpacticoida/">Harpacticoida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Arthropoda/">Arthropoda</a>)</li> <li><a class="taxon-link rank-species" href="/accounts/Corycaeus_amazonicus/">Corycaeus amazonicus</a> (Order <a class="taxon-link rank-order" href="/accounts/Poecilostomatoida/">Poecilostomatoida</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Arthropoda/">Arthropoda</a>)</li> <li><span rank="Species" class="taxon-name rank-species">Oodinium jordani</span> (Order <span class="taxon-name">Blastodinida</span>, Phylum <span class="taxon-name">Myzozoa</span>)</li> </ul> </div> </section> <section class="hyphenate"> <h3 id="economic_importance_positive">Economic Importance for Humans: Positive</h3> <p audience="advanced intermediate">Chaetognaths are important to humans not only in terms of scientific research possibilities, but also as prey items for a variety of fish eaten by humans. <span class="citations"> (<a href="#AC9F6A9C-9AE7-11E2-AD9C-002500F14F28" class="citation">Shapiro, 2012</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Positive Impacts</li> <li> <span>research and education</span> </li> </ul> </section> <section class="hyphenate"> <h3 id="economic_importance_negative">Economic Importance for Humans: Negative</h3> <p audience="advanced intermediate">Chaetognaths may negatively impact humans if they pass along parasites to fishes eaten by humans. <span class="citations"> (<a href="#AC9F6A9C-9AE7-11E2-AD9C-002500F14F28" class="citation">Shapiro, 2012</a>)</span></p> </section> <section class="hyphenate"> <h3 id="conservation_status">Conservation Status</h3> <p audience="advanced intermediate">Neither this phylum, nor its constituent species is considered at risk of becoming threatened or endangered. <span class="citations"> (<a href="#AC9F6A9C-9AE7-11E2-AD9C-002500F14F28" class="citation">Shapiro, 2012</a>)</span></p> <ul class="aside block-grid donthyphenate one-up"> <li> <dl> <dt>IUCN Red List <a href="http://www.iucnredlist.org/">[Link]</a></dt> <dd>Not Evaluated</dd> </dl> </li> </ul> </section> <section class="hyphenate"> <h3 id="comments">Other Comments</h3> <p audience="advanced intermediate">In spite of being soft-bodied, chaetognaths are known in the fossil record, dating back to the early Cambrian Period. <span class="citations"> (<a href="#422B673A-6F4A-11E3-AD78-002500F14F28" class="citation">Chen and Huang, 2002</a>; <a href="#A0930EFA-6F49-11E3-8C46-002500F14F28" class="citation">Szaniawski, 2005</a>; <a href="#CFEAA57A-6F49-11E3-B927-002500F14F28" class="citation">Vannier, et al., 2007</a>)</span></p> </section> <section class="hyphenate"> <h3 id="contributors">Contributors</h3> <p>Jeremy Wright (author), University of Michigan-Ann Arbor, Leila Siciliano Martina (editor), Animal Diversity Web Staff. </p> </section> <section class="offscreen"> <h3 id="glossary">Glossary</h3> <div id="20020916135918"> <dl> <dt>Antarctica</dt> <dd> <p>lives on Antarctica, the southernmost continent which sits astride the southern pole.</p> </dd> </dl> </div> <div id="20020917113601"> <dl> <dt>Arctic Ocean</dt> <dd> <p>the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.</p> </dd> </dl> </div> <div id="20020917114102"> <dl> <dt>Atlantic Ocean</dt> <dd> <p>the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.</p> <p align="center"> <img alt="World Map" src="/images/worldmap.2001.jpg" /> </p> </dd> </dl> </div> <div id="20020916135737"> <dl> <dt>Australian</dt> <dd> <p>Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.</p> <p align="center"> <img alt="World Map" src="/images/worldmap.2001.jpg" /> </p> </dd> </dl> </div> <div id="20020916134510"> <dl> <dt>Ethiopian</dt> <dd> <p>living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.</p> <p align="center"> <img alt="World Map" src="/images/worldmap.2001.jpg" /> </p> </dd> </dl> </div> <div id="20020914235803"> <dl> <dt>Nearctic</dt> <dd> <p>living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.</p> <p align="center"> <img alt="World Map" src="/images/worldmap.2001.jpg" /> </p> </dd> </dl> </div> <div id="20020915000403"> <dl> <dt>Neotropical</dt> <dd> <p>living in the southern part of the New World. In other words, Central and South America.</p> <p align="center"> <img alt="World Map" src="/images/worldmap.2001.jpg" /> </p> </dd> </dl> </div> <div id="20020917114731"> <dl> <dt>Pacific Ocean</dt> <dd> <p>body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.</p> <p align="center"> <img alt="World Map" src="/images/worldmap.2001.jpg" /> </p> </dd> </dl> </div> <div id="20020915001330"> <dl> <dt>Palearctic</dt> <dd> <p>living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.</p> <p align="center"> <img alt="World Map" src="/images/worldmap.2001.jpg" /> </p> </dd> </dl> </div> <div id="20020904145323"> <dl> <dt>abyssal</dt> <dd> <p>on or near the ocean floor in the deep ocean. Abyssal regions are characterized by complete lack of light, extremely high water pressure, low nutrient availability, and continuous cold (3 degrees C).</p> </dd> </dl> </div> <div id="20020904145431"> <dl> <dt>benthic</dt> <dd> <p>Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.</p> </dd> </dl> </div> <div id="20020904145642"> <dl> <dt>bilateral symmetry</dt> <dd> <p>having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.</p> </dd> </dl> </div> <div id="20020904145435"> <dl> <dt>brackish water</dt> <dd> <p>areas with salty water, usually in coastal marshes and estuaries.</p> </dd> </dl> </div> <div id="20020904145419"> <dl> <dt>carnivore</dt> <dd> <p>an animal that mainly eats meat</p> </dd> </dl> </div> <div id="20020904145606"> <dl> <dt>chemical</dt> <dd> <p>uses smells or other chemicals to communicate</p> </dd> </dl> </div> <div id="20020904145825"> <dl> <dt>coastal</dt> <dd> <p>the nearshore aquatic habitats near a coast, or shoreline.</p> </dd> </dl> </div> <div id="20020904145620"> <dl> <dt>cosmopolitan</dt> <dd> <p>having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.</p> </dd> </dl> </div> <div id="20020904145752"> <dl> <dt>crepuscular</dt> <dd> <p>active at dawn and dusk</p> </dd> </dl> </div> <div id="20020904145414"> <dl> <dt>diurnal</dt> <dd> <ol class="arabic simple"> <li>active during the day, 2. lasting for one day.</li> </ol> </dd> </dl> </div> <div id="20020916131519"> <dl> <dt>ectothermic</dt> <dd> <p>animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature</p> </dd> </dl> </div> <div id="20020904145350"> <dl> <dt>estuarine</dt> <dd> <p>an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.</p> </dd> </dl> </div> <div id="20020904145746"> <dl> <dt>female parental care</dt> <dd> <p>parental care is carried out by females</p> </dd> </dl> </div> <div id="20020904145546"> <dl> <dt>fertilization</dt> <dd> <p>union of egg and spermatozoan</p> </dd> </dl> </div> <div id="20020916125902"> <dl> <dt>heterothermic</dt> <dd> <p>having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.</p> </dd> </dl> </div> <div id="200304045530"> <dl> <dt>holarctic</dt> <dd> <p>a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.</p> <p align="center"> <img alt="World Map" src="/images/worldmap.2001.jpg" /> </p> <p>Found in northern North America and northern Europe or Asia.</p> </dd> </dl> </div> <div id="20020904145427"> <dl> <dt>internal fertilization</dt> <dd> <p>fertilization takes place within the female's body</p> </dd> </dl> </div> <div id="20020904145554"> <dl> <dt>iteroparous</dt> <dd> <p>offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).</p> </dd> </dl> </div> <div id="20020904145472"> <dl> <dt>motile</dt> <dd> <p>having the capacity to move from one place to another.</p> </dd> </dl> </div> <div id="20020914213156"> <dl> <dt>natatorial</dt> <dd> <p>specialized for swimming</p> </dd> </dl> </div> <div id="20020904145365"> <dl> <dt>native range</dt> <dd> <p>the area in which the animal is naturally found, the region in which it is endemic.</p> </dd> </dl> </div> <div id="20020904145503"> <dl> <dt>nocturnal</dt> <dd> <p>active during the night</p> </dd> </dl> </div> <div id="20020915001348"> <dl> <dt>oriental</dt> <dd> <p>found in the oriental region of the world. In other words, India and southeast Asia.</p> <p align="center"> <img alt="World Map" src="/images/worldmap.2001.jpg" /> </p> </dd> </dl> </div> <div id="20020904145572"> <dl> <dt>oviparous</dt> <dd> <p>reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.</p> </dd> </dl> </div> <div id="20020904145836"> <dl> <dt>pelagic</dt> <dd> <p>An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).</p> </dd> </dl> </div> <div id="20020904145612"> <dl> <dt>photic/bioluminescent</dt> <dd> <p>generates and uses light to communicate</p> </dd> </dl> </div> <div id="20020904145838"> <dl> <dt>piscivore</dt> <dd> <p>an animal that mainly eats fish</p> </dd> </dl> </div> <div id="20020904145368"> <dl> <dt>planktivore</dt> <dd> <p>an animal that mainly eats plankton</p> </dd> </dl> </div> <div id="20020904145371"> <dl> <dt>polar</dt> <dd> <p>the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.</p> </dd> </dl> </div> <div id="20020904145483"> <dl> <dt>polygynandrous</dt> <dd> <p>the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.</p> </dd> </dl> </div> <div id="20020904145675"> <dl> <dt>reef</dt> <dd> <p>structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.</p> </dd> </dl> </div> <div id="20020904145582"> <dl> <dt>saltwater or marine</dt> <dd> <p>mainly lives in oceans, seas, or other bodies of salt water.</p> </dd> </dl> </div> <div id="20020904145584"> <dl> <dt>seasonal breeding</dt> <dd> <p>breeding is confined to a particular season</p> </dd> </dl> </div> <div id="20020904145585"> <dl> <dt>sedentary</dt> <dd> <p>remains in the same area</p> </dd> </dl> </div> <div id="20020904145786"> <dl> <dt>sexual</dt> <dd> <p>reproduction that includes combining the genetic contribution of two individuals, a male and a female</p> </dd> </dl> </div> <div id="20020904145381"> <dl> <dt>solitary</dt> <dd> <p>lives alone</p> </dd> </dl> </div> <div id="20020904145500"> <dl> <dt>tactile</dt> <dd> <p>uses touch to communicate</p> </dd> </dl> </div> <div id="20020904145595"> <dl> <dt>temperate</dt> <dd> <p>that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).</p> </dd> </dl> </div> <div id="20020904145598"> <dl> <dt>tropical</dt> <dd> <p>the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.</p> </dd> </dl> </div> <div id="20020904145397"> <dl> <dt>venomous</dt> <dd> <p>an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).</p> </dd> </dl> </div> <div id="20020904145852"> <dl> <dt>vibrations</dt> <dd> <p>movements of a hard surface that are produced by animals as signals to others</p> </dd> </dl> </div> <div id="20020904145694"> <dl> <dt>visual</dt> <dd> <p>uses sight to communicate</p> </dd> </dl> </div> </section> <section class="hyphenate"> <h3 id="references">References</h3> <p id="5ECFF7E3-9AF3-11E2-8B77-002500F14F28">2002. 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Accessed April 02, 2013 at <tt><a href="http://www.jstor.org/stable/1541587">http://www.jstor.org/stable/1541587</a></tt>. </p> <p id="DB5B9D38-9AE7-11E2-AD99-002500F14F28">Thuesen, E. 2009. "<span class="taxon-link rank-unspecified">Chaetognatha</span>" (On-line). Accessed April 01, 2013 at <tt><a href="http://academic.evergreen.edu/t/thuesene/chaetognaths/chaetognaths.htm">http://academic.evergreen.edu/t/thuesene/chaetognaths/chaetognaths.htm</a></tt>. </p> <p id="CFEAA57A-6F49-11E3-B927-002500F14F28">Vannier, J., M. Steiner, E. Renvoise, S. Hu, J. Casanova. 2007. Early Cambrian origin of modern food webs: evidence from predator arrow worms. <span style="font-style: italic">Proceedings of the Royal society B: Biological Science</span>, 274: 627-633. </p> <p id="18471078-6F4B-11E3-A5F7-002500F14F28">Zhang, Z. 2011. Animal biodiversity: An introduction to higher-level classification and taxonomic richness. <span style="font-style: italic">Zootaxa</span>, 3148: 7-12. </p> <p id="B302A980-9AF1-11E2-A5C0-002500F14F28">Zo, Z. 1973. Breeding and growth of the chaetognath <a class="taxon-link rank-species" href="/accounts/Parasagitta_elegans/">Parasagitta elegans</a> in Bedford Basin. <span style="font-style: italic">Limnology and Oceanography</span>, 18/5: 750-756. Accessed April 01, 2013 at <tt><a href="http://www.aslo.org/lo/toc/vol_18/issue_5/0750.pdf">http://www.aslo.org/lo/toc/vol_18/issue_5/0750.pdf</a></tt>. </p> <p id="189FF5DC-9BAA-11E2-8CA8-002500F14F28">Øresland, V. 1986. Parasites of the chaetognath <span rank="Species" class="taxon-name rank-species">Sagitta setosa</span> in the western English Channel. <span style="font-style: italic">Marine Biology</span>, 92/1: 87-91. Accessed April 02, 2013 at <tt><a href="http://link.springer.com/article/10.1007/BF00392750?LI=true">http://link.springer.com/article/10.1007/BF00392750?LI=true</a></tt>. </p> </section> </div> </div> <div class="span2_5 right sidebar"> <div class="well" id="pocket-guide-link"> <a href="https://itunes.apple.com/us/app/adw-pocket-guide/id916179421?mt=8" target="_blank"><i class="icon-download icon-white" style="vertical-align: bottom"></i> ADW Pocket Guides on the iOS App Store! </a> <p>The Animal Diversity Web team is excited to announce ADW Pocket Guides!</p> <p> <a href="/news/5009059054038197651/">Read more...</a> </p> </div> <h2 class="offscreen">Search</h2> <div id="site-search"> <form action="/search" method="GET"> <label for="q" class="offscreen">Enter search text</label> <input value="" id="q" name="q" class="span12" size="15" type="text" placeholder="Search ADW" /> <button class="btn"> <i class="icon-zoom-in"></i> <span class="offscreen">Search</span> </button> <p style="max-height: 35px"> <label for="feature-list" class="offscreen">Search in feature</label> <select size="1" name="feature" class="feature-list input-medium" id="feature-list"> <option value="INFORMATION">Taxon Information</option> <option value="COLLECTIONS">Contributor Galleries</option> <option value="TOPICS">Topics</option> <option value="CLASSIFICATION">Classification</option> </select> </p> </form> <ul class="unstyled"> <li> <a href="https://animaldiversity.ummz.umich.edu/quaardvark/">Explore Data @ Quaardvark</a> </li> <li> <a href="/search_guide/">Search Guide</a> </li> </ul> </div> <h2 class="offscreen">Navigation Links</h2> <dl class="tabbed features"> <dd class="feature-information active"> <a name="feature-information" href="/accounts/Chaetognatha/" class="active" id="feature-information"> Information </a> </dd> <dd class="feature-pictures"> <a name="feature-pictures" href="/accounts/Chaetognatha/pictures/" id="feature-pictures"> Pictures </a> </dd> <dd class="feature-classification"> <a name="feature-classification" href="/accounts/Chaetognatha/classification/#Chaetognatha" id="feature-classification"> Classification </a> </dd> </dl> <div class="classification well"> <h3>Classification</h3> <ul class="unstyled"> <li> <span class="rank">Kingdom</span> <a href="/accounts/Animalia/" class="taxon-name rank-kingdom">Animalia</a> <span class="vernacular-name">animals</span> <div class="features"> <a href="/accounts/Animalia/" class="feature feature-information" rel="tooltip" data-original-title="Animalia: information (1)" data-delay="250" data-total="4749">Animalia: information (1)</a> <a href="/accounts/Animalia/pictures/" class="feature feature-pictures" rel="tooltip" data-original-title="Animalia: pictures (22861)" data-delay="250">Animalia: pictures (22861)</a> <a href="/accounts/Animalia/specimens/" class="feature feature-specimens" rel="tooltip" data-original-title="Animalia: specimens (7109)" data-delay="250">Animalia: specimens (7109)</a> <a href="/accounts/Animalia/sounds/" class="feature feature-sounds" rel="tooltip" data-original-title="Animalia: sounds (722)" data-delay="250">Animalia: sounds (722)</a> <a href="/accounts/Animalia/maps/" class="feature feature-maps" rel="tooltip" data-original-title="Animalia: maps (42)" data-delay="250">Animalia: maps (42)</a> </div> </li> <li class="active"> <span class="rank">Unspecified</span> <a href="/accounts/Chaetognatha/" class="taxon-name rank-unspecified">Chaetognatha</a> <span class="vernacular-name">arrow worms</span> <div class="features"> <a href="/accounts/Chaetognatha/" class="feature feature-information" rel="tooltip" data-original-title="Chaetognatha: information (1)" data-delay="250" data-total="1">Chaetognatha: information (1)</a> <a href="/accounts/Chaetognatha/pictures/" class="feature feature-pictures" rel="tooltip" data-original-title="Chaetognatha: pictures (7)" data-delay="250">Chaetognatha: pictures (7)</a> <span class="feature-off feature-specimens"></span> <span class="feature-off feature-sounds"></span> <span class="feature-off feature-maps"></span> </div> </li> </ul> </div> </div> </div> </div> </div> <div id="footer" aria-role="contentinfo"> <div class="inner-footer"> <div class="page-citation"> <p class="content">To cite this page: Wright, J. 2014. "Chaetognatha" (On-line), Animal Diversity Web. Accessed February 16, 2025 at https://animaldiversity.org/accounts/Chaetognatha/</p> </div> <div class="disclaimer"> <p class="content"><strong>Disclaimer:</strong> The Animal Diversity Web is an educational resource <strong>written largely by and for college students</strong>. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control. </p> </div> <div class="footer-links"> <ul class="unstyled"> <li><a href="https://www.umich.edu/">U-M Gateway</a> | <a href="https://lsa.umich.edu/ummz/">U-M Museum of Zoology</a></li> <li> <a href="https://lsa.umich.edu/eeb/">U-M Ecology and Evolutionary Biology</a> </li> <li> © 2020 Regents of the University of Michigan </li> <li><a href="/feedback/error_form/">Report Error</a> / <a href="/feedback/comment_form/">Comment</a></li> </ul> </div> <div class="thanks-links"> <p>This material is based upon work supported by the <a href="https://nsf.gov">National Science Foundation</a> Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. 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ADW: Chaetognatha: INFORMATION