ADW: Placozoa: INFORMATION

<!DOCTYPE html> <html xmlns:og="http://ogp.me/ns#" lang="en" xml:lang="en"> <head> <title>ADW: Placozoa: INFORMATION</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <link rel="canonical" href="https://animaldiversity.org/accounts/Placozoa/" /> <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/Placozoa/" /> <meta content="Placozoa (flat animals)" 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/Placozoa/Trichoplax_adhaerens/medium.jpg" property="og:image" /> <meta name="twitter:card" content="summary" /> <meta name="twitter:site" content="@AnimalDiversity" /> <meta name="twitter:title" content="Placozoa (flat animals)" /> <meta name="twitter:description" content="Read about Placozoa (flat animals) on the Animal Diversity Web." /> <meta name="twitter:image:src" content="https://animaldiversity.org/collections/contributors/Grzimek_inverts/Placozoa/Trichoplax_adhaerens/medium.jpg" /> <meta name="twitter:image:height" content="480" /> <meta name="twitter:image:width" content="555" /> <meta name="twitter:url" content="https://animaldiversity.org/accounts/Placozoa/" /> <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=Placozoa&search=Go">Encyclopedia of Life</a> </li> </ul> </div> </div> <div class="span7_5 blahblahblah main" aria-role="main"> <h2 class="rank-unspecified">Placozoa<span class="vernacular-name">flat animals</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/Placozoa/pictures/collections/contributors/Grzimek_inverts/Placozoa/Trichoplax_adhaerens/"> <img alt=" " src="/collections/contributors/Grzimek_inverts/Placozoa/Trichoplax_adhaerens/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> </ul> <ul> <li> <a href="#reproduction">Reproduction</a> </li> <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> </ul> <ul> <li> <a href="#ecosystem_roles">Ecosystem Roles</a> </li> <li> <a href="#economic_importance_positive">Economic Importance for Humans: Positive</a> </li> <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="#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">Phylum <span class="taxon-link rank-unspecified">Placozoa</span> contains just two species of very small (2 to 3 mm in diameter and only 15 to 20 µm in width), simply organized, non-bilaterian metazoan organisms that superficially resemble amoebas. <span rank="Species" class="taxon-name rank-species">Treptoplax reptans</span> has not been seen since it was first described from the waters of Naples, Italy in 1896, but <a class="taxon-link rank-species" href="/accounts/Trichoplax_adhaerens/">Trichoplax adhaerens</a>, first discovered on the walls of a marine aquarium in Australia in 1883, is found in tropical and subtropical marine waters around the world. These organisms are composed of differentiated dorsal and ventral epithelial cell layers, which enclose a mesenchymal syncytial net. Placozoans move via gliding, aided by the ciliated cells of the basal epithelial layer, and feed by engulfing particles of organic detritus. They are able to reproduce asexually via fission, but are also known to reproduce sexually. <span class="citations"> (<a href="#0543ABBD-A131-11E2-8333-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#117720D9-7248-11E3-859F-002500F14F28" class="citation">Martinelli and Spring, 2003</a>; <a href="#E86F1AD9-7247-11E3-A7D6-002500F14F28" class="citation">Minot, 1883</a>; <a href="#505B872B-7249-11E3-A56D-002500F14F28" class="citation">Monticelli, 1893</a>; <a href="#5A648DE1-A132-11E2-B7BB-002500F14F28" class="citation">Pearse and Voigt, 2007</a>; <a href="#A3028D1E-A131-11E2-8A36-002500F14F28" class="citation">Schierwater, et al., 2011</a>; <a href="#AE8196F5-7247-11E3-B28D-002500F14F28" class="citation">Schulze, 1883</a>)</span></p> </section> <section class="hyphenate"> <h3 id="geographic_range">Geographic Range</h3> <p audience="advanced intermediate">Placozoans are found globally in tropical and subtropical marine waters. <span class="citations"> (<a href="#5A648DE1-A132-11E2-B7BB-002500F14F28" class="citation">Pearse and Voigt, 2007</a>; <a href="#A3028D1E-A131-11E2-8A36-002500F14F28" class="citation">Schierwater, et al., 2011</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> <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> </ul> </section> <section class="hyphenate"> <h3 id="habitat">Habitat</h3> <p audience="advanced intermediate">Placozoans were first identified from the walls of a marine aquarium. While they are considered benthic organisms, they are also found in the water column. They are most commonly found near shore, in the littoral zone, in warm waters. <span class="citations"> (<a href="#5A648DE1-A132-11E2-B7BB-002500F14F28" class="citation">Pearse and Voigt, 2007</a>; <a href="#11AB182B-A133-11E2-A0A0-002500F14F28" class="citation">Voigt, et al., 2004</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="#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> <a class="gloss" href="#20020904145825">coastal</a> </li> </ul> <ul class="keywords donthyphenate last"> <li class="keywords-header">Other Habitat Features</li> <li> <a class="gloss" href="#20020904145633">intertidal or littoral</a> </li> </ul> </section> <section class="hyphenate"> <h3 id="taxonomic_history">Systematic and Taxonomic History</h3> <p audience="advanced intermediate"><a class="taxon-link rank-species" href="/accounts/Trichoplax_adhaerens/">Trichoplax adhaerens</a> was first described by the German zoologist Franz Eilhard Schulze in 1883, with an English-language report of his findings published in the United States in the same year by Charles S. Minot. <span rank="Species" class="taxon-name rank-species">Treptoplax reptans</span>, the only other named member of phylum <span class="taxon-link rank-unspecified">Placozoa</span>, was described by the Italian biologist Francesco Monticelli in 1893. However, this species has not been observed since, and many question whether it ever existed as a valid taxon. <span class="citations"> (<a href="#1D11D3A3-724F-11E3-A4F8-002500F14F28" class="citation">Eitel, et al., 2013</a>; <a href="#117720D9-7248-11E3-859F-002500F14F28" class="citation">Martinelli and Spring, 2003</a>; <a href="#F42C3C94-A131-11E2-853C-002500F14F28" class="citation">Miller and Ball, 2005</a>; <a href="#E86F1AD9-7247-11E3-A7D6-002500F14F28" class="citation">Minot, 1883</a>; <a href="#505B872B-7249-11E3-A56D-002500F14F28" class="citation">Monticelli, 1893</a>; <a href="#AE8196F5-7247-11E3-B28D-002500F14F28" class="citation">Schulze, 1883</a>)</span></p> <p audience="advanced intermediate">At its first discovery, it was obvious to many scientists that <a class="taxon-link rank-species" href="/accounts/Trichoplax_adhaerens/">Trichoplax adhaerens</a> presents significant differences from other known groups of organisms. However, a report classified it as the larval form of the cnidarian species <span rank="Species" class="taxon-name rank-species">Eleutheria krohi</span>, which became the accepted hypothesis for the next several decades. In the 1970s, scientists, particularly the German protozoologist Karl Gottlieb Grell, renewed examinations of this species and demonstrated that the individuals examined were, in fact, adults. <a class="taxon-link rank-species" href="/accounts/Trichoplax_adhaerens/">Trichoplax adhaerens</a> has since been widely accepted as the sole representative of the phylum <span class="taxon-link rank-unspecified">Placozoa</span>, a name coined by Grell in 1971. Several recent morphological and molecular phylogenetic analyses have indicated that many additional species likely exist within this phylum, including several higher order taxonomic groups. To date, however, none of these have been formally described or named. <span class="citations"> (<a href="#0543ABBD-A131-11E2-8333-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#1D11D3A3-724F-11E3-A4F8-002500F14F28" class="citation">Eitel, et al., 2013</a>; <a href="#B59F27C5-724C-11E3-9D78-002500F14F28" class="citation">Grell, 1971a</a>; <a href="#C7F3920C-724E-11E3-8432-002500F14F28" class="citation">Grell, 1971b</a>; <a href="#2617F551-7250-11E3-876B-002500F14F28" class="citation">Guidi, et al., 2011</a>; <a href="#7538C730-724E-11E3-9575-002500F14F28" class="citation">Krumbach, 1907</a>; <a href="#713E8E61-7253-11E3-9959-002500F14F28" class="citation">Lecointre and Le Guyader, 2006</a>; <a href="#117720D9-7248-11E3-859F-002500F14F28" class="citation">Martinelli and Spring, 2003</a>; <a href="#E3021C1C-724E-11E3-9FE4-002500F14F28" class="citation">Miller, 1971</a>; <a href="#9418A619-724F-11E3-BB63-002500F14F28" class="citation">Signorovitch, et al., 2006</a>; <a href="#EA360878-A133-11E2-AABE-002500F14F28" class="citation">Syed and Schierwater, 2002</a>; <a href="#11AB182B-A133-11E2-A0A0-002500F14F28" class="citation">Voigt, et al., 2004</a>)</span></p> <p audience="advanced intermediate">Our understanding of the relationships of placozoans to other animal phyla remains in a state of flux. Early molecular phylogenetic analyses generally recovered them as the sister group to <a class="taxon-link" href="/accounts/Cnidaria/">cnidarians</a> or <a class="taxon-link" href="/accounts/Ctenophora/">ctenophores</a>. Subsequent studies, using much higher numbers of independent genetic markers, indicated that they occupy a basal position within metazoans as the sister group to the <span class="taxon-name">Eumetozoa</span>, being placed between sponges (phylum <a class="taxon-link rank-unspecified" href="/accounts/Porifera/">Porifera</a>) and all other multicellular animals. In contrast, results from analyses of mitochondrial genomes and total evidence approaches suggested that animals form two clades based on the organization of their tissues, with <span class="taxon-link rank-unspecified">Placozoa</span> representing the basal lineage in the dibloblast clade, which also includes sponges, cnidarians, and ctenophores. However, the most recent molecular phylogenetic analyses indicate that there is no strong support for any of these hypotheses, leaving the true phylogenetic position of placozoans as a matter of intense, widespread scientific interest and debate. <span class="citations"> (<a href="#E9670AB5-725A-11E3-A723-002500F14F28" class="citation">DeSalle and Schierwater, 2008</a>; <a href="#1D11D3A3-724F-11E3-A4F8-002500F14F28" class="citation">Eitel, et al., 2013</a>; <a href="#955FB4B5-7257-11E3-937B-002500F14F28" class="citation">Osigus, et al., 2013</a>; <a href="#EF48CB85-7257-11E3-B7F4-002500F14F28" class="citation">Phillipe, et al., 2011</a>; <a href="#1778C87D-725B-11E3-9017-002500F14F28" class="citation">Schierwater, et al., 2009a</a>; <a href="#A4220638-725B-11E3-AB92-002500F14F28" class="citation">Schierwater, et al., 2009b</a>; <a href="#9A538026-7258-11E3-AF57-002500F14F28" class="citation">Schierwater, et al., 2010</a>; <a href="#56CC72D7-7258-11E3-BE4A-002500F14F28" class="citation">Siddall, 2010</a>; <a href="#2E068A51-7259-11E3-8D6A-002500F14F28" class="citation">Srivastava, et al., 2008</a>; <a href="#00E10A26-725A-11E3-B4A0-002500F14F28" class="citation">Srivastava, et al., 2010</a>)</span></p> <ul class="aside block-grid donthyphenate two-up"> <li> <dl> <dt>Synonyms</dt> <dd> <ul> <li><span rank="Species" class="taxon-name rank-species">Eleutheria krohi</span> (Krumbach, 1907)</li> </ul> </dd> </dl> </li> <li> <dl> <dt>Synapomorphies</dt> <dd> <ul> <li>Placozoans have two cell layers delimiting a space containing nucleated mesenchyme cells in an extracellular matrix.</li> <li>These organisms have external digestion via temporary formation of a digestive chamber on the ventral surface.</li> </ul> </dd> </dl> </li> </ul> </section> <section class="hyphenate"> <h3 id="physical_description">Physical Description</h3> <p audience="advanced intermediate">Placozoans are very small animals, measuring just 2 to 3 mm in diameter and typically 15 to 20 µm thick. They have traditionally been described as being composed only four types of cells: cover (squamous), columnar, glandular, and fiber. They are asymmetrical (although smaller animals tend to be circular), and their bodies lack anterior or posterior ends. They do, however, have distinct ventral and dorsal sides, and are essentially made up of three layers: dorsal epithelia, mesenchyme, and ventral epithelia. Dorsal epithelial cells are cover, or squamous, cells; they are flattened, contain lipid droplets, and each has a single cilia. Ventral epithelial cells are more columnar, lack lipid droplets, but are also mainly monociliate. The ventral layer also has unciliated glandular cells. Between these two layers, forming the interior of the animal, is a layer of mesenchyme, composed of star-shaped fiber cells. The points of the “stars” are connected, creating a network. There appears to be no basement membrane between the epithelial layers and mesenchyme. <span class="citations"> (<a href="#0543ABBD-A131-11E2-8333-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#117720D9-7248-11E3-859F-002500F14F28" class="citation">Martinelli and Spring, 2003</a>; <a href="#F42C3C94-A131-11E2-853C-002500F14F28" class="citation">Miller and Ball, 2005</a>; <a href="#5A648DE1-A132-11E2-B7BB-002500F14F28" class="citation">Pearse and Voigt, 2007</a>)</span></p> <p audience="advanced intermediate">In situ hybridization studies of gene expression in the cells of <a class="taxon-link rank-species" href="/accounts/Trichoplax_adhaerens/">Trichoplax adhaerens</a> have indicated that this organism likely possesses more than just four cell types. Though the newly identified cell types are morphologically indistinguishable, differential gene expression patterns between them and previously characterized cell types strongly suggest that they possess unique, albeit currently unknown, functions. <span class="citations"> (<a href="#117720D9-7248-11E3-859F-002500F14F28" class="citation">Martinelli and Spring, 2003</a>; <a href="#F42C3C94-A131-11E2-853C-002500F14F28" class="citation">Miller and Ball, 2005</a>)</span></p> <ul class="keywords donthyphenate "> <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> </ul> <ul class="keywords donthyphenate last"> <li class="keywords-header">Sexual Dimorphism</li> <li> <span>sexes alike</span> </li> </ul> </section> <section class="hyphenate"> <h3 id="development">Development</h3> <p audience="advanced intermediate">New animals may be produced via binary fission or budding. Budding creates multicellular flagellated “swarmers,” each of which becomes a new individual. Sexual reproduction may occur, in which case holoblastic cell division proceeds following fertilization. At the 64 cell stage, cell division ceases, while nuclear DNA multiplication continues until the nucleus bursts. <span class="citations"> (<a href="#0543ABBD-A131-11E2-8333-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#3F6E2417-A131-11E2-9129-002500F14F28" class="citation">Collins, 2000</a>; <a href="#F42C3C94-A131-11E2-853C-002500F14F28" class="citation">Miller and Ball, 2005</a>)</span></p> </section> <section class="hyphenate"> <h3 id="reproduction">Reproduction</h3> <p audience="advanced intermediate">Reproduction in placozoans is mainly asexual. Sexual reproduction may be observed during times of high population density, high water temperature (23°C and greater), and food depletion. Sexual reproduction occurs only through degeneration of the mother. A single egg/oocyte as well as small, unflagellated cells (assumed to be sperm) develops in the interspace of a degenerating placozoan. <span class="citations"> (<a href="#0543ABBD-A131-11E2-8333-002500F14F28" class="citation">Brusca and Brusca, 2003</a>; <a href="#3F6E2417-A131-11E2-9129-002500F14F28" class="citation">Collins, 2000</a>; <a href="#B04E1745-A132-11E2-A829-002500F14F28" class="citation">Eitel, et al., 2011</a>; <a href="#F42C3C94-A131-11E2-853C-002500F14F28" class="citation">Miller and Ball, 2005</a>)</span></p> <p audience="advanced intermediate">Placozoans may reproduce asexually (via transverse fission or budding) or sexually. Sexual reproduction seems to be triggered by environmental factors including water temperature; this implies that, in some regions, animals may have both sexual and asexual phases that may be dependent on the season. <span class="citations"> (<a href="#B04E1745-A132-11E2-A829-002500F14F28" class="citation">Eitel, et al., 2011</a>; <a href="#5A648DE1-A132-11E2-B7BB-002500F14F28" class="citation">Pearse and Voigt, 2007</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Key Reproductive Features</li> <li> <a class="gloss" href="#20020904145584">seasonal breeding</a> </li> <li> <a class="gloss" href="#20020904145698">year-round breeding</a> </li> <li> <a class="gloss" href="#20020904145786">sexual</a> </li> <li> <a class="gloss" href="#20020904145314">asexual</a> </li> </ul> <p audience="advanced intermediate">Parental investment is not known to occur in placozoans. <span class="citations"> (<a href="#F42C3C94-A131-11E2-853C-002500F14F28" class="citation">Miller and Ball, 2005</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Parental Investment</li> <li> <span>no parental involvement</span> </li> </ul> </section> <section class="hyphenate"> <h3 id="lifespan_longevity">Lifespan/Longevity</h3> <p audience="advanced intermediate">While strains of <a class="taxon-link rank-species" href="/accounts/Trichoplax_adhaerens/">Trichoplax adhaerens</a> have been maintained in lab settings for many years, little data is available regarding their lifespans. <span class="citations"> (<a href="#B04E1745-A132-11E2-A829-002500F14F28" class="citation">Eitel, et al., 2011</a>)</span></p> </section> <section class="hyphenate"> <h3 id="behavior">Behavior</h3> <p audience="advanced intermediate">Placozoans move using ciliary action and changes in body shape; there is evidence that smaller (presumably younger) individuals may swim. <span class="citations"> (<a href="#0543ABBD-A131-11E2-8333-002500F14F28" class="citation">Brusca and Brusca, 2003</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Key Behaviors</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">Little is known regarding how placozoans may perceive their environments. In laboratory settings, they have been observed to react strongly when exposed to ultraviolet radiation. <span class="citations"> (<a href="#5A648DE1-A132-11E2-B7BB-002500F14F28" class="citation">Pearse and Voigt, 2007</a>)</span></p> <ul class="keywords donthyphenate last"> <li class="keywords-header">Perception Channels</li> <li> <span>ultraviolet</span> </li> </ul> </section> <section class="hyphenate"> <h3 id="food_habits">Food Habits</h3> <p audience="advanced intermediate">Placozoans feed by phagocytosis, using their ventral surfaces (some of the glandular cells located there produce digestive enzymes). In laboratory settings, they are known to feed on flagellated chromists (<span rank="Genus" class="taxon-name rank-genus">Cryptomonas</span> sp.) and chlorophytes (<span rank="Genus" class="taxon-name rank-genus">Chlorella</span> sp.), other algae, the nauplii of <a class="taxon-link rank-genus" href="/accounts/Artemia/">Artemia</a> species, and commercial fish food. It is suspected that they are opportunistic grazers, and they may feed on organic detritus as well. <span class="citations"> (<a href="#3F6E2417-A131-11E2-9129-002500F14F28" class="citation">Collins, 2000</a>; <a href="#F42C3C94-A131-11E2-853C-002500F14F28" class="citation">Miller and Ball, 2005</a>; <a href="#5A648DE1-A132-11E2-B7BB-002500F14F28" class="citation">Pearse and Voigt, 2007</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> <span>eats non-insect arthropods</span> </li> </ul> </li> <li> <a class="gloss" href="#20020904145426">herbivore</a> </li> </ul> </section> <section class="hyphenate"> <h3 id="predation">Predation</h3> <p audience="advanced intermediate">Potential predators have been observed reacting negatively to placozoans. In one instance, a snail was observed touching a placozoan with its tentacle, then recoiling; in another study, placozoans dropped onto the tentacles of hydroids caused paralysis. Structures known as "shiny spheres," present in the upper epithelium of placozoans may somehow serve as predator deterrents, though the mechanism by which they may do this is completely unknown. The only predators reported for placozoans are snails in genus <a class="taxon-link rank-genus" href="/accounts/Rhodope/">Rhodope</a> and a small <a class="taxon-link" href="/accounts/Nemertea/">nemertean</a> species. <span class="citations"> (<a href="#5A648DE1-A132-11E2-B7BB-002500F14F28" class="citation">Pearse and Voigt, 2007</a>)</span></p> <ul class="aside block-grid donthyphenate one-up"> <li> <dl> <dt>Known Predators</dt> <dd> <ul> <li><a class="taxon-link rank-genus" href="/accounts/Rhodope/">Rhodope</a> species (Class <a class="taxon-link rank-class" href="/accounts/Gastropoda/">Gastropoda</a>, Phylum <a class="taxon-link rank-unspecified" href="/accounts/Mollusca/">Mollusca</a>)</li> <li>ribbon worms (Phylum <a class="taxon-link rank-unspecified" href="/accounts/Nemertea/">Nemertea</a>)</li> </ul> </dd> </dl> </li> </ul> </section> <section class="hyphenate"> <h3 id="ecosystem_roles">Ecosystem Roles</h3> <p audience="advanced intermediate">Although they are <span class="taxon-name">ciliates</span>, <span class="taxon-name">nematodes</span>, and other small animals have been observed around or even on placozoans, they do not seem to elicit any response and no parasitic or commensal relationships are known. <span class="citations"> (<a href="#5A648DE1-A132-11E2-B7BB-002500F14F28" class="citation">Pearse and Voigt, 2007</a>)</span></p> </section> <section class="hyphenate"> <h3 id="economic_importance_positive">Economic Importance for Humans: Positive</h3> <p audience="advanced intermediate">Beyond potential scientific interest, there are no positive effects of placozoans on humans.</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">There are no known adverse affects of placozoans on humans.</p> </section> <section class="hyphenate"> <h3 id="conservation_status">Conservation Status</h3> <p audience="advanced intermediate">There is no concern of either known placozoan species becoming threatened or endangered at this time. <span class="citations"> (<a href="#CE64C6F3-7642-11E3-BCA0-002500F14F28" class="citation">IUCN, 2013</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="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="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="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="20020904145314"> <dl> <dt>asexual</dt> <dd> <p>reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents</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="20020904145419"> <dl> <dt>carnivore</dt> <dd> <p>an animal that mainly eats meat</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="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="20020904145426"> <dl> <dt>herbivore</dt> <dd> <p>An animal that eats mainly plants or parts of plants.</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="20020904145633"> <dl> <dt>intertidal or littoral</dt> <dd> <p>the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.</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="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="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="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="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="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="20020904145698"> <dl> <dt>year-round breeding</dt> <dd> <p>breeding takes place throughout the year</p> </dd> </dl> </div> </section> <section class="hyphenate"> <h3 id="references">References</h3> <p id="0543ABBD-A131-11E2-8333-002500F14F28">Brusca, R., G. 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Schierwater. 2004. <span class="taxon-link rank-unspecified">Placozoa</span> – no longer a phylum of one. <span style="font-style: italic">Current Biology</span>, 14/22: R944-R945. Accessed April 09, 2013 at <tt><a href="http://www.sciencedirect.com/science/article/pii/S0960982204008413">http://www.sciencedirect.com/science/article/pii/S0960982204008413</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/Placozoa/" class="active" id="feature-information"> Information </a> </dd> <dd class="feature-pictures"> <a name="feature-pictures" href="/accounts/Placozoa/pictures/" id="feature-pictures"> Pictures </a> </dd> <dd class="feature-classification"> <a name="feature-classification" href="/accounts/Placozoa/classification/#Placozoa" 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/Placozoa/" class="taxon-name rank-unspecified">Placozoa</a> <span class="vernacular-name">flat animals</span> <div class="features"> <a href="/accounts/Placozoa/" class="feature feature-information" rel="tooltip" data-original-title="Placozoa: information (1)" data-delay="250" data-total="1">Placozoa: information (1)</a> <a href="/accounts/Placozoa/pictures/" class="feature feature-pictures" rel="tooltip" data-original-title="Placozoa: pictures (1)" data-delay="250">Placozoa: pictures (1)</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. "Placozoa" (On-line), Animal Diversity Web. Accessed February 17, 2025 at https://animaldiversity.org/accounts/Placozoa/</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. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services. </p> <p> The ADW Team gratefully acknowledges their support. </p> </div> </div> </div> <script></script> </div> <script src="/static/js/jquery.colorbox.js"></script> <script src="/static/js/pica.information.js"></script> <script type="text/javascript"> var gaJsHost = (("https:" == document.location.protocol) ? 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ADW: Placozoa: INFORMATION