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Introduction to the Hemichordata The fossil record of one group of hemichordates, the graptolites, is very well known and is often used to correlate rocks. Hemichordates are distinguished by a tripartite (threefold) division of the body. The name "hemichordate" means "half chordate," and hemichordates share some (but not all) of the typical chordate characteristics. www.ucmp.berkeley.edu /chordata/hemichordata.html   (601 words)

urochordate   (Site not responding. Last check: 2007-10-22) Note that the tripartate coelom of hemichordates is considered homologous to the three pairs of echinoderm coeloms. Analyses of hemichordate phylogeny: Branches are drawn to scale (Kimura 2 parameter distances) to emphasize the potential for artifacts due to unequal rate effects. Hemichordate classes (bold) and families are indicated to the right. chuma.cas.usf.edu /~garey/deuterostome.html   (471 words)

hemichordate --  Britannica Concise Encyclopedia - The online encyclopedia you can trust! The adult hemichordate is distinguished by the division of its body and body cavities, or coeloms, into three basic parts: the proboscis, collar, and trunk. Many hemichordates have a larval stage in their life cycle; the larva is called a tornaria. The hemichordates have remained a general primitive group, at a low level of evolution, closely linked with the echinoderms (e.g., starfish, sea urchins) and sharing with them and the other protochordate groups a sessile (i.e., fixed to a surface) or semi-sessile ancestor, which was bilaterally symmetrical and had a tripartite body and coelom. www.britannica.com /ebc/article-9039959   (1019 words)

GSS Abstracts: Rychel   (Site not responding. Last check: 2007-10-22) Hemichordates are the sister group to echinoderms and may resemble the body plan of ancestral chordates. Of the five defining chordate characteristics, pharyngeal gills present in hemichordates and chordates are considered homologous based on Pax1/9 gene expression data. However, the developmental origin of gill slits in hemichordates is not well understood. octavia.zoology.washington.edu /gss/spring04/rychel.html   (192 words)

Peterson.abs First, in contrast to the two-dimensional sheets of cells found in "diploblasts", mesoderm allows for the dramatic increase in three-dimensional size found in bilaterians; second mesodermal patterning is an integral component of each phylum's unique body plan. We examined the expression pattern of Brachyury in conjuction with the formation of embryonic and adult mesoderm in the enteropneust hemichordate Ptychodera flava, and compared it with the embryonic and larval expression pattern in the sea urchin Stronglyocentrotus purpuratus. However, Brachyury is then expressed in the invaginating ectodermal vestibule and in the left and right hydrocoels, the homologoues of the hemichordate left and right mesocoels. www.mbl.edu /CASSLS/Peterson.abs.html   (407 words)

Codon reassignment and amino acid composition in hemichordate mitochondria -- Castresana et al. 95 (7): 3703 -- ... Codon reassignment and amino acid composition in hemichordate mitochondria -- Castresana et al. Codon reassignment and amino acid composition in hemichordate mitochondria in the ancestral lineages of hemichordates and chordates. www.pnas.org /cgi/content/full/95/7/3703   (3008 words)

Phylum Cycliophora Hemichordates are a group of benthic dwelling deposit feeding or filter-feeding animals that are unremarkable in most regards. Hemichordates have a stiff structure in the collar called a proboscis skeleton that they use to anchor the heart and muscles in the proboscis. But the hemichordate heart is a better token of modern love, no truer words were spoken. comenius.susqu.edu /bi/322/IZLecture37.htm   (927 words)

Center for Developmental Biology On the other hand, their nervous system is a neuroepithelial network in the epidermis, the most primitive level of organization among the bilateria and similar to that of the cnidarian and ctenophoran. Recent phylogeny suggests that among extant bilateria, deuterostome may best present a variety of plesiomorphic bilaterian characters and therefore, hemichordates occupy a unique phylogenetic position for understanding the link between the body plans of basal bilaterians, protostomes, deuterostomes and chordates. Fromour molecular examinations of developmental genes in the Hawaiian hemichordate, Ptychodera flava, new ideas about the relationships between gene expression patterns and body plans have been generated. www.cdb.riken.go.jp /seminar/ext_10034.html   (215 words)

The Hemichordates (Phylum Hemichordata) The Hemichordates, or Acorn Worms are a small phylum of generally small animals that were once considered to be a part of the Chordata. This is a modified proboscis and in many species it is short, it is these species that have given the Hemichordates their common name of 'Acorn Worms'. The fertilised egg develops into a 'tornaria' larvae and lives as part of the plankton (floating in the sea) for several weeks until it undergoes a metamorphosis into the 3 body sections that the adult possesses and sinks to the sea-floor. www.earthlife.net /inverts/hemichordata.html   (1348 words)

Zool Grad Faculty: T. Humphreys   (Site not responding. Last check: 2007-10-22) The receptors that recognize contact with non-self cells, the molecules of the signaling pathways that lead to activation of the immune response upon contact with foreign cells and the effector molecules are targets of these molecular studies. We are attempting to elucidate the transmutation in gene expression and activity as fundamentally new body plans and phyla evolve. Characterization of a hemichordate fork head/HNF-3 gene expression. www2.hawaii.edu /~zoology/graduate/faculty/humphreys.htm   (310 words)

graptolite.home3.3 Since 1999 I am involved in revision of the Volume V (Graptolithina), Treatise on Invertebrate Paleontology, as a co-leading author of chapters devoted to pterobranchs (with Susan Rigby, Amanda J. Chapman, and Peter N. Dilly) and non-dendroid sessile graptolites (with Adam Urbanek). The fossil remains of a hemichordate exoskeleton, recognized as fragments of the stolons and their cyst-like swellings connected with the fusellar zooidal tubes, were derived by chemical isolations from Late Permian (Kazanian) mudstones of the Svalis Dome (central Barents Sea, Norway). The fossil unites certain characters of cephalodiscid pterobranchs and camaroid graptolites but is not interpreted as a truly transient link between these two hemichordate groupes. graptolite.home.pl   (1209 words)

Session 4 Development and Evolution   (Site not responding. Last check: 2007-10-22) Hemichordate acorn worms: pattern of developmental gene expression and evolution of chordate body plan. Hemichordates occupy a critical phylogenetic position among deuterostomes since they exhibit echinoderm-like larval morphology and chordate-like adult morphology. Analyses of the expression and function of hemichordate developmental genes with therefore provide insight into the evolution of deuterostome body plan. www.cib.nig.ac.jp /nemi3/talk.34.html   (168 words)

Pharyngula::Torquarator bullocki The deuterostomes are a superphylum of animals that includes three phyla: the chordates (us!), the familiar echinoderms (sea urchins and starfish), and a peculiar group called the hemichordates (at times, you will see another phylum, the chaetognaths or arrow worms, grouped in the deuterostomes, but there is now evidence that they don't belong there). The hemichordates are probably unfamiliar to most people reading this. There are two classes of hemichordate, the pterobranchs and the enteropneusts, which differ greatly in appearance and lifestyle. pharyngula.org /index/weblog/comments/torquarator_bullocki   (1363 words)

Ordovician Fossils In The Toquima Range, Central Nevada   (Site not responding. Last check: 2007-10-22) The pastel-colored to fl shaley siltstones which sandwhich a prominent bed of whitish-brown quartzite (a knob of the quartzite is visible at the extreme upper right) near Petes Summit furnish paleontology enthusiasts with loads of fascinating graptolite remains, an extinct variety of hemichordate that reached its zenith of adaptation in the Ordovician Period. Paleontologists then realized that the graptolite colony most closely resembled the modern pterobranch, a tiny marine hemichordate, which by definition is a primitive chordate whose notochord (a spine-like notch) is restricted to the basal part of the head. What generated most of the early enthusiasm for the theory was that his Cephalodiscus apparently possesses an extended spine-like protrusion from the main colony, a structure similar to what paleontologists call a nema on fossil graptolites. members.aol.com /Waucoba7/tr/toquima.html   (2545 words)

Jahrbuch-CD der MPG 2003 - The gene for a cytoplasmic inte As expected, the priapulid protein shows the long coil 1b subdomain and the lamin tail homology segment already known for cytoplasmic IF proteins from 11 other protostomic phyla. Surprisingly, the hemichordate protein follows in domain organisation much more closely the protostomic IF proteins than the chordate IF proteins. Thus, the lack of a lamin tail homology segment together with a deletion of 42 residues in the coil 1b domain is a molecular feature restricted to the chordates. www.mpg.de /forschungsergebnisse/wissVeroeffentlichungen/archivListenJahrbuch/2002/17/publZIM82.html   (182 words)

Welcome to my Web site High levels of halogenated substances are common and natural sources of these substances are marine organisms such as polychaete and hemichordate worms. Hemichordate or acorn worms inhabit mucus-lined burrows in the sediment of shallow water. High concentrations of brominated compounds have been found externally to the worms in the mucus lining these burrows. www.sjsu.edu /depts/Biology/RUMBA/RECHRUMBA.htm   (420 words)

The Mitochondrial Genome of the Hemichordate Balanoglossus carnosus and the Evolution of Deuterostome Mitochondria -- ... of the hemichordate Balanoglossus carnosus (acorn worm) was carnosus (hemichordate) mitochondrial genome compared to that of (B) human (vertebrate) and (C) the sea urchin Arbacia lixula (echinoderm). the hemichordates to be the sister taxon of echinoderms rather www.genetics.org /cgi/content/full/150/3/1115   (4484 words)

Smithsonian: Spotlight on Science These characteristics were typical of an enteropneust hemichordate, along with an expanded tentaculate structure resembling the feeding tentacles (lophophore) of a pterobranch hemichordate. When the scientists examined their specimen, they found that it did not have collar tentacles and, thus, was not a lophenteropneust. Besides refuting the hypothesis that these hemichordates have a tentaculate structure and are, therefore, an evolutionary intermediate important in the history of the chordates, the authors have provided the first formal description of these worms.  www.si.edu /research/spotlight/printable/3_4.htm   (1522 words)

Special Feature: Evolution of the chordate body plan: New insights from phylogenetic analyses of deuterostome phyla -- ... Hemichordates have been considered a sister group to echinoderms (14, 17, 26) and to chordates (15). This study found strong support for hemichordate monophyly and for an echinoderm + hemichordate clade. Hemichordates lack a dorsal postanal tail and segmentation of the major functional systems, such as the muscular and nervous www.pnas.org /cgi/content/full/97/9/4469   (4168 words)

Bilateria -- Facts, Info, and Encyclopedia article   (Site not responding. Last check: 2007-10-22) It was previously thought that acoelomates gave rise to the other group, but it now appears that in the main acoelomate phyla ((Parasitic or free-living worms having a flattened body) flatworms and (Click link for more info and facts about gastrotrich) gastrotrichs) the absence is secondary. The (Click link for more info and facts about deuterostome) deuterostomes include the (Marine invertebrates with tube feet and calcite-covered five-part radially symmetrical bodies) echinoderms, (Click link for more info and facts about hemichordate) hemichordates, (Any animal of the phylum Chordata having a notochord or spinal column) chordates, and possibly a few smaller phyla. There are a number of differences, most notably in how the embryo develops. www.absoluteastronomy.com /encyclopedia/b/bi/bilateria.htm   (293 words)

IngentaConnect Hemichordates and deuterostome evolution: robust molecular phylog...   (Site not responding. Last check: 2007-10-22) IngentaConnect Hemichordates and deuterostome evolution: robust molecular phylog... Hemichordates and deuterostome evolution: robust molecular phylogenetic support for a hemichordate + echinoderm clade Hemichordates were traditionally allied to the chordates, but recent molecular analyses have suggested that hemichordates are a sister group to the echinoderms, a relationship that has important consequences for the interpretation of the evolution of deuterostome body plans. www.ingentaconnect.com /content/bsc/ede/1999/00000001/00000003/art99026   (204 words)

Yannanozoon lividum, Earliest Known Hemichordate Numerous problematic forms are known as well, some of which may have represented failed attempts at diversity that did not persist to the present day. As the earliest of the hemichordates, its study casts light upon the early evolution of both the chordates and the vertebrates that sprung from them as the story of life unfolded. The linear structure is the gut, which in some specimens is filled with silt, an indication that it derived sustenance by ingesting the mud of the seafloor. www.fossilmuseum.net /Fossil_Galleries/Chengjiang/Yannanozoon_lividum/Yannanozoon_lividum.htm   (262 words)

Reinterpretation of Yunnanozoon as the earliest known hemichordate   (Site not responding. Last check: 2007-10-22) Reinterpretation of Yunnanozoon as the earliest known hemichordate , which we reinterpret here as the earliest known hemichordate. Hemichordates comprise two main groups: the enteropneusts, or 'acorn worms', and the pterobranchs. www.nature.com /nature/journal/v380/n6573/abs/380428a0.html   (383 words)

Inhibition of microbial activity in marine sediments by a bromophenol from a hemichordate   (Site not responding. Last check: 2007-10-22) Inhibition of microbial activity in marine sediments by a bromophenol from a hemichordate Bromophenols, a member of this class, are found in marine algae and invertebrates, particularly annelids, phoronids and hemi-chordates Here I report inhibition of microbial activity in marine sediments by the common bromophenol, 2,4-dibromophenol (DBP), from the hemichordate Saccoglossus kowalewskii and demonstrate that anaerobic microbial metabolism in sediments is relatively unaffected by DBP whereas aerobic metabolism is particularly sensitive. www.nature.com /nature/journal/v323/n6085/abs/323257a0.html   (326 words)

IngentaConnect Deuterostome evolution: early development in the enteropneust hem...   (Site not responding. Last check: 2007-10-22) Much less is known about the development of the hemichordates compared to other deuterostomes. Single blastomeres were iontophoretically labeled with DiI at the 2- through 16-cell stages, and their fates followed through development to the tornaria larval stage. Finally, isolated blastomeres prepared at either the two- or the four-cell stage are capable of forming normal-appearing, miniature tornaria larvae. www.ingentaconnect.com /content/bsc/ede/2001/00000003/00000006/art01051   (400 words)

Yannanozoon lividum, Earliest Known Hemichordate Description: This fine fossil is Yunnanozoon lividum, has been designated as the earliest known hemichordate. Possessing many of the characteristic chordate features and providing an anatomical link between invertebrates and chordates, the Hemichordata is a minor but important phylum in evolutionary biology. The diversity of soft-tissue fossils is astonishing: algae, medusiforms, sponges, priapulids, annelid-like worms, echinoderms, arthropods (including trilobites), hemichordates, chordates, and the first agnathan fish make up just a small fraction of the total. fossilmall.com /EDCOPE_Enterprises/Chengjiang/CJF014/CJF014.htm   (296 words)

Deuterostome phylogeny and the sister group of the chordates: evidence from molecules and morphology -- Turbeville et ... hemichordate and an echinoid and ophiuroid echinoderm were obtained and urochordates form the sister taxon to the hemichordates, and together this hemichordates and a sister group relationship of this clade to chordates. mbe.oxfordjournals.org /cgi/content/abstract/11/4/648   (727 words)

Rhabdopleura compacta Hincks, 1880 At right there are SEM micrographs showing three coenecia of the hemichordate Young coenecium built of a sicula and three zooidal tubes. Mierzejewski, P. and Kulicki, C. Cortical fibrils and secondary deposits in periderm of the hemichordate kulicki.mierzejewski.biz /compacta.html   (181 words)

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