DOCSLIB.ORG

Hemichordates: Are They Chordates? Module 2

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Hemichordates: Are They Chordates? Module 2 HEMICHORDATES: ARE THEY CHORDATES? MODULE 2 MODULE 2 HEMICHORDATES: ARE THEY CHORDATES? Unit 1 Hemichordates Most zoologists agree that the evolutionary ties between the chordates and hemichordates are closer than those between echinoderms and either phylum. The hemichordates were formerly considered a subphylum of the chordates, based on their possession of gill slits and a rudimentary notochord. It is now known that a notochord is lacking and what is present is a stomocord, which is a forwardly directed diverticulum of the gut, issuing from the buccal cavity. The gill slits in the pharynx are used primarily for filter feeding and only secondarily for breathing and are thus comparable to those in the protochordates. A tubular dorsal nerve cord in the collar zone may represent an early stage of the condition in chordates; a diffused set of nerve cells is similar to the uncentralised subepithelial plexus of echinoderms. Classification Class Enteropneusta (Gr. entero, intestine + pneustikos, for breathing) Examples: Balanoglossus, Saccoglossus, Ptychodera, etc. Class Pterobranchia (Gr. pteron, wing or feathers + branchia, gills). Order Cephalodiscida, example: Cephalodiscus Order Rhabdopleurida, example: Rhabdopleura Figure 1: Hemichordate (Saccoglossus) Source: Google images Unit 2 Biology of Balanoglossus Balanoglossus is a common genus of the class Enteropneusta. Members of the class, commonly called acorn worms, are marine worms which range in size between 10 and 40cm, although some can be as long as 2m. They are sluggish, worm-like animals that live in burrows or under stones, usually in mud or sand flats of intertidal zones. AOE 1 HEMICHORDATES: ARE THEY CHORDATES? MODULE 2 The body of Balanoglossus is soft, cylindrical with a ciliated and mucus-covered surface. The body is divided into a short conical (or tongue-like) proboscis, a short collar and a long trunk. The proboscis probes about in the mud and collects food in mucous strands on its surface. These detritus and food particles are carried posteriorly and ventrally to the groove at the edge of the collar and into the mouth before being swallowed. Large particles can be rejected by pulling the proboscis against the collar, thereby covering the mouth. The proboscis is also used to excavate. There is a coelomic sac (protocoel) in the posterior end of the proboscis into which extends the buccal diverticulum, a slender, blinding ending pouch of the gut that reaches forward into the buccal region. A slender canal connects the protocoel with a proboscis pore to the outside. By taking in water through the pores into the coelomic sacs, the proboscis and collar can be stiffened to aid burrowing. Contraction of the body musculature then forces the excess water Figure 2: External features of Balanoglossus (dorsal view) out through the gill slits, reducing the hydrostatic pressure and allowing the animal to move forward. The collar is short and muscular, cylinder-like, enclosing a pair of coelomic cavities (collar coelom) and opens by a pair of collar pores on the dorsal surface. The trunk is superficially ringed. It is divisible into anterior branchio-genital region, a middle hepatic region and a posterior abdominal region. A row of gill pores is located dorso-laterally on each side of the trunk just behind the collar. These open from a series of gill chambers that in turn connect with a series of gill slits in the sides of the pharynx. Cilia associated with the gill slits circulate water into the mouth and out of the body through pharyngeal gill slits. As water passes through the gill slits, gases are exchanged by diffusion between water and blood sinuses surrounding the pharynx. Respiratory gases and metabolic waste products (principally ammonia) can also be exchanged by diffusion through the body wall. Balanoglossus has a digestive tract which is a simple tube. Food particles caught are brought to the mouth by ciliary action, and directed along the ventral part of the pharynx and oesophagus to the intestine. Food is digested as diverticula of the gut, called hepatic sacs, release enzymes. The worm extends its posterior end out of the burrow during defaecation. At low tides, coils of faecal material, called castings lie in the substrate at burrow openings. AOE 2 HEMICHORDATES: ARE THEY CHORDATES? MODULE 2 The nervous system is ectodermal in origin and lies at the base of the ciliated epidermis. It consists of the dorsal and ventral nerve cords and a network of epidermal nerve cells, called a nerve plexus. Sensory receptors are unspecialized and widely distributed over the body. The circulatory system comprise a dorsal and ventral contractile vessel. Blood moves anteriorly in the dorsal vessel and posteriorly in the ventral vessel. All blood flowing anteriorly pass into a series of blood sinuses, called the glomerulus, at the base of the proboscis. The glomerulus also serves an excretory function. Sexes are separate (dioecious). Two rows of gonads are arranged dorso-laterally at the anterior region of the trunk. Each gonad opens separately to the outside. Fertilization is external. A ciliated larva, called the tornaria, swim in the plankton for several days to a few weeks. The larva settles to the substrate and gradually transform into the adult form. Conclusion Hemichordates are commonly referred to as acorn worms and dwell in marine environments. Hemichordates do not possess the five principal features of chordates, hence they are not chordates. However, two of the five features of chordates can be observed in hemichordates and these are the dorsal nerve cord and the pharyngeal gill slit. Assignment 1. Are hemichordates chordates? Explain. 2. List the three body regions of a typical hemichordate. Reference Tropical Zoology (2013; 3rd Edition) by Ademola O. Segun AOE 3 .
Load more

Recommended publications
  • Bermuda Biodiversity Country Study - Iii – ______
    Bermuda Biodiversity Country Study - iii – ___________________________________________________________________________________________ EXECUTIVE SUMMARY • The Island’s principal industries and trends are briefly described. This document provides an overview of the status of • Statistics addressing the socio-economic situation Bermuda’s biota, identifies the most critical issues including income, employment and issues of racial facing the conservation of the Island’s biodiversity and equity are provided along with a description of attempts to place these in the context of the social and Government policies to address these issues and the economic needs of our highly sophisticated and densely Island’s health services. populated island community. It is intended that this document provide the framework for discussion, A major portion of this document describes the current establish a baseline and identify issues requiring status of Bermuda’s biodiversity placing it in the bio- resolution in the creation of a Biodiversity Strategy and geographical context, and describing the Island’s Action Plan for Bermuda. diversity of habitats along with their current status and key threats. Particular focus is given to the Island’s As human use or intrusion into natural habitats drives endemic species. the primary issues relating to biodiversity conservation, societal factors are described to provide context for • The combined effects of Bermuda’s isolation, analysis. climate, geological evolution and proximity to the Gulf Stream on the development of a uniquely • The Island’s human population demographics, Bermudian biological assemblage are reviewed. cultural origin and system of governance are described highlighting the fact that, with 1,145 • The effect of sea level change in shaping the pre- people per km2, Bermuda is one of the most colonial biota of Bermuda along with the impact of densely populated islands in the world.
    [Show full text]
  • New Observations on Rhabdopleura Kozlowskii (Pterobranchia) from the Bathonian of Poland
    ACT A PAL A EON T 0 LOG IC A POLONICA Vol. XVI 1971 No. ( CYPRIAN KULICKI NEW OBSERVATIONS ON RHABDOPLEURA KOZLOWSKII (PTEROBRANCHIA) FROM THE BATHONIAN OF POLAND Abstract. - Specimens of Rh. kozlowskii Kulicki, 1969 have here been described from the Bathonian of southern Poland. A secondary layer, never observed before, has been found inside zooidal tubes. INTRODUCTION At present, the genus Rhabdopleura is represented by at least two species clearly different from each other, Le. Rh. normani Allman, 1869 and Rh. striata Schepotieff, 1909. All other Recent species display a con­ siderable similarity to Rh. normani and the necessity to distinguish them is called in question by many investigators (Schepotieff, 1906; Dawydoff 1948; Thomas & .Davis, 1949; Burdon-Jones, 1954 and others). The species Rh. compacta Hincks, 1880 has recently been restored by Stebbing (1970), who concludes that Rh. compacta differs from Rh. normani mostly in the form of colonies and lack of ring-shaped part of the stolon. The following three fossil species have hitherto been described: Rh. vistulae Kozlowski, 1956 from the Danian of Poland, Rh. eocenica Tho­ mas & Davis, 1949 from the Eocene of England, and Rh. kozlowskii Kulicki, 1969 from the Callovian of Poland. The specimens of Rh. kozlowskii, described in the present paper, were etched with hydrochloric acid fTom ca1careous-marlyconcretions which occur in black and dark-gray Bathonian clays, Morrisiceras morrisi Zone (R6zycki, 1953) of Blanowice near Zawiercie. The concretions, varying in shape, are mostly spherical or ellipsoidal and fluctuate in size between a few and some scores of centimetres. Many of the concretions collected contain a macrofauna of molluscs or pieces of wood.
    [Show full text]
  • Hemichordate Phylogeny: a Molecular, and Genomic Approach By
    Hemichordate Phylogeny: A molecular, and genomic approach by Johanna Taylor Cannon A dissertation submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Auburn, Alabama May 4, 2014 Keywords: phylogeny, evolution, Hemichordata, bioinformatics, invertebrates Copyright 2014 by Johanna Taylor Cannon Approved by Kenneth M. Halanych, Chair, Professor of Biological Sciences Jason Bond, Associate Professor of Biological Sciences Leslie Goertzen, Associate Professor of Biological Sciences Scott Santos, Associate Professor of Biological Sciences Abstract The phylogenetic relationships within Hemichordata are significant for understanding the evolution of the deuterostomes. Hemichordates possess several important morphological structures in common with chordates, and they have been fixtures in hypotheses on chordate origins for over 100 years. However, current evidence points to a sister relationship between echinoderms and hemichordates, indicating that these chordate-like features were likely present in the last common ancestor of these groups. Therefore, Hemichordata should be highly informative for studying deuterostome character evolution. Despite their importance for understanding the evolution of chordate-like morphological and developmental features, relationships within hemichordates have been poorly studied. At present, Hemichordata is divided into two classes, the solitary, free-living enteropneust worms, and the colonial, tube- dwelling Pterobranchia. The objective of this dissertation is to elucidate the evolutionary relationships of Hemichordata using multiple datasets. Chapter 1 provides an introduction to Hemichordata and outlines the objectives for the dissertation research. Chapter 2 presents a molecular phylogeny of hemichordates based on nuclear ribosomal 18S rDNA and two mitochondrial genes. In this chapter, we suggest that deep-sea family Saxipendiidae is nested within Harrimaniidae, and Torquaratoridae is affiliated with Ptychoderidae.
    [Show full text]
  • Benthic Field Guide 5.5.Indb
    Field Identifi cation Guide to Heard Island and McDonald Islands Benthic Invertebrates Invertebrates Benthic Moore Islands Kirrily and McDonald and Hibberd Ty Island Heard to Guide cation Identifi Field Field Identifi cation Guide to Heard Island and McDonald Islands Benthic Invertebrates A guide for scientifi c observers aboard fi shing vessels Little is known about the deep sea benthic invertebrate diversity in the territory of Heard Island and McDonald Islands (HIMI). In an initiative to help further our understanding, invertebrate surveys over the past seven years have now revealed more than 500 species, many of which are endemic. This is an essential reference guide to these species. Illustrated with hundreds of representative photographs, it includes brief narratives on the biology and ecology of the major taxonomic groups and characteristic features of common species. It is primarily aimed at scientifi c observers, and is intended to be used as both a training tool prior to deployment at-sea, and for use in making accurate identifi cations of invertebrate by catch when operating in the HIMI region. Many of the featured organisms are also found throughout the Indian sector of the Southern Ocean, the guide therefore having national appeal. Ty Hibberd and Kirrily Moore Australian Antarctic Division Fisheries Research and Development Corporation covers2.indd 113 11/8/09 2:55:44 PM Author: Hibberd, Ty. Title: Field identification guide to Heard Island and McDonald Islands benthic invertebrates : a guide for scientific observers aboard fishing vessels / Ty Hibberd, Kirrily Moore. Edition: 1st ed. ISBN: 9781876934156 (pbk.) Notes: Bibliography. Subjects: Benthic animals—Heard Island (Heard and McDonald Islands)--Identification.
    [Show full text]
  • Uncorrected Proof
    JrnlID 12526_ArtID 933_Proof# 1 - 07/12/2018 Marine Biodiversity https://doi.org/10.1007/s12526-018-0933-2 1 3 ORIGINAL PAPER 2 4 5 On the larva and the zooid of the pterobranch Rhabdopleura recondita 6 Beli, Cameron and Piraino, 2018 (Hemichordata, Graptolithina) 7 F. Strano1,2 & V. Micaroni3 & E. Beli4,5 & S. Mercurio6 & G. Scarì7 & R. Pennati6 & S. Piraino4,8 8 9 Received: 31 October 2018 /Revised: 29 November 2018 /Accepted: 3 December 2018 10 # Senckenberg Gesellschaft für Naturforschung 2018 11 Abstract 12 Hemichordates (Enteropneusta and Pterobranchia) belong to a small deuterostome invertebrate group that may offer insights on 13 the origin and evolution of the chordate nervous system. Among them, the colonial pterobranchOF Rhabdopleuridae are recognized 14 as living representatives of Graptolithina, a taxon with a rich fossil record. New information is provided here on the substrate 15 selection and the life cycle of Rhabdopleura recondita Beli, Cameron and Piraino, 2018, and for the first time, we describe the 16 nervous system organization of the larva and the adult zooid, as well as the morphological, neuroanatomical and behavioural 17 changes occurring throughout metamorphosis. Immunohistochemical analyses disclosed a centralized nervous system in the 18 sessile adult zooid, characterized by different neuronal subsets with three distinctPRO neurotransmitters, i.e. serotonin, dopamine and 19 RFamide. The peripheral nervous system comprises GABA-, serotonin-, and dopamine-immunoreactive cells. These observa- 20 tions support and integrate previous neuroanatomical findings on the pterobranchD zooid of Cephalodiscus gracilis. Indeed, this is 21 the first evidence of dopamine, RFamide and GABA neurotransmittersE in hemichordates pterobranchs. In contrast, the 22 lecithotrophic larva is characterized by a diffuse basiepidermal plexus of GABAergic cells, coupled with a small group of 23 serotonin-immunoreactive cells localized in the characteristic ventral depression.
    [Show full text]
  • Graptolite-Like Fibril Pattern in the Fusellar Tissue of Palaeozoic Rhabdopleurid Pterobranchs
    Graptolite-like fibril pattern in the fusellar tissue of Palaeozoic rhabdopleurid pterobranchs PIOTR MIERZEJEWSKI and CYPRIAN KULICKI Mierzejewski, P. & Kulicki, C. 2001. Graptolite-like fibril pattern in the fusellar tissue of Palaeozoic rhabdopleurid pterobranchs. - Acta Palaeontologica Polonica 46, 3, 349-366. The fusellar tissue of Palaeozoic rhabdopleurid ptdrobranchs has been studied using the SEM techniques. The fibrillar material of Ordovician Kystodendron ex gr. longicarpus and Rhabdopleuritesprimaevus exhibits a distinct dimorphism, comprising: (1) thinner, wavy and anastomosing/branching fusellar fibrils proper, producing a tight three-dimen- sional meshwork; and (2) long, more or less straight and unbranched cortical fibrils, sometimes beaded, and arranged in parallel. These fibrils are similar to the fusellar and cortical fibrils of graptolites, respectively. Until now, dimorphic fibrils and their arrange- ment within fusellar tissue were regarded as unique characters of the Graptolithina. In general, the fibrillar material of these fossils is partially preserved in the form of flaky material (new term) composed offlakes (new term). Flakes are interpreted as flattened structures originating from the fusion of several neighbouring tightly packed fibrils. A Permian rhabdopleurid, referred to as Diplohydra sp., reveals a fabric and pattern of fusellar tissue similar to that of both Ordovician rhabdopleurids but devoid (?)of cortical fibrils. The results presented here question views that: (1) substantial differences in fab- ric and pattern of fusellar tissue exist between fossil pterobranchs and graptolites; and (2) the ultrastructure of pterobranch periderm has remained unchanged at least since the Ordovician. The Palaeozoic rhabdopleurids investigated are closer ultrastructurally to graptolites than to contemporary pterobranchs. The pterobranchs and the graptolites should be treated as members of one class - the Graptolithoidea.
    [Show full text]
  • The Early History of the Metazoa—A Paleontologist's Viewpoint
    ISSN 20790864, Biology Bulletin Reviews, 2015, Vol. 5, No. 5, pp. 415–461. © Pleiades Publishing, Ltd., 2015. Original Russian Text © A.Yu. Zhuravlev, 2014, published in Zhurnal Obshchei Biologii, 2014, Vol. 75, No. 6, pp. 411–465. The Early History of the Metazoa—a Paleontologist’s Viewpoint A. Yu. Zhuravlev Geological Institute, Russian Academy of Sciences, per. Pyzhevsky 7, Moscow, 7119017 Russia email: [email protected] Received January 21, 2014 Abstract—Successful molecular biology, which led to the revision of fundamental views on the relationships and evolutionary pathways of major groups (“phyla”) of multicellular animals, has been much more appre ciated by paleontologists than by zoologists. This is not surprising, because it is the fossil record that provides evidence for the hypotheses of molecular biology. The fossil record suggests that the different “phyla” now united in the Ecdysozoa, which comprises arthropods, onychophorans, tardigrades, priapulids, and nemato morphs, include a number of transitional forms that became extinct in the early Palaeozoic. The morphology of these organisms agrees entirely with that of the hypothetical ancestral forms reconstructed based on onto genetic studies. No intermediates, even tentative ones, between arthropods and annelids are found in the fos sil record. The study of the earliest Deuterostomia, the only branch of the Bilateria agreed on by all biological disciplines, gives insight into their early evolutionary history, suggesting the existence of motile bilaterally symmetrical forms at the dawn of chordates, hemichordates, and echinoderms. Interpretation of the early history of the Lophotrochozoa is even more difficult because, in contrast to other bilaterians, their oldest fos sils are preserved only as mineralized skeletons.
    [Show full text]
  • New Insights from Phylogenetic Analyses of Deuterostome Phyla
    Evolution of the chordate body plan: New insights from phylogenetic analyses of deuterostome phyla Chris B. Cameron*†, James R. Garey‡, and Billie J. Swalla†§¶ *Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada; †Station Biologique, BP° 74, 29682 Roscoff Cedex, France; ‡Department of Biological Sciences, University of South Florida, Tampa, FL 33620-5150; and §Zoology Department, University of Washington, Seattle, WA 98195 Edited by Walter M. Fitch, University of California, Irvine, CA, and approved February 24, 2000 (received for review January 12, 2000) The deuterostome phyla include Echinodermata, Hemichordata, have a tornaria larva or are direct developers (17, 21). The and Chordata. Chordata is composed of three subphyla, Verte- three body parts are the proboscis (protosome), collar (me- brata, Cephalochordata (Branchiostoma), and Urochordata (Tuni- sosome), and trunk (metasome) (17, 18). Enteropneust adults cata). Careful analysis of a new 18S rDNA data set indicates that also exhibit chordate characteristics, including pharyngeal gill deuterostomes are composed of two major clades: chordates and pores, a partially neurulated dorsal cord, and a stomochord ,echinoderms ؉ hemichordates. This analysis strongly supports the that has some similarities to the chordate notochord (17, 18 monophyly of each of the four major deuterostome taxa: Verte- 24). On the other hand, hemichordates lack a dorsal postanal ,brata ؉ Cephalochordata, Urochordata, Hemichordata, and Echi- tail and segmentation of the muscular and nervous systems (9 nodermata. Hemichordates include two distinct classes, the en- 12, 17). teropneust worms and the colonial pterobranchs. Most previous Pterobranchs are colonial (Fig. 1 C and D), live in secreted hypotheses of deuterostome origins have assumed that the mor- tubular coenecia, and reproduce via a short-lived planula- phology of extant colonial pterobranchs resembles the ancestral shaped larvae or by asexual budding (17, 18).
    [Show full text]
  • HEMICHORDATA 2Nd Sem (C3T)
    HEMICHORDATA 2nd Sem (C3T) Dr. Ranajit Kr. Khalua Assistant Professor Dept. zoology Narajole Raj College Paschim Medinipur GENERAL CHARACTERS 1. Exclusively marine worm like and soft-bodied animals. 2. Body is divisible into proboscis, collar and trunk. 3. Notochord Occurs only in the anterior end of the body. Recently it has been called “buccal diverticulum” due to its doubtful nature. 4. Numerous paired gill slita are present. Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College 5. Nervous tissues lie embedded in the epidermis and occur both on the dorsal and ventral surfaces 6. Coelom is usually divided into three distinct portion corresponding to the three regions. 7. Blood vascular system is simple . 8. Sexes are separate and the development may be direct or indirect. Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Classification Hemichordata has been divided into following four classes : Class 1. Enteropneusta I. Solitary and burrowing worm-like marine forma commonly known as "acorn” or 'tongue worm . II. Body consists of the usual divisions viz., proboscis Separated by the narrow stalk from the ring Shaped collar, which is succeeded by an engated trunk. III. epidermis is ciliated and glandular. IV. Numerous gill sants and gonads are present. V. Alimentary canal straight with a terminal anus. Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Example : Saccoglossus and ptychodera Fig : Saccoglossus Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Class 2. Pterobranchi I. Sedentary, solitary or colonial and marine form.
    [Show full text]
  • Pterobranchia, Hemichordata)
    Illinois Wesleyan University Digital Commons @ IWU Honors Projects Biology 2006 The Development and Structure of Feeding Arms in Antarctic Species of Pterobranchs (Pterobranchia, Hemichordata) Catherine Krahe '06 Illinois Wesleyan University Follow this and additional works at: https://digitalcommons.iwu.edu/bio_honproj Part of the Biology Commons Recommended Citation Krahe '06, Catherine, "The Development and Structure of Feeding Arms in Antarctic Species of Pterobranchs (Pterobranchia, Hemichordata)" (2006). Honors Projects. 4. https://digitalcommons.iwu.edu/bio_honproj/4 This Article is protected by copyright and/or related rights. It has been brought to you by Digital Commons @ IWU with permission from the rights-holder(s). You are free to use this material in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This material has been accepted for inclusion by faculty at Illinois Wesleyan University. For more information, please contact [email protected]. ©Copyright is owned by the author of this document. Draft The development and structure of feeding arms in Antarctic species of pterobranchs (Pterobranchia, Hemichordata) Senior Honors Research Catherine Krahe Abstract. Pterobranchs are ofparticular interest to evolutionary biologists because as members ofthe phylum Hemichordata, they share characteristics with vertebrate animals and other chordates. The focus ofthis study is an examination ofthe development, structure, and function of the feeding arms in several species of pterobranchs collected from depths greater than 500 m from waters surrounding Antarctica.
    [Show full text]
  • On the Development of the Plumes in Buds of Cephalodiscus. by W. O
    PLUMES OF CEPHALODISCUS. 221 On the Development of the Plumes in Buds of Cephalodiscus. By W. O. Ridcwood, D.Sc, Lecturer on Biology at St. Mary's Medical School, University of London. Witli 11 Text-flgures. PAGE Introduction ....... 221 Methods . .223 Development of the Plumes in Buds of Cephalodiscus hodgsoni ...... 224 Development of the Plumes in Buds of Cephalodiscus dodecalophus ...... 230 Development of the Plumes in Buds of Cephalodiscus nigrescens ...... 235 Development of the Plumes in Buds of Cepbalodiscus gilchristi . .242 General Remarks on the Collar and its Appendages . 245 Summary ....... 251 Explanation of the Abbreviations employed in Text-figures 2, 3,4, 6, 7, and 9 . .252 INTRODUCTION. During the progress of an investigation on the anatomy of three recently discovered species of Cephalodiscus (C. nigrescens, C. hodgsoni, and C. gilchristi), kindly entrusted to me for description by Prof. B. Ray Lankester, F.R.S., Director of the Natural History Museum, London, I noticed that in the development of the buds there is no torsion of the first and second plume-axes such as is de- scribed by Masterman as occurring in buds of C. dodeca- 222 W. G. MDEWOOD. lophus,1 and that the last plumes do not develop between the earlier plumes and the buccal shield, as recorded by the same writer, but on the side of those plumes remote from the buccal shield. His figures 64—68 are reproduced as text- fig. 1. I was unable to settle the point satisfactorily in time for the introduction of my results iuto the two papers describing the structure of the polypides and tubaria of the new species/ but since the completion of those papers I have made an exhaustive study of the growth, of the plumes in buds of TEXT-FIGUHE 1.—Diagrammatic transverse sections of plumes and buccal shield of Ceplialodiscus dodecaloplius at five stages of development.
    [Show full text]
  • The Genome Sequence of the Colonial Chordate, Botryllus Schlosseri
    RESEARCH ARTICLE elifesciences.org The genome sequence of the colonial chordate, Botryllus schlosseri Ayelet Voskoboynik1,2*, Norma F Neff3†, Debashis Sahoo1†, Aaron M Newman1†, Dmitry Pushkarev3†, Winston Koh3†, Benedetto Passarelli3, H Christina Fan3, Gary L Mantalas3, Karla J Palmeri1,2, Katherine J Ishizuka1,2, Carmela Gissi4, Francesca Griggio4, Rachel Ben-Shlomo5, Daniel M Corey1, Lolita Penland3, Richard A White III3, Irving L Weissman1,2,6*, Stephen R Quake3* 1Department of Pathology, Institute for Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, United States; 2Hopkins Marine Station, Stanford University, Pacific Grove, United States; 3Departments of Applied Physics and Bioengineering, Howard Hughes Medical Institute, Stanford University, Stanford, United States; 4Dipartimento di Bioscienze, Università degli Studi di Milano, Milano, Italy; 5Department of Biology, University of Haifa-Oranim, Tivon, Israel; 6Ludwig Center for Cancer Stem Cell Research and Medicine, Stanford University School of Medicine, Stanford, United States Abstract Botryllus schlosseri is a colonial urochordate that follows the chordate plan of development following sexual reproduction, but invokes a stem cell-mediated budding program during subsequent rounds of asexual reproduction. As urochordates are considered to be the closest living invertebrate relatives of vertebrates, they are ideal subjects for whole genome sequence analyses. Using a novel method for high-throughput sequencing of eukaryotic genomes, we sequenced and assembled 580 Mbp of the B. schlosseri genome. The genome assembly is *For correspondence: ayeletv@ comprised of nearly 14,000 intron-containing predicted genes, and 13,500 intron-less predicted stanford.edu (AV); irv@stanford. genes, 40% of which could be confidently parceled into 13 (of 16 haploid) chromosomes.
    [Show full text]