DOCSLIB.ORG

On the Development of the Plumes in Buds of Cephalodiscus. by W. O

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read 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. Copied from A. T. MasLermau's paper in the 'Trans. Roy. Soc. Edin.,' vol. xxxix, part 3, 1898, plate 4, figs. 64—68. The original numbering- has been retained. Oephalodiscus hodgsoni, 0. nigrescens, and C. gil- christi, aud having made from the abundant material at my disposal a well-graded series of buds of each species, I was enabled to confirm my earlier conclusions. I finally prepared a series of buds of the " Challenger " species, Cephalodiscus dodecalophus, with the result that I am satisfied that the buds of this species agree with 1 'Trans. Roy. Soc. Edin.,' vol. xxxix, part 3, 1898, p. 521. 3 '"Discovery" Expedition Reports,' vol. ii, 1007, and 'Marine Investi- gations in South Africa,' vol. iv, 190(5. PLUMES OF CEPHALODISOUS. 223 those of the other three species. The torsion described by Masterman does not occur, but the grooves of the first and second pairs of plumes, developed iu such a manner that they face ventrally towards the buccal shield, continue to face the shield. The last two pairs of plumes are not deve- loped between the first two pairs and the shield, but on the dorsal side of them, i.e. on the side remote from the shield. The gi-ooves of these last plumes (fifth and sixth pairs) are not directed towards the shield, but away from it. Although the four series of plumes of buds were prepared for the purpose oE deciding the points raised by Mastermau, they serve to show a number of other interesting features, such as (1) the difference of plume development in the buds of the four species; (2) the relation which the last-formed pair of plumes bear to the edge of the post-oral lamella; and (3) the conversion, iu the later stages of growth, of the line of the bases of the collar-outgrowths (plumes and post- oral lamella) from a circle to a double crescent, or two incomplete ellipses. I have selected from each of the four series a number of preparations to illustrate these points; they are reproduced in text-figures 2, 3, 4, 6, 7, aud 9, and are described under headings of the respective species. METHODS. In the case of the youngest stages the whole bud was mounted iu diluted glycerine, aud gold size was run round the edge of the cover-glass to keep it firmly iu position, and to prevent the glycerine from accumulating dust. Most of the buds were dissected, the shield being first removed by tearing through its stalk by the aid of fine mounted needles, and then the collar region, with plumes and post-oral lamella (e.g. text-fig. 2, J), was removed by carefully manipulating the needles between these parts and the " body" of the bud. The three parts, shield, collar region, aud " body " with its stalk, were then mounted on the same slide in dilute glyce- rine. 224 W. G. EIDEWOOD. The relation which the collar region, as dissected out, bears to the whole bud will be made clear by reference to text- fig. 5, A, a diagrammatic side view of a bud with three pairs of plumes, and text-fig. 10, a diagram of a longitudinal section of the adult polypide; in the latter figure the limit of the collar region is marked by two lines of heavy dashes. The results here recorded and illustrated are based upon 135 preparations of buds made and mounted as above ex- plained. In some cases (e.g. text-fig. 6, F) the three parts— " body," collar appendages, and shield—were drawn sepa- rately on tracing paper, and the perfect bud was recon- structed by a superposing of these transparent sheets. No staining fluids were used. The dissections were made under a Greenough binocular erecting microscope magni- fying 20 and 40 diameters; the drawings were made by the aid of a compound microscope with Zeiss apochromatic 8 mm. objective and No. 6 compensating ocular with eye-piece micrometer. The figures in text-figs. 2, 3, 4, 6, 7, and 9 are all reproduced to the same scale of enlargement, viz. 62 diameters. DEVELOPMENT OF THE PLUMES IN BUDS OF OEPHALODISCUS HODGSONI. In the earliest phase of development the bud is ovoid or pyriform (text-fig. 2, A) without signs of buccal shield or plumes. The shield and the first pair of plumes make their appearance simultaneously (B and c). The plumes are at first small mounds, later hemispherical (D), and still later longer than broad (K, F, etc.). The second pair of plumes appear on the external side of the first pair (D, 2), and in contact with them. The two plumes of the first pair are not in con- tact with one another at their bases. The third pair of plumes appear lateral to the second pair (E, 3), and in con- tact with them. The bud increases considerably in size before the fourth PLUMBS OF OEPHALODISCUS. 225 plumes appear; the buccal shield assumes its definitive shape by becoming flattened, and by the differentiation of the pos- b.s. ,-b.s. G. TEXT-FIGUHE 2.—Cephalodiscus hodgsoni. Figures illustrating the development of the plumes of the buds. C and L are side views, the others are dorsal views. J represents the collar and its appendages (plumes and post-oral lamella) dissected from a bud a little older than H. The Qrst pair of plumes are-just appearing in B and C, the second in D, the third in E, the fourth in H, and the fifth in K and L. The series is continued in text-fig. 3. All figures enlarged 62 diameters. Eor explanation of the lettering see end of paper. terior lobe. In G and H the dotted line marks the position of the free edge of the posterior lobe. The fourth plumes 226 "W. G. RIDEWOOD. appear when the bud has reached the stage of development represented in H. The structure which in G is marked po.l. might at first glance be taken for the developing fourth plume; it is the lateral part of the post-oral lamella. Figure J represents the collar region and its appendages (the plumes and post-oral lamella) of a bud a little older than that shown in figure H; the buccal shield has been dissected off from the one side, and the "body" and stalk from the other. The position of the mouth is indicated in the figure, but this region is always more or less damaged in making such a dissection as that described. The torn stalk of the buccal shield in this preparation—as also in the similar pre- parations shown in text-fig. 3, N, O, and u, and in other of the text-figures—occupies a position intermediate between the mouth aud the bases of the first pair of plumes. In figure J the fourth plumes are hemispherical projections at the bases of the third plumes, touching these on the one side, aud in continuity with the post-oral lamella on the other. Traces of pinnules are appearing on the first and second plume-axes, and the terminal end-bulbs of these same plumes are swelling out. In K the fourth plumes are now longer than broad, and the fifth pair are making their appearance, L is a side view of a bud of about the same stage as K, as may be determined by comparing the development of the fourth aud fifth plumes in the two buds. Pinnules are now appearing on the third plumes, and it will be noticed, in the case of the first, second, and third plumes, that the pinnules are not laterally placed on the plume-axes, but ventro-laterally, and the groove between the two rows of pinnules of each of the plumes in question opens ventrally, or ventro-laterally, towards the dorsal or stalked side of the shield.
Load more

Recommended publications
  • 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]
  • The Problem of Graptolite Affinities in the Light of Ultrastructural Studies on Peridermal Derivatives in Pterobranchs
    ACT A PAL A EON T 0 LOG ICA POLONICA Vol. 21 1976 No 1 ADAM URBANEK THE PROBLEM OF GRAPTOLITE AFFINITIES IN THE LIGHT OF ULTRASTRUCTURAL STUDIES ON PERIDERMAL DERIVATIVES IN PTEROBRANCHS Abstract. - The ultrastructure of the organic coenecium in living Cephalodiscus (Cephalodiscus) inaequatus (Andersson) studied with the transmission electron mi­ croscope reveals a fabric and pattern very similar to that recognized in living Rhab­ dopleuTa compacta (Hincks) by Dilly (1971). The same techniques used to study the ultrastructure of Jurassic Rhabdopleura kozlowskii Kulicki and Ordovician Rhab­ dopleurites primaevus Kozlowski indicate that the nature of the fibrous unit ele­ ments of the periderm and their characteristic pattern remain unchanged within the Pterobranchia, at least since the Ordovician. The results combined with those of previous studies on the ultrastructure of p,eridermal derivatives in graptolites (Towe & Urbanek, 1972; Urbanek & Towe, 1974, 1975), reveal a substantial difference at the submicroscopic level between the fusellar component of the periderm in the pterobranchia and that of the Graptolithina. The presumed homology between fusellar tissues of both groups constitutes the main argument in Kozlowski's suggestion (1938, 1949, 1966a) of a close affinity between pterobranchs and graptolites. A reevaluation of his line of reasoning enables us to conclude that Kozlowski's main criterion of homology was the specificity of the structures involved. This requirement is not fulfilled at the ultrastructural level because of substantial differences in the nature of the unit elements and their pat­ tern. Moreover, other data on the ultrastructural anatomy of graptolites (very early deposition of cortical tissue over juvenile thecae; presence of cortical deposits over the inner surface of thecae; simultaneous secretion of successive fuselli and cor­ responding layers of cortical tissue) contradict the mode of secretion of the grap­ tolite skeleton as suggested in the classical Kozlowski hypothesis.
    [Show full text]
  • Phylogenomic Resolution of the Hemichordate and Echinoderm Clade
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Current Biology 24, 2827–2832, December 1, 2014 ª2014 Elsevier Ltd All rights reserved http://dx.doi.org/10.1016/j.cub.2014.10.016 Report Phylogenomic Resolution of the Hemichordate and Echinoderm Clade Johanna T. Cannon,1,2,5,* Kevin M. Kocot,1,3,5 history. Although debates surround chordate interrelation- Damien S. Waits,1 David A. Weese,1,4 Billie J. Swalla,5 ships [2, 4, 12] as well as the positions of the controversial Scott R. Santos,1 and Kenneth M. Halanych1,5,* flatworm-like Xenoturbellida [2, 13] and Acoelomorpha [13], 1Department of Biological Sciences and Molette Biology Ambulacraria (Hemichordata + Echinodermata) has been Laboratory for Environmental and Climate Change Studies, consistently recovered [2, 4, 13]. Relationships within these Auburn University, Auburn, AL 36849, USA two phyla, however, have remained unresolved, and numbers 2Department of Zoology, Naturhistoriska Riksmuseet, of sampled hemichordate taxa in phylogenomic studies to 104 05 Stockholm, Sweden date have been limited. Within Hemichordata, there is dispute 3School of Biological Sciences, University of Queensland, as to whether colonial, tube-dwelling pterobranchs are sister Brisbane, QLD 4072, Australia to, or nested within, vermiform enteropneusts [1, 5–7, 14]. 4Department of Biological and Environmental Sciences, Placement of pterobranchs has major implications for under- Georgia College and State University, Milledgeville, standing origins and early evolution of graptolite hemichor- GA 31061, USA dates, which have an extensive fossil record [15]. Furthermore, 5Friday Harbor Laboratories, University of Washington, there are conflicting hypotheses regarding the position of 620 University Road, Friday Harbor, WA 98250, USA ophiuroid brittle stars within echinoderms.
    [Show full text]
  • Phylogenetic Analysis Reveals That Rhabdopleura Is an Extant Graptolite
    Phylogenetic analysis reveals that Rhabdopleura is an extant graptolite CHARLES E. MITCHELL, MICHAEL J. MELCHIN, CHRIS B. CAMERON AND JO¨ RG MALETZ Mitchell, C.E., Melchin, M.J., Cameron, C.B. & Maletz, J. 2013: Phylogenetic analysis reveals that Rhabdopleura is an extant graptolite. Lethaia,Vol.46,pp.34–56. A phylogenetic analysis of morphological data from modern pterobranch hemichordates (Cephalodiscus, Rhabdopleura) and representatives of each of the major graptolite orders reveals that Rhabdopleura nests among the benthic, encrusting graptolite taxa as it shares all of the synapomorphies that unite the graptolites. Therefore, rhabdopleurids can be regarded as extant members of the Subclass Graptolithina (Class Pterobranchia). Com- bined with the results of previous molecular phylogenetic studies of extant deuterosto- mes, these results also suggest that the Graptolithina is a sister taxon to the Subclass Cephalodiscida. The Graptolithina, as an important component of Early–Middle Palaeo- zoic biotas, provide data critical to our understanding of early deuterostome phylogeny. This result allows one to infer the zooid morphology, mechanics of colony growth and palaeobiology of fossil graptolites in direct relation to the living members of the clade. The Subdivision Graptoloida (nom. transl.), which are all planktic graptolites, is well sup- ported in this analysis. In addition, we recognize the clade Eugraptolithina (nov.). This clade comprises the Graptoloida and all of the other common and well-known grapto- lites of the distinctive Palaeozoic fauna. Most of the graptolites traditionally regarded as tuboids and dendroids appear to be paraphyletic groups within the Eugraptolithina; however, Epigraptus is probably not a member of this clade. The Eugraptolithina appear to be derived from an encrusting, Rhabdopleura-like species, but the available informa- tion is insufficient to resolve the phylogeny of basal graptolites.
    [Show full text]
  • The Pterobranchia of the Scottish National Antarctic Expedition (1902 to 1904)
    ( 531 ) VII.—The Pterobranchia of the Scottish National Antarctic Expedition (1902 to 1904). By S. F. Harcner, Sc.D., F.R.S., Keeper of the Department of Zoology in the British Museum; and W. G. Ridewood, D.Sc, Lecturer on Biology in the Medical School of St Mary's Hospital, University of London. Communicated by Dr J. H. ASHWORTH. (With Five Text-Figures and Two Plates.)* (MS. received February 15, 1913. Read March 17, 1913. Issued separately July 4, 1913.) INTRODUCTION. The genus Cephalodiscus was instituted by M'INTOSH for a species, C. dodecalophus, which had been obtained by the Challenger Expedition. After the publication of the full account of this species, by M'INTOSH and HARMER (87) in the Challenger Report, succeeding papers for nearly twenty years were all based on the original Challenger material. The subject was in particular re-investigated by MASTERMAN in a series of papers (971, 972, 98, 99, 03). The Siboga report, published by HAKMER (05) in 1905, added three Oriental species to the genus. SCHEPOTIEFF (05, 07, 08) devoted several papers to a further description of the Challenger material; while, more recently (09), he has described an interesting new species, C. indicus, from Ceylon. In 1906 RIDEWOOD (06) described C. gilchristi from South Africa; and in the following year he gave an account (071) of the two species which had been dredged by the Discovery Expedition; and (07z) of the development of the plumes in four species of Cephalodiscus. One of the Discovery species, C. nigrescens, had been described two years earlier by LANKESTER (05), in a preliminary paper; and RIDEWOOD (L2) has recently brought forward evidence to show that this species had been dredged by the Erebus and Terror Expedition in 1841 or 1842.
    [Show full text]