PhD thesis

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Introduction 9 Chapter I Introduction Brachiopoda The phylogenetic relationship of Brachiopoda is intensely debated among biologists and paleontologists alike. Brachiopods were already known by Linné, and 370 extant and more than 12.000 described fossil species are known (Linné 1758; Ax 2003; Logan 2007). Brachiopods were significant members of the early Cambrian marine fauna and thus are one of the few phyla which are represented throughout the 550 million years of the Phanerozoic era, which extends from the first widespread appearance of organisms with mineralized skeletons until modern times (James et al. 1992). Historically, brachiopods have been assigned to different invertebrate groups, including molluscs (Lamarck 1801; Cuvier 1805), bryozoans (Huxley 1853; Hancock 1858), bryozoans and phoronids (Hatschek 1888 ‘Tentaculata’; Hyman 1959 ‘Lophophorata’), or annelids (Morse 1871). The three lophophorate groups or Brachiopoda alone have subsequently sometimes been regarded as deuterostomes (Brusca and Brusca 1990; Schram 1991; Eernisse et al. 1992; Nielsen 1995). Since the appearance of molecular research tools, brachiopods have commonly been accepted to be protostomes (Field et al. 1988; Lake 1990; Halanych 1995; Hejnol et al. 2009). Brachiopod internal phylogeny distinguishes three clades; the inarticulate Linguliformea and Craniiformea and the articulate Rhynchonelliformea (Williams et al. 1996). Members of Linguliformea live buried in mud and have swimming juveniles instead of a true larval stage (Yatsu 1902). Members of craniiformea live with their ventral valve attached to stones and have two-lobed lecithotrophic larvae (Rowell 1960). Members of Rhynchonelliformea have a pedicle with which they attach themselves to rocks or other hard substrates (Williams et al. 1997). Their larvae have three lobes and are lecithotrophic (Freeman 2003). Traditionally, Linguliformea and Craniiformea have been grouped together as Inarticulata, while Rhynchonelliformea have been named Articulata because their valves are connected by a hinge (James et al. 1992). Brachiopods are certainly a comparatively minor phylum when only the number of recent species is considered. Nevertheless, they are present in all of the world’s oceans within all depth zones and the approximately 12.000 fossils species represent a rich source of paleontological information (Logan 2007).
10 Introduction Nervous system Microanatomical features related to the nervous system and the musculature of brachiopod larvae are virtually unknown. The literature on the nervous system of adult brachiopods boils down to descriptions by two authors on four species, Gryphus vitreus, Novocrania anomala, Discinisca lamellosa and Lingula anatina (van Bemmelen 1883; Blochmann 1892a, 1892b). Subsequent reviews of the same data are available from several authors (Helmcke 1939; Hyman 1959; Bullock and Horridge 1965a; Williams et al. 1997). In the rhynchonelliform brachiopod Gryphus vitreus the main body of nervous tissue is found around the esophagus and nerves emanate laterally from two ganglia, one subenteric ventral of the esophagus and one supraenteric dorsal of the esophagus (Rudwick 1970). The nervous system of brachiopod larvae or juveniles is only known for the linguliform Lingula anatina and Glottidia sp. and consists of a ventral lophophore system innervating the ciliary bands and a dorsal lophophore system innervating the body musculature (Hay-Schmidt 1992, 2000). In order to fill the gap of knowledge concerning the brachiopod nervous system in rhynchonelliform and craniiform brachiopods, this study investigates the larval and juvenile neuroanatomy of Novocrania anomala (Craniiformea) and Terebratalia transversa (Rhynchonelliformea). Muscular system Adult brachiopods possess two main forms of muscular tissue. These are either bundles of muscle fibers that control the movement of the valves or myoepithelia in the lophophore (Williams et al. 1997). The muscles may be smooth, cross striated, or obliquely striated (Reed and Cloney 1977). Adult rhynchonelliform brachiopods comprise a pair of adductors, a pair of diductors, and a dorsal and a ventral pair of adjustor muscles that extend between the pedicle and the valves, moving the entire shell relative to the pedicle (Richardson and Watson 1975). The adult craniiform Novocrania anomala comprises a pair of posterior as well as anterior adductors, a pair of oblique internal, and a pair of oblique lateral muscles (Bulman 1939). The muscular system of brachiopods and their larvae has been described by several authors (Hancock 1858; Kowalevski 1883; Blochmann 1892b; Helmcke 1939; Rudwick 1961; Reed and Cloney 1977), but no studies are available that use the benefit of up-to-date techniques such as immunocytochemistry in combination with confocal laserscanning microscopy and 3D reconstruction software in order to visualize in detail the more cryptic muscle sets of larval and adult brachiopods. Investigation of myogenesis was carried out in the course of the present <strong>PhD</strong> study in order to obtain a clearer picture of the entire brachiopod muscular bauplan as well as the dynamics of
Page 1 and 2: Comparative neurogenesis, muscle de
Page 3 and 4: 2 Principal supervisor Assoc. P
Page 5 and 6: 4 Preface This thesis presents
Page 7 and 8: 6 Abstract Brachiopods are a sm
Page 9: 8 Acknowledgements The endeavou
Page 13 and 14: 12 Material and methods Material an
Page 15 and 16: 14 Material and methods purpuratus,
Page 17 and 18: 16 Results and discussion Results a
Page 19 and 20: 18 Results and discussion posterior
Page 21 and 22: 20 Results and discussion Myogenesi
Page 23 and 24: 22 Results and discussion Wanninger
Page 25 and 26: 24 Results and discussion Growth pa
Page 27 and 28: 26 Results and discussion argument
Page 29 and 30: 28 References References Abdelkhale
Page 31 and 32: 30 References priapulids and protos
Page 33 and 34: 32 References James, M. A., Ansell,
Page 35 and 36: 34 References regionalization, prol
Page 37 and 38: 36 References 211. Williams, A., Ca
Page 39 and 40: 38 Chapter II Frontiers in Zoology
Page 53 and 54: 52 Chapter III Chapter III Altenbur
Page 55 and 56: 54 Chapter III Altenburger and Wann
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60 Chapter III Altenburger and Wann
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62 Chapter IV Chapter IV Altenburge
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64 Submitted manuscript Chapter IV
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PhD thesis

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