MMORPHOLOGY OF THE TESTES AND SPERMATOGENESIS IN AACOELA && NNEMERTODERMATIDA MIEKE BOONE PROMOTORS: PROF. DR. WIM BERT (UGENT) PROF. DR. TOM ARTOIS (UHASSELT) DR. MAXIME WILLEMS (UGENT) Thesis submitted to obtain the degree of doctor in sciences, biology. Proefschrift voorgelegd tot het bekomen van de graad van doctor in de wetenschappen, biologie. 3 4 “But morphology is a much more complex subject than it at first appears” Darwin, 1872:584 5 6 TABLE OF CONTENTS Chapter 1: Introduction ......................................................................................................... 13 1. General introduction ................................................................................................... 13 2. Characteristics of Acoela and Nemertodermatida ................................................. 14 2.1. Acoela ................................................................................................................... 14 2.2. Nemertodermatida .............................................................................................. 16 3. Phylogeny .................................................................................................................... 17 3.1. Phylogenetic position of Acoela and Nemertodermatida .............................. 17 3.2. Internal phylogenetic relationships ................................................................... 20 3.2.1. Acoela ............................................................................................................ 20 3.2.2. Nemertodermatida ....................................................................................... 21 3.3. Importance and implications of phylogenetic position ................................... 21 3.4. Character evolution ............................................................................................. 22 4. Germ line & gonads ...................................................................................................... 24 Ctenophora .................................................................................................................. 24 Cnidaria ........................................................................................................................ 24 Platyhelminthes ........................................................................................................... 25 Xenoturbella ................................................................................................................ 26 Echinodermata ............................................................................................................ 26 Urochordata ................................................................................................................. 26 Acoela and Nemertodermatida ................................................................................. 27 5. Aims ................................................................................................................................. 28 Chapter 2: First record of Nemertodermatida from Belgian marine waters ................. 29 Background ......................................................................................................................... 31 Introduction ......................................................................................................................... 31 Material & methods ............................................................................................................ 32 Results ................................................................................................................................. 33 Discussion ........................................................................................................................... 35 Acknowledgements ............................................................................................................ 36 7 Chapter 3: Spermatogenesis and the structure of the testes in Nemertodermatida .. 37 Background ......................................................................................................................... 39 Abstract ................................................................................................................................ 39 Introduction ......................................................................................................................... 40 Material and methods ........................................................................................................ 41 Results ................................................................................................................................. 42 Structure of the testes ................................................................................................... 42 Spermatogenesis in Flagellophora apelti ................................................................... 43 The spermatogonium ................................................................................................. 43 The primary spermatocyte ........................................................................................ 43 The secondary spermatocyte ................................................................................... 44 The spermatid ............................................................................................................. 45 The mature spermatozoon F. apelti ......................................................................... 48 Mature spermatozoon in N. westbladi ......................................................................... 49 Discussion ........................................................................................................................... 50 Structure of the testes ................................................................................................... 50 Spermatogenesis ........................................................................................................... 52 Mature spermatozoon .................................................................................................... 53 Acknowledgements ............................................................................................................ 55 Chapter 4: Spermatogenesis and the structure of the testes in Isodiametra pulchra (Isodiametridae, Acoela) ....................................................................................................... 57 Background ......................................................................................................................... 58 Abstract ................................................................................................................................ 58 Introduction ......................................................................................................................... 59 Materials and Methods ...................................................................................................... 61 Cultures ............................................................................................................................ 61 Transmission electron microscopy and sectioning ................................................... 61 8 Results ................................................................................................................................. 62 Structure of the testes ................................................................................................... 62 Spermatogenesis ........................................................................................................... 64 The spermatogonium ................................................................................................. 64 The primary spermatocyte ........................................................................................ 65 The secondary spermatocyte ................................................................................... 66 The spermatid ............................................................................................................. 67 The mature spermatozoon ........................................................................................ 69 Discussion ........................................................................................................................... 70 Spermatogenesis ........................................................................................................... 70 Implications of the structure of the testes ................................................................... 71 Acknowledgements ............................................................................................................ 72 Chapter 5: Acoela .................................................................................................................. 73 Introduction ......................................................................................................................... 73 Material and Methods ........................................................................................................ 74 Results of ultrastructural analysis .................................................................................... 76 Organisation of the testes ............................................................................................. 76 Spermatogenesis ........................................................................................................... 77 Philocelis karlingi .......................................................................................................