Advances in the Biology of Turbellarians and Related Platyhelminthes

Developments in Hydrobiology 32

Series editor

H.J. Dumont

Advances in the Biology of Turbellarians and Related Platyhelminthes

Proceedings of the Fourth International Symposium on the Turbellaria held at Fredericton, New Brunswick, Canada, August 5 -10, 1984

Edited by Seth Tyler

With the assistance of the Editorial Board: Reinhard M. Rieger Julian P.S. Smith, III

Michael D.B. Burt Nathan W. Riser

Barbara M. McKinnon

Reprinted from Hydrobiologia, vol. 132 (1986)

1986 DR W. JUNK PUBLISHERS a member of the KLUWER ACADEMIC PUBLISHERS GROUP DORDRECHTI BOSTON I LANCASTER

Distributors

for the United States and Canada: Kluwer Academic Publishers, 190 Old Derby Street, Hingham, MA 02043, USA for the UK and Ireland: Kluwer Academic Publishers, MTP Press Limited, Falcon House, Queen Square, Lancaster LAI IRN, UK for all other countries: Kluwer Academic Publishers Group, Distribution Center, P.O. Box 322, 3300 AH Dordrecht, The Netherlands

Library of Congress Cataloging in Publication Data

International Symposium on the Turbellaria (4th : 1984 : Fredericton, N.B.) Advances in the biology of turbellarians and related

platyhelminths.

(Developments in hydrobiology ; 32) "Reprinted from Hydrology vol. 131 (1985)." Includes index. 1. Turbellaria--Congresses. 2. Platyhelminththes-­

Congresses. I. Tyler, Seth. II. Rieger, Reinhard M. III. Title. IV. Series. QL391. P7I57 1984 595.1' 23 85-23984

ISBN-13: 978-94-010-8632-5 e-ISBN-13: 978-94-009-4810-5 DOl: 10.1007/978-94-009-4810-5

Cover design Max Velthuijs

Copyright

© 1986 by Dr W. Junk Publishers, Dordrecht.

Softcover reprint of the hardcover 1 st edition 1986

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publishers, Dr W. Junk Publishers, P.O. Box 163, 3300 AD Dordrecht, The Netherlands.

v

Preface

While the reality of the taxon Turbellaria has been called into question lately, turbellarians are nevertheless the subject of active research by a sizable group of biologists. Turbellarians are relatives of the major groups of parasitic platyhelminthes - monogeneans, digeneans, and tapeworms - and most are free-living. Because the ancestors to the major parasitic groups would be classified as turbellarians, strict application of princi­ples of phylogenetic systematics dictates that the Turbellaria is not properly considered a separate taxon; i.e., it is, in the parlance of systematics, a paraphyletic group. The relationships of turbellarians to other inver­tebrates are even more problematic than their relationships to other platyhelminthes; their relatively simple morphology has been variously interpreted as quintessentially primitive - meaning a turbellarian-like ances­tor would have given rise to most of the major groups of invertebrates - or as secondary simplification, meaning they would essentially be a dead-end group.

Modern research on turbellarians covers a broad spectrum. Questions of phylogenetics have inspired ultrastructural studies; the simply structured nervous systems of turbellarians make them good subjects for neurophysiology; simplicity of their tissue structure and the limited number of cell types make them good subjects of embryological and regeneration studies; they are emerging as iIIJ.portant indicator species in ecolo­gy; and improvements in biochemical methodology have meant they are at last amenable - despite their small size - to molecular biological study.

The 45 papers in this volume are representative of current research on turbellarians. These papers were presented at the Fourth International Symposium on the Turbellaria held on the campus of the University of New Brunswick, Fredericton, Canada, in August of 1984. As with the other three symposia in this series (1970 at Chicago; 1977 at Tvaerminne, Finland; and 1980 at Diepenbeek, Belgium), invitations were sent to all biologists publishing research dealing with turbellarians; but the scope of this particular symposium was expanded with invitations also to biologists working on parasitic platyhelminth taxa. It was hoped by this to open the way to gaining a better perspective on the position of the Turbellaria in evolution and to bridge the artifical gap that now stands between studies on parasitic and studies on free-living platyhelminthes. Hence, the title' of this volume departs from the tradition followed in the published proceedings of the preceeding symposia*: obviously the scope is broadened with inclusion of other platyhelminths related to the turbellarians, and, in deference to phylogenetic systematists, we use the term 'turbellarian' in its vernacu­lar sense.

The program for the symposium encompassed 70 titles submitted for presentation by scientists from 19 countries. The task of managing the program as well as the accommodation, feasting, and entertainment of the participants was handled in a truly herculean manner by Dr. Michael D. B. Burt, Chairman of the Department of Biology at the University of New Brunswick, with help from many members of that Depart-

* Proceedings of the other symposia are published as - Riser, N. W. & M. P. Morse (eds), Biology of the TurbeIIaria. McGraw-HilI, New York, 533 pp. - KarIing, T. G. & M. Meinander (eds), The Alex. Luther Centennial Symposium on the TurbeIIaria. Acta zool. fenn. 154: 1- 207. - Schockaert, E. R. & I. R. Ball (eds), The Biology of the Turbellaria, Developments in Hydrobiology 6. Dr. W. Junk Publishers, The

Hague, Boston, London, 301 pp.

VI

ment. Undaunted by the unexpectedly sultry weather of those August days, he directed all of the local ar­rangements, making the entire gathering feel royally entertained. Other members of the organizing commit­tee, with admittedly smaller roles, were Reinhard Rieger, N. W. Riser, and Seth Tyler.

We gratefully acknowledge the University of New Brunswick for so graciously making its facilities availa­ble to the symposium and for the financial support it provided. We thank, also, for financial support, the City of Fredericton, the Natural Sciences and Engineering Research Council of Canada, and the US National Science Foundation (Systematic Biology Program, grant BSR 8401462).

For help in reviewing manuscripts, the Editorial Board thanks Ian R. Ball, Daniel R. Brooks, J. Richard Cook, Stephen R. Fegley, Roman Kenk, Marianne D. Klauser, J. Klima, Irving L. Kornfield, Charles W. Major, Edward E. Ruppert, Mary Beth Thomas, 1. M. Turbeville, W. Wieser, and Bonnie G. Wood.

Seth Tyler

Contents

Preface................................................................................ V

List of participants and contributors ...................................................... XIII

PHYWGENY

Comments on a phylogenetic system of the Platyhelminthes by U. Ehlers ........................................................................ .

Is the Turbellaria polyphyletic? by J. P. S. Smith, S. Tyler and R. M. Rieger ............................................. 13

The major parasitic platyhelminth classes - progressive or regressive evolution? by O. Malmberg ...................................................................... 23

Initial morphological diversity as a criterion in deciphering turbellarian phylogeny by Yu. V. Mamkaev ................................................................... 31

Asexual reproduction and the turbellarian archetype by R. M. Rieger.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Ultrastructure of the frontal organ in Convoluta and Macrostomum spp.: significance for models of the turbellarian archetype by M. D. Klauser, J. P. S. Smith, III and S. Tyler. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

The phylogenetic significance of sperm morphology in the Platyhelminthes by J. Hendelberg ..................................................................... 53

Phylogenetic relationships of the Temnocephaloidea (Platyhelminthes) by J. B. Williams ..................................................................... 59

An ultrastuctural and cytochemical study of the digestive system in Oxyposthia praedator (Turbellaria: Acoela) by T. O. Markosova ................................................................... 69

Frontal organs in the Acoelomorpha (Turbellaria): ultrastructure and phylogenetic significance by J. P. S. Smith and S. Tyler .......................................................... 71

NERVOUS SYSTEM AND SENSORY STRUCTURES

On the evolution of central nervous systems: implications from polyclad turbellarian neurobiology by H. Koopowitz ..................................................................... 79

Comparative characterization of the nervous system of the Turbellaria by E. A. Kotikova ..................... : ................................ _ - . . . . . . . . . . . . 89

VIII

Neuropeptides III free-living and parasitic flatworms (Platyhelminthes). An immunocytochemical study by M. Wikgren, M. Reuter and M. Gustafsson ........................................... 93

Aspects of photoreceptor structure and phototactic behavior in Platyhelminthes, with particular reference to the symbiotic turbellarian Paravortex by A. W. Pike and R. Wink ........................................................... 101

ONTOGENY

Embryology of the Turbellaria and its phylogenetic significance by M. B. Thomas ..................................................................... 105

Experimental evidence for the origins of determinative development in the polyclad turbellarians by B. C. Boyer ....................................................................... 117

Electron microscopic study of larval eye development in Turbellaria Polycladida by A. Lanfranchi and C. Bedini ........................................................ 121

REPRODUCTIVE SYSTEM

Eggshell formation in polyclads (Turbellaria) by S. Ishida and W. Teshirogi .......................................................... 127

Fine-structural characters in female and male germ cells of Proseriata Otoplanidae (Platyhelminthes) by B. Sopott = Ehlers ................................................................ 137

Ultrastructural features of oogenesis in some marine neoophoran turbellarians by V. Gremigni, M. Nigro and M. Settembrini ........................................... 145

Ultrastructural investigations on the differentiation of genital hard structures in free-living platy­helminths and their phylogenetic significance by J. Briiggeman ..................................................................... 151

Ultrastructure of the copulatory stylet and accessory spines in Haplopharynx quadristimulus (Turbel­laria). by D. A. Doe ........................................................................ 157

Comparative ultrastructure of copulatory organs having a stylet in the Proseriata (Turbellaria) by E. E. Martens ..................................................................... 165

Development of the reproductive apparatus of the land planarian Rhynchodemus sylvaticus (Turbel­laria: Tricladida) and its significance for classification in the genus by R. E. Ogren ....................................................................... 175

REGENERATION

Cell migration and differentiation during wound healing and regeneration in Microstomum lineare (Tur bellaria) by 1. Palmberg ....................................................................... 181

Physiological regeneration of the digestive parenchyma in Convoluta convoluta and Oxyposthia praedator (Turbellaria, Acoela) by 1. M. Drobysheva .................................................................. 189

Asexual reproduction, regeneration, and somatic embryogenesis in the planarian Dugesia tigrina (Turbellaria) by E. B. Krichinskaya ................................................................. 195

IX

Positional information and gonadal differentiation in the planarian Dugesia lugubris (Turbellaria) by E. Ghirardelli, A. Di Marcotullio and F. Persi ......................................... 201

On the origins of neoblasts in freshwater planarians (Turbellaria) by W. Teshirogi ...................................................................... 207

Ultrastructural observations on gastrodermal regeneration in the planarian Dugesia japonica (Turbel­laria) by I. Hori ........................................................................... 217

Protein phosphorylation and the role of Ca2 + in planarian turbellarian regeneration by J. Moraczewski, I. Martelly and R. Franquinet ........................................ 223

Biology of long slender land planarians (Turbellaria) in Tokyo and environs by N. Makino and Y. Shirasawa ........................................................ 229

SYSTEMATICS AND CYTOWGY

Karyology of a marine population of Gyratrix hermaphroditus (Turbellaria, Rhabdocoela) and chro­mosomal evolution in this species complex by J.-P. eHardy ...................................................................... 233

Chromosomal evolution in marine triclads and polyclads (Turbellaria) by L. Galleni and I. Puccinelli ......................................................... 239

Variation in karyotypes of Dl4gesia japonica japonica (Turbellaria) from Osaka Prefecture, central Japan by S. Tamura ........................................................................ 243

On the karyology of Dugesia gonocepha/a s.l. (Turbellaria, Tricladida) from Montpellier, France by E. J. de Vries ...................................................................... 251

Taxonomic studies on marine triclads (Turbellaria, Tricladida, Maricola) by R. Sluys .......................................................................... 257

ECOLOGY

Ontogenetic patterns and phylogenetic trends in freshwater flatworms (Tricladida); constraint or selection? by P. Calow and D. A. Read ........................................................... 263

Reproductive ecology of Dendrocoelum lacteum (Turbellaria) in a rapid stream in southern Sweden and comparisons with a lake population by J. Herrmann ...................................................................... 273

Salinity-temperature tolerance of two closely related triclad species, Dugesia lugubris and D. polychroa (Turbellaria), in relation to their distribution in The Netherlands by G. Van der Velde, F. Hiisken and L. Van Welie ........................................ 279

Distribution, abundance, and size of rhabdoids in Dugesia polychroa (Turbellaria: Tricladida) by F. 1. Wrona ....................................................................... 287

The importance of turbellarians in the marine meiobenthos: a review by P. M. Martens and E. R. Shockaert .................................................. 295

SYMBIOTIC RELATIONSHIPS

An overview of surface specializations in the digenetic trematodes by B. J. Bogitsh ...................................................................... 305

x

Occurrence of symbiotic turbellarians in the oyster Crassostrea virginica by L. C. Fleming ..................................................................... 311

HISTORY

History of the study of Turbellaria in China. Part 1: Ages of Materia Medica and of early expeditions by westerners by K. Y. Lue and M. Kawakatsu ................................. . ... ... . . . . .. ... .. . .. .. 317

APPENDIX

Electron microscopy of turbellarian platyhelminths - a bibliography by S. Tyler, 1. P. S. Smith, R. M. Rieger, U. Ehlers and V. Gremigni

Index to authors

Index to subjects

323

345

347

XI

AJ A. Jarecka HS Harvey Sarnat LG Lodovico Galleni PS Peter Schwank AL Alberto Lanfranchi IH Isao Hori LJ Lena Jarecka RA Renate Ax AMC Aage M",ner Christensen IPa Irmeli Palm berg MBB Mary Beverly-Burton RB Rod Bray AWP Alan W. Pike IRB Ian R. Ball MB Maria Ball REO Robert E. Ogren BCB Barbara C. Boyer JBB Jay Boyd Best MBT Mary Beth Thomas RMR Reinhard M. Rieger BM Barbara M. MacKinnon JBr Jochen Briiggemann MC-G Marco Curini-Galletti RW Robert Wink DAD David A. Doe JHen Jan Hendelberg MOB M. D. B. Burt SI Sachiko Ishida DB Don Beattie JHer Jan Hermann MDK Marianne D. Klauser STa Sachiko Tamura OM Daniele Murith JK Jerzy Kolasa MGG M. Gabriella Gremigni STy Seth Tyler EdV Elisabeth J. de Vries JO Jean Ogren MR Maria Reuter IJE Ulrich Ehlers EEM Els E. Martens JPS Julian P. S. Smith, III NM Naoya Makino VG Vittorio Gremigni EG E. Ghirardelli JRe J. Reuter NS Naomi Sarnat WF Witold Ferens ERS Ernest R. Schockaert JRi Jean Riser NWR Nathan W. Riser WS Wolfgang Sterrer FJW Frederick J. Wrona KYL Kwang-Yang Lue PA Peter Ax WT Wataru Teshirogi GM G6ran Malmberg LB Louise Bush PC Peter Calow YS Yasuko Shirasawa GV Gerard Van der Velde LCF Lesley C. Fleming PMM Paul M. Martens ZH Zenia Heller HK Harold Koopowitz LC Leser Cannon

XIII

List of participants and contributors

Peter Ax, II. Zoologisches Institut und Museum der Universitat, Berliner Strasse 28, D-3400, Gottingen, Fed­eral Republic of Germany.

Renate Ax, II. Zoologisches Institut und Museum der Universitiit, Berliner Strasse 28, D-3400, Gottingen, Federal Republic of Germany.

Ian R. Ball, Instituut voor Taxonomische Zoologie, Universiteit van Amsterdam, Postbox 20125, NL-1000 HC Amsterdam, The Netherlands.

Maria Ball, Instituut voor Taxonomische Zoologie, Universiteit van Amsterdam, Postbox 20125, NL-1000 HC Amsterdam, The Netherlands.

Don Beattie, Department of Biology, University of New Brunswick, Fredericton, N.B., Canada E3B 6El.

Celina Bedini, Istituto di Biologia Generale, Universita di Pisa, Via Volta 6, 1-56100 Pisa, Italy.

Jay Boyd Best, Colorado State University, Fort Collins, Colorado, USA.

Burton J. Bogitsh, Department of General Biology, Vanderbilt University, Nashville, Tennessee 37235, USA.

Barbara C. Boyer, Department of Biological Sciences, Union College, Schenectady, New York 12308, USA.

Rod Bray, British Museum of Natural History, Cromwell Road, London, England.

Jochem Briiggemann, II. Zoologisches Institut und Museum der Universitiit, Berliner Strasse 28, D-3400, Gottingen, Federal Republic of Germany.

M. D. B. Burt, Department of Biology, University of New Brunswick, Fredericton, N.B. E3B 6E1, Canada.

Mary Beverly-Burton, Department of Zoology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.

Louise Bush, Gray Museum, Marine Biology Laboratory, Woods Hole, Massachusetts 02543, USA.

Peter Calow, Department of Zoology, University of Sheffield, Sheffield SlO 2TN, England.

Lester Cannon, Queensland Museum, Brisbane, Queensland, Australia.

Aage M0ller Christensen, University of Copenhagen, Helsing0r, Denmark.

XIV

Marco Curini Galletti, Istituto di Zoologia e Anatomia Comparata, Universita di Pisa, Via A. Volta 4, Pis a, Italy.

Elisabeth J. de Vries, Instituut voor Taxonomische Zoologie, Universiteit van Amsterdam, Postbox 20125, NL-1000 HC Amsterdam, The Netherlands.

A. Di Marcotullio, Sez. Zoologia, Dipartimento di Biologia, Universita degli Studi, 1-34127, Trieste, Italy.

David A. Doe, Westfield State College, Westfield, Massachusetts 01086, USA.

I. M. Drobysheva, Laboratory of Evolutionary Morphology, Zoological Institute, Academy of Sciences, Leningrad 199034, USSR.

Ulrich Ehlers, II. Zoologisches Institut und Museum der Universitat, Berliner Strasse 28, D-~400 G6ttingen, Federal Republic of Germany.

Witold Ferens, Department of Biology, University of New Brunswick, Fredericton, N.B. E3B 6El, Canada.

Lesley C. Fleming, Department of Biology, University of New Brunswick, Fredericton, N.B. E3B 6E1, Canada.

R. Franquinet, Laboratoire de Biologie Animale, Universite Paris Val de Marne, Avenue General de Gaulle, Creteil 94010, Cedex, France.

Lodovico Galleni, Istituto di Zoologia E Anatomia Comparata, Universita di Pisa, Via A. Volta 4, Pisa, Italy.

E. Ghirardelli, Sez. Zoologia, Dipartimento di Biologia, Universita degli Studi, 1-34127, Trieste, Italy.

M. Gabriella Gremigni, Istituto di Zoologia e Anatomia Comparata, Universita di Pisa, Via Volta n. 4, 56100 Pis a, Italy.

Vittorio Gremigni, Istituto di Zoologia e Anatomia Comparata, Universita di Pisa, Via Volta n. 4, 56100 Pis a, Italy.

Margaretha Gustafsson, Institute of Biology, Abo Akademi, Porthansgatan 3 - 5, SF-20500 Abo 50, Finland.

Zenia Heller, Universita do Vale do Rio dos Sinos, Pra<;a Tiradentes, 35-CXP 275, 93.000 Sao Leopoldo, Brasil.

Jan Hendelberg, Department of Zoology, University of G6teborg, Box 25509, S-40031 Goteborg, Sweden S-40031.

Sherman Hendrix, Department of Biology, Gettysburg College, Gettysburg, Pennsylvania 17325, USA.

Jan Herrmann, Department of Animal Ecology, University of Lund, S-223 62 Lund, Sweden.

Isao Hori, Department of Biology, Kanazawa Medical University, Uchinada-machi, Ishikawa-ken, 920-02, Japan.

Sachiko Ishida, Department of Biology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori-ken 036, Japan.

xv

Lena Jarecka, Department of Biology, University of New Brunswick, Fredericton, N.B. E3B 6El, Canada.

Masaharu Kawakatsu, Biological Laboratory, Fuji Women's College, Kita-16, Nishi-2, Kita-ku, Sapporo (Hokaido) 001, Japan.

Marianne D. Klauser, Department of Zoology, Murray Hall, University of Maine, Orono, Maine 04469, USA.

Jerzy Kolasa, Yale Arbovirus Research Unit, 60 College St., P.O. Box 3333, New Haven, Connecticut 06510, USA.

Harold Koopowitz, Developmental & Cell Biology, University of California, Irvine, California 92717, USA.

E. A. Kotikova, Laboratory of Evolutionary Morphology, Zoological Institute, Academy of Sciences, Leningrad 199034, USSR.

Elena B. Krichinskaya, Department of Embryology, State University of Leningrad, 199164 Leningrad, USSR.

Alberto Lanfranchi, Istituto di Biologia Generale, Universita di Pisa, Via Volta 6, 1-56100 Pisa, Italy.

J.-P. VHardy, Laboratoire de Biologie Animale, Universite du Maine, B. P. 53572017 Le Mans-Cedex, France.

Kwang-Yang Lue, Department of Biology, National Taiwan Normal University, 88 Section 5, Roosevelt Road, Taipei, Taiwan 117.

Barbara M. MacKinnon, Department of Biology, University of New Brunswick, Fredericton, N.B. E3B 6El, Canada.

Naoya Makino, Biology Laboratory, Tokyo Medical College, 6-1-1 Shijuku, Shinjukuku, Tokyo 160, Japan.

Goran Malmberg, Department of Zoology, University of Stockholm, S-106 91 Stockholm, Sweden.

Yu. V. Mamkaev, Laboratory of Evolutionary Morphology, Zoological Institute, Academy of Sciences, Leningrad, 199034, USSR.

T. G. Markosova, Laboratory of Evolutionary Morphology, Zoological Institute, Academy of Sciences, Leningrad 199034, USSR.

I. Martelly, Laboratoire de Biologie Animale, Universite Paris Val de Marne, Avenue General de Gaulle, Creteil 94010, Cedex, France.

Els E. Martens, Department SBM, Limburgs Universitair Centrum, B-361O Diepenbeek, Belgium.

Paul M. Martens, Department SBM, Limburgs Universitair Centrum, B-361O Diepenbeek, Belgium.

J. Moraczewski, Laboratoire de Biologie Animale, Universite Paris Val de Marne, Avenue General de Gaulle, Creteil 94010, Cedex, France.

Daniele Murith, Department of Zoology, University of Guelph, Guelph, Ontario, Canada.

XVI

J. Murith, Department of Zoology, University of Guelph, Guelph, Ontario, Canada.

M. Nigro, Istituto di Zoologia e Anatomia Comparata, Universita di Pisa, Via Volta n. 4, 56100 Pisa, Italy.

Jean Ogren, Department of Biology, Wilkes College, Wilkes-Barre, Pennsylvania 18766, USA.

Robert E. Ogren, Department of Biology, Wilkes College, Wilkes-Barre, Pennsylvania 18766, USA.

Irmeli Palmberg, Institute of Biology, Abo Akademi, Faculty of Education, Kyrkoesplanaden 12-14, 65100 Vasa 10, Finland.

F. Persi, Sez. Zoologia, Dipartimento di Biologia, Universita degli Studi, 1-34127, Trieste, Italy.

Alan W. Pike, Department of Zoology, University of Aberdeen, Tillydrone Ave., Aberd~en AB9 2TN, Scotland.

Ileana Puccinelli, Istituto di Zoologia e Anatomia Comparata, Universita di Pisa, Via A. Volta 4, Pisa, Italy.

D. A. Read, Department of Biology, University of Southampton, Southampton, S09 3TU, England.

Maria Reuter, Institute of Biology, Abo Akademi, Porthansgatan 3 - 5, SF-20500 Abo 50, Finland.

Reinhard M. Rieger, Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27514, USA. [present address: Zoologisches Institut, Universitat Innsbruck, Universitatstrasse 4, A-6020 Innsbruck, Austria.]

Jean Riser, Marine Science Institute, Northeastern University, Nahant, Massachusetts 01908, USA.

Nathan W. Riser, Marine Science Institute, Northeastern University, Nahant, Massachusetts 01908, USA.

Harvey Sarnat, Alberta Children's Hospital, 1820 Richmond Road SW., Calgary, Alberta T2T 5C7, Canada.

Naomi Sarnat, Alberta Children's Hospital. 1820 Richmond Road SW., Calgary, Alberta T2T 5C7, Canada.

Ernest R. Schockaert, Dept. SBM, Limburgs Universitair Centrum, B-361O Diepenbeek, Belgium.

Peter Schwank, Limnologische Flusstation des Max-Planck-Institutes fUr Limnologie, D-6407 Schlitz, Feder­al Republic of Germany.

M. S. Settembrini, Istituto di Zoologia e Anatomia Comparata, Universita di Pis a, Via Volta n. 4, 56100 Pisa, Italy.

Yasuko Shirasawa, Biology Laboratory, Tokyo Medical College, 6-1-1-Shijuku, Shinjukuku, Tokyo 160, Japan.

Ronald Sluys, Instituut voor Taxonomische Zoologie, Universiteit van Amsterdam, Postbox 20125, 1000 HC Amsterdam, The Netherlands.

Julian P. S. Smith, III, Department of Zoology, Murray Hall, University of Maine, Orono, Maine 04469, USA.

XVII

Beate Sopott-Ehlers, II. Zoologisches Institut und Museum der Universitat, Berliner Strasse 28, D-3400 Got­tingen, Federal Republic of Germany.

Wolfgang Sterrer, Bermuda Biological Station, Ferry Reach, 1-15, Bermuda.

Sachiko Tamura, Osaka Prefectural Institute of Public Health, Nakamichi-l-chome 3-69, Higashinari-ku, Osaka 537, Japan.

Wataru Teshirogi, Department of Biology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori-ken 036, Japan.

Mary Beth Thomas, Department of Biology, University of North Carolina, Charlotte, North Carolina 28223, USA.

Seth Tyler, Department of Zoology, Murray Hall, University of Maine, Orono, Maine 04469, USA.

Gerard van der Velde, Laboratory of Aquatic Ecology, Catholic University, Toernooiveld, 6525 ED, Nijme­gen, The Netherlands.

Marianne Wikgren, Institute of Biology, Abo Akademi, Porthansgatan 3 - 5, SF-20500 Abo 50, Finland.

Joan Bowman Williams, Department of Zoology, University of Canterbury, Christchurch, New Zealand.

Robert Wink, Department of Zoology, University of Aberdeen, Tillydrone Ave., Aberdeen AB9 2TN, Scotland.

Frederick 1. Wrona, Department of Biology, University of Calgary, Calgary, Alberta T2N IN4, Canada.