x
2.3 Structure and Development of Brood Chambers in Cheilostomata ................... 131
2.3.1 Brood Chambers of Calloporidae: Basic Type
and Structural Diversity ......................................................................... 131
2.3.2 Structure and Development of Ovicells in Other
Cheilostome Families ............................................................................ 137
2.3.3 Internal Brood Sacs ................................................................................ 144
2.3.4 Bivalved Ovicells ................................................................................... 146
2.3.5 Acanthostegal Brood Chambers ............................................................ 147
2.4 Evolution of Brood Chambers in Cheilostomata ............................................... 148
2.4.1 External Membranous Brood Sacs ........................................................ 148
2.4.2 Origin of Brooding in Cheilostomata: Overview
of the Major Hypotheses ........................................................................ 149
2.4.3 Early Stages in Ovicell Evolution .......................................................... 151
2.4.4 Evolution of Ovicells in the Family Cribrilinidae ................................. 152
2.4.5 Evolution of Ovicells in the Genera Monoporella
and Macropora ...................................................................................... 153
2.4.6 Acanthostegal Brood Chambers of Tendridae and Ovicells
of Bellulopora ........................................................................................ 154
2.4.7 Evolution of the Unitary Ooecium and Frontal Shield .......................... 154
2.4.8 Major Trends in the Evolution of Cheilostome Ovicells ....................... 157
2.4.9 Brood Chambers in the Scrupariidae, Thalamoporellidae
and Alysidiidae ...................................................................................... 165
2.5 Conclusions ........................................................................................................ 166
References ................................................................................................................... 221
3 Evolution of Reproductive Patterns in Cheilostomata .......................................... 229
3.1 Modifi cation of Oogenesis and Its Evolutionary Consequences ....................... 230
3.1.1 Changes in Oogenesis and Evolution of the Lecithotrophic Larva ....... 230
3.1.2 Other Consequences of Modifi cations to Oogenesis ............................. 236
3.2 Early Fertilization and Origin of Nurse Cells .................................................... 243
3.3 Evolution of Matrotrophic Incubation in Cheilostomata ................................... 245
3.3.1 Origin of Placentotrophy ....................................................................... 245
3.3.2 Multiple Origins of Placentotrophy in Cheilostomata ........................... 248
3.3.3 Plausibility of an Alternative Scenario .................................................. 248
3.3.4 Origin of Viviparity in the Family Epistomiidae ................................... 249
3.3.5 Adaptive Importance of Placental Analogues in Cheilostomata ........... 250
3.3.6 Prerequisites and Role of Embryo in Evolution of Matrotrophy ........... 251
3.3.7 Matrotrophy and Evolution of Sexual Polymorphism
in Cheilostomata .................................................................................... 251
3.3.8 Distribution of Placentotrophy in Bryozoa ............................................ 251
3.4 Causes, Stages and Consequences of Transition to Endotrophy
in Cheilostomata and Ctenostomata .................................................................. 252
3.4.1 Lecithotrophy and Brooding .................................................................. 252
3.4.2 Fertilization and Modifi cation of Oogenesis ......................................... 257
3.4.3 Oviposition in Cheilostome Brooders ................................................... 258
3.4.4 Evolution of Sexual Reproduction Within the Order Ctenostomata...... 258
3.4.5 Environmental Factors and Radiation of Cheilostomata
in the Late Cretaceous ........................................................................... 264
3.4.6 Possible Consequences of Transition to the New
Reproductive Pattern .............................................................................. 267
3.5 Evolution of Sexual Reproduction in Bryozoa .................................................. 269
3.6 Conclusion ......................................................................................................... 271
References ................................................................................................................... 272
Contents
2.3 Structure and Development of Brood Chambers in Cheilostomata ................... 131
2.3.1 Brood Chambers of Calloporidae: Basic Type
and Structural Diversity ......................................................................... 131
2.3.2 Structure and Development of Ovicells in Other
Cheilostome Families ............................................................................ 137
2.3.3 Internal Brood Sacs ................................................................................ 144
2.3.4 Bivalved Ovicells ................................................................................... 146
2.3.5 Acanthostegal Brood Chambers ............................................................ 147
2.4 Evolution of Brood Chambers in Cheilostomata ............................................... 148
2.4.1 External Membranous Brood Sacs ........................................................ 148
2.4.2 Origin of Brooding in Cheilostomata: Overview
of the Major Hypotheses ........................................................................ 149
2.4.3 Early Stages in Ovicell Evolution .......................................................... 151
2.4.4 Evolution of Ovicells in the Family Cribrilinidae ................................. 152
2.4.5 Evolution of Ovicells in the Genera Monoporella
and Macropora ...................................................................................... 153
2.4.6 Acanthostegal Brood Chambers of Tendridae and Ovicells
of Bellulopora ........................................................................................ 154
2.4.7 Evolution of the Unitary Ooecium and Frontal Shield .......................... 154
2.4.8 Major Trends in the Evolution of Cheilostome Ovicells ....................... 157
2.4.9 Brood Chambers in the Scrupariidae, Thalamoporellidae
and Alysidiidae ...................................................................................... 165
2.5 Conclusions ........................................................................................................ 166
References ................................................................................................................... 221
3 Evolution of Reproductive Patterns in Cheilostomata .......................................... 229
3.1 Modifi cation of Oogenesis and Its Evolutionary Consequences ....................... 230
3.1.1 Changes in Oogenesis and Evolution of the Lecithotrophic Larva ....... 230
3.1.2 Other Consequences of Modifi cations to Oogenesis ............................. 236
3.2 Early Fertilization and Origin of Nurse Cells .................................................... 243
3.3 Evolution of Matrotrophic Incubation in Cheilostomata ................................... 245
3.3.1 Origin of Placentotrophy ....................................................................... 245
3.3.2 Multiple Origins of Placentotrophy in Cheilostomata ........................... 248
3.3.3 Plausibility of an Alternative Scenario .................................................. 248
3.3.4 Origin of Viviparity in the Family Epistomiidae ................................... 249
3.3.5 Adaptive Importance of Placental Analogues in Cheilostomata ........... 250
3.3.6 Prerequisites and Role of Embryo in Evolution of Matrotrophy ........... 251
3.3.7 Matrotrophy and Evolution of Sexual Polymorphism
in Cheilostomata .................................................................................... 251
3.3.8 Distribution of Placentotrophy in Bryozoa ............................................ 251
3.4 Causes, Stages and Consequences of Transition to Endotrophy
in Cheilostomata and Ctenostomata .................................................................. 252
3.4.1 Lecithotrophy and Brooding .................................................................. 252
3.4.2 Fertilization and Modifi cation of Oogenesis ......................................... 257
3.4.3 Oviposition in Cheilostome Brooders ................................................... 258
3.4.4 Evolution of Sexual Reproduction Within the Order Ctenostomata...... 258
3.4.5 Environmental Factors and Radiation of Cheilostomata
in the Late Cretaceous ........................................................................... 264
3.4.6 Possible Consequences of Transition to the New
Reproductive Pattern .............................................................................. 267
3.5 Evolution of Sexual Reproduction in Bryozoa .................................................. 269
3.6 Conclusion ......................................................................................................... 271
References ................................................................................................................... 272
Contents