Palaeoecology and environmental conditions 3

Size and developmental stages 5

Systematic status of orsten arthropods 6

Material and methods 6

Material 6

Methods 7

Processing and measurements 7

Two larval series 8

Terminology 8

Systematic palaeontology 10

Rehbachiella kinnekullensis Müller, 1983 10

Postembryonic development 13

General remarks 13

Development of series A 13

Naupliar phase 13

Post-naupliar phase 20

Development of series B 30

Naupliar phase 30

Post-naupliar phaev31

Unassigned specimens and further instars 39

Life history 41

Ontogenetic stages 41

Two larval series 41

Growth 42

Morphogenesis 44

Intraspecific variation 50

Functional morphology and life habits 50

Early Larvae 50

Remarks 50

Locomotion and feeding of the nauplii 51

Advanced stages 54

Functional ontogenetic changes 54

Function of the advanced apparatus 56

Mode of life and habitat 61

Discussion 61

Affinities of Rehbachiella 61

Position within Crustacea s. str. (= crown-group Crustacea 61

Exclusion of closer relationships with non-branchiopods 64

General features and systematic status of Branchiopoda 67

Relationships within Branchiopoda and possible taxonomic position of Rehbachiella 70

Characters of the two branchiopod lineages 73

Anostraca 73

Phyllopoda 77

Comparative ontogeny 80

Remarks 80

Development of Rehbachiella as a comparative reference series 82

Comparisons 83

Results 83

Conclusions 90

Comparisons of locomotory and feeding apparatuses 95

General remarks 95

The bipartite locomotory and feeding apparatus 99

Comparisons 100

The branchiopod model of the limb apparatus of Rehbachiella 105

Significance of morphological details 107

Neck organ 108

Cephalic shields and carapaces 110

Structures in the head region 114

Appendages 115

Ventrocaudal processes 120

Segmental organs 120

Tagmosis 120

Concluding remarks 121

Acknowledgements 124

References 125

Addendum 133

Plates 134

List of abbreviations 202

List of Figures