Evolution of clam shrimps - Systematics, comparative morphology and limb functionality

Branchiopoda is a relative small taxon (~1200 described species) of mainly freshwater dwelling crustaceans, including the “large branchiopods” Anostraca (fairy shrimps), Notostraca (tadpole shrimps), Spinicaudata, Cyclestherida, and Laevicaudata (all being clam shrimps) and the smaller sized but more species rich Cladocera (water fleas). Most large branchiopods are strictly found in temporary freshwater bodies that dry out during the year. They depend on producing resting eggs that can survive the periodically/seasonally disappearances of their habitats. In this PhD thesis the Laevicaudata is the main group of focus, however, Cyclestherida, Spinicaudata, and Cladocera are included in some of the works. Laevicaudatans, or smooth clam shrimps, is a troublesome group within Branchiopoda and among the most understudied groups of crustaceans. Laevicaudata is a small group which, previous to this work contained 38 species placed in a single family, Lynceidae, consisting of the three genera Lynceus, Paralimnetis, and Lynceiopsis. Lynceus holds the majority of species (33) and is found nearly worldwide, whereas Paralimnetis (3 species) and Lynceiopsis (2 species), are restricted to the Americas and Africa, respectively. Despite several larger taxonomical contributions, minor revisions/species descriptions, and molecular work on a limited number of species, virtually no attempts have been made in addressing the systematics, phylogenetic relationship and biogeographic distribution of the group, neither based on morphological nor molecular data. Due to the fluctuating, rather unpredictable habitats of Laevicaudata, obtaining material is not straight forward, but thanks to a larger number of museum loans and donations, it has within the scope of this thesis been possible to address several evolutionary and classificatory questions relating to these peculiar, rare animals. Here is presented the first comprehensive insig ht into the phylogeny, systematics, and biogeography of laevicaudatan clam shrimps, includingmolecular- and morphology-based phylogenetic hypotheses, descriptions of four new species, and a deeper general insight into the previously poorly studied group. A comparative study on musculature and functionality of the exotic clam shrimp group Cyclestherida and the more widespread Cladocera, reaches into other parts of the branchiopod taxonomy and present evolutionary similarities and variations in relation to morphology and usage of swimming antennae and filtratory trunk limbs. This Phd thesis provides new knowledge on the evolution of branchiopods and a framework for future studies, especially within the field of smooth clam shrimps.