Syme, A., 2007. A systematic revision of the Cylindroleberididae (Crustacea: Ostracoda: Myodocopa). Zoology Department, University of Melbourne, Melbourne. PhD Thesys.

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Ostracods of the family Cylindroleberididae are speciose, widespread, and well defined by morphological features including the possession of gills. Despite the family having been divided into three subfamilies, five tribes, 32 genera, and more than 200 species, the relationships between its species have never been analysed phylogenetically. Twenty-five of the 32 genera are not defined by unique features but rather combinations of characters, and may therefore be historical constructions rather than evolutionary groups. The classification is of limited functional and predictive use, and requires a systematic revision. This work resolves several outstanding taxonomic issues. A checklist of the 219 described species is presented, including comments on taxonomic uncertainty. One of the key points of uncertainty concerns the missing specimen upon which the type species Cypridina mariae and the type genus of the family (Cylindroleberis) is based. A neotype is therefore described which clarifies taxonomically important morphological characters, particularly of the first antenna and mandible. To facilitate identification of cylindroleberidid species in ecological surveys and biodiversity estimates, an interactive key is produced, applicable to species in all geographic areas. Three new cylindroleberidid species are described from coastal Australian waters. A cladistic analysis is undertaken in order to test current subfamily and generic concepts against phylogenetic criteria. Using Bayesian likelihood methods, a phylogeny is inferred from both morphological and molecular data. The morphological data come from 141 species and 66 characters. The molecular data are based on predominantly new sequences of both nuclear (28S) and mitochondrial (16S) DNA, for 22 species. The results of the phylogenetic analyses of both morphological and molecular data strongly support the monophyly of the Cylindroleberididae; however, the two phylogenies differ in the topology of subfamily relationships. Where the morphologybased phylogeny suggests that Asteropteroninae and Cyclasteropinae are sister taxa, and then sister to Cylindroleberidinae, the molecular-based phylogeny places Asteropteroninae within the paraphyletic Cylindroleberidinae. The position of the Cyclasteropinae is uncertain. There is much homoplasy in the morphological characters, and the molecular phylogeny is considered more accurate in its representation of relationships within the family. Character mapping on both the morphology- and molecular-based phylogenies indicates that most existing generic diagnostic character states do not uniquely define clades and are likely to be of limited use in any phylogenetically-based classification. However, one character of use is the posterior ridge on the inner carapace which defines two genus level clades. Two new characters are identified of taxonomic use: a lateral seta on the first antenna, and the shape of the posterior of the body. A known fossil cylindroleberidid is dated at 425 million years old; this date was used to calibrate divergence times between clades in the molecular phylogeny. A genuslevel clade in the phylogeny is calibrated to 110 million years old. In the light of this temporal framework, it is not surprising that morphological characters show high levels of homoplasy, representing potential evolutionary convergence. Based on the resolution of taxonomic issues and phylogenetic results, six genera are revised. Cylindroleberis is re-diagnosed based on the neotype Cypridina mariae. The emended diagnosis results in the synonymy of the monotypic Polyleberis with Cylindroleberis. Synasterope is re-diagnosed based on the important morphological character of the posterior ridge, and Postasterope and Heptonema become synonymized with it. Although the monophyly of Parasterope is not demonstrated, it is retained as a broadly-defined genus and its diagnosis expanded to accommodate all former species of Synasterope that lack the posterior ridge.

Systematics, Taxonomy

Ostracoda

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