Revision of the taxonomy, systematics and biogeography of Natatolana (Crustacea: Isopoda: Cirolanidae)
Taxonomic and biogeographical information is reviewed for all species of Natatolana. A revised diagnosis of the genus and a key to species is presented. Fifteen new species from Australia and New Zealand are described. Redescriptions and/or new illustrations are provided for thirteen poorly known species and lectotypes are designated for three species. One subspecies is identified as a species and four species are placed in synonymy. Four species in three genera related to Natatolana are also described. The reliability of morphological characters in separating species of Natatolana is supported by a case study utilising allozyme electrophoresis.
The systematics of Natatolana is revised using cladistic techniques to analyze phylogenetic relationships among species in the genus and among genera of the Cirolanidae. This indicates that the classification of Natatolana and Dolicholana in the subfamily Conilerinae is inappropriate. The setation pattern of pereopod 7 is recognised as a unambiguous synapomorphy of the species placed within Natatolana. This can be used, with several homoplastic synapomorphies, to define the genus as a monophyletic group. Several clades within Natatolana are also identified. However, the relationships within and among these clades are not well resolved. It is suggested that this is a consequence of evolutionary processes, such as stabilisation of selection pressures and hybridization, resulting in homoplasy and difficulties in defining morphological characters which can be used in phylogenetic analysis. Comparison of the distribution of species of Natatolana with hypothesised phylogenetic relationships indicates that the genus may have diversified prior to the early Cretaceous period, 144 million years before present, and become widespread as a result of continental drift. Studies, which examine functional morphology, utilise molecular techniques and obtain specimens from additional geographic areas, are recommended to further clarify species relationships and biogeographic patterns.