Biodiversity of marine flatworms (Polycladida, Platyhelminthes) in southeastern Australia

Polycladida is an order of free-living invertebrates of the Phylum Platyhelminthes, commonly referred to as flatworms. The functional roles of polyclad flatworms in ecological communities are anticipated to be complex and variable but our understanding of such processes is currently hampered by a lack of information on fundamental knowledge, such as the taxonomy of species in various habitats and regions. These gaps in the knowledge of the group are mostly related to the small number of researchers actively working on it, and to the discontinuity in time of the studies conducted so far. Southeastern Australia is a known biodiversity hotspot for several groups of marine organisms, yet only nine research articles have been published that include species from the southeastern region since 1855. This thesis explores the biodiversity, taxonomy and systematics of southeastern Australian polyclad flatworms, and new insights into the ecology and genomics of polyclads, as well as potential new avenues for species description and identification, are provided. The research conducted contributes new and original data concerning biodiversity, type material, DNA sequences, and phylogeny of Polycladida, filling the gaps about intertidal polyclad fauna in this region. New ecological data is employed to determine hotspot locations for flatworm occurrence in boulder beaches across southeastern Australia and improve our understanding of the factors that shape flatworm distribution and abundance in these environments. Moreover, the usefulness of different genes for molecular systematics in this taxon are analysed, contributing to the effort towards reconstructing a robust Polycladida phylogeny. Lastly, novel imaging techniques to create 3D objects from 2D histological sections are explored, creating for the first time a reproducible method of species identification and a way to store and share valuable knowledge for current and future generations. The knowledge provided by this thesis will give vital information for the conservation and management of this understudied group of animals.