Platyhelminth systematics and the emergence of new characters

Abstract

Summary :Since the inclusion of molecular data in modern phylogenetic analyses, significant progress in resolving the origins and radiation of flatworms has been made, although some key problems remain. Here I review developments in the supply and use of systematic characters that provide the basis for diagnosis and phylogeny reconstruction, that in turn have driven systematic revisions and the interpretation of broader evolutionary patterns and processes; focus is placed on the parasitic taxa. Although useful tools have been refined to the point of becoming established systematic markers of broad utility, attention to the need for denser gene and taxon sampling is addressed in the light of unresolved questions and current trends in molecular systematics, from nucleotide to genome. Tradition and the nature of available comparative information tends to dictate the choice of systematic markers, but faced with incongruent phylogenies, the emergence of new technologies and the need for rapid species diagnosis, there is a pressing need to assess and standardize our choice of tools so they are fit for purpose, available to all and used widely. I present a brief review of existing and potential sources of phylogenetic characters and discuss their likely value in the context of the systematics and diagnostics of parasitic flatworms.

Spermatological characters of the aspidogastrean Aspidogaster limacoides Diesing, 1835

“…The presence of the long undulating membrane and continuous row of cortical microtubules in the aspidogastreans seem to be more related to the polyopisthocotylean monogeneans, which may support the assumption that the Monogenea are a paraphyletic group, formed by unrelated monopisthocotyleans and polyopisthocotyleans (Littlewood 2008).…”

Ultrastructure of the ovarian follicles, oviducts and oocytes of Gyrocotyle urna (Neodermata: Gyrocotylidea)

“…Among the Neoophora some Proseriata and some Fecampiidae have an arrangement of the ovary in the form of isolated follicles and collecting ducts. Recent molecular phylogenetic studies have shown that Adiaphanida (including Prolecitophora, Tricladida and Fecampiidae) are a sister taxon to the Neodermata, but Proseriata appear to be basal to Neodermata and Adiaphanida (Lockyer et al 2003, Willems et al 2006, Littlewood 2008.…”

Constraining the Deep Origin of Parasitic Flatworms and Host-Interactions with Fossil Evidence

“…Furthermore, molecular analyses have considerably shifted our views on flatworm phylogeny (Lockyer et al, 2003a;Olson and Tkach, 2005;Littlewood, 2008;Perkins et al, 2010;Laumer and Giribet, 2014) with implications for older hypotheses of parasiteehost coevolution. Due to the patchy fossil record, establishing the phylogeny of flatworms is particularly important for establishing a timeline for the group.…”