Trematoda Taxonomy

[Jenifer Griffard]

DisclaimerThe NCBI taxonomy database is not an authoritative source for nomenclature or classification - please consult the relevant scientific literature for the most reliable information.

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To date, morphological analysis has been the cornerstone to trematode systematics. However, since the late-1980s we have seen an increased integration of genetic data to overcome problems encountered when morphological data are considered in isolation. Here, we provide advice regarding the 'best molecular practice' for trematode taxonomy and systematic studies, in an attempt to help unify the field and provide a solid foundation to underpin future work. Emphasis is placed on defining the study goals and recommendations are made regarding sample preservation, extraction methods, and the submission of molecular vouchers. We advocate generating sequence data from all parasite species/host species/geographic location combinations and stress the importance of selecting two independently evolving loci (one ribosomal and one mitochondrial marker). We recommend that loci should be chosen to provide genetic variation suitable to address the question at hand and for which sufficient 'useful' comparative sequence data already exist. Quality control of the molecular data via using proof-reading Taq polymerase, sequencing PCR amplicons using both forward and reverse primers, ensuring that a minimum of 85% overlap exists when constructing consensus sequences, and checking electropherograms by eye is stressed. We advise that all genetic results are best interpreted using a holistic biological approach, which considers morphology, host identity, collection locality, and ecology. Finally, we consider what advances next-generation sequencing holds for trematode taxonomy and systematics.

The platyhelminth class Trematoda comprises two subclasses with largely disparate species diversity, the small Aspidogastrea with c.80 species and the speciose Digenea with c.18,000 species, which has attracted much effort towards our understanding of evolutionary relationships among suprageneric taxa. This chapter focuses on insights into the classification of the Digenea that have become apparent from our advanced understanding of both morphological and molecular data. The field of molecular systematics of the Digenea has experienced significant advances over the past 15 years. Phylogenetic analyses of sequence data predominantly from the 18S and 28S rRNA genes have incorporated a considerable diversity of taxa thus increasing the accuracy of phylogenetic inferences at higher taxonomic levels. As a result, the status of long-standing supraspecific taxa has been revised, new higher-level taxa have been defined, and inferences made in association with morphological and life-cycle evidence. A substantial effort has been made towards a classification reflecting the natural system of the Digenea by considering morphological evidence in conjunction with phylogenies inferred from molecular data; this has resulted in considerable congruence. However, limited taxon sampling in the phylogeny of the Digenea still remains relevant especially in relation to some higher-level taxa, and an outline of these omissions is presented. A framework that has led to robust estimates of phylogeny is outlined, and the application of advanced morphological and molecular approaches in digenean taxonomy and systematics is illustrated using the most comprehensively studied digenean superfamilies.

Crowcroft, PW 1945, 'A Description of Sterrhurus macrorchis n. sp., with notes onthe taxonomy of the Genus Sterrhurus Looss (Trematoda-Hemiuridae)', Papers and Proceedings of the Royal Society of Tasmania , 39--48 .

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