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Abstract
Marine hydroids are important benthic components of shallow and deep waters worldwide, but their taxonomy is controversial because diagnostic morphological characters to categorize taxa are limited. Their genetic relationships are also little investigated. We tested taxonomic hypotheses within the highly speciose superfamily Plumularioidea by integrating a classical morphological approach with DNA barcoding of the 16S and COI mitochondrial markers for 659 and 196 specimens of Plumularioidea, respectively. Adding Genbank sequences, we inferred systematic relationships among 1,114 plumularioids, corresponding to 123 nominal species and 17 novel morphospecies in five families of Plumularioidea. We found considerable inconsistencies in the systematics of nominal families, genera and species. The families Kirchenpaueriidae and Plumulariidae were polyphyletic and the Halopterididae paraphyletic. Most genera of Plumularioidea are not monophyletic. Species diversity is considerably underestimated. Within our study, at least 10% of the morphologically-distinctive morphospecies are undescribed, and about 40% of the overall species richness is represented by cryptic species. Convergent evolution and morphological plasticity therefore blur systematic relationships. Additionally, cryptic taxa occur frequently in sympatry or parapatry, complicating correspondence with type material of described species. Sometimes conspecificity of different morphotypes was found. The taxonomy of hydroids requires continued comprehensive revision.
Highlights
Hypothesizing common ancestry of each group of taxa in a hierarchic ordering, taxonomists seek diagnostic morphological homologous characters for each cluster, and name the resulting assemblages
We propose desirable taxonomic practices to clarify the systematics of the superfamily Plumularioidea, which in general should be applied to the phylum Cnidaria or other problematic taxonomic groups
We analyzed in further detail phylogenetic relationships for 250 Plumularioidea specimens with concatenated c oxidase subunit I (COI) and 16S sequence data
Summary
Hypothesizing common ancestry of each group of taxa in a hierarchic ordering, taxonomists seek diagnostic morphological (and physiological and molecular) homologous characters for each cluster, and name the resulting assemblages. We sequenced fragments of both the 16S and COI mitochondrial genes from many members of the highly speciose superfamily Plumularioidea (Order Leptothecata, Class Hydrozoa; Fig. 1). Despite the general ubiquity and prominent colony sizes of many plumularioid species, the taxonomy of Plumularioidea has been highly disputed and unsettled. Previous molecular analyses of some assemblages of Plumularioidea have revealed taxonomic inconsistencies, including polyphyletic or paraphyletic groupings, synonymies and cryptic lineages[6,9,16,18,19,23,24,25]. We test taxonomic relationships within the group through the integration of morphologic characters and molecular phylogenetic analyses of two mitochondrial genetic markers - 16S and COI. We investigate geographic and bathymetric distributions of some species
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