Abstract
Meiofauna represent one of the most abundant and diverse communities in marine benthic ecosystems. However, an accurate assessment of diversity at the level of species has been and remains challenging for these microscopic organisms. Therefore, for many taxa, especially the soft body forms such as nemerteans, which often lack clear diagnostic morphological traits, DNA taxonomy is an effective means to assess species diversity. Morphological taxonomy of Nemertea is well documented as complicated by scarcity of unambiguous character states and compromised by diagnoses of a majority of species (and higher clades) being inadequate or based on ambiguous characters and character states. Therefore, recent studies have advocated for the primacy of molecular tools to solve the taxonomy of this group. DNA taxonomy uncovers possible hidden cryptic species, provides a coherent means to systematize taxa in definite clades, and also reveals possible biogeographic patterns. Here, we analyze diversity of nemertean species by considering the barcode region of the mitochondrial gene Cytochrome Oxidase subunit I (COI) and different species delineation approaches in order to infer evolutionarily significant units. In the aim to uncover actual diversity of meiofaunal nemerteans across different sites in Central America, COI sequences were obtained for specimens assigned here to the genera Cephalothrix, Ototyphlonemertes, and Tetrastemma-like worms, each commonly encountered in our sampling. Additional genetic, taxonomic, and geographic data of other specimens belonging to these genera were added from GenBank. Results are consistent across different DNA taxonomy approaches, and revealed (i) the presence of several hidden cryptic species and (ii) numerous potential misidentifications due to traditional taxonomy. (iii) We additionally test a possible biogeographic pattern of taxonomic units revealed by this study, and, except for a few cases, the putative species seem not to be widely distributed, in contrast to what traditional taxonomy would suggest for the recognized morphotypes.
Highlights
Reports of species occurrences and species lists are the basis for any biogeographic analysis
We examine the barcode region of the mitochondrial gene Cytochrome Oxidase subunit I (COI) and use different species delimitation approaches to quantify the putative presence of cryptic species within marine meiofaunal Nemertea, and uncover, at least in part, their actual diversity
Traditional taxonomy Out of the total 222 specimens collected from 49 sites in the three major localities, a total of 67 morphotypes were designated
Summary
Reports of species occurrences and species lists are the basis for any biogeographic analysis. Meiofauna constitute among the most diverse, species-rich, and abundant communities of marine biocenoses; suites of organisms from many completely different evolutionary histories are present in the same habitat and in a relatively small sample at that [4]. This provides an invaluable model to identify generalities in macroecology and biogeography that transcend phylogenetic constraints [5]. With molecular approaches but even with higher resolution microscopy, complexes of cryptic species are reported from a broad systematic range of small marine animals, such as cycliophorans [9], copepods [10], [11], interstitial polychaetes [12], [13], platyhelminthes [14], [15], [16], rotifers [17], [18], nematodes [19], [20], [21], [22], gastrotrichs [23], and nemerteans [24], [25]
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