Contributions to Zoology, 85 (2) – 2016Fabio Scarpa; Piero Cossu; Tiziana Lai; Daria Sanna; Marco Curini-Galletti; Marco Casu: Meiofaunal cryptic species challenge species delimitation: the case of the Monocelis lineata (Platyhelminthes: Proseriata) species complex

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Discrepancies among markers and methods may contribute to the elucidation of their limits. Indeed, although genetic data have recently became the primary workhorse used for species delimitation, an uncritical adoption of any species delimitation method in this case would have resulted in a taxonomic resolution that might have not reflected the evolutionary history and speciation processes of the M. lineata complex.

Purely genetic methods can inadequately describe diversity and require significant amounts of genetic data to delimit rapid radiation (Edwards and Knowles, 2014 and references therein), and evolutionary processes may impact the detection of species using only a single datatype (either genetic or morphological). The integration of information from as many markers as possible, i.e., integrative taxonomy, remains thus the best option for overcoming the limits of a single source of data.

Although we partially resolved the M. lineata complex by describing two new species, there is evidence pointing to the existence of an Atlantic-Mediterranean hyper-cryptic complex, which still needs to be explored. More researches involving more populations across biogeographic breaks, more inclusive cross-breeding experiments, and the adoption of molecular markers better tailored to tackle the rapid radiations that occur along morphological/ecological axes (see Wagner et al., 2013 and references therein) are still needed.

Our research has involved a number of populations and extensive coverage of a geographic area, which is unusual in studies of meiofauna, and a potentially interesting outcome is that these minute organisms, which are usually completely neglected in overviews of marine biodiversity conservation (e.g., Bianchi, 2007), may have restricted distributions (see also Casu and Curini-Galletti, 2006; Casu et al., 2009, 2011a, 2012, 2014; Leasi and Norenburg, 2014), and can be particularly affected by the alteration of habitats, facing the threats of silent extinction.