Morphometry and taxonomy
Molecular analyses currently tend to displace morphometry in studies trying to discriminate within closely related morphotypes for taxonomic purposes (Blaxter, 2004; Hebert and Gregory, 2005; Godfray, 2007). However, most taxonomists agree that combining the different approaches, applying the so-called Integrative Taxonomy, is the most effective strategy to build a stable and robust taxonomy (Will et al., 2005; Padial et al., 2010). Hence, the importance of morphology must not be forgotten in the genomics era (Giribert, 2015). Moreover, it is not always possible to obtain adequate material for genetic studies because the used preservation methods are destructive, while there is no fresh material available. In such cases morphometry may be the only approach allowing to identify distinguishing characters within species complexes.
Among polychaetes, many taxonomically robust morphological characters may be defined by measurements and/or proportions, some of them being size-dependent (Ben-Eliahu, 1987; Fauchald, 1991; Sigvaldadóttir and Mackie, 1993). This approach has been used independently of molecular analyses to successfully resolve the taxonomy of several sibling species complexes, often leading to the description of new species (Orrhage and Sundberg, 1990; Fauchald, 1991; Blake, 2000; Koh and Bhaud, 2003; Koh et al., 2003; Martin et al., 2003, 2006, 2009; Ford and Hutchings, 2005; Garraffoni and de Garcia Camargo, 2006; Glasby and Glasby, 2006; Lattig et al., 2007; Hernández-Alcántara and Solís-Weiss, 2014; Coutinho et al., 2015). However, Ford and Hutchings (2005) were the first to consider the use of the statistical dissimilarities derived from the SIMPER routine of the PRIMER software (Clarke and Warwick, 2001; Clarke and Gorley, 2006), based on a matrix of morphometric measurements, as a robust support to distinguish between morphologically close species. Accordingly, they described three new species whose average dissimilarities ranged between 11-19%, later finding morphological evidences supporting the erection of the new species. Our morphometric approach, in turn, clearly discriminates the two populations of “O. humesi” which, despite their close morphologies, showed average dissimilarities ranging from 30 to 36% in the SIMPER, thus almost three times higher than the Australian species of Owenia. A detailed comparison of character variability, particularly those that were responsible for the intra-population similarity and the inter-population dissimilarity, led to a reliable way to solve this question. There were significant differences in size range between the Iberian and the Congolese populations (more restricted in the later, leading us to find less size-correlated parameters in Congolese worms). Our approach to compare the two populations led to evident and consistent differences in the appendage measurements and relative proportions (Tables 6, 8) that are considered as robust enough to formally describe the Iberian specimens as the new species O. okupa sp. nov. In addition, we further validate these differences by means of discriminant analyses, whose respective discriminant functions were able to identify the members of the two species with a reliability of 96 to 100% in all tests.