Although the systematic position of the family Orbiniidae within the Annelida is still under discussion, and the relationships within the Orbiniidae are not yet clear (Hoffman and Hausen, 2007; Bleidorn et al., 2009), the validity and monophyly of the genus Leitoscoloplos seems adequate (Bleidorn et al., 2009). However, the presence of numerous subpodal and stomach papillae in some specimens from the Gulf of California could modify this claim, because these specimens can be distinguished from all other species of the genus only by the higher number and distribution of these papillae.
As previously mentioned, the occurrence of stomach papillae in other genera of the family, as well as their number and distribution, constitute diagnostic characters to identify and differentiate species (Hartman, 1957; Blake, 1996). However, in the genus Leitoscoloplos, this character had been observed only in L. obovatus Mackie, 1987 (1 stomach papilla), and now in the taxa analysed in this study, Leitoscoloplos sp. (1-2 stomach papilla) and L. multipapillatus sp. nov. (up to 14 stomach papillae). Therefore, to fully understand the importance of these papillae to classify species within the genus, we must wait to find other species bearing this character.
With the current information, we cannot discard the possibility that specimens of Leitoscoloplos sp. can be L. panamensis forms with some stomach papillae. Unfortunately, detailed comparison between specimens coming from different marine regions is not possible, since the available type material of L. panamensis consists of only three syntypes that are poorly preserved; also, earlier reports of specimens of L. panamensis from other localities, besides Panama and the Gulf of California, could be questionable: for example, in specimens collected from the central Mexican Pacific (Salazar-Vallejo et al., 1990), branchiae start on chaetigers 11-12 so that, according to the revision by Mackie (1987) and our comments in this study, they could not correspond to L. panamensis.
The distribution of the various species of Leitoscoloplos is still poorly known; most of them have been recorded only from their type localities, while others, initially reported as widely distributed, like L. kerguelensis (McIntosh, 1885), have been revised and found to belong to other morphologically similar species (Mackie, 1987). The genus Leitoscoloplos in the Tropical Eastern Pacific is relatively well represented, since seven species (L. bajacaliforniensis De León-González and Rodríguez-Valencia, 1996, L. fragilis (Verrill, 1873), L. kerguelensis (McIntosh, 1885), L. mexicanus Fauchald, 1972, L. panamensis (Monro, 1933), L. pugettensis (Pettibone, 1957) and L. multipapillatus sp. nov. have been recorded (29% of all described species). However, in order to assess the phylogeny of the genus Leitoscoloplos, more studies aimed at assessing their important anatomical features and at analysing their intraspecific morphological variability in different geographical regions are necessary.
The morphometric analysis carried out here complements the anatomical observations and contributes to a more detailed taxonomic evaluation. Despite the lack of information on the origin and function of the subpodal and stomach papillae in orbiniids, and on their variations related to their geographic distribution, the designation of this new species of Leitoscoloplos based on classical taxonomy was significantly supported by morphometric tests. This shows that the morphometric approach can be a valuable tool to differentiate cryptic taxa and to choose which anatomical features are more important in identifying species.