The increasing availability of molecular and ecological data has placed the integrative taxonomy (as defined by Dayrat 2005) as a viable alternative to traditional species description. Several authors advocate its use in different animal groups (Padial and De La Riba 2010; Schlick-Steiner et al. 2010; Heethoff et al. 2011; but see Yeates et al. 2011 for iterative taxonomy instead) and particularly in earthworms (Blakemore and Kupriyanova 2010; Novo et al. 2012), whose taxonomy is in need of deep revision in the light of molecular phylogeny (Jamieson et al. 2002; Pop et al. 2003, 2007; Chang et al. 2008; Briones et al. 2009; Pérez-Losada et al. 2009, 2011; Novo et al. 2011; Fernández et al. 2012).

Fernández et al. (2014) have developed a new tool based in micro-computed tomography to study specimens in a non-destructive way which could help as an additional source of information.

Taxonomic characters traditionally used for the study of earthworms are few and sometimes present high intraspecific variability (Michaelsen 1900 and Stephenson 1930 on their global fauna; Pop et al. 2003 and Briones et al. 2009 about lumbricid earthworms). Recent findings show that cryptic diversity is common in these animals (but see critique in Blakemore et al. 2010), therefore earthworm taxonomy can particularly benefit from an integrative approach.

Novo et al. (2011) presented a molecular phylogeny of Hormogastridae (Oligochaeta, Annelida), whose taxonomy has historically been built on morphological characters, which highlighted some interesting evolutionary aspects. On one hand, hormogastrid distribution across the Western Mediterranean is biogeographically consistent, reflecting the geological events that affected the region in the Tertiary (which confirms previous studies, e.g Bouché 1972, Sbordoni et al. 1992). Two species -Xana omodeoi Diaz Cosin, Briones & Trigo, 1989 and the morphospecies Hormogaster elisae Álvarez, 1977 -, however, are found in locations far apart from the family main range in the Iberian Peninsula. While all the other Iberian species are distributed in Northeastern Spain, Xana omodeoi inhabits Northwestern Spain and Hormogaster elisae is found in Central Spain (Segovia, Madrid and Guadalajara). The result is a disjunct distribution.

Novo (2010) found Hormogaster elisae complex to be monophyletic, and thus the likely result of a single colonisation event presumably from the North or the East of the Iberian Peninsula. There could be remaining populations of the migrating lineage in the geographic gap, which haven’t been discovered yet.

On the other hand, it seems that most key characters used for hormogastrid traditional taxonomy and phylogeny (notably the shape, number and position of the spermathecae) are highly homoplasic, showing little or no phylogenetic signal across the family.

Due to its relevance for this subject, the intermediate area between the main ranges of hormogastrids in Spain has been subject to recent sampling campaigns. Both Zaragoza and Teruel (Aragón, Spain) were suitable regions as they have been poorly sampled for earthworms unlike the surrounding provinces. While no success was met in Zaragoza, a population assignable to a new species of Hormogastridae was recently found in Teruel.

This paper focuses on the description of Hormogaster joseantonioi sp. n. from an integrative point of view, following the example of Novo et al. (2012). The new molecular and morphological data are interpreted to gain insight into the diversification and morphological radiation of the family, with some considerations about its constituent genera.

Both morphological and molecular characters of Hormogaster joseantonioi sp.n. separate it clearly from all known hormogastrid species, the number of typhosole lamellae and the kind and location of the spermathecae being particularly distinctive. Those characters, while failing to resolve internal relationships within Hormogastridae, have been shown to be suitable for species diagnosis (Rota 1993 on typhlosole importance; Novo et al. 2012 on spermathecae number to separate Hormogaster abbatissae from Hormogaster sylvestris).

The species Hormogaster riojana, while distantly related according to molecular phylogeny, shows many similarities in morphology to Hormogaster joseantonioi (Table 3). However, Hormogaster joseantonioi differ by its lower number of lamellae in its typhlosole and shorter tubercula pubertatis. Moreover it is longer and heavier. While the two species share a very similar position and shape of the spermathecae, some Hormogaster joseantonioi individuals show an additional spermatheca in segment 10 (on the right or left side). These cases don’t seem to be teratologic, as the supernumerary spermathecae have their own pore in the body surface and contain sperm, thus being fully functional.

Other hormogastrid species possess double or multiple spermathecae, but never of the multicameral, disc shaped kind.

The geographically closest species, Hormogaster castillana (from Puerto Querol, Castellón), is neither morphologically nor phylogenetically closely related (Table 3).

Hormogaster joseantonioi sp. n. appears nested on a weakly supported clade on the phylogenetic tree, consisting in Hemigastrodrilus monicae, Xana omodeoi, Hormogaster pretiosa from Villamassargia, Hormogaster najaformis (and HPA from Omodeo, see Novo et al. 2011) and Hormogaster elisae. Genetic distances were high in all cases (16.47–19.08% for COI, 12.50–17.40% for 16S) according to the reference intervals given by Chang and James (2011). Aside from Hormogaster elisae, none of them showed significant morphological likeness to the new species, with the very different spermathecae configurations being noteworthy (Table 3).

The Hormogaster elisae morphospecies was recovered as sister clade to Hormogaster joseantonioi sp. n. with high support. From a morphological point of view, most of their external characters overlap, except for a slightly longer clitellum and tubercula pubertatis, bigger average size and stronger pigmentation in Hormogaster joseantonioi sp. n. However, internal characters are very different and these species match neither in the number of lamellae in the typhlosole (five versus nine) nor in the structure of the spermathecae, which are tubular in Hormogaster elisae and disc-shaped and multicameral in Hormogaster joseantonioi. It’s worth noting that Hormogaster elisae shares the backwardly displaced disposition of the 9/10 septum.

Based on their phylogenetic and morphological relatedness, an origin of Hormogaster elisae from a common ancestor with Hormogaster joseantonioi sp. n. seems likely. This scenario is sensible from a biogeographical point of view, as the locality of the new species is intermediate between the ranges of Hormogaster elisae and the northeastern main hormogastrid range. A connection of emerged lands would have been possible from the Cretaceous-Tertiary boundary onwards (Andeweg 2002).

While Hormogaster joseantonioi status as a good species and its phylogenetic relationships seem quite clear, generic assignment is a more problematic matter. Novo et al. (2011) recovered the genus Hormogaster as paraphyletic in their molecular phylogeny, pointing out the need for a deep taxonomical revision of the family Hormogastridae, currently in preparation (author’s work in progress).

Based on its distinctive morphology and geographic range, high genetic divergence and consistent recovery as a well-defined clade, Novo (2010) suggested the Hormogaster elisae species complex should be established as an independent genus. Due to the close phylogenetic position and morphological similarity of Hormogaster joseantonioi to this clade it could be argued they both should be included in the same genus.

At this stage it is more conservative to assign Hormogaster joseantonioi to the genus Hormogaster until the revision of the family is completed, which will allow to establish (if possible) a well-founded genera system on Hormogastridae. This work narrows the discontinuity between the North-Eastern and Central ranges of the Spanish hormogastrids. At the same time it highlights the importance of an intensive sampling of the area between Teruel and the center of the Iberian Peninsula (mainly zones of Soria and Guadalajara) to hopefully find new species along the hypothetical colonization route.