Fjordia Korshunova et al. , 2017

Genus Fjordia Korshunova et al., 2017 View in CoL , reinstated

( Figs 1, 2, 13; Table 5)

Korshunova et al. 2017a: 29–30.

Type species: Aeolis lineata Loven, 1846 .

Diagnosis: Body moderately narrow. Notal edge present, discontinuous. Cerata in several groups. Rhinophores smooth. Anterior foot corners present. Central teeth with non-compressed narrow cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens very short, expands into a broad penial sheath, prostate indistinct. Penis broad, lobe-shaped.

Species included: Fjordia browni (Picton, 1980) comb.nov., Fjordia capensis ( Thiele, 1925) comb. nov., Fjordia lineata (Loven, 1846) comb. nov, Fjordia chriskaugei Korshunova et al., 2017 comb. nov., and Fjordia (?) insolita (Garcia-Gomez and Cervera, 1989) comb. nov. Detailed morphological data for Fjordia browni , F. lineata , and Fjordia chriskaugei are presented in Korshunova et al. (2017a).

Remarks: The newly added Fjordia capensis forms a separate clade within Fjordia , sister to F. browni , F. chriskaugei , and F. lineata ( Figs 1, 13). The genus Fjordia invariably forms a distinct, stable phylogenetic group ( Figs 1, 2, 13) and morphologically is differentiated from any coryphellid genera by a combination of the presence of a discontinuous notal edge, relatively weak cusp of the central teeth, and very short vas deferens. The phylogenetically sister-genus Gulenia readily differs from Fjordia by the stable presence of a continuous notal edge and stronger cusp of the central teeth (see below). The genus Fjordia remarkably encompasses several species over quite a large biogeographic range in the NE Atlantic from temperate South Africa ( Fjordia capensis ) to Norway and the UK ( Fjordia lineata , F. browni , and F. chriskaugei ), but fundamentally keeps essential morphological similarity and molecular unity ( Figs 1, 2, 13). Importantly, the placement of the South African species F. capensis (original description in: Thiele 1925) within Fjordia was predicted using only morphological data in Korshunova et al. 2017a because molecular data for F. capensis was not available at that time. Coryphellidae taxa precisely predicted to their particular fine genus-levels by morphological data in 2017 are indicated by tick marks in Figure 13 with molecular data profoundly confirming that placement appearing significantly later ( Ekimova et al. 2024) under the pan-lumping name ‘ Coryphella ’. This is clear evidence for the validity of both the fine-scale morphological approach and fine-scale genus- and family-level taxonomic differentiation. Interestingly, the sister to the Fjordia genus, Gulenia , is so far restricted exclusively to the Norwegian coast and partly adjacent waters of Denmark and Sweden. In other words, it is clearly restricted to Scandinavian waters, compared to the much broader distribution of the genus Fjordia , which encompasses both the northern and southern Atlantic Ocean. In that respect, since the genus Gulenia is characterized by the ancestral feature of a continuous notal edge, unlike the broader distribution of Fjordia with its discontinuous, partly reduced notal edge, it may suggest that the restricted distribution of the genus Gulenia represents a relic of an initial evolutionary radiation of an ancestral taxon of the genera Gulenia and Fjordia , which, therefore, probably had a continuous notal edge. Comparison of the genus Fjordia with all valid, currently included Coryphellidae genera is presented in Table 5. All these data and results well highlight the reliability and obvious necessity of fine-scale taxonomic differentiation for careful documentation of both large- and small-scale evolutionary changes.