Microchlamylla Korshunova et al. , 2017

Microchlamylla Korshunova et al., 2017 View in CoL , reinstated

( Figs 1, 2, 13, 17; Table 5)

Korshunova et al. 2017a: 40.

Type species: Eolis gracilis Alder and Hancock, 1844 .

Diagnosis: Body moderately narrow. Notal edge present, discontinuous. Cerata in several groups. Rhinophores smooth. Anterior foot corners present. Central teeth rather square in shape with narrow to moderately wide cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Very long, convoluted vas deferens expands into a narrow penial sheath, prostate indistinct. Penis narrow, conical.

Species included: Microchlamylla gracilis gracilis (Alder and Hancock, 1844) comb. nov., Microchlamylla gracilis zfi Korshunova et al., 2017 comb. nov., and Microchlamylla amabilis ( Hirano and Kuzirian, 1991) comb. nov. Detailed morphological data in Korshunova et al. (2017a).

Remarks: The genus Microchlamylla is particularly unique among the family Coryphellidae in possessing a very long, coiled vas deferens ( Fig. 17). This feature is rather characteristic of the different basally placed family, Paracoryphellidae , and the basal-most to Flabellinoidea family, Flabellinopsidae ( Figs 1, 2) and cannot in any way be considered merely part of ‘natural variability’ ( Ekimova et al. 2022). In living adult specimens, several loops of the vas deferens even shine through the anterior part of the dorsal side; this, in combination with a discontinuous notal edge, makes the genus Microchlamylla immediately recognizable. Further, the reproductive system of Microchlamylla gracilis gracilis and M. amabilis differs in the details of the proportions of the seminal receptacles, as well as the details of the coiling of the vas deferens ( Fig. 17A, B), but this needs to be addressed further. Remarkably, the valid subspecies Microchlamylla gracilis zfi from the high Arctic instead differs from both the North Atlantic boreal M. gracilis gracilis and the North Pacific M. amabilis by having a considerably wider vas deferens ( Korshunova et al. 2017a). The relatively square shape of the central radular teeth of the genus Microchlamylla is also distinct from the central teeth shape in a majority of the genera of the family Coryphellidae ( Hirano and Kuzirian 1991, Korshunova et al. 2017a). In the molecular phylogenetic analysis, the genus Microchlamylla invariably forms a distinct maximally supported clade (PP = 1, BS = 100), which is placed basally to a majority of the coryphellid genera ( Figs 1, 2, 13), and together with genus Itaxia represents relics of early coryphellid evolutionary radiation. Twelve Microchlamylla gracilis formed a separate highly-supported clade (PP = 1, BS = 91), but 10 M. amabilis ( Fig. 13) branched directly from the clade. Uncorrected COI p -distances between the 10 M. amabilis are 0.4%–2.0%, between the 12 M. gracilis are 0.2%–1.6%. Uncorrected COI p -distances between M. amabilis and M. gracilis are 3.8%–6.1%. There are analyses and a discussion of Microchlamylla gracilis and M. amabilis in Ekimova et al. (2022), where conflicting information on the taxonomy M. gracilis and M. amabilis is provided (Supporting Information, Fig. S2). Microchlamylla amabilis is defined as a combination of Microchlamylla amabilis , Coryphella amabilis , and Coryphella gracilis . Completely opposite conclusions are presented in the Discussion and in the Abstract: ‘We suggest treating M. gracilis and M. amabilis as two separated allopatric species’ and ‘for Microchlamylla gracilis and M. amabilis , their synonymization under the name M. gracilis is suggested’. Reproductive systems of two ‘ Coryphella ’ gracilis are presented in Ekimova et al. (2022: fig. 8E, F) according to the caption under figure 8, but in the Discussion, figure 8E, F is used to illustrate the reproductive systems of ‘ Borealea nobilis and B. sanamyanae ’ noting that ‘the reproductive system was found to be similar in these two species ( Ekimova et al. 2022: fig. 8E, F)’. Microchlamylla gracilis and M. amabilis were reasonably indicated as two separate species in Korshunova et al. (2017a) and in the present study additional data is provided. Comparison of the genus Microchllamylla with all valid, currently included Coryphellidae genera is presented in Table 5.

In this respect the case of the family Coryphellidae is again particularly relevant for the most general understanding of how to maximally coherently represent the evolutionary-derived biological diversity in a system of apparently ‘static’ taxonomic names, an ultimate goal of any systematic study even in the current profoundly ‘phylogenetic era’. Because if all the coryphellid diversity were lumped into the single genus ‘ Coryphella ’, then, for example, the genus Microchlamylla —a genus that, according to the molecular phylogenetic data ( Figs 1, 2, 13), is very distant from the true Coryphella , and shows the presence of a very long vas deferens in the reproductive system ( Fig. 17), which is more characteristic of the completely different molecular clade of the family Paracoryphellidae ( Korshunova et al. 2017a, present study, Synopsis; Figs 1, 2, 10)—disappears. Thus, if Microchlamylla were lumped into the genus Coryphella , then not only that particular genus would be dismissed, but also the entire superfamily Flabellinoidea in all its large-scale and fine-scale diversity ( Figs 1, 2, 5, 13; Tables 1–4).

All three currently recognized valid taxa of the genus Microchlamylla , including M. gracilis gracilis , M. gracilis zfi , and M. amabilis , show distinct phylogeographic patterns in their distribution ( Fig. 17C). Microchlamylla gracilis gracilis inhabits boreal waters with some cold-water influence on both sides of the North Atlantic, including the Barents Sea, M. gracilis zfi inhabits the high Arctic latitudes at least at Franz Joseph Land ( Korshunova et al. 2017a, present study; Fig. 17C), whereas M. amabilis is distributed in the North Pacific on both western and eastern coasts with no known overlap in the Arctic ( Fig. 17C).

Occidenthella Korshunova et al., 2017 , reinstated

( Figs 1, 2, 13; Table 5)

Korshunova et al. 2017a: 42–3.

Korshunova et al. 2017b: 140.

Type species: Coryphella athadona Bergh, 1875 .

Diagnosis: Body narrow. Notal edge almost completely reduced. Cerata in several groups. Rhinophores smooth. Anterior foot corners absent. Central teeth with non-compressed moderately wide cusp and distinct denticles. Lateral teeth denticulated with moderately attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens very short, expands into a broad penial sheath with a very distinct, strongly protruding accessory gland external to penis. Penis small, amorphous.

Species included: Occidenthella athadona ( Bergh, 1875) comb. nov.. Detailed morphological data in Korshunova et al. (2017a).

Remarks: The genus Occidenthella Korshunova et al., 2017 is one of the most aberrant genera not only within the family Coryphellidae , but within almost all taxa of the superfamily Flabellinoidea . The genus Occidenthella is different from an absolute majority of triserial aeolids by the complete reduction of anterior foot corners ( Bergh 1875, Baba 1987a, Korshunova et al. 2017a), a feature common for the different, distantly related superfamily Fionoidea ( Figs 1, 2), but not for Flabellinoidea (see the Synopsis of all the Aeolidacean families and consideration of the aeolidacean superfamilies under Remarks to a new family Chudidae above), and the presence of a very distinct accessory gland ( Korshunova et al. 2017a), which is also partly similar to the supplementary gland of Cuthonidae , Trinchesiidae , Eubranchidae , and other fionoidean families (but definitely independent in its origin, see molecular phylogenetic tree; Figs 1, 2; Tables 3, 4). Externally, Occidenthella is commonly a very narrow coryphellid (even with all the reservation about the relativity of the terms ‘narrow’ and ‘wide’) with almost a completely reduced notal edge (in this case, the last remnants of the notal edge are possible to distinguish mostly at anterior ceratal clusters only after careful examination under a stereomicroscope or in macro photographs), which in combination with significant differences in its internal morphology, makes this genus immediately recognizable. This example is especially relevant for the confirmation of the importance and validity of the multilevel fine-scale diversity methodology, because according to the molecular data, the genus Occidenthella is a sister-genus to Orienthella ( Figs 1, 13), which is fundamentally different both externally and internally from Occidenthella ( Korshunova et al. 2017a) . Thus, the significant morphological differences, comparable with family-level differences, may arise phylogenetically relatively fast, but this does not mean that we should lump all that diversity into a single genus. This would be a truly anti-evolutionary action, because, obviously, evolution is not merely a genetic divergence, but a complex ontogeny-based process, which includes both genetic and epigenetic elements ( Martynov and Korshunova 2022). Clade Occidenthella has the closest sister-position to the clade Orienthella ( Korshunova et al. 2017a, b, present study; Figs 1, 13). Comparison of the genus Occidenthella with all valid, currently included Coryphellidae genera is presented in Table 5.