Paracoryphellidae Miller, 1971

Family Paracoryphellidae Miller, 1971 View in CoL

( Figs 1, 2, 5B, 10, 11; Table 4)

Family Paracoryphellidae Miller 1971: 311 View in CoL , 315.

‘Genus Flabellina sensu latissimo ’ Gosliner and Griffiths 1981: 105 , 109–15.

Family Paracoryphellidae View in CoL restored, Korshunova et al. 2017a: 13.

Diagnosis: Body wide. Notal edge present, well-defined, continuous. Cerata not stalked, in continuous numerous rows. Ceratal rows branched. Rhinophores smooth to wrinkled. Anus pleuroproctic under the notal edge. Commonly no elaborate oral glands. Masticatory edges of jaws bear several rows of compound, sharpened or tubercle-like denticles. Radula formula 1.1.1. Additional one to three rows of asymmetrically placed small, reduced lateral teeth may be present. Central teeth commonly with strong cusp, usually not compressed by adjacent lateral denticles in adult state in a majority of genera, except the genus Mgueolia . Lateral teeth narrow or with attenuated process basally, usually denticulated. Commonly only a single distal receptaculum seminis present, but two receptaculums may occur. Vas deferens always long, prostate tubular or elaborated, wide granulated. Accessory gland absent. Massive external permanent penial collar with internal penis inside presents in the genus Chlamylla . Penis unarmed, elongated conical, internal in majority of genera, or fully external in the genus Paracoryphella .

Genera included. Chlamylla Bergh, 1886 , Paracoryphella Miller, 1971 , Polaria Korshunova et al., 2017 , Ziminella Korshunova et al., 2017 , and Mgueolia Korshunova et al., 2025 .

Remarks: The family Paracoryphellidae encompasses several notably ancestral, highly archaic features, as, for example, an invariably continuous notal edge, especially significantly pronounced in the genus Chlamylla , without distinct ceratal clusters or stalks, together with an invariably pleuroproctic anus toward the middle part of the lateral side of body. Furthermore, the genus Chlamylla is the only taxon within the suborder Aeolidacea ( Korshunova et al. 2017a) that possesses a massive, distinct external penial collar in combination with internal penis, which otherwise is present only within the order Pleurobranchida ( Martynov and Schrödl 2008, Martynov et al. 2022), an order definitely ancestral to the order Nudibranchia . In this study, molecular data are presented for Chlamylla borealis orientalis (Volodchenko, 1941) for the first time. ( Figs 1, 2; morphological data see: Korshunova et al. 2017a).

Moreover, a uniquely, deeply ancestral feature is preserved within the genus Paracoryphella —the penis is attached directly to the body wall. This feature is present invariably in all taxa of the order Acteonida (Martynov 2011) , but is only known within the order Nudibranchia in one taxon of one of the basal-most families, Notaeolidiidae ( Wägele 1990) , and thus in a single genus within the family Paracoryphellidae , Paracoryphella ( Korshunova et al. 2017a) .

Herein we further describe in details the amazing discovery of Mgueolia almamater ( Fig. 10), which, according to the present molecular phylogenetic analysis, is robustly placed within the family Paracoryphellidae , as a sister-genus to all the previously known paracoryphellid genera: Chlamylla Bergh, 1886 , Paracoryphella Miller, 1971 , Polaria Korshunova et al., 2017 , and Ziminella Korshunova et al., 2017 ( Figs 1, 2). Externally Mgueolia almamater is well suited to the family Paracoryphellidae ( Fig 10A–F), whereas internally, while Mgueolia almamater possesses a predominantly flabellinoidean (including Paracoryphellidae ) triserial radula, the radular patterns ( Fig 10K–P) readily recall those in the very distantly related family, Eubranchidae , from a completely different superfamily, Fionoidea (see Synopsis above and Figs 1, 2). On the other hand, radular patterns of Mgueolia almamater partly approach the radula of the genus Carronella of the family Flabellinidae ( Korshunova et al. 2017a) , which may imply how the distinct Flabellinidae radula has been formed during the evolutionary radiation of the superfamily Flabellinoidea . This is one more remarkable case, among several others already presented in this study (Synopsis, Figs 1, 2) that unequivocally and unambiguously confirms the profound multilevel mosaicism within novel taxa with unique patterns, which in turn undoubtedly demonstrates that any ‘pan-lumping’ suggestion would obscure the immense, evolutionary-fuelled fine-scale natural diversity at every taxonomic level in the suborder Aeolidacea .

The creation of the paracoryphellid genus Ziminella Korshunova et al., 2017 , established as part of a major revision of the super-lumped ‘genus Flabellina ’, included descriptions of two new species Ziminella abyssa Korshunova et al., 2017 and Ziminella circapolaris Korshunova et al., 2017 , and provided data for Ziminella japonica (Volodchenko, 1941) ( Korshunova et al. 2017a) . However, in Valdes et al. (2018), this morphological and molecularly highly consistent major rearrangement of the main taxonomic patterns of aeolidacean was rejected, despite that the tree in Valdes et al. (2018) had a fundamentally similar topology regarding major Coryphellidae , Flabellinidae , and Paracoryphellidae clades, as well as new species within the genus Ziminella . In this study we present molecular data for all currently recognized valid Ziminella species, Z. abyssa Korshunova et al., 2017 , Z. circapolaris Korshunova et al., 2017 , reinstated, Z. japonica (Voldochenko, 1941) , Z. salmonacea (Couthouy, 1838) , and Z. vrijenhoeki Valdes et al., 2018 ( Fig. 5B), and also for the first time morphological data for the true Z. japonica both from the NW and NE Pacific, including external, jaw, and radular morphology ( Fig. 11). Furthermore, an absolute majority of the included species differ by their penial morphology, which was discovered more than 30 years ago ( Martynov 1992b), when unequivocal differences were shown between copulative apparatuses of the taxa that are currently recognized under the genus name Ziminella , Z. salmonacea , and Z. japonica , and further confirmed in Martynov (2012) and Korshunova et al. (2017a). Despite this, Valdes et al. (2018) commented that allegedly ‘no data’ were presented for penial morphology in the first description of Z. circapolaris , despite that in the original description of this species the data for the copulative apparatus were unequivocally provided ( Korshunova et al. 2017a: 22). At the same time, the data for the penial morphology for Z. vrijenhoeki provided in Valdes et al. (2018) was highly ambiguous: while in the description of Z. vrijenhoeki ( Valdes et al. 2018: 415) it is described as ‘penis simple, elongate’, but in the remarks to the description ( Valdes et al. 2018: 420) it was described as ‘folded’, whereas according to the figures ( Valdes et al. 2018: figs 11, 12) the penis does not look to be especially ‘folded’, and appears as rather an entire structure with a somewhat blunt tip. In the present study we also for the first time apply molecular data ( Figs 1, 2, 5 В) to a group of populations closely related to the true Z. japonica , which also inhabits shallow water regions in the northern parts of NE Pacific, despite that its type locality is situated very distantly at moderate depths of c. 100–1000 m in the Sea of Japan and neighbouring waters. We also confirm that not only Z. salmonacea and Z. japonica , but also Z. circapolaris and Z. salmonacea are well distinguished by their penial morphology.

Morphological data are supported by the results of the molecular-phylogenetic analyses. All Ziminella species constitute a highly-supported clade (PP = 1, BS = 100; Fig. 5B). One NW Pacific and two NE Pacific Z. japonica formed a highly-supported clade (PP = 1, BS = 98), sister to the Z. vrijenhoeki clade (PP = 1, BS = 100). Uncorrected COI p -distances within the Z. japonica clade are 0.3%–0.6% and within the Z. vrijenhoeki clade are 0%–0.3%. The COI minimal uncorrected COI p -distance between Z. japonica and Z. vrijenhoeki is 8.1%. Only COI data for Z. vrijenhoeki MIMB 42255 among all publicly available data were used due to possible contamination by Carronella pellucida data (for details see Supporting Information, Table S2). Ziminella japonica and Z. vrijenhoeki clustered in two separate sister-clades that had the closest position to the clade, including Z. salmonacea and Z. circapolaris (PP = 1, BS = 100), but with low support (PP = 0.73, BS = 45). Ziminella circapolaris , reinstated formed a separate clade (PP = 1, BS = 100), but within the Z. salmonacea clade, which can be explained by the insufficient number of 16S, H3, and 28S genes in the dataset and will be investigated in a separate study. Uncorrected COI p -distances within the Z. salmonacea clade are 0–1.1% and within the Z. circapolaris clade is 0. The COI minimal uncorrected COI p -distance between Z. salmonacea and Z. circapolaris is 2.3%. Ziminella abyssa clustered in a distinct separate clade, sister to Z. japonica , Z. vrijenhoeki , Z. salmonacea , and Z. circapolaris ( Fig. 5B). The COI minimal uncorrected p -distances between the Z. japonica clade and the Z. salmonacea , Z. circapolaris , and Z. abyssa clades are 15.3%, 15.3%, and 17.6% respectively.