Body wide. Notal edge present, well-defined, continuous. Cerata not stalked, in continuous numerous rows. Rhinophores smooth to wrinkled. Anus pleuroproctic under the notal edge. No distinct oral glands. Radula formula 1.1.1. Asymmetrically placed additional 1–3 rows of small reduced lateral teeth may be present. Rachidian teeth with strong cusp, never compressed by adjacent lateral denticles. Lateral teeth narrow or with attenuated process basally, usually denticulated. Commonly only single distal receptaculum seminis present. Vas deferens always long, with wide granulated or tubular prostate. External permanent penial collar present in some taxa. Penis elongated conical, internal or fully external, unarmed.

Chlamylla Bergh, 1886, Paracoryphella Miller, 1971, Polaria gen. n., Ziminella gen. n.

Chlamylla borealis Bergh, 1886

Body wide. Notal edge present, well-defined, continuous. Cerata not stalked, continuous. Rhinophores smooth to wrinkled, longer than oral tentacles. Anterior foot corners absent. Anus pleuroproctic under the notal edge. Rachidian teeth with strong denticulated cusp; lateral denticles not clearly delineated from cusp. Lateral teeth weakly denticulated to smooth without attenuated process basally. Single distal receptaculum seminis. Wide granulated prostate. Thin, long vas deferens clearly separated from prostate. External permanent penial collar. Penis elongated conical, internal.

Chlamylla borealis borealis Bergh, 1886, stat. n. (= Gonieolis atypica Bergh, 1899, syn. n.) (Fig. 3) (original description in Bergh 1886, 1899, 1900a), Ch. borealis orientalis (Volodchenko, 1941), comb. n. (Fig. 4) (original description in Volodchenko 1941), Chlamylla intermedia (Bergh, 1899), comb. n. (Figs 5, 6) (original description in Bergh 1899, 1900a).

Bergh (1886) described the genus Chlamylla based on the species Ch. borealis with a continuous notum, wide granulated prostate, and aberrant radula (lateral teeth with very broad bases, rachidian teeth completely lacking denticles and having instead a pair of unusual long processes (Bergh 1886: Taf. 1, fig. 14). The true identity of the type species Ch. borealis with our extensive recent paracoryphellid specimens from the Arctic is a complicated question. Such radular features are completely unknown in the group of the Arctic Paracoryphellidae usually assigned to the genus Chlamylla (Roginskaya 1987; Martynov 2006a) Figs 1, 3H, 4H, 5H, 6E). However, the general shape of the body, shape of the jaws, presence of a wide granulated prostate, and penial collar in Ch. borealis agree with specimens that are currently assigned to the species Ch. atypica and Ch. intermedia. Bergh in the same work (1886) described the radula of another species “Goniaeolis typica” in detail (Bergh 1886: Taf. 3, fig. 14) as a normal triserial radula. However, Bergh (1886) also noted that the radula of Ch. borealis was in a poor condition. This may imply that either Bergh studied an abnormal specimen or had damaged the radula in some way during preparation. For this study we specially investigated the holotype of Ch. borealis (NHMD GAS-2055). It is dry and heavily dissected, but a separate cut-off of the external penial collar is left; the penis and damaged jaws are preserved. Comparison of available information from the holotype of Ch. borealis with figures from the original description (Bergh 1886: Taf. 1, fig. 22) confirms the presence of an external penial collar with caudal genital fold. According to our data only two paracoryphellid species with a complex folded penial collar are known from Arctic seas and are currently identified as Chlamylla atypica and Ch. intermedia (Figs 3, 4C, 4I, 5J, 6F, 7). Morphologically these taxa differ from the rest of the traditional flabellinids, forming a distinct compact clade according to the present molecular analysis (Figs 1, 2), which demonstrates significant molecular divergence (more than 11%) from other members of the family Paracoryphellidae. Based on the details in the original description of Chlamylla and type material, we can conclude, under supposition that the radula was malformed or wrongly processed, that the type species Ch. borealis belongs to the same genus as known paracoryphellid species from the Arctic, currently identified as Ch. atypica and Ch. intermedia. Given that Ch. borealis was never found again, but inhabited the same region our other samples, it is highly likely that Ch. borealis is actually conspecific with one of the two currently known Chlamylla species. One of these species, Ch. intermedia (Bergh, 1899) possesses an external penial collar but without any traces of a caudal genital fold (Fig. 5J), whereas Ch. borealis, according to both its original description (Bergh 1886: Taf. 1, fig. 22a) and our novel information from the holotype, possesses a short but evident caudal genital fold. Thus, we can conclude that Ch. intermedia cannot be a synonym of Ch. borealis. Another species, Ch. atypica which was described under the genus Goniaeolis from the Davis Strait, Greenland (Bergh 1899, 1900a) readily differs from other Chlamylla species by the presence of a special long external genital fold towards the anal opening (Bergh 1899, 1900a: Tab 4, fig. 6) (Fig. 3). Because Ch. borealis also possesses a genital fold, and given a high similarity of prostate patterns between our specimens previously identified as Ch. atypica (Fig. 3J) and the figure of the reproductive system with the characteristically bent prostate as in Ch. borealis in Bergh’s original description of Ch. borealis (Bergh 1886, Taf. 1, fig. 21) we therefore conclude that Ch. atypica is most likely is a junior synonym of Ch. borealis. The differences between length of the genital fold of the holotype of Ch. atypica (also investigated in the present study, NHMD GAS-2090) and Ch. borealis is possibly due to considerable differences in the length of holotypes of Ch. borealis and Ch. atypica (the former is nearly two times shorter than the latter). Smaller specimens previously identified as Ch. atypicas. l. may possess a considerably shorter genital fold, especially in the preserved state (Fig. 4C). Therefore, in order to preserve current usage of the genus Chlamylla that has already appeared in a number of publications on Russian nudibranch fauna, we therefore synonymise here the species Ch. atypica with Ch. borealis.

The Japan Sea specimens are consistent with the Arctic specimens in the presence of the external genital fold, but due to minor differences in the radula and also a very large geographic gap we consider it as a subspecies Chlamylla borealis orientalis (Volodchenko, 1941), comb. n. (Fig. 4). Chlamylla borealis orientalis is locally abundant during winter in Northern Japan (Hirano 1997, as Ch. atypica) and in the Russian part of the Sea of Japan (Martynov, unpublished course work (1991) as Ch. atypica; Martynov and Korshunova 2011; present study). Several specimens of other Chlamylla without such a fold from the Arctic seas (distributed at least from the Barents Sea to Laptev Sea) have no significant molecular differences between them (Figs 1, 2) and have consistent morphology (Figs 5–6) and clearly belong to the same species. The oldest name for this Chlamylla without a genital fold is Goniaeolis intermedia Bergh, 1899 also from the Davis Strait, Greenland. The lateral teeth of Goniaeolis intermedia with a broad base and slightly attenuated lateral processes (Bergh 1899: tab 4, fig. 16) are similar to our material from the Arctic seas (Figs 5H, 6E). However, G. intermedia lacked denticles on the lateral teeth. The Arctic specimens show small, sometimes almost diminishing denticles (Fig. 6E). Such denticles are not always clearly evident. Possibly this species reaches at least the Bering Strait and potentially may enter the coldest shelf waters of the NW Pacific (i.e., Bering and Okhotsk Sea, Martynov 2006a). Coryphella barentsi Derjugin, 1924 (Derjugin 1924a, b, preoccupied by Coryphella barentsi Vayssière, 1913 (Vayssière 1913, see Gosliner and Griffiths 1981 suggesting a replacement name) is a possible synonym of Ch. intermedia (Bergh, 1899).

Coryphella islandica Odhner, 1937

Body wide. Notal edge present, well-defined, continuous. Cerata not stalked, continuous. Rhinophores smooth to wrinkled, shorter than or similar in size to oral tentacles. Anterior foot corners present. Anus pleuroproctic under the notal edge. Rachidian teeth with strong cusp; lateral denticles not clearly delineated from cusp. Lateral teeth weakly denticulated without attenuated process basally. Reduced additional rows of of small lateral teeth may present. Single distal receptaculum seminis. Long vas deferens without separate granulated prostate. Penis not internal, permanently attached externally.

Paracoryphella ignicrystalla sp. n. (Fig. 8), P. islandica (Odhner, 1937) (Fig. 9) (original description in Odhner 1937), Paracoryphella parva (Hadfield, 1963), comb. n. (original description in Hadfield 1963) (Fig. 10).

The genus Paracoryphella and the family Paracoryphellidae were initially proposed by Miller (1971) because of the putative presence of a second asymmetrical row of lateral teeth in the original description of the species “Coryphella” islandica (see Odhner 1937). However, the latter character is not very evident compared to the true unique feature of the genus Paracoryphella, a non-retractable, permanently external penis, which is attached directly to the body wall and does not possesses any penial sheath (Figs 8J, 9M, 10C). Importantly, all three known species of this genus invariably possess this feature. This character is unique not only within traditional flabellinids, but also within the majority of Aeolidacea. Only a single species of the family Notaeolidiidae also has such an external penis (Wägele 1990). Furthermore, several members of the notaspid family Pleurobranchidae with an internal shell (Martynov and Schrödl 2008) and very basal Acteonidae with an external solid shell also possess an external penis. Therefore, this character within the genus Paracoryphella may be either a basal plesiomorphy, or an ontogenetic reversion to the basal plesiomorphy. Molecular data shows that in either case it occurs within one of the most basal clades of the traditional flabellinids. Additionally, analysis of the light microscopy images of the radula of both the type species P. islandica and the new species confirm the possible presence of 1–3 very reduced, asymmetrically placed, additional rows of lateral teeth (Figs 8F, 9K). During preparation for the SEM study these apparently reduced additional teeth became fully indistinguishable. Their correspondence to the normal lateral teeth needs to be further investigated.

Coryphella parva, only known from its original description from Swedish waters (Hadfield 1963), was described as having a permanent external penis and therefore is included here in the genus Paracoryphella. Here, for the first time, we have studied type material of C. parva from the Natural History Museum of Denmark (NHMD-91476) (Fig. 10) and confirmed that it possesses a non-retractable external penis (Fig. 10C) and other external features that align with the diagnosis of the genus Paracoryphella. The drawings of the radula (Fig. 10D, E) and reproductive systems (Fig. 10F) in the original description of P. parva in Hadfield (1963) are also very consistent with two other species of the genus Paracoryphella. Remarkably, even though the length of living specimens of P. parva do not exceed 3.5 mm (fixed not more than 2 mm, Fig. 10A, B), the animals at that size were fully mature and produced egg masses (Hadfield 1963). Because both P. ignicrystalla sp. n. and the type species of the genus P. islandica reach mature size in specimens at least three times larger than P. parva, the latter species thus is clearly a separate one and may represent an example of a partial paedomorphosis. According to the molecular phylogenetic analysis, the genus Paracoryphella is the sister of the Chlamylla clade (Figs 1, 2, 7). We retain the genus Paracoryphella as separate because of unique morphological characteristics including a permanent external penis and also the apparent presence of additional rudimentary lateral teeth rows.

Holotype, ZMMU Op-490, 11.5 mm long (fixed), The Sea of Japan, Vostok Bay, intertidal, 17.03.1994, coll. A.V. Martynov. 1 paratype, ZMMU Op-491, 5 mm long (fixed, dissected), The Sea of Japan, Vostok Bay, intertidal, 14.03.1994, coll. A.V. Martynov. 1 paratype, ZMMU Op-492, 12 mm long (fixed, dissected), The Sea of Japan, Vostok Bay, intertidal, 18.02.1990, coll. A.V. Martynov.

The Sea of Japan, Vostok Bay.

From igni (= fire, Latin) and crystallum (= ice, rock crystal, Latin), in reference to the double combination of peculiar morphological and ecological features: short flame-like cerata with icy speckles on dorsum and peculiar environmental characteristics of the type locality which combines icy sea water temperatures (down to -2 °C) in winter and warm subtropical conditions in summer (water temperature up to +26 °C) as an allusion to the George R. R. Martin “A Song of Ice and Fire” novels.

Continuous notal edge, colour translucent white with scattered opaque white dots, cerata orange-brown to reddish-brown, rachidian tooth with up to 12 denticles not clearly delineated from relatively low central cusp, lateral teeth with few distinct basal denticles, distal receptaculum seminis, penis not internal, permanently attached externally.

External morphology. Body wide. Foot and tail wide, anterior foot corners short. Oral tentacles long. Rhinophores ca. 1.5 times shorter than oral tentacles, smooth to slightly wrinkled. Dorsal cerata fusiform, relatively short, continuously attached to well-defined uninterrupted notal edge without forming clusters. Apices of cerata pointed. Notum narrow but distinct throughout both lateral sides of body. Digestive gland diverticulum fills significant volume of the cerata. Anal opening on right side below notal edge close to middle body part. Reproductive openings lateral and non-retractable penis below second ceratal row. Tail short and pointed, extending only a short distance beyond last cerata.

Colour (Fig. 8A). Background colour translucent white. Digestive gland diverticula orange-brown to reddish-brown. Small opaque white spots cover the entire dorsum, commonly on ceratal bases and less on cerata. Rhinophores and oral tentacles similar in colour to body; apical parts covered with opaque white pigment. Apical parts of cerata without opaque cap of white pigment.

Jaws (Fig. 8E). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears ca. 40–50 denticles that continue to form several reduced rows of denticles on the body of the masticatory processes.

Radula (Fig. 8F, H). Radula formula: 10–12 × 1.1.1(2–3). Rachidian tooth elongate-triangular with strong non-compressed cusp of nealy 1/3 of the tooth length (Fig. 8G). Rachidian tooth bears up to 15 well-defined separated (but adpressed towards the cusp) long lateral denticles. Cusp is not clearly delineated from the adjacent first lateral denticles. Lateral teeth (Fig. 8F, H) narrowly triangular with peculiar widened base and few indistinct denticles on internal edge. There are one to three rudimentary additional lateral teeth on the right side only.

Reproductive system (Fig. 8I, J). Diaulic. Hermaphroditic duct leads to strong convoluted ampulla of about two whorls. Vas deferens is relatively long, no distinct prostate. No penial sheath. Penis is attached to the external body wall, vas deferens enters the base of penis from the internal side. Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Distal receptaculum seminis.

Stony intertidal to 5–6 m. Feeds on athecate solitary hydroids. This species is locally abundant. Egg mass is white to pinkish narrow cord. Reproduction period from December to April. Development is about one month. The larva is a planktotrophic veliger with spiral shell.

Northwest part of the Sea of Japan.

Paracoryphella ignicrystalla sp. n. clearly differs from the type species of the genus P. islandica (Fig. 9K, H) in having considerably shorter cusps of the rachidian teeth (Fig. 8F, G). We have not yet obtained molecular data for this Sea of Japan Paracoryphella, but regard the morphological differences sufficient to warrant a new species.

Coryphella polaris Volodchenko, 1946

After the northern Polar region, the predominant area of distribution of this genus.

Body wide. Notal edge present, well-defined, continuous. Cerata not stalked, continuous. Rhinophores smooth to wrinkled, longer than oral tentacles. Anterior foot corners present. Anus pleuroproctic under the notal edge. Rachidian teeth with strong smooth cusp and distinct denticles. Lateral teeth strongly denticulated with considerably attenuated process basally. Single distal receptaculum seminis. Long vas deferens without separate granulated prostate. No penial collar. Penis elongated conical.

Polaria polaris (Volodchenko, 1946), comb. n. (Figs 7, 11) (original description in Volodchenko 1946).

The type and single species of the genus Polaria, Coryphella polaris is the only available valid name (Volodchenko 1946) for the species Goniaeolis typica M. Sars, 1861 as incorrectly identified by Bergh (1886), Odhner (1907), and Roginskaya (1987, 1997). True Goniaeolis typica possesses a triserial radula but has no digestive gland branches or cnidosacs in the cerata and the shape of radular teeth is very different from any traditional flabellinid (M. Sars 1861; G.O. Sars 1872; Odhner 1922). The name Coryphella polaris Voldochenko, 1946 was therefore resurrected to avoid this misidentification (Martynov 2006a). The genus Polaria forms a separate clade within Paracoryphellidae according to the molecular phylogenetic analysis (Figs 1, 2). By combination of relatively long vas deferens without distinct prostate (Figs 7, 10H, I), retractable penis without external collar, and lateral teeth with strongly attenuated process (Fig. 10G), the genus Polaria morphologically differs from all other genera of the family Paracoryphellidae.

Eolis salmonacea Couthouy, 1838

In honour of Olga Zimina, scientist at Murmansk Marine Biology Institute; she made a considerable contribution in collecting Arctic paracoryphellid species for this study.

Body wide. Notal edge present, well-defined, continuous. Cerata not stalked, continuous. Rhinophores smooth to wrinkled, similar in size to oral tentacles. Anterior foot corners present. Anus pleuroproctic under the notal edge. Rachidian teeth with strong denticulated cusp; lateral denticles not clearly delineated from cusp. Lateral teeth weakly denticulated to smooth without attenuated process basally, significantly smaller than rachidian teeth. Receptaculum seminis not evident. Long vas deferens without separate granulated prostate. No penial collar. Penis folded or elongated conical.

Ziminella abyssa sp. n. (Fig. 12), Ziminella circapolaris sp. n. (Fig. 13), Ziminella japonica (Volodchenko, 1941), comb. n. (Fig. 14) (original description in Volodchenko 1941; lectotype designated in Martynov 2013), Ziminella salmonacea (Couthouy, 1838), comb. n. (Fig. 15) (original description in Couthouy 1838; redescription in Kuzirian 1979).

Ziminella considerably differs morphologically from the genus Chlamylla by the absence of a granulated prostate and external penial collar (Fig. 7) and by the shape of the radular teeth, from the genus Paracoryphella by the presence of a penial sheath and by the shape of the radular teeth, from the genus Polaria by the absence of a very long, conspicuous distal receptaculum seminis and by the shape of the radular teeth. On the molecular tree, both species of the genus Ziminella place as a well-separated clade within the family Paracoryphellidae (Figs 1, 2). Four species currently known within the genus Ziminella are well-separated by the penial morphology (Z. salmonacea possesses a slightly folded penis, whereas Z. abyssa and Z. japonica have an entire conical penis; for discussion see Martynov 2013). Molecular data (Figs 1, 2) published here for the first time show that three species are placed together within a larger clade.

Holotype, ZSM Mol-20100647, 19 mm long (fixed), R/V ‘‘Akademik Lavrentyev”, sta. B5–10, 24.08.2010, The Sea of Japan, depth 2676 m. 8 paratypes, ZMMU Op-248, up to 20 mm long (fixed), R/V ‘‘Vityaz’’, sta. 6657, 15.06.1972, The Sea of Japan, depth 3560 m. 9 paratypes, ZMMU Op-249, up to 24 mm long (fixed), R/V ‘‘Vityaz’’, sta.7462, 29.05.1976, The Sea of Japan, 41°19.8'N, 131°15.2'E, depth 3290 m. 57 paratypes, ZMMU Op-250, up to 25 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7463, 29.05.1976, The Sea of Japan, 40°45.0'N, 131°16.0'E, depth 3300 m. 1 paratype, ZMMU Op-252, 9 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7476, 06.06.1976, The Sea of Japan, 40°39.5'N, 132°32.8'E, depth 3425 m. 7 paratypes, ZMMU Op-253, up to 15 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7479, 07.06.1976, The Sea of Japan, 39°09.1'N, 131°03.2'E,, depth 3120 m. 2 paratypes, ZMMU Op-255, up to 14 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7492, 12.06.1976, The Sea of Japan, 38°21.8'N, 134°49.5'E, depth 3020–3030 m. 2 paratypes, ZMMU Op-256, up to 19 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7494, 14.06.1976, The Sea of Japan, 38°48.0'N, 136°04.6'E, depth 2740 m. Two paratypes, ZMMU Op-257, 15 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7496, 01.07.1976, The Sea of Japan, 40°36.60'N, 139°00.002'E, depth 3340 m. 48 paratypes, ZMMU Op-258, up to 21 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7517, The Sea of Japan, 42°28.2'N, 138°20.9'E, depth 3620 m. 6 paratypes, ZMMU Op-259, up to 18 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7519, 02.06.1976, The Sea of Japan, 41°28.8'N, 136°06.1'E, depth 3460 m. 11 paratypes, ZMMU Op-264, up to 12 mm long (fixed), R/V ‘‘Akademik Lavrentyev’’(SoJaBio), sta. A3–11, 14.06.2010, The Sea of Japan, 44°47.6338'N, 137°15.3182'E, depth 1494–1525 m.

The Sea of Japan.

From abyssum (= depth, Latin) in reference to abyssal habitat of the new species, one of the deepest among aeolidacean nudibranchs.

Continuous notal edge, lateral branches of digestive gland (ceratal basis) dark violet, rachidian tooth with up to 30 (and more) fold-like or fork-shaped denticles clearly delineated from central cusp, lateral teeth with few denticles on teeth edge, receptaculum seminis not evident, penis elongate conical.

External morphology (Fig. 12A, B). Body wide. Foot and tail wide, anterior foot corners short. Rhinophores similar in size to oral tentacles, smooth to slightly wrinkled. Dorsal cerata elongate, thin, continuously attached to well-defined uninterrupted notal edge without forming clusters. Apices of cerata pointed. Notum narrow but distinct throughout both lateral sides of body. Digestive gland diverticulum fills significant volume of the cerata. Anal opening on right side below notal edge close to middle body part. Reproductive openings on right side. Tail long and pointed, extending only short distance beyond last cerata

Colour. Background colour translucent milky white. Digestive gland diverticula probably reddish. Rhinophores light orange at the bases and pale on most of the rest of the length. Lateral branches of digestive gland (that shine through lateral dorsum sides) characteristically dark violet (estimated from a field colour photograph).

Jaws (Fig. 12C, D). Jaws broad, yellowish in colour. Masticatory processes of jaws covered with several compound denticles.

Radula (Fig. 12E–H). Radula formula up to 40 × 1.1.1 (in adult specimen 20–24 mm in length). Rachidian tooth with strongly protracted non-compressed cusp of ca. 1/3 of the tooth length (Fig. 12E). Rachidian tooth bears up to 30 (and more) special, fold-like or fork-like lateral denticles, which are sometimes greatly disordered. Larger denticles typically intermingled with the smaller ones. Cusp is clearly delineated from the adjacent first lateral denticles. Lateral teeth (Fig. 12F–H) narrowly triangular with few small denticles on internal edge.

Reproductive system (Fig. 12J). Diaulic. Hermaphroditic duct leads to long, relatively narrow convoluted ampulla of several whorls. Vas deferens extremely long, without distinct prostate. Penial sheath elongated. Penis entire, conical. Oviduct connects through insemination duct into female gland complex. No distal or proximal receptaculum seminis detected.

Deep sea basins at 1494–3620 m depth, soft bottom. This species is most common in the deepest parts of the Sea of Japan at about 3000 m. Upper bathymetric limit needs to be refined. Feeds on sea anemones of the family Edwardsiidae.

Central deepest basins of the Sea of Japan.

By presence of an entire copulative organ Z. abyssa sp. n. is similar to Z. japonica (Volodchenko, 1941), but clearly differs in the pattern of the rachidian radular teeth. While Z. japonica has regular lateral denticles of the rachidian teeth, all similar in size, no more 20 in number even in very large specimens (30 mm), Z. abyssa sp. n. has highly irregular lateral denticles of the rachidian teeth, different in size, fold- and fork-shape (Fig. 12F, G), sometimes even placed disorderly (Fig. 12H), up to at least 30 (and more) in number even in specimens which are much smaller than in the previous species with specimens reaching 20–24 mm in length. Remarkably, the irregularity of the rachidian teeth in Z. abyssa sp. n. persists even in very small juveniles (2 mm), in which larger denticles already intermingle with the smaller ones (Fig. 12I). The morphological differences between these two species agree with the considerable bathymetric differences: Z. japonica is a shelf and upper bathyal species (ca. 100–500 m), whereas Z. abyssa sp. n. inhabits predominantly the deepest (approximately 3000 m) basins of the Sea of Japan.

Holotype, ZMMU Op-598, 35 mm long (fixed), Arctic Ocean, Franz Josef Land, Wiltona Island, 23.08.2013, depth 18–25 m, collected by O.V. Savinkin. 1 paratype, ZMMU Op-482, 14 mm long (fixed), Arctic Ocean, Franz Josef Land, Northbrook Island, 26.08.2013, depth 18–23 m, collected by O.V. Savinkin. 1 Paratype, ZMMU Op-483, 12 mm long (preserved), Arctic Ocean, Franz Josef Land, Pioneer Island, 17.08.2013, depth 21–23 m, collected by O.V. Savinkin.

Franz Josef Land.

From circa (= near, Latin) and polaris (= polar, Latin) in reference to the proximity of the habitat of the new species (Franz Josef Land) to the North Pole.

Continuous notal edge, colour yellowish, cerata reddish-brown, few apical white dots, rachidian tooth with up to ten denticles clearly delineated from central cusp, lateral teeth with numerous denticles (up to 24) which cover whole edges of lateral teeth, receptaculum seminis not evident, penis folded.

External morphology. Body wide. Foot and tail wide, anterior foot corners short. Rhinophores similar in size to oral tentacles, smooth to slightly wrinkled. Dorsal cerata elongate, thick, continuously attached to well-defined uninterrupted notal edge without forming clusters. Notum narrow but distinct throughout both lateral sides of body. Digestive gland diverticulum fills significant volume of cerata. Anal opening on right side below notal edge close to middle body part. Reproductive openings on right side. Tail long and pointed, extending only a short distance beyond last cerata.

Colour (Fig. 13A, B). Background colour yellowish-white. Digestive gland diverticula reddish-brown. Rhinophores light orange-yellowish. Lateral branches of digestive gland (that shine through lateral dorsum sides) not distinct.

Jaws (Fig. 13E, F). Jaws broad, yellowish in colour. Masticatory processes of jaws covered with several simple denticles.

Radula (Fig. 13G–J). Radula formula up 26 × 1.1.1 (specimens 20–24 mm in length). Rachidian tooth elongate with strongly protracted, pointed, non-compressed cusp of almost 1/3 of tooth length (Fig. 13G, I). Rachidian tooth bears five to ten lateral denticles. Larger denticles not intermingled with smaller ones. Cusp clearly delineated from the adjacent first lateral denticles. Lateral teeth (Fig. 13H, J) narrowly triangular with 19–24 denticles on internal edge.

Reproductive system (Fig. 13K, L). Diaulic. Hermaphroditic duct leads to long, relatively narrow convoluted ampulla of several whorls. Vas deferens long, without distinct prostate. Penial sheath elongated. Penis folded. Oviduct connects through insemination duct into female gland complex. No distal or proximal receptaculum seminis detected.

Soft bottom with stones 18 to 23 m.

Franz Josef Land.

According to the molecular phylogenetic analysis Ziminella circapolaris sp. n. forms a separate sister clade to Z. salmonacea (Fig. 1). Specimens from the West Atlantic North American coast (type locality of Z. salmonacea) and Spitzbergen belong to Z. salmonacea, according to molecular data, whereas specimens from Franz Josef Land belong to the separate species Z. circapolaris sp. n. This is concordant with a considerable level of endemism of the nudibranch fauna of Franz Josef Land recently demonstrated for other nudibranch groups (Martynov and Korshunova 2017). Morphological analysis reveals differences in the denticulation of the lateral teeth between Z. salmonacea and Z. circapolaris sp. n.: in the first species denticulation on the lateral teeth tends to be restricted to the first half of the length of lateral teeth or the teeth can be completely smooth, whereas in the new species denticulation runs up to the very end of the lateral teeth, and the teeth are always denticulated. Kuzirian (1979) studied the radulae of 15 specimens of Z. salmonacea from near the type locality and all of them have considerably smoother lateral teeth than Z. circapolaris sp. n.

Body relatively wide. Notal edge discontinuous. Cerata in separate clusters on broad extensions. Rhinophores perfoliated or granulated. Anus pleuroproctic under reduced notal edge. No distinct oral glands. Radula formula 1.1.1. Rachidian teeth usually with cusp compressed by adjacent lateral denticles. Lateral teeth narrow or with attenuated process basally, denticulated or smooth. Single distal receptaculum seminis. Vas deferens long, with or without distinct prostate. External permanent penial collar absent. Penis elongated conical, internal unarmed.

Baenopsis gen. n., Flabellinopsis MacFarland, 1966.

One of the unexpected results of the present molecular analysis is the most basal position of the species Flabellina iodinea (Cooper, 1863) in relation to the families Paracoryphellidae, Coryphellidae, and Flabellinidae (Figs 1, 2). This is prima facie not very consistent with the morphological data since F. iodinea is similar to the members of the family Flabellinidaes. str. as it possesses a medium-sized body with cerata on lateral extensions. However, this may be a case of morphological convergence since F. iodinea's relatively broad, flap-like lateral modifications of the notal edge and absence of distinct oral glands is different from the majority of the Flabellinidaes. str. Furthermore, the vas deferens in F. iodinea is considerably longer than in the taxa of the Flabellinidaes. str. On all trees obtained, Flabellina iodinea invariably appears most basally and separate from all other families. Therefore, in this case our results speak for preference of the molecular data in revealing the very separate position of this particular taxon. It is most likely that the Flabellina-like external appearance has evolved in F. iodinea independently from Flabellinidaes. str. by parallel modifications of a continuous ancestral notal edge into flap-like ceratal structures. We therefore resurrect the genus Flabellinopsis MacFarland, 1966, which was previously proposed for the species Aeolis (Phidiana?) iodinea Cooper, 1863. On the present molecular tree, the NE Pacific Flabellinopsis iodinea clustered together with a NE Atlantic species, “Flabellina” baetica Garcia-Gomez, 1984, in the same clade (Figs 1, 2, 7). The NE Atlantic species has ceratal and reproductive morphology somewhat similar to the genus Flabellinopsis but possesses very peculiar folded and granulated rhinophores and smooth lateral teeth (Garcia-Gomez 1984). Therefore, rather than uniting it into the genus Flabellinopsis making that morphologically not very consistent, we propose a separate new genus for Flabellina baetica (see below). The diversity of the family Flabellinopsidae fam. n. is more considerable than currently understood. On our tree, an undetermined species of “Piseinotecus” sp. appeared as possibly related to this family (Fig. 1). Furthermore, Furfaro et al. (2017) have shown that “Piseinotecus” soussi Tamsouri, Carmona, Moukrim and Cervera, 2014 (original description in Tamsouri et al. 2014) has appeared basally to “Flabellina” baetica and Facelina quatrefagesi (Vayssière, 1888). Further investigations need to be made on these taxa.

Flabellina baetica Garcia-Gomez, 1984

The genus name is derived from the type species name, “F.” baetica, originally named after one of the main historical provinces of Spain.

Body relatively wide. Notal ridge discontinuous. Cerata in separate clusters on broad lateral extensions. Rhinophores with ridges and granules, similar in size to oral tentacles. Anterior foot corners present. Anus pleuroproctic. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth smooth with attenuated process basally. Single distal receptaculum seminis. Long vas deferens with distinct prostate. Penis conical (?).

Baenopsis baetica (Garcia-Gomez, 1984), comb. n. (original description in Garcia-Gomez 1984).

Aeolis (Phidiana?) iodinea Cooper, 1863.

Body relatively wide. Notal ridge discontinuous. Cerata in separate clusters on broad flaps. Rhinophores perfoliated, shorter than oral tentacles. Anterior foot corners present. Anus pleuroproctic. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Single distal receptaculum seminis. Long vas deferens without distinct prostate. Penis bluntly conical.

Flabellinopsis iodinea (Cooper, 1863) (original description in Cooper 1863; detailed redescriptions in MacFarland 1966 and Marcus and Marcus 1967).

Body wide to narrow. Notal edge reduced continuous, discontinuous, or fully reduced. Cerata not stalked, in continuous or discontinuous numerous rows. Rhinophores smooth, wrinkled, rarely annulated or perfoliated. Anus pleuroproctic under the reduced notal edge. Distinct oral glands commonly absent. Radula formula 1.1.1. Rachidian teeth usually with strong cusp, only rarely compressed by adjacent lateral denticles. Lateral teeth narrow or with attenuated process basally, always denticulated. Commonly both distal and proximal receptaculum seminis present. Vas deferens usually short, rarely long, with indistinct prostate. External permanent penial collar absent. Penis in many cases broad to disk-shaped, more rarely elongated conical, always internal, unarmed.

Borealia gen. n., Coryphella Gray, 1850, Fjordia gen. n., Gulenia gen. n., Himatina Thiele, 1931, Itaxia gen. n., Microchlamylla gen. n., Occidentella gen. n., Orientella gen. n.

The molecular analysis showed the presence of a well-supported (PP = 1, BS = 94) big clade (Figs 1, 2) which encompassed the majority of the traditional Coryphella (originally suggested by Gray 1850) including type species C. verrucosa, and also C. lineata, C. nobilis and C. gracilis. This clade is clearly distinct from the other traditional Flabellinidae as well as traditional basal Coryphellidae now placed in the separate family Paracoryphellidae (see above). However, even in the restricted sense Coryphella remains extremely heterogeneous by morphology of the notal ridge (continuous to discontinuous) and reproductive system anatomy (relatively long as in C. gracilis and C. amabilis, S-shaped in the type species C. verrucosa, or very short as in C. lineata or C. browni; C. athadona instead possesses an aberrant penial gland distal part of the prostate). The penis usually appears as a wide lobe in many species but may also be narrow and conical as in C. gracilis and C. nobilis). Thus, a further separation of more narrow genera within the reinstated family Coryphellidae is clearly necessary. The molecular analysis based on broad sampling of many Coryphellidae across both northern and southern hemispheres supports such a decision since it resulted in the formation of many well-supported smaller clades within the family Coryphellidae (Fig. 2). For example, the morphologically quite different C. athadona and C. trilineata stand apart and cluster more basally from the majority of the traditional Coryphella. Presence within the traditional genus Coryphella of wide bodied taxa like C. nobilis, C. trophina with continuous notal ridges, and the complete separateness (along with paraphyly) of the genus Flabellina implies that transformation of the continuous well-defined ancestral notal ridge into derived stalks or elevations has occurred several times independently within the family Flabellinidae. It is notable that wide bodied (new and resurrected) genera with a continuous notal edge, namely Borealia, Itaxia and Himatina, hold the most basal positions within various smaller clades of the family Coryphellidae (Fig. 2) suggesting that the common ancestor of all Coryphellidae was wide-bodied with a well-defined notal edge, as in the more basally placed members of the family Paracoryphellidae. The minimum uncorrected p-distances for the partial COI gene between the species of family Coryphellidae are given in Table 1. The minimum uncorrected p-distances between all genera range 10.1–18.3%. The lowest distances occurred between Himatina trophina and Fjordia chriskaugei (10.1%). Whereas the maximal uncorrected p-distances for the COI fragments between Fjordia browni and Fjordia lineata reach 6.4%, between Fjordia lineata and Fjordia chriskaugei sp. n. they reach 6.1%. Intra-genera variability reached significantly smaller values than variability between genera. The biggest distances occurred between Itaxia falklandica and other genera of family Coryphellidae (range 12.0–18.3%). Such considerable molecular divergences between taxa of the family Coryphellidae (Table 1) support the reliability of a multi-genera approach consistently applied in this study.

Coryphella nobilis Verrill, 1880

After boreo (north in Latin) because of the amphiboreal distribution of the two species included.

Body wide. Notal ridge present, reduced, continuous. Cerata in continuous rows. Rhinophores wrinkled. Anterior foot corners present. Rachidian teeth with compressed narrow cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Separated distal and proximal receptaculum seminis. Moderately long vas deferens expands to narrow penial sheath. Penis narrow, tubular.

Borealia nobilis (Verrill, 1880), comb. n. (Fig. 16) (original description in Verril, 1880, detailed redescripton in Kuzirian 1977), Borealia sanamyanae sp. n. (Fig. 17).

The genus Borealia is clearly distinguished from any other Coryphellidae by a combination of continuous notal edge, long tubular penis, and compressed cusp of the rachidian radular teeth. In this study we discovered a closely related but clearly distinct (according to molecular data) new species of the genus Borealia from the North Pacific which forms separate sister clade to B. nobilis (Fig. 1).

Holotype, ZMMU Op-518, 5 mm long (fixed), Middle Kurile Islands, Matua Island, Cape Klyuv, 25.08.2016, depth 17 m, coll. N.P. Sanamyan.

North West Pacific, Middle Kurile Islands.

In honour of Nadezhda Sanamyan, marine biologist from Kamchatka. She has made a considerable contribution in collecting North West Pacific nudibranchs.

Continuous notal edge, background colour translucent white, digestive gland diverticula dark-red to pinkish, apical parts of cerata with white pigment, radula consists of more than 24 teeth, rachidian tooth with up to seven distinct denticles adpressed to central cusp, lateral teeth with few denticles on teeth edge.

External morphology (Fig. 17A–C). Body relatively wide. Foot and tail moderate, anterior foot corners relatively short. Rhinophores similar in size to oral tentacles, slightly wrinkled, robust. Dorsal cerata fusiform, long, continuously attached to rudimentary but uninterrupted notal edge without forming clusters. Apices of cerata pointed. Notum narrow but distinct throughout both lateral sides of body. Digestive gland diverticulum fills significant volume of cerata. Anal opening on right side below notal edge in first half of body but closer to middle. Reproductive openings lateral, below notal edge around middle part of body.

Colour (Fig. 17A). Background colour translucent white. Digestive gland diverticula dark-red to pinkish. Apical parts of cerata with opaque cap of white pigment.

Jaws (Fig. 17D–F). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears ca. 20 denticles that continue to form several reduced rows of denticles on body of masticatory processes.

Radula (Fig. 17G). Radula formula: 24 × 1.1.1. Rachidian tooth elongate-triangular with small narrow cusp. Rachidian tooth bears 5-7 well-defined separated lateral denticles. Cusp is adpressed by adjacent first lateral denticles. Lateral teeth broadly triangular with obtuse and distinctly attenuated posteriorly outer process and between six and nine sharp long denticles on internal edge.

Reproductive system (Fig. 17H). The available material contains only a non-mature reproductive system, which do not allow recognition of characters in detail.

Shallow waters, stony and rocky habitats.

Northwest Pacific.

According to the molecular phylogenetic analysis Borealia sanamyanae sp. n. forms a separate sister clade to B. nobilis (Fig. 1). The following morphological characters distinguish B. sanamyanae sp. n. from B. nobilis: larger number of radular rows (max up to 22 in 40–50 mm length B. nobilis (Kuzirian 1979); our specimens from the White and Barents Seas are about 20–30 mm in length and have max 20 rows, whereas a ten times smaller 5-mm specimen of B. sanamyanae sp. n. has 24 rows), and the cusp of the central tooth in B. nobilis, though relatively low, is almost not adpressed by the adjacent lateral denticles (Fig. 16H), whereas in B. sanamyanae sp. n. it is considerably adpressed (Fig. 17G).

Eolidia verrucosa M. Sars, 1829

Body narrow. Notal ridge completely reduced. Cerata in several groups. Rhinophores smooth with small tubercles. Anterior foot corners present. Rachidian teeth with non-compressed cusp and distinct denticles. Lateral teeth denticulated without attenuated process basally. Separated distal and proximal receptaculum seminis. S-shaped thick prostatic vas deferens. Penis disk-shaped with numerous small triangular processes at the disk edge.

Coryphella pseudoverrucosa Martynov, Sanamyan, Korshunova, 2015 (Fig. 18) (original description in Martynov et al. 2015), Coryphella verrucosa (M. Sars, 1829) (Figs 19, 20) (original description in M. Sars 1829).

In the restricted sense the genus Coryphella Gray, 1850 represents a well-defined unit of narrow-bodied coryphellids with completely reduced notal edge and characteristic thick S-shaped prostatic vas deferens (Figs 18H, 19J, 20I, 21). Two morphologically similar species, the North Atlantic type species of the genus C. verrucosa and the North Pacific C. pseudoverrucosa, are clearly distinguished both morphologically (particularly the shape of the rachidian teeth of the radula) and according to our molecular analysis (Fig. 1).

Aeolis lineata Lovén, 1846.

After the Norwegian word “fjord” because of the type locality of the Oslofjord and also this is a very common species at Gulen at the mouth of the Sognefjord, where many of the studied materials come from.

Body narrow. Notal edge present, moderately reduced, discontinuous. Cerata in several groups. Rhinophores smooth, similar in length or shorter than oral tentacles. Anterior foot corners present. Rachidian teeth with non-compressed cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Separated distal and proximal receptaculum seminis. Vas deferens very short, expanding to a broad penial sheath. Penis broad, lobe-shaped.

Fjordia browni (Picton, 1980), comb. n. (original description in Picton 1980) (Fig. 22), Fjordia (?) capensis (Thiele, 1925), comb. n. (original description in Thiele 1925), Fjordia lineata (Lovén, 1846), comb. n. (original description in Lovén 1846), Fjordia chriskaugei sp. n., Fjordia (?) insolita (Garcia-Gomez & Cervera, 1989), comb. n. (original description in Garcia-Gomez and Cervera 1989).

According to combined morphological and molecular evidence, the traditional species Coryphella lineata was found to be a very heterogeneous species complex. This complex includes at least five species, which are clearly separated into two major clades according to molecular analysis (Figs 1, 2) and by the morphological data (presence or absence of continuous notal edge). According to these data two new genera are proposed for the former C. lineata complex. First is the group of narrow-bodied coryphellids with discontinuous notal edge which included the proper C. lineata, C. browni, and a new species (see below); it is named as the new genus Fjordia gen. n. The second group with a continuous notal edge includes two new species and the previously enigmatic species Coryphella borealis Odhner, 1922 (not to be confused with Chlamylla borealis Bergh, 1886, see above), which represents specimens wrongly identified as Coryphella gracilis in a barcoding project by Barco et al. (2016) and which have been fully investigated for the first time in the present studies (Fig. 25) including both morphological and molecular study (Figs 1, 2). Our sequences of real C. borealis are identical to the above-mentioned wrongly identified C. gracilis from GenBank. Real C. gracilis has very different morphological features and this species is recovered in a completely different clade in our molecular tree (Figs 1, 2). These two clades, clearly delineated by morphology and molecular analysis are therefore named Fjordia gen. n. (with discontinuous notal edge) and Gulenia gen. n. (with continuous notal edge).

In this study it is also confirmed for the first time that the enigmatic C. borealis Odhner, 1922 belongs to the genus Gulenia according to integrative morphological and molecular studies (Figs 1, 2, 25). Both new genera share a similar reproductive system with a very short vas deferens and wide penis (Fig. 21), that imply a common ancestry, confirmed by molecular data (Figs 1, 2). Fjordia browni (Fig. 22) unlike other species of the genus Fjordia does not possess both dorsal and lateral white lines, but the presence of rudimentary notal edges, shape of the radular teeth, short vas deferens, and broad penial lobe are consistent with F. lineata. Molecular results place this species as sister to Fjordia chriskaugei sp. n. and in a clade where other members have dorsal and lateral white lines. All studied specimens from the Gulen region demonstrate a high degree of uniformity both in body shape and colour. Originally described from the UK where specimens were significantly smaller than exemplars from Gulen, nevertheless it keeps all essential diagnostic characters; discontinuous notal ridge, complete absence of the white lines, and radular pattern. The specimens from Gulen measured up to 100 mm in length. According to the morphological data, we included two more species (the South African Coryphella capensis and western Mediterranean Flabellina insolita) in the genus Fjordia, but further molecular data are necessary to confirm this.

Holotype, ZMMU Op-477, 45 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 19.03.2015, depth 20 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-402, 28 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 18.03.2015, depth 10–20 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-404, 28 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 16.03.2015, depth 20 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-405, 30 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 16.03.2015, depth 20 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-412, 42 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 17.03.2015, depth 10–20 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-499, Achill Island, Co. Mayo, Ireland, 06.04.2015, coll. B.E. Picton.

Gulen Dive Resort, Norway.

In honour of Christian Skauge (Gulen Dive Resort and Scubapixel), the organiser of the “Nudibranch Safari” and our great friend, who first noticed the heterogeneity of the traditional C. lineata in the field in Norway, including photographic records.

Discontinuous notal edge, background colour translucent white, digestive gland diverticula pink, orange-brown to reddish-brown, apical parts of cerata with white pigment, usually one to several punctuated fine white lines run along dorsal face of cerata, thin opaque white lines on dorsal and lateral sides, rachidian tooth with up to 10 distinct denticles delineate from central cusp, lateral teeth with up to eleven denticles on teeth edge, penis is a broad lobe.

External morphology (Fig. 23A–E). Body relatively narrow. Foot and tail moderate, anterior foot corners long. Oral tentacles long. Rhinophores ca. 1.5 times longer than oral tentacles, slightly wrinkled. Dorsal cerata finger-shaped to fusiform, forming several clusters along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosac. Distinct notal edge remains mostly below cerata clusters. Digestive gland diverticulum fills significant volume of cerata. Anal opening on right side below second large cluster of cerata. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 23A, D). Background colour translucent white. Digestive gland diverticula pale pink, orange-brown to reddish-brown depending on locality and diet. Pinkish oral tube, oesophagus, hindgut, and gonads shine through dorsal sides. Thin opaque zigzag white line runs along middle of whole dorsum from head to tail. Similar single thin median line runs on both lateral sides of the body. Rhinophores background colour similar to body; along dorsal side of rhinophores runs a thin white line; apical white pigment absent. Dorsal sides of oral tentacles covered with thin opaque white line. One to several punctuated fine white lines run along dorsal face of cerata, sometimes absent. Apical parts of cerata without any opaque cap of white pigment.

Jaws (Fig. 23G, H). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears ca. 60 denticles that continue to form several reduced rows of denticles on body of masticatory processes.

Radula (Fig. 23I). Radula formula: 13 × 1.1.1. Rachidian tooth elongate-triangular with short narrow cusp of less than 1/3 of tooth length (Fig. 23I). Rachidian tooth bears between seven and ten well-defined separated long lateral denticles not adpressed towards the cusp. Cusp delineated from adjacent first lateral denticles. Lateral teeth (Fig. 23I) broadly triangular with obtuse and considerably attenuated posteriorly outer process and between eight and eleven sharp long denticles on internal edge.

Reproductive system (Fig. 23J–L). Diaulic. Hermaphroditic duct leads to convoluted ampulla of about two whorls. Vas deferens very short, attached to dorsal side of penial sheath, no distinct prostate. Penial sheath large, wide. Penis is broad lobe (Fig. 23L). Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Proximal receptaculum seminis large, oval, swollen. Distal receptaculum seminis present.

Associates with Tubularia colonies usually at depth 20–40 m. Attacks and feeds on polyps of Tubularia indivisa L., 1758. Juveniles probably start to feed on Eudendrium spp. or other smaller athecate hydroids. This species is abundant in some localities. Egg mass narrow cord; forms irregular, compressed pink or off-white spirals. Reproduction period from February to June; larva planktotrophic veliger with oval shell.

Northeast Atlantic, including Ireland, Great Britain (Scotland, England, Wales), Norway.

Fjordia chriskaugei sp. n. is distinguished morphologically from F. lineata (Lovén, 1846) s. str. (Fig. 24) by faint dotted lines on the dorsal surface of the cerata, the complete absence of the apical white cap, by rhinophores longer than oral tentacles, and by the distinct cusp of the rachidian teeth which is placed above the adjacent lateral denticles. Molecular analysis corroborates the morphological data (see Discussion) showing F. chriskaugei sp. n. as a species distinct from F. lineatas. str. (Fig. 1). Thompson and Brown (1984, pl. 27) and Picton and Morrow (1994, p. 95) illustrate this species as Coryphella lineata and their descriptions are a composite of the two species. The majority of specimens demonstrate significant uniformity in the body shape and colour. In some specimens from Ireland the irregular white lines on the cerata can be completely absent.

Original type material lost. Neotype, NTNU-VM-72483, 11 mm long (fixed) is designated here from the Svarte Jan, Idefjorden, Sweden, 06.06.2015, depth 22 m, coll. Mats Larsson, close to Lovén’s original type locality.

One specimen, ZMMU Op-403, 19 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 18.03.2015, depth 10–20 m, coll. Jørn Ari, Tina Malmgren. One specimen, ZMMU Op-406, 27 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 17.03.2015, depth 10–20 m, coll. T.A. Korshunova, A.V. Martynov. One specimen, ZMMU Op-506, 34 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 17.03.2015, depth 20 m, coll. T.A. Korshunova, A.V. Martynov. One specimen, ZMMU Op-506, 37 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 17.03.2015, 20 m depth, coll. T.A. Korshunova, A.V. Martynov. One specimen, ZMMU Op-507, 21 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 01.03.2014, depth 20 m depth, coll. T.A. Korshunova, A.V. Martynov. One specimen, ZMMU Op-508, 21 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 17.03.2015, 20 m depth, coll. T.A. Korshunova, A.V. Martynov.

Oslofjord, Norway.

Discontinuous notal edge, background colour translucent white, digestive gland diverticula pink, orange-brown to reddish-brown, apical parts of cerata with white pigment, along dorsal face of cerata runs thin straight or slightly curved line, thin opaque white lines on dorsal and lateral sides, rachidian tooth with up to seven distinct denticles delineate from central cusp, lateral teeth with up to 14 denticles on teeth edge, penis is a broad lobe.

External morphology (Fig. 24A–E). Body elongate, graceful, laterally compressed. Foot narrow, tail moderate, anterior foot corners long. Oral tentacles long. Rhinophores long and slightly wrinkled, similar in length to oral tentacles. Dorsal cerata finger-shaped forming two to four indistinct clusters. Apices of cerata pointed. Distinct notum remains only below cerata clusters. Digestive gland diverticulum fills significant volume of the cerata. Anal opening on right side of body between first and second pair of dorsolateral processes. Reproductive openings lateral, below first pair of dorsolateral cerata on right side.

Colour (Fig. 24A). Background colour translucent white. Digestive gland diverticula orange-brown to salmon to bright red to dark brown, almost black when feeding on Bougainvillea. Thin continuous opaque white line runs over middle of dorsum from head to tail. Similar single thin median line runs on both lateral sides of the body. Rhinophores similar in colour to body; apical parts covered with faint opaque white pigment. Dorsal sides of oral tentacles covered with thin opaque white line. Along dorsal face of cerata runs thin straight or slightly curved line. Apical parts of cerata covered with opaque oblique ring of white pigment which connects to median cerata line. Cnidosac obscured by white pigment ring. Scattered small white dots over cerata absent.

Jaws (Fig. 24G, H). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears ca. 70 denticles that continue to form several reduced rows of denticles on body of masticatory processes.

Radula (Fig. 24I). Radula formula: 17 × 1.1.1. Rachidian tooth horseshoe-shaped without evident cusp (Fig. 24I). Rachidian tooth bears six or seven well-defined separated long lateral denticles. Cusp indistinct and sunken below adjacent first lateral denticles. Lateral teeth (Fig. 24I) narrowly triangular with sharpened and attenuated outer process and between eleven and fourteen sharp long denticles on internal edge.

Reproductive system (Fig. 24J–L). Diaulic. Hermaphroditic duct leads to convoluted ampulla of about two whorls. Vas deferens very short, no distinct prostate. Penial sheath large, wide. Penis is broad lobe (Fig. 24K). Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Proximal receptaculum seminis large, oval, swollen. Distal receptaculum seminis present.

Associates with the Tubularia indivisa and Ectopleura larynx colonies usually at depths of 10–40 m. Attacks and feeds on polyps of Tubularia, Ectopleura, Eudendrium, Bougainvillea and other athecate hydroids. Juveniles probably start to feed on species with smaller polyps. This species is abundant in some localities. Egg mass is irregular compressed spiral cord. Reproduction period from February to June; the larva is a planktotrophic veliger with an oval shell.

Confirmed specimens of F. lineata Northeast Atlantic, including Ireland, Great Britain, Norway (Oslofjord to Lofoten Islands) (Odhner 1939; present study), Sweden (Bohuslän region) (Malmberg and Lundin 2015) western Mediterranean (Thompson and Brown 1984, Trainito and Doneddu 2014).

Coryphella lineata in the traditional sense (e.g., Odhner 1939; Thompson and Brown 1984; Evertsen and Bakken 2005) is a genera complex (see below) according to both morphological and molecular data (Fig. 1). Lovén’s (1846) original description of Aeolis lineata is short and uninformative. In order to maintain the current usage of the specific name Fjordia lineata (Lovén, 1846) a neotype is designated here (Fig. 24). The neotype was collected in shallow waters in the Idefjord on the south-eastern coast of Sweden, in the vicinity of the original type locality in the Bohuslän region (Lovén 1846). All studied specimens shared the characteristic for this species of an expanded white pigment ring at the ceratal tip which is continued as a thin white line down the ceratal body. This feature persists both in subadult and fully mature specimens. The latter differ from subadults in having a broader body and pinkish body colour.

Gulenia orjani gen. et sp. n.

After Gulen Dive Resort (Norway) from where many of the studied materials come.

Body moderately wide. Notal ridge present, reduced, continuous. Cerata in continuous rows. Rhinophores smooth to wrinkled. Anterior foot corners present. Rachidian teeth with non-compressed broad cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens very short, expands to broad penial sheath. Penis broad, lobe shaped.

Gulenia borealis (Odhner, 1922), comb. n. (Fig. 25), Gulenia monicae sp. n. (Fig. 26), Gulenia orjani sp. n. (Fig. 27).

See above under the genus Fjordia.

Holotype, ZMMU Op-466, 34 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 17.03.2015, depth 29–30 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-408, 23.5 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 17.03.2015, depth 20 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-411, 24.5 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 17.03.2015, depth 10–20 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-475, 25 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 02.04.2016, depth 20–25 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-475, 31 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 02.04.2016, 25–30 m depth, coll. T.A. Korshunova, A.V. Martynov.

Gulen Dive Resort, Norway.

After Monica Bakkeli, proprietor of the Gulen Dive Resort, who significantly helped in organizing the scientific meetings and collecting activities in Gulen.

Continuous notal edge, background colour translucent white, digestive gland in cerata orange-brown to reddish-brown, apical parts of cerata without white pigment, usually small white spots scattered on dorsal face of cerata, thick opaque white lines on dorsal and lateral sides, rachidian tooth with up to nine distinct denticles, not delineated from central cusp, lateral teeth with up to 18 denticles on teeth edge, penis is broad lobe.

External morphology (Fig. 26A–E). Body relatively narrow. Foot and tail moderate, anterior foot corners long. Oral tentacles long and robust. Rhinophores ca. 1.5 times shorter than oral tentacles, slightly wrinkled, robust. Dorsal cerata fusiform, short, continuously attached to rudimentary but uninterrupted notal edge without forming clusters. Apices of cerata pointed. Notum narrow but distinct throughout both lateral sides of body. Digestive gland diverticulum fills significant volume of the cerata. Anal opening on right side below notal edge in first half of body but closer to middle. Reproductive openings lateral, below notal edges around middle part of body. Tail short and pointed, extending only short distance beyond last cerata.

Colour (Fig. 26A). Background colour translucent white. Digestive gland diverticula orange-brown to reddish-brown. Thick opaque white line runs along middle of whole dorsum from head to tail, varying in width and often spreading as lateral lobes amongst ceratal bases. Similar single thick median line runs on both lateral sides of body. Rhinophores similar in colour to body; apical parts covered with opaque white pigment. Dorsal sides of oral tentacles covered with thick opaque white line. No line along dorsal face of cerata, instead small white dots and speckles scattered over ceratal surfaces. Apical parts of cerata without opaque cap of white pigment.

Jaws (Fig. 26F, G). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears about 60–80 denticles that continue to form several reduced rows of denticles on the body of the masticatory processes.

Radula (Fig. 26H). Radula formula: 16–17 × 1.1.1. Rachidian tooth elongate-triangular with very strong cusp of nearly 1/3 of the tooth length (Fig. 26H). Rachidian tooth bears eight or nine well-defined separated (but adpressed towards the cusp) long lateral denticles. Cusp delineated from the adjacent first lateral denticles. Lateral teeth (Fig. 26H) narrowly triangular with obtuse and distinctly attenuated posteriorly outer process and between 13 and 18 sharp long denticles on internal edge.

Reproductive system (Fig. 26I, J). Diaulic. Hermaphroditic duct leads to convoluted ampulla of about two whorls. Vas deferens very short, not attached to dorsal side of the penial sheath, no distinct prostate. Penial sheath large, wide. Penis is broad lobe. Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Proximal and distal receptaculum seminis placed relatively close to each other (Fig. 26J).

Associates with the Tubularia colonies usually at depth 20–30 m. Feeds on small athecate hydroids and Eudendrium spp. which grow on the stalks of the Tubularia and the adjacent rock surfaces. This species is locally abundant. Egg mass is a narrow spiral cord. Reproduction period from February to May; the larva is a planktotrophic veliger with oval shell.

In the Northeast Atlantic has been found only in Norway (present study) and possibly in Sweden.

According to the present molecular phylogenetic analysis Gulenia monicae sp. n. forms a separate clade within the genus Gulenia, sister to G. orjani sp. n. The genetic distance of the mitochondrial barcode marker (COI) separates sympatric G. monicae sp. n. with high genetic divergence (11.3%). The mean COI p-distance value within the G. monicae sp. n. clade (5 specimens) is 0.45% and within the G. orjani sp. n. clade (14 specimens) is 0.41%. While this species shows a considerable minimal COI p-distance (10.97 ± 1.2%) compared to G. orjani sp. n., morphologically it is difficult to distinguish. G. monicae sp. n. can be tentatively distinguished externally from G. orjani sp. n. by a narrower body and shorter cerata.

Holotype, NTNU-VM-72482, 22 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 19.03.2015, depth 20–30 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-407, 30 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 18.03.2015, depth 20 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-409, 27 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 18.03.2015, depth 20–30 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-410, 22 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 18.03.2015, depth 20–30 m depth, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-467, 35 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 02.04.2016, depth 10–15 m, coll. T.A. Korshunova, K. Malmberg, A.V. Martynov. 1 specimen, ZMMU Op-468, 19 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, depth 20–25 m depth, 03.04.2016, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-469, 33 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 02.04.2016, depth 20–25 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-470, 21 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 03.04.2016, depth 25–30 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-471, 19.5 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 05.04.2016, depth 20–30 m, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-472, 22.5 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 07.04.2016, depth 20–30 m, coll. T.A. Korshunova, B. Picton. 1 paratype, ZMMU Op-473, 32 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, depth 20–25 m, 03.04.2016, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-474, 32 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, depth 20–25 m, 03.04.2016, coll. T.A. Korshunova, A.V. Martynov. 1 paratype, ZMMU Op-538, 19 mm long (live), Norway, entrance of the Sognefjord, Gulen Dive Resort, 19.03.2015, depth 20 m depth, coll. T.A. Korshunova, A.V. Martynov.

Gulen Dive Resort.

After Ørjan Sandnes, proprietor of the Gulen Dive Resort where the majority of the material for this study has been collected, who has been immensely supportive of this work.

Continuous notal edge, background colour translucent white, digestive gland in cerata orange-brown to reddish-brown, sometimes almost blackish, apical parts of cerata without white pigment, usually small white spots scattered on dorsal face of cerata, thick opaque white lines on dorsal and lateral sides, rachidian tooth with up to nine distinct denticles, not delineated from rachidian cusp, lateral teeth with up to 18 denticles on teeth edge, penis is a broad lobe.

External morphology (Fig. 27A–E). Body relatively wide. Foot and tail moderate, anterior foot corners long. Oral tentacles long and robust. Rhinophores ca. 1.5 times shorter than oral tentacles, slightly wrinkled, robust. Dorsal cerata fusiform, long, continuously attached to rudimentary but uninterrupted notal edge without forming clusters. Apices of cerata pointed. Notum narrow but distinct throughout both lateral sides of body. Digestive gland diverticulum fills significant volume of cerata. Anal opening on right side below notal edge in first half of body but closer to middle. Reproductive openings lateral, below notal edge around middle part of body. Tail short and pointed, extending only short distance beyond last cerata.

Colour (Fig. 27A). Background colour translucent white. Digestive gland diverticula orange-brown to reddish-brown, sometimes dark brown to blackish. Thick opaque white line runs down middle of whole dorsum from head to tail, varying in width and often spreading as lateral lobes amongst ceratal bases. Similar single thick median line runs on both lateral sides of the body. Rhinophores similar in colour to body; apical parts covered with opaque white pigment. Dorsal sides of oral tentacles covered with thick opaque white line. No line along dorsal face of cerata, instead small white dots and speckles scattered over the surfaces of cerata (Fig. 27F). Apical parts of cerata without opaque cap of white pigment.

Jaws (Fig. 27H, I). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears ca. 40–50 denticles that continue to form several reduced rows of denticles on body of the masticatory processes.

Radula (Fig. 27G). Radula formula: 16–19 × 1.1.1. Rachidian tooth elongate-triangular with very strong cusp of around 1/3 of the tooth length. Rachidian tooth bears eight or nine well-defined separated (but adpressed towards the cusp) long lateral denticles. Cusp strongly delineated from adjacent first lateral denticles. Lateral teeth narrowly triangular with obtuse and distinctly attenuated posteriorly outer process and between 13 and 18 sharp long denticles on internal edge.

Reproductive system (Fig. 27J–L). Diaulic. Hermaphroditic duct leads to convoluted ampulla of about two whorls. Vas deferens very short, not attached to dorsal side of penial sheath, no distinct prostate. Penial sheath large, wide. Penis is a broad lobe (Fig. 27K). Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Proximal and distal receptaculum seminis placed close to each other and similar in size (Fig. 27L).

Associates with the Tubularia colonies usually at depth 20–30 m. Feeds on small athecate hydroids growing on the Tubularia stems and the adjacent rock as well as on Eudendrium species. Egg mass is a narrow cord. Reproduction period from February to April; the larva is a planktotrophic veliger with oval shell.

In the Northeast Atlantic has been found only in Norway (present study) and possibly in Sweden.

Gulenia orjani sp. n. is readily distinguished morphologically from other superficially similar taxa of the family Coryphellidae (e.g., Fjordia lineata, F. chriskaugei) as well as from the majority of the North Atlantic flabellinids by a combination of continuous notal edge with cerata not in clusters, a broad dorsal medial white line, and strong cusp of the rachidian radular tooth. Another distinctive feature of G. orjani sp. n. is absence of the white line on the dorsal surface of the cerata, which is substituted often by scattered white dots. The continuous notal edge resembles that in the genus Chlamylla; the latter, however, is very different in having a distinct granulose prostate and complicated external penial collar. Two North Atlantic genera and species of the family Coryphellidae also possess a continuous notal edge, namely Gulenia borealis and Borealia nobilis. However, unlike G. orjani both these taxa do not possess dorsal and lateral continuous white lines and differ considerably in radular and reproductive morphology. Molecular analysis corroborates the morphological data (see Discussion). Colour may vary significantly. The reddish colour of the digestive diverticulum in the cerata is most common; however, specimens with light brown and even almost black diverticulum may occur. The medial white line also may vary to a considerable degree - including specimens with broad and narrow lines. White pigment spots on the cerata may be dense or almost absent. For differences from G. monicae sp. n. see above.

Himatella trophina Bergh, 1894

Body moderately wide. Notal ridge present, reduced, continuous. Cerata in continuous rows. Rhinophores perfoliated. Anterior foot corners present. Rachidian teeth with moderately compressed narrow cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Short vas deferens expands to broad penial sheath. Penis broad, discoid.

Himatina trophina (Bergh, 1894) (Fig. 28) (original description in Bergh 1894).

The genus Himatina Thiele, 1931 was established as a replacement (Thiele 1931) for a single species Himatella trophina Bergh, 1894 and possesses a unique combination of morphological and molecular characteristics (Figs 1, 2). Himatina trophina is a wide-bodied coryphellid with continuous notal edge, perfoliated rhinophores and very short vas deferens and broad penis (Fig. 21). According to our molecular phylogenetic analysis Himatina forms a separate clade basally to the genera Fjordia and Gulenia. These morphological and molecular data clearly delineate Himatina from all known Atlantic and Pacific coryphellids.

Coryphella falklandica Eliot, 1907

After itax (meaning “south” in Yagán (Yaghan), a nearly extinct language) because Yagáns are regarded as the southernmost peoples in the world who traditionally inhabited the very end of South America thus are close to the range of the only known coryphellid nudibranchs from the southern sub-Antarctic waters.

Body moderately wide. Notal ridge present, reduced, continuous. Cerata in continuous rows. Rhinophores wrinkled. Anterior foot corners present. Rachidian teeth with non-compressed broad cusp and distinct denticles. Lateral teeth denticulated without attenuated process basally. Receptaculum seminis unknown. Vas deferens very short, thick. Penis broad, lobe-shaped.

Itaxia falklandica (Eliot, 1907), comb. n. (Fig. 29) (original description in Eliot 1907, morphological data in Odhner 1944; Marcus 1959, Schrödl 2003; neotype from southern Chile (Bahía Mansa) designated by Schrödl 2003).

Externally the single included species Itaxia falklandica is similar to the species of the genus Borealia, with a moderately wide body and continuous notal margin; however, the reproductive system with short vas deferens and broad penis more closely resembles the genera Gulenia and Fjordia. In the present study, molecular data for I. falklandica was obtained for the first time from the specimens from southern Chile. Most unexpectedly, our molecular analysis places Itaxia falklandica as sister to the genus Microchlamylla (see below) which differs considerably from Itaxia by the presence of a discontinuous notal edge and a remarkable reproductive system with several loops of thin vas deferens without a distinct prostate and a small narrow penis (Figs 21, 30I).

Eolis gracilis Alder & Hancock, 1844

After micro- and chlamylla; in reference to the unusually long vas deferens of this genus typical for the genus Chlamylla of the family Paracoryphellidae, but smaller body size and discontinuous notal edge, common in the family Coryphellidae.

Body narrow. Notal edge present, moderately reduced, discontinuous, formed by a distinct series of lateral pieces. Cerata in several groups. Rhinophores smooth, similar in length or shorter than oral tentacles. Anterior foot corners present. Rachidian teeth with relatively wide cusp and distinct denticles. Lateral teeth denticulated without attenuated process basally. Separated distal and proximal receptaculum seminis. Long convoluted thin vas deferens expands distally to narrow penial sheath. Penis narrow, conical.

Microchlamylla gracilis gracilis (Alder & Hancock, 1844), comb. n. (Fig. 30) (original description in Alder and Hancock 1844), Microchlamylla gracilis zfi subsp. n. (Fig. 31), Microchlamylla amabilis (Hirano & Kuzirian, 1991), comb. n. (original description in Hirano and Kuzirian 1991).

The genus Microchlamylla gen. n. is clearly delineated from all known taxa of the family Coryphellidae by a combination of narrow body with a discontinuous notal edge, smooth rhinophores, and long narrow vas deferens which forms several loops (Fig. 21). The molecular phylogenetic analysis places Microchlamylla gen. n. in a clade very distinct from the rest of the coryphellids (Figs 1, 2) with the only relatively close genus being Itaxia gen. n. The genus Microchlamylla gen. n. is comprised of two species which are morphologically quite similar but molecularly well delineated - the North Atlantic M. gracilis and North Pacific M. amabilis.

Holotype. ZMMU Op-501, 11 mm long (fixed), Franz Josef Land, Northbrook Island, 26.08.2013, depth 20 m, coll. O.V. Savinkin.

After common acronym in Russian “ZFI” (Zemlya Franza Iosifa) for Franz Josef Land.

Franz Josef Land.

Discontinuous notal edge, background colour translucent white, digestive gland in cerata dark red, apical parts of cerata with white pigment, rachidian tooth with up to ten distinct denticles, delineated from central cusp, lateral teeth with up to eleven denticles on teeth edge, penis conical.

External morphology (Fig. 31A–D). Body relatively narrow. Foot and tail moderate, anterior foot corners long. Oral tentacles long. Rhinophores ca. 1.5 times longer than oral tentacles, slightly wrinkled. Dorsal cerata finger-shaped to fusiform, forming several clusters along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosac. Distinct notal edge remains mostly below cerata clusters. Digestive gland diverticulum fills significant volume of the cerata. Anal opening on right side below second large cluster cerata. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 31A, B, D). Background colour translucent white. Digestive gland diverticula dark red. Rhinophores background colour similar to body; along dorsal side of rhinophores runs thin white line. Dorsal sides of oral tentacles covered with thin opaque white line. Apical parts of cerata with opaque cap of white pigment.

Jaws (Fig. 31F). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears several denticles that continue to form several reduced rows of denticles on the body of the masticatory processes.

Radula (Fig. 31G). Radula formula: 21 × 1.1.1. Rachidian tooth elongate-triangular with very broad cusp up to 1/2 of the tooth length, with a peculiar notch at the base. Rachidian tooth bears between seven and ten well-defined lateral denticles not adpressed towards the cusp. Some denticles form clusters, outermost denticles are considerably enlarged. Cusp is delineated from the adjacent first lateral denticles. Lateral teeth (Fig. 31G) broadly triangular with obtuse and attenuated posteriorly outer process and between five and eleven sharp denticles of various lengths on the internal edge.

Reproductive system (Fig. 31H). Diaulic. Hermaphroditic duct leads to swollen short ampulla. Vas deferens is long, broad, comprising at least three whorls, no distinct prostate. Penial sheath is narrow. Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Receptaculum seminis oval, swollen. Distal receptaculum seminis present.

Associates with hydroid colonies usually at depths around 20 m. Apart from the holotype, several more specimens of this new subspecies can be traced from the original in situ photographs, but they were not collected. The egg mass is narrow cord that forms irregular, compressed pink or off-white spirals (Fig. 31E). Reproduction recorded in August.

So far known only from the northernmost locality, Franz Joseph Land Archipelago.

Microchlamylla gracilis zfi subsp. n. differs considerably from Microchlamylla gracilis gracilis by a peculiarly enlarged base with a prominent notch of the cusp of the rachidian radular teeth (compare Fig. 30H and Fig. 31G). In M. gracilis gracilis such a character was never reported before, either in literature (e.g., Odhner 1939; Thompson and Brown 1984) or according to our study of the specimens from geographically very distant regions, including the White Sea and southwest Norway. The lateral denticles of the rachidian teeth of M. gracilis zfi subsp. n. demonstrate considerable differences from M. gracilis gracilis in the presence of clustered denticles and very enlarged outermost lateral denticles (compare Fig. 30H and Fig. 31G). In addition, the vas deferens is much broader in M. gracilis zfi subsp. n. and differs considerably from M. gracilis gracilis (compare Fig. 30I and Fig. 31H). Thus, morphologically M. gracilis zfi subsp. n. is well-distinguished from the nominative subspecies; however, according to the molecular data, these two taxa are similar (maximal COI p-distance is 0.62% whereas mean COI p-distance value within the M. gracilis clade is 0.56%) and therefore we here consider their status to be at the subspecies level. More study is clearly necessary in this case. Microchlamylla graciliss. l. was never reported prior to this study from Franz Josef Land and the presence of a separate taxon in this region can be explained also by isolation of this Archipelago from the main North Atlantic streams. This agrees with other our findings; namely, the presence of a new species of paracoryphellid Ziminella circapolaris sp. n. at Franz Josef Land (this study) and a new species of the onchidoridid genus Adalaria (Martynov and Korshunova 2017).

Coryphella athadona Bergh, 1875.

After the Western Pacific (from occidens = “west” in Latin), where the type species predominantly occurs.

Body narrow. Notal ridge completely reduced. Cerata in several groups. Rhinophores smooth. Anterior foot corners absent. Rachidian teeth with non-compressed cusp and distinct denticles. Lateral teeth denticulated without attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens very short, expanding into broad penial sheath with an additional glandular formation. Penis small, amorphous.

Occidentella athadona (Bergh, 1875), comb. n. (Fig. 32) (original description in Bergh 1875; redescription in Baba 1987a)

The genus Occidentella with only a single known species O. athadona has unique external and internal morphological features compared to all described Coryphellidae taxa: a rounded anterior part of the foot (no foot corners) and a highly developed glandular part of vas deferens which is similar to a true penial gland in some other families (e.g., Tergipedidae and Eubranchidae) (Fig. 21). Millen and Hermosillo (2007) indicated that some other taxa, e.g., Coryphella trilineata possess in a some degree a similar glandular structure; however, the penial complex in C. trilineata is still similar (see MacFarland 1966) to other coryphellids and not so obviously separated from the penial sheath as in O. athadona. By other features, e.g., presence of annulated rhinophores and anterior foot corners, C. trilineata differs considerably from O. athadona. Possibly in agreement with data on the similarity of a glandular formation in the penis, C. trilineata is placed within the same clade with O. athadona according to our molecular analysis (Figs 1, 2). However, this result may also be because we do not have molecular data for other coryphellids which are morphologically similar to C. trilineata from the Eastern Pacific (e.g., C. cooperi (Cockerell, 1901), Flabellina fogata Millen & Hermosillo, 2007) and C. trilineata together with these other species will probably be further separated from O. athadona. However, because it is morphologically very different from all other coryphellid taxa, C. athadona deserves its own genus. This is consistent with one of the general rules of integration of morphological and molecular data which were outlined above (see Materials and methods section), when a morphologically strongly aberrant taxon should not be merged with a phylogenetically relatively close taxon. This implies that if we merge the morphologically strongly aberrant C. athadona with the morphologically different but phylogenetically possibly relatively close C. trilineata we will considerably mask the natural diversity and will therefore make further classification much more difficult. If more species are discovered within these species complexes, we will need to compare them with morphologically very disparate taxa instead of making a comparison within narrow morphological and molecular units. According to these principles, the species Coryphella trilineata O’Donoghue, 1921 is separated here into another new genus (see below), within which we tentatively include at least two more Eastern Pacific species C. cooperi and Flabellina fogata Millen & Hermosillo, 2007 with similar external characters (rhinophores annulated in two species and warted in one species) and reproductive features (glandular formation at the base of penis).

Coryphella trilineata O’Donoghue, 1921.

After orientis (Latin, east), in reference to the predominantly Eastern Pacific range of the type species C. trilineata and further species included in the genus.

Body narrow. Notal ridge discontinuous. Cerata in several groups. Rhinophores annulated or tuberculated. Anterior foot corners present. Rachidian teeth with non-compressed cusp and distinct denticles. Lateral teeth denticulated without attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens very short, expands into broad penial sheath with an additional glandular formation. Penis discoid with small papillae.

Orientella (?) cooperi (Cockerell, 1901), comb. n. (original description in Cockerell 1901), Orientella (?) fogata (Millen & Hermosillo, 2007), comb. n. (original description in Millen and Hermosillo 2007), Orientella trilineata (O’Donoghue, 1921), comb. n. (original description in O’Donoghue 1921). Probably this clade and genus includes more Eastern Pacific coryphellid species, since several undescribed species have already been reported from Chile (Schrödl 2003).

Coryphella abei Baba, 1987 (original description in Baba 1987b), Coryphella verta Marcus, 1970 (original description in Marcus 1970, redescription in Millen and Hamann 2006).

Body commonly narrow. Notal edge discontinuous or fully reduced. Cerata in separate clusters, on elevations or distinct stalks. Rhinophores smooth, annulated or papillated. Anus mixed (pleuroproctic in higher acleioproctic position) or pleuroproctic under the reduced notal edge. Distinct oral glands present, commonly penetrate below anterior cerata. Radula formula 1.1.1. Rachidian teeth usually compressed by adjacent lateral denticles. Lateral teeth with attenuated process basally, usually denticulated, rarely smooth. Number and position of receptaculum seminis variable: two separate ones, or double proximal and single distal, or double distal one, in few cases proximal receptaculum not evident. Vas deferens usually long, with indistinct prostate. External permanent penial collar absent. Penis usually elongated conical, narrow, always internal unarmed.

Calmella Eliot, 1910, Carronella gen. n., Coryphellina O’Donoghue, 1929, Edmundsella gen. n., Flabellina Gray, 1833 in Griffith and Pidgeon, 1833–1834, Paraflabellina gen. n., Piseinotecus (?) Marcus, 1955.

The name Flabellinidae has been used for a long time to encompass all the diversity of aeolidaceans with a triseriate radula and without a clearly defined supplementary (or penial) gland in the male part of reproductive system. However, according to our present molecular phylogenetic analysis (Figs 1, 2), the former Flabellinidae form several distinct clades. Remarkably, some of them appear to be closely related to traditional Tergipedidae or Facelinidae thus making any notion that traditional Flabellinidae can be saved as a monophyletic unit highly unlikely.

Therefore, following the phylogenetic pattern discovered from the DNA analysis (Fig. 1) and consolidated morphological data (Fig. 2) we consistently utilise a differential approach, and propose several family level groups within traditional “Flabellinidae”. The super-cluster of the majority of traditional Flabellinidae holds a central position within this group and is apparently monophyletic (Fig. 2). It is, however, comprised of three clearly defined clades, which roughly correspond to the traditional genera Chlamylla, Coryphella, and Flabellina. However, a decision to maintain these phylogenetic superclusters just at generic levels will considerably obscure the complicated evolutionary patterns discovered from the molecular analysis (Fig. 1) which must be consistently reflected in a classification. Importantly, every large phylogenetic cluster has clear morphological trends. For example, the reinstated family Paracoryphellidae is characterised by the invariable presence of a wide body and continuous notal edge, elongated penis, and presence of complicated external penial collars or external permanent penis in two genera, and also invariably an uncompressed cusp of the rachidian teeth. The reinstated family Coryphellidae contains mostly taxa with a narrow body and discontinuous notal edge, but importantly there are several genera not directly related to other coryphellids (e.g., Borealia, Himatina, Gulenia, Itaxia, see above) that possess a continuous notal edge, which are all basal to various clades of narrow-bodied coryphellids. Internally most of the genera of the family Coryphellidae possess a non-compressed cusp of the rachidian teeth, short vas deferens, and broad penis always without an external penial collar. In turn, the considerably restricted family Flabellinidaes. str. includes taxa which usually have various ceratal elevations, up to highly ramified stalks in the genus Flabellinas. str. The family Flabellinidae in the restricted sense also includes such clear morphological trends as an almost invariably compressed cusp of the rachidian teeth, lateral teeth with attenuated bases, commonly large oral glands and usually a relatively long vas deferens and elongated penis (see below).

The minimum uncorrected p-distances of the mitochondrial barcode marker (COI) between the species of family Flabellinidae are given in Table 2. The minimum uncorrected p-distances between all genera range from 13.1 to 20.2%. The lowest distances occurred between Coryphellina rubrolineata and Edmundsella pedata (13.1%). Such considerable molecular divergence between taxa of the family Flabellinidae supports the reliability of the multi-genera approach consistently applied in this study.

Eolidia cavolini Vérany, 1846.

Body narrow. Notal edge completely absent. Cerata on short stalks in several groups. Rhinophores smooth, larger than oral tentacles or similar in size. Anterior foot corners present. Anus mixed: pleuroproctic shifted towards dorsal acleioproctic position. Distinct oral glands. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth weakly denticulated to smooth with attenuated process basally. Single distal receptaculum seminis. Moderately long prostatic non-granulated vas deferens. Penis conical.

Calmella cavolini (Vérany, 1846) (Fig. 33) (original description in Vérany 1846, detailed description in Schmekel and Portmann 1982), Calmella gaditana (Cervera, García-Gómez & García, 1987), comb. n. (original description in Cervera et al. 1987, = “Flabellina” confusaGonzález-Duarte et al. 2008, original description in González-Duarte et al. 2008; for discussion see Furfaro et al. 2017), Calmella bandeli Marcus, 1976 (original description in Marcus 1976).

The genus Calmella was established by Eliot (1910) and since that time it has never been synonymised with Flabellina, until the most recent Furfaro et al. (2017) study. According to the present phylogenetic analysis Calmella is valid, related to the true Flabellinas. str. (Fig. 2) and differs morphologically regarding its much less ramified and raised ceratal stalks and presence of smooth rhinophores. See remarks also under the genus Piseinotecus.

Eolis pellucida Alder & Hancock, 1843.

After Loch Carron, a sea loch on the west of the Scottish Highlands, where numerous specimens of Eolis pellucida have been observed over many years, feeding on Eudendrium arbusculum growing on flame shell (Limaria hians) reefs.

Body relatively wide. Notal ridge present, reduced, discontinuous, in several indistinct pieces which continue to low elevations of cerata, in several groups. Rhinophores smooth, similar in size to oral tentacles. Anterior foot corners present. Anus pleuroproctic. Distinct oral glands. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth smooth with attenuated process basally. Distal and proximal receptaculum seminis. Moderately long vas deferens without distinct prostate. Penis conical.

Carronella enne sp. n., Carronella pellucida (Alder & Hancock, 1843), comb. n. (Fig. 36) (original description in Alder and Hancock 1843; original description of radula in Alder and Hancock 1845–1855).

The genus Carronella gen. n. differs from other genera of the family Flabellinidaes. str. by the absence of distinct ceratal elevations or stalks and by the presence of smooth lateral denticles. The absence of distinct elevations or stalks represents a plesiomorphic feature, but according to the molecular phylogenetic analysis Carronella appears in a quite derived position (Figs 1, 2). This is therefore one more interesting case of discrepancy between morphological and molecular data that needs to be further investigated.

Holotype, ZMMU Op-526, 5 mm long, North Atlantic W of Ireland, 48.7089'N, 10.5607'W, 11.06.2014, depth 1131 m, collected by Enrico Schwabe.

North Atlantic west of Ireland.

In honour of our friend, the malacologist Enrico (Enne) Schwabe (Bavarian State Collection of Zoology, Munich).

Mostly reduced notal edge, forming several clusters, background colour translucent white, digestive gland in cerata dull reddish, apical parts of cerata without white pigment, rachidian tooth with up to ten distinct denticles, adpressed to central cusp, lateral teeth smooth, penis conical.

External morphology (Fig. 35A–E). Body relatively wide. Foot and tail narrow, anterior foot corners long. Rhinophores ca. 1.5 times longer than oral tentacles, slightly wrinkled. Dorsal cerata finger-shaped to fusiform, forming several clusters along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosac. Distinct notal edge remains mostly below ceratal clusters and forms slight elevations. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic on right side in between first and second large ceratal clusters. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 35A). Background colour translucent white. Digestive gland diverticula dull reddish. There are no opaque white lines on the body. Rhinophore background colour similar to body; a thin white line runs along dorsal side of rhinophores runs; apical white pigment absent. Apical parts of cerata with opaque cap of white pigment.

Jaws (Fig. 35G, H). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears ca. 30 denticles that continue to form several reduced rows of denticles on body of masticatory processes.

Radula (Fig. 35I). Radula formula: 24 × 1.1.1. Rachidian tooth elongate-triangular with short narrow cusp of less than 1/3 of the tooth length (Fig. 35I). Rachidian tooth bears between eight and ten well-defined separated long lateral denticles strongly adpressed towards the cusp. Cusp is compressed by adjacent first lateral denticles. Lateral teeth (Fig. 35I) broadly triangular with obtuse and very attenuated posteriorly outer process, completely smooth.

Reproductive system (Fig. 35J). Diaulic. Hermaphroditic duct leads to convoluted ampulla of about two whorls. Vas deferens moderately long, no distinct prostate. Penial sheath small. Penis narrow conical. Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Proximal receptaculum seminis oval. Distal receptaculum seminis present, small.

Deep sea species (deeper than 1000 m).

Northeast Atlantic, off Ireland.

According to the molecular phylogenetic analysis Carronella enne sp. n. forms a separate sister clade to Carronella pellucida (Fig. 1). Morphological analysis reveals differences in proportions of lateral teeth in C. enne sp. n. The lateral teeth of C. enne sp. n. are more elongated (Fig. 35I) than in C. pellucida (Fig. 36H).

Coryphellina rubrolineata O’Donoghue, 1929.

Body narrow. Notal ridge present, reduced, discontinuous, in several indistinct pieces. Cerata on low elevations, in several groups. Rhinophores similar in length or shorter than oral tentacles, densely papillated. Anterior foot corners present. Anus pleuroproctic. Distinct oral glands. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Proximal receptaculum seminis usually bilobed. Distal receptaculum seminis present. Short prostatic, not granulated vas deferens. Penis conical to bulbous.

Coryphellina albomarginata (Miller, 1971) comb. n. (original description in Miller 1971), Coryphellina arveloi (Ortea & Espinosa, 1998), comb. n. (original description in Ortea and Espinosa 1998), Coryphellina (?) delicata (Gosliner & Willan, 1991), comb. n. (original description in Gosliner and Willan 1991), Coryphellina exoptata (Gosliner & Willan, 1991), comb. n. (Fig. 37) (original description in Gosliner and Willan 1991), Coryphellina (?) hamanni (Gosliner, 1994), comb. n. (original description in Gosliner 1994), Coryphellina indica (Bergh, 1902) comb. n. (original description in Bergh 1902), Coryphellina lotos sp. n. (Fig. 38), Coryphellina marcusorum (Gosliner & Kuzirian, 1990), comb. n. (original description in Gosliner and Kuzirian 1990), Coryphellina (?) poenicia (Burn, 1957), comb. n. (original description in Burn 1957), Coryphellina rubrolineata O’Donoghue, 1929 (Fig. 39) (original description in O’Donoghue 1929), Coryphellina (?) westralis (Burn, 1964), comb. n. (original description in Burn 1964).

The genus Coryphellina is well delineated from all Flabellinidaes. str. taxa. Morphologically most of Coryphellina species are characterised by papillated rhinophores and a peculiar bilobed receptaculum seminis. Externally Coryphellina has a discontinuous but still distinct notal edge which forms only slightly raised ceratal elevations (compared to the compound stalks in the true Flabellina and Calmella). These morphological characteristics are consistent with the molecular phylogenetic analysis where all Coryphellina place in a compact clade (Fig. 2). However, the type species Coryphellina rubrolineata forms a separate subclade within other Coryphellina. This may be consistent with previous information (Gosliner and Willan 1991) that C. rubrolineata has a “triaulic” reproductive system, which is unusual for most aeolidaceans. Since the fine precise relation between postampullar ducts and ducts of seminal reservoirs has not been studied in detail in the majority of traditional Flabellinidae and also because putative triauly in C. rubrolineata is different from well-defined “typical” triauly of dorid nudibranchs, we consider all flabellinids with papillated rhinophores and a bilobed receptaculum seminis as belonging to the same genus Coryphellina.

The genus Nossis Bergh, 1902 was established for a type species of N. indica from the Gulf of Siam (Bergh 1902). When he established the genus Coryphellina O’Donoghue (1929) did not mention the previously described genus Nossis but later a close relationship between Nossis and Coryphellina was noticed (e.g., Nordsieck 1972; McDonald 2009) and the type species of the genus Coryphellina has been treated under the name Nossis rubrolineata. However, the genus name Nossis Bergh, 1902 for nudibranchs was preoccupied by the name Nossis Kinberg, 1865 which was established for a polychaete (Kinberg 1865). Therefore these two names are homonyms, and the junior one should therefore be replaced with the available name Coryphellina O’Donoghue, 1929. In the present study we have investigated two syntypes of Nossis indica Bergh, 1902 (NHMD GAS-2008) and confirm that their external characters are concordant with the genus Coryphellina. We also find in both syntypes of Nossis indica densely papillated rhinophores essentially similar to those in the genus Coryphellina, contrary to the description of rhinophores of N. indica in the first description of Bergh (1902: 211) as bearing “leaves” that instead imply a perfoliate condition (Burn 1964). Perhaps, Bergh recognized the rhinophoral papillae but just described it as “leaves”. In addition, Burn (1964) also described another species of Nossis, N. westralis, and mentioned the genera Nossis and Coryphellina, but did not synonymise them; instead he highlighted their differences most likely because of the description of N. indica in Bergh (1902) regarding the rhinophoral leaves (instead of rhinophoral papillae). Accordingly, the species Nossis indica is transferred here to the genus Coryphellina, but its exact relationship to other common Indo-West Pacific Coryphellina such as C. rubrolineata and C. exoptata remains to be investigated. We are not excluding the possibility that C. indica is the same or a closely related species to the type species of Coryphellina, C. rubrolineata. We also tentatively assign Nossis westralis as a species of the genus Coryphellina but it needs to be further studied. The proposed family Nossidae Odhner, 1968 thus is a junior synonym of Flabellinidaes. str. Odhner (Odhner 1968) also proposed a few more genera within the family "Nossidae"; no descriptions were provided for these genera and they are nomina nuda according to article 13. 1 (ICZN 1999).

Holotype. ZMMU Op-515, 15.5 mm long (live), Japan, Pacific coast of Honshu, Osezaki, 10–15 m depth, 10.09.2016, coll. T.A. Korshunova, A.V. Martynov. 2 paratypes, ZMMU Op-516, up to 17 mm long (live), same locality and dates as holotype.

Osezaki, Pacific coast of Honshu, Japan.

Considerably reduced notal edge, forming several clusters, background colour light violet, digestive gland in cerata light brownish, subapical parts of cerata reddish lilac, apical parts of cerata without white pigment, rachidian tooth with up to seven distinct denticles, adpressed to rachidian cusp, lateral teeth with up to nine denticles, penis conical.

After the lotus flower in reference to the similarity of the colour of the new species to the common colour of the lotus flower.

External morphology (Fig. 38A–E). Body relatively narrow. Foot and tail narrow, anterior foot corners long. Rhinophores ca. 1.5 times shorter than oral tentacles, strongly papillate. Dorsal cerata finger-shaped to fusiform, forming several slightly elevated clusters along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosac. Distinct notal edge remains mostly below cerata clusters. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic on right side below second large ceratal clusters. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 38A). Background colour light violet. Digestive gland diverticula light brownish. Rhinophore background colour similar to body. Oral tentacles lilac (except for translucent tips). Subapical parts of cerata and rhinophores brighter reddish lilac. Apical parts of cerata without opaque cap of white pigment.

Jaws (Fig. 38G, H). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears ca. 35 sharp denticles that continue to form at least two rows of denticles on body of masticatory processes.

Radula (Fig. 38I). Radula formula: 26 × 1.1.1 (31 mm). Rachidian tooth elongate-triangular with short narrow cusp of less than 1/3 of the tooth length (Fig. 38I). Rachidian tooth bears between four and seven well-defined separated long lateral denticles strongly adpressed towards cusp. Cusp is compressed by adjacent first lateral denticles. Lateral teeth (Fig. 38I) broadly triangular with obtuse and very attenuated posteriorly outer process, bear seven to nine sharp denticles.

Reproductive system (Fig. 38J). Diaulic. Hermaphroditic duct leads to convoluted ampulla of about two whorls. Vas deferens is relatively long, no distinct prostate. Penial sheath is large, wide. Penis is conical. Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Receptaculum seminis large, oval, bilobed. Distal receptaculum seminis present, small.

Shallow water species, stony and rocky habitats.

Pacific side of middle Japan (Honshu).

The three specimens of Coryphellina lotos sp. n. demonstrate uniformity in the body shape and colour and are readily distinguished from any previously described Coryphellina species, including C. rubrolineata, which is sister to C. lotos sp. n. according to the molecular phylogenetic analysis (Fig. 1).

Doris pedata Montagu, 1815.

In honour of distinguished opisthobranch taxonomist Malcolm Edmunds (UK) who died in January 2017.

Body narrow. Notal edge reduced. Cerata on low elevations, in several groups. Rhinophores wrinkled, similar in length to or shorter than oral tentacles. Anterior foot corners present. Anus pleuroproctic. Distinct oral glands. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Separated distal and proximal receptaculum seminis. Short prostatic, non-granulated vas deferens. Penis conical to bulbous.

Edmundsella albomaculata (Pola et al., 2014), comb. n. (original description in Pola et al. 2014), Edmundsella pedata (Montagu, 1815), comb. n. (Fig. 40) (original description in Montagu 1815), Edmundsella (?) vansyoci (Gosliner, 1994), comb. n. (original description in Gosliner 1994).

The genus Edmundsella gen .n. clearly differs morphologically from other flabellinid genera by the presence of smooth rhinophores, non-stalked cerata on low elevations, and a relatively short vas deferens. Molecular distances between Edmundsella gen. n. and other genera of the family Flabellinidae are significant (13%–19%; see Table 1).

Dorisaffinis Gmelin, 1791.

Body narrow. Notal ridge completely absent. Cerata on high compound stalks. Rhinophores with ring lamellae, shorter than oral tentacles. Anterior foot corners present. Anus pleuroproctic. Distinct oral glands. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Two closely placed distal seminal receptacles. Long vas deferens without distinct prostate. Penis elongated conical.

Flabellina affinis (Gmelin, 1791) (original description in Gmelin 1791; detailed redescription in Schulze and Wägele 1998).

After the restrictions imposed at the family level, the genus Flabellina (to which morphologically and molecularly extremely disparate taxa were formerly assigned) is thus returned to its original definition (Gray 1833 in Griffith and Pidgeon 1833–1834). It is characterised by very ramified tall ceratal stalks and a relatively long vas deferens. In our molecular analysis, the type species of the genus Flabellina affinis was placed basally and separate from the morphologically similar F. funeka and F. ischitana. Further complicating this case is the position of the genus Calmella which may be more closely related to F. funeka and F. ischitana rather than to F. affinis. Thus, to keep the genus Flabellina with the inclusion of F. funeka and F. ishitana is not fully consistent with the molecular data. Therefore, the clade that contains “F.” funeka, “F.” ischitana and “Piseinotecus” gabienerei must be separated in another new genus, Paraflabellina gen. n. (see below).

Flabellina ischitana Hirano & Thompson, 1990.

From Ancient Greek παρα (= beside, adjacent to) and Flabellina in reference to the external similarity of the type species F. ischitana to Flabellinas. str., but disparate molecular results that render the genus Flabellinas. l. paraphyletic in relation to the genus Calmella if F. ischitana is included within Flabellina.

Body narrow. Notal ridge completely absent. Cerata on high compound stalks. Rhinophores with ring lamellae, shorter than oral tentacles. Anterior foot corners present. Anus pleuroproctic. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Proximal and distal receptaculum seminis. Long vas deferens without distinct prostate. Penis conical.

Paraflabellina funeka (Gosliner & Griffiths, 1981), comb. n. (original description in Gosliner and Griffiths 1981), Paraflabellina gabinierei (Vicente, 1975), comb. n. (original description in Vicente 1975; additional data in Schmekel 1980), Paraflabellina ischitana (Hirano & Thompson, 1990) (original description in Hirano and Thompson 1990; redescription in Cervera et al. 1998), Paraflabellina (?) rubromaxillarubromaxilla (Edmunds, 2015), comb. n. (original description in Edmunds 2015).

Piseinotecus divae Er. Marcus, 1955.

Body narrow. Notal ridge fully reduced. Cerata on low compound stalks. Rhinophores smooth, similar in size to oral tentacles. Anterior foot corners present. Anus pleuroproctic. Rachidian teeth with non-compressed cusp and distinct denticles. Lateral teeth absent. Proximal receptaculum seminis. Short vas deferens with distinct prostate. Penis conical.

Piseinotecus divae Er. Marcus, 1955 (original description in Marcus 1955), Piseinotecus (?) sphaeriferus (Schmekel, 1965) (original description in Schmekel 1965).

The genus Piseinotecus is commonly considered to belong to a separate family Piseinotecidae Edmunds, 1970 because of the presence of a uniserial radula instead of the triserial radula common for traditional Flabellinidae. However, external features, including the presence of compound ceratal stalks in the type species of the genus Piseinotecus, P. divae, and the other species (e.g., P. sphaeriferus) suggest a relationship to Flabellina. Preliminary data suggest that this genus is deeply nested within the traditional family Flabellinidae (Gosliner et al. 2007; Tamsouri et al. 2014). This is confirmed by our analysis (Figs 1, 2) and therefore we have considered Piseinotecus a genus within the family Flabellinidaes. str., after removal of the families Coryphellidae, Paracoryphellidae, and others. While this paper was under review an analysis was published (Furfaro et al. 2017) that at least some species previously considered within the genus Piseinotecus (i.e., “P.” gabinierei and “P.” gaditanus) actually possess a triserial radula and thus must be firmly included into the family Flabellinidae in its restricted sense. There are more undescribed species of the putative genus Piseinotecus that appear within some clades which are not closely related, e.g., Flabellinopsidae fam. n. (see above) (Fig. 2). Because of that and also since there are no molecular data for the type species P. divae, the validity and monophyly of this genus still needs to be confirmed. Therefore, until molecular data on the type species P. divae becomes available, we consider the genus Piseinotecus only tentatively as belonging to the family Flabellinidaes. str. According to the first description (Marcus 1955) P. divae has no distinct oral glands but has rather strong cusp of rachidian tooth. These features contradict to the diagnosis of the family Flabellinidaes. str. but still need to be confirmed by novel material. Since the Mediterranean “P.” gabinierei is closely related to Paraflabellina ishitana (Fig. 1) we include “P.” gabinierei into the genus Paraflabellina (see above). Another species “P.” gaditanus is nested within Calmella clade and therefore assigned to that genus. Whether the triserial radula has been overlooked in the type species P. divae or not is currently unclear. Therefore Piseinotecus is not synonymised in the present study with any existing genera, but awaits assignment until more data becomes available. In addition, based on the morphological data we do not include species without ceratal stalks in the genus Piseinotecus or species with more disparate ceratal and radular morphology, such as “Piseinotecus” gonja Edmunds, 1970 and “Piseinotecus” minipapilla Edmunds, 2015 (Edmunds 1970, 2015).

Flabellina alternata Ortea & Espinosa, 1998 (original description in Ortea and Espinosa 1998), Flabellina bertschi Gosliner & Kuzirian, 1990 (original description in Gosliner and Kuzirian 1990), Flabellina dana Millen & Hamann, 2006 (original description in Millen and Hamann 2006), Flabellina dushia (Marcus & Marcus, 1963) (original description in Marcus and Marcus 1963, redescription in Millen and Hamann 2006), Flabellina engeli Marcus & Marcus, 1968 (original description in Marcus and Marcus 1968), Flabellina engeli lucianae DaCosta, Cunha, Simone, Schrödl, 2007 (original description in DaCosta et al. 2007), Flabellina evelinae Edmunds, 1989 (original description in Edmunds 1989), Flabellina ilidioi Calado, Ortea & Caballer, 2005 (original description in Calado et al. 2005), Flabellina llerae Ortea, 1989 (original description in Ortea 1989).

Some of these species are insufficiently described (e.g., Flabellina alternata Ortea & Espinosa, 1998, Flabellina llerae Ortea, 1989) whilst some others have been described in detail (e.g., Flabellina engeli lucianae DaCosta, Cunha, Simone & Schrödl, 2007), but in the absence of the molecular data in this case, we prefer not to assign these species into particular genera. Most likely, more new genera need to be created for some of these species.

Body narrow. Notum fully reduced. Cerata in separate clusters, on distinct elongated elevations. Rhinophores smooth. Anus pleuroproctic or mixed (pleuroproctic in higher acleiproctic position). Distinct oral glands present. Radula formula 0.1.0. Rachidian teeth with non-compressed cusp. Lateral teeth always absent. Number and position of receptaculum seminis variable: two separate ones, or double or single proximal ones. Vas deferens moderately long, with distinct prostate. External permanent penial collar absent. Adjacent penial gland present or absent. Penis conical, armed or unarmed, always internal.

Pacifia gen. n., Unidentia Millen & Hermosillo, 2012.

This is a very interesting case which shows the polyphyletic nature of the traditional Flabellinidae. In 2010 a species with uniseriate radula and unusual supplementary penial gland was added to the traditional genus Flabellina (Gosliner 2010) despite the fact that the outlined characters directly contradict such a decision. The present molecular phylogenetic analysis fully confirms this species to be extremely disparate from the majority of Flabellinidaes. str. as suggested by its morphology. Flabellina goddardi and a new closely related species from the Pacific coast of Japan (see below) were clustered together in the same clade which was placed basally to the family Facelinidae and not clustering with any other Flabellinidae (Figs 1, 2). Importantly, this taxon is invariably placed basally to Facelinidae in any variants of the obtained trees and not nested within the family Flabellinidaes. str. as was suggested by Gosliner (2010: 630). Remarkably, two other new species of the genus Unidentia from Japan and from Indonesia also possess a uniserial radula and pleuroproctic anus in a higher acleioproctic position. This challenging taxon, with a new genus and two species, is confirmed for the first time in the present study as belonging to the family Unidentiidae Millen & Hermosillo, 2012.

Currently, many researchers are actively debating phylogenetic relationships and higher taxonomy of one of the most diverse nudibranch groups, Aeolidacea (e.g., Carmona et al. 2013; Padula et al. 2014; Kienberger et al. 2016; Korshunova et al. 2017a; Korshunova et al. 2017c). However, until recently no molecular analysis of aeolidacean nudibranchs has included the family Unidentiidae. When Gosliner (2010) described F. goddardi he only mentioned a preliminary molecular phylogeny, but no trees or molecular analyses have been presented since his publication. In addition, Gosliner (2010: 630) has highlighted that his data “strongly suggest that F. goddardi, despite having a uniseriate radula, is most closely related to other species of Flabellina”. However, the first molecular analysis of this group presented here has clearly and robustly shown that the family Unidentiidae (including the newly described Pacifia amica gen. n. et sp. n. and Pacifia goddardi comb. n.) is not related to any real Flabellina, but instead to the family Facelinidae. Since all members of the Facelinidae have a uniserial radula (i.e., as in Unidentiidae) in strong contrast to a triserial radula in traditional Flabellinidae, the phylogenetic relationship of Unidentiidae to Facelinidae (Fig. 1) uncovered in the present study is in much greater agreement with the morphological data on radula, thus confirming the general integrative agenda for taxonomy (Dayrat 2005; Korshunova et al. 2017b).

The morphological cladistic analysis (Millen and Hermosillo 2012) also placed the uniserial family Unidentiidae as a basal group to the triserial Flabellinidae, but included including some uniserial groups like Piseinotecus and Babakina. However, most recently (Furfaro et al. 2017) it was shown, in remarkable agreement with our molecular phylogenetic study, that some species placed in Piseinotecus actually possess a triserial radula and are closely related to the true Flabellinidae, and that delicate lateral teeth were previously simply unrecognised. Since on the morphological cladogram the genus Piseinotecus was clustered basally to the also uniserial genus Babakina (the family Babakinidae) it may thus not reflect the real phylogenetic placement. In our phylogenetic analysis, the genus Babakina is not related to any Flabellinidae or Unidentiidae, but instead placed basally to the family Aeolidiidae (Fig. 1).

Thus, this first molecular data and molecular analysis of the family Unidentiidae clearly shows that previous morphological estimations of the F. goddardi as a proper flabellinid (Gosliner 2010) (despite the uniserial radula) or a group closely related to the traditional family Flabellinidae (Millen and Hermosillo 2012) were incorrect. However, Millen and Hermosillo (2012) prophetically separated Unidentia into an independent family that is now fully confirmed by our molecular analysis. Our new data also confirm the reliability of the detailed morphological analysis on an integrative basis (Korshunova et al. 2017a) since striking differences of the uniserial F. goddardi and Unidentia with the triserial traditional Flabellinidae, previously considered as just an independent case of reduction of lateral teeth, (e.g., according to the cladogram in Millen and Hermosillo 2012) is actually an indication of phylogenetic relationship with the uniserial traditional Facelinidae. The retaining of a pleuroproctic anus, or pleuroproctic in a higher acleioproctic position in Unidentiidae, can be considered therefore as a plesiomorphic feature (see Korshunova et al. 2017c for a discussion of the plesiomorphic pleuroproctic position in Nudibranchia).

The present new findings and the first molecular phylogenetic analysis involving members of the family Unidentiidae thus not only has particular taxonomic importance but also makes important contributions for the understanding of the phylogeny of the whole Nudibranchia group and for the general discussion about the plausibility of using morphological data for phylogenetic analysis and high-level systematics.

In the combined phylogenetic tree, all Unidentiidae species clustered in a highly supported clade together (PP = 1, BS = 98) that is dramatically separated from the Flabellinidae clade. All Unidentia species clustered together (PP = 1, BS = 100) in a maximum-supported clade that is sister to the maximum-supported (PP = 1, BS = 100) clade with the species of Pacifia gen. n.

The family Unidentiidae originally was incorrectly spelled as Unidentiidae (Millen and Hermosillo 2012). The name is based on Unidentia with the stem therefore being Unidenti-, so the original name Unidentiidae should be corrected to Unidentiidae with the same author and date (ICZN 1999, article 29.3).

Pacifia amica sp. n.

After the Pacific Ocean and also in reference to another meaning of the word “pacific” = “peaceful” and “amica” = “friend”, “friendly” because this paper represents a friendship-based collaboration between American, British, German, Japanese, Indonesian, Norwegian, Russian, and Swedish colleagues, as opposed to recent antagonistic political relationships.

Body narrow. Notum fully reduced. Cerata on elevations. Rhinophores smooth. Anterior foot corners present. Anus pleuroproctic. Rachidian teeth with narrow non-compressed cusp covers with small denticles; lateral denticles distinct. Lateral teeth absent. Proximal and distal receptaculum seminis. Moderately long vas deferens with thickened non-granulated prostate. No external penial collar. Penis conical, unarmed. Adjacent penial gland may be present.

Pacifia amica sp. n., P. goddardi (Gosliner, 2010), comb. n.

From Unidentia, the only currently known genus of the family Unidentiidae, Pacifia gen. n. is readily distinguished by the presence of a distal receptaculum seminis, absence of the penial stylet and considerable molecular distance. Despite differing in some morphological characteristics from P. amica sp. n. (including the presence in F. goddardi Gosliner, 2010 of distinct ceratal elevations and an accessory gland near the penis, and also by the absence of distinct denticles on the cusp of the rachidian teeth throughout the whole radula) Flabellina goddardi Gosliner, 2010, forms a sister molecular clade to Pacifia amica sp. n. and also shares with the latter the presence of a distal stalked receptaculum seminis. We therefore include F. goddardi in the new genus Pacifia as a new combination Pacifia goddardi (Gosliner, 2010), comb. n. Presence of an accessory gland near the penis in P. goddardi needs in further confirmation.

Holotype, ZMMU Op-614, 6.5 mm long (live), NE Pacific, Sullivan Point, Rich Passage, 25.01.2017, depth 15.2 m, stones, collector Karin Fletcher. 1 paratype, ZMMU Op-615, same locality and collector as holotype.

NE Pacific, Rich Passage.

See under the genus description above.

Four to five ceratal clusters, colour translucent white with opaque white mid-dorsal line, cerata orange red to light pink, rachidian tooth with up to six denticles, central cusp bears small denticles, distinct distal receptaculum seminis, no accessory penial gland, penis unarmed.

External morphology (Fig. 41A–B). Body elongate, 6.5 mm in length (live). Rhinophores similar in size to oral tentacles, smooth. Dorsal cerata finger-shaped to fusiform, forming four to five ceratal clusters along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosac. Notal edge discontinuous. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic towards acleioproctic position on right side below second large ceratal clusters. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 41A–B). General colour translucent white. Oral tentacles with opaque white lines, which meet on middle of head and continue through middle part of body to the tail. Digestive gland in the cerata orange-red to light pink; scattered small spots on cerata, ceratal tip transparent (Fig. 41C).

Jaws (Fig. 41D–E). Jaws broadly-triangular, masticatory borders with weak tubercles.

Radula (Fig. 41F–H) Radula formula 28 × 0.1.0. Rachidian tooth with up to six distinct denticles. Rachidian cusp bears small denticles at the base (Fig. 41H). No lateral teeth.

Reproductive system (Fig. 41I). Diaulic. Ampulla wide, folded twice (Fig. 41I, am). Prostate thick (Fig. 41I, pr). Vas deferens short (Fig. 41I, vd), penial sheath elongate (Fig. 41I, ps), conical penis unarmed. Distal seminal receptaculum long, with distinct stalk and oval reservoir (Fig. 41I, rsd). Proximal receptaculum seminis oval.

Subtidal, on stones with hydroids (Fig. 41B).

Presently found only at a Port Orchard locality in Washington State, NE Pacific.

See Remarks under the new genus Pacifia above.

Unidentia angelvaldesi Millen & Hermosillo, 2012.

Body narrow. Notum fully reduced. Cerata on distinct elonagate elevations. Rhinophores smooth. Anterior foot corners present. Anus mixed (pleuroproctic in higher cleiproctic position) or pleuroproctic. Rachidian teeth with narrow non-compressed cusp and distinct denticles. Lateral teeth absent. Proximal double or single receptaculum seminis. Distal receptaculum seminis absent. Moderately long vas deferens with widened prostatic part. Penis conical, with hollow stylet. Adjacent penial absent.

Unidentia angelvaldesi Millen & Hermosillo, 2012 (first description in Millen and Hermosillo 2012), U. nihonrossija sp. n. (Fig. 42), U. sandramillenae sp. n. (Fig. 43).

Holotype. ZMMU Op-517, 4.5 mm long (preserved), Japan, Osezaki, depth 10–15 m, 11.09.2016, coll. T.A. Korshunova, A.V. Martynov.

Osezaki, Japan.

After nihon (“日本” (=“にほん”), meaning “Japan” in Japanese) and rossija (“Россия” meaning “Russia” in Russian) in reference to the international group of Russian and Japanese scientists who organised the field work in Japan, during which this unique representative of the family Unidentiidae was collected.

Five to seven ceratal clusters, background colour whitish with dispersed light violet middorsal line, cerata orange to reddish orange, subapical parts of cerata with broad opaque white line, apical parts of cerata with white pigment, rachidian tooth with up to six denticles, central cusp bears small denticles, distinct distal receptaculum seminis, no accessory penial gland, penis with hollow stylet.

External morphology (Fig. 42A–E). Body relatively narrow. Foot and tail narrow, anterior foot corners long. Rhinophores ca. 1.5–2 times shorter than oral tentacles, smooth. Dorsal cerata finger-shaped to fusiform, forming several distinctly elongate elevations with ceratal clusters along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosac. Distinct notal edge absent. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic on right side below second large ceratal clusters. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 42A). Background colour whitish. Digestive gland diverticula reddish orange. Rhinophores and oral tentacles light violet. A narrow dispersed light violet band runs from base of oral tentacles through middle part of dorsal side. Subapical parts of cerata with broad opaque white line. Apical parts of cerata without opaque cap of white pigment.

Jaws (Fig. 42G, H). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears several rows of ridge-shaped denticles.

Radula (Fig. 42I). Radula formula: 39 × 0.1.0. Rachidian tooth elongate-triangular with short broad cusp. Rachidian tooth bears four to seven well-defined separated long lateral denticles strongly adpressed towards cusp (Fig. 42I). Cusp is not compressed by adjacent first lateral denticles. Lateral teeth absent.

Reproductive system (Fig. 42J). Diaulic. Hermaphroditic duct leads to convoluted ampulla of about two whorls. Vas deferens relatively long, no distinct prostate. Penial sheath narrow. Penis narrow conical, armed with curved hollow stylet. Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Double proximal receptaculum seminis. Supplementary (“penial”) gland absent.

Shallow waters, stony habitats.

Pacific side of middle Japan (Honshu).

From the type species of the genus Unidentia, the Eastern Pacific Mexican species U. angelvaldesi Millen & Hermosillo, 2012, U. nihonrossija sp. n. differs substantially both morphologically and by colouration, details of the radular teeth, and presence of double proximal receptacles (U. angelvaldesi possesses a single receptaculum seminis). From the tropical Indo-West Pacific species U. sandramillenae sp. n. (see below), U. nihonrossija sp. n. differs both morphologically and according to the molecular phylogenetic analysis (Figs 1, 2).

Holotype, ZMMU Op-617, 7 mm long (preserved), Bali, Tulamben, 02.02.2017, 5–10 m depth, stones, collector I Wayan Mudianta.

Bali Island, Indonesia.

In honour of prominent nudibranch researcher, Sandra Millen (The University of British Columbia), who for almost 50 years has conducted fine taxonomic studies, including separation of the new family, Unidentiidae, together with Alicia Hermosillo.

Eight to ten ceratal clusters, ground colour and cerata whitish with violet hue, purple middorsal line, rachidian tooth with up to eight denticles, central cusp bears small denticles only in anterior radula, two proximal seminal receptacles, no accessory penial gland, penis with hollow stylet.

External morphology (Fig. 43A–C). Body elongate 7 mm in length (preserved). Rhinophores similar in size to oral tentacles, smooth. Cerata finger-shaped to fusiform, placed on several distinctly elongate elevations with ceratal clusters along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosac. Distinct notal edge absent. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic towards acleioproctic position on right side below second large ceratal clusters. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 43A–D). General colour translucent white with purple thin middorsal line; oral tentacles covered in purple pigment nearly half its length; subapical purple rings on cerata.

Jaws (Fig. 43E). Jaws broadly triangular, masticatory borders with special elaborate long denticles placed in clusters.

Radula (Fig. 43H, I). Radula formula 25 × 0.1.0. Rachidian tooth with up to eight distinct denticles. Central cusp smooth, widened in the middle and distinctly narrowed towards the tip; no small denticles at the base in posterior and middle teeth; vestigial denticles may present on the cusp of a few anterior teeth (Fig. 43I). No lateral teeth.

Reproductive system (Fig. 43K). Diaulic. Ampulla very voluminous, folded twice (Fig. 43K, am). Prostate thick (Fig. 43K, pr). Vas deferens short (Fig. 43K, vd), penial sheath elongate, conical penis armed with hollow stylet (Fig. 43K). Double proximal receptaculum seminis (Fig. 43K, rsp).

On stones and algae covered with athecate hydroids (Fig. 43C, D).

Currently Indonesia, but probably Indo-West Pacific.

Unidentia sandramillenae sp. n. differs considerably from the only other known species of the genus Unidentia, U. angelvaldesi Millen & Hermosillo, 2012, both externally and internally. Externally, Unidentia sandramillenae sp. n. has a whitish ground colour whereas the Mexican specimens of U. angelvaldesi often have a red-orange ground colour. Internally, Unidentia sandramillenae sp. n. differs from U. angelvaldesi in the shape of the central cusp of the rachidian teeth, the shape of the ampulla and the presence of a distinct second seminal reservoir. Furthermore, in the original description of U. angelvaldesi several distinct species from various regions of the Pacific were commingled. Because the holotype was originally from Mexico in the eastern Pacific, the species U. angelvaldesi should be restricted to specimens from the tropical eastern Pacific. There are no molecular data available for the Mexican U. angelvaldesi; however, according to our new data, a separate species of Unidentia, which clearly differs from the Unidentia sandramillenae sp. n. from Bali, is also present in Japan and described here as U. nihonrossija sp. n. (Figs 42, 44, red lines). Therefore, taking into consideration the considerable morphological differences between U. angelvaldesi and Unidentia sandramillenae sp. n. these species should also have a considerable molecular gap (Fig. 44, blue line), that should be proved in further studies. In addition, the clade U. angelvaldesi is distant from Flabellinopsidae fam. n. according to a recent publication (Goodheart et al. 2017).

Uncorrected p-distances of the mitochondrial barcode marker (COI) between U. sandramillenae sp. n. and U. nihonrossija sp. n. reach 14.2%. Uncorrected p-distances between P. amica sp. n. and P. goddardi reach 12.2%. In contrast, the distance values between Unidentia and Pacifia ranged between 18.3–20.7% supporting the decision to create the new genus Pacifia.

Body narrow. Notum discontinuous. Cerata in separate clusters, on elevations. Rhinophores perfoliated. Anus pleuroproctic under the reduced notal edge or mixed (pleuroproctic in higher acleioproctic position). Distinct oral glands present, commonly penetrate below anterior cerata. Radula formula 1.1.1. Rachidian teeth usually with strong cusp, only rarely compressed by adjacent lateral denticles. Lateral teeth denticulated narrow or with attenuated process basally. Distal and proximal receptaculum seminis or only proximal receptaculum. Vas deferens usually short, with indistinct prostate. External permanent penial collar absent. Penis in many cases conical, narrow, always internal and unarmed.

Luisella gen. n., Samla Bergh, 1900.

The genus Samla and related taxa were invariably considered as synonyms of the traditional genus Flabellina throughout all the recent history of nudibranch taxonomy (e.g., Gosliner and Griffiths 1981; McDonald 2009). Previously it was listed sometimes as valid (e.g., Burn 1964) but without detailed discussion. However, the Indo-Pacific tropical genus Samla differs morphologically from the Flabellinidaes. str.in the absence of compound stalks, often non-compressed cusp of the rachidian teeth, and also by having a short vas deferens. The present molecular phylogenetic analysis not only confirmed such disparate morphology from true Flabellinidae, but also revealed a very profound problem: species of the genus Samla and some related taxa are basal to the Aeolidacea as a whole and the major complex of aeolidacean families, including Aeolidiidae, Facelinidae, Tergipedidae, and Eubranchidae, rendering the Flabellinidae polyphyletic! Such topology with minor variations has appeared invariably on all trees obtained in the present analysis and was hinted at as soon as Flabellina babai was sequenced (Carmona et al. 2011). This result is of great importance because it clearly implies that 1) Understanding of the real phylogenetic and taxonomic patterns of the traditional “Flabellinidae” is possible only with inclusion of all major families of the nudibranch suborder Aeolidacea in the analysis, as is performed in the present study, and 2) The traditional “Flabellinidae” cannot be by any means maintained as single family, but must be separated into several smaller morphologically and molecularly consistent families (Fig. 2). Therefore, the genus Samla Bergh, 1900 (Bergh 1900b, 1908) is resurrected and the new family Samlidae is established here.

Apart from the taxa that belong to the genus Samla, which are clustered in a compact clade (Figs 1, 2, 45) the species Flabellina babai Schmekel, 1972 appears as a closely related clade. Flabellina babai differs considerably from Samla including the character of a distinct granulated prostate (Schmekel 1972; Schmekel and Portmann 1982), unique for the majority of the Paracoryphellidae, Coryphellidae and Flabellinidae. This feature is so far known only for the paracoryphellid genus Chlamylla, which is dramatically different from Flabellina babai externally. Therefore, a new genus for F. babai, Luisella gen. n., is proposed here (see below).

Flabellina babai Schmekel, 1972.

Named to honour an eminent expert of nudibranchs, Luise Schmekel, who named Flabellina babai and authored the well-recognised monograph Opisthobranchia des Mittelmeeres.

Body narrow. Notal ridge completely absent. Cerata in several distinct rows. Rhinophores perfoliated, shorter than oral tentacles. Anterior foot corners present. Anus mixed: pleuroproctic shifted towards dorsal acleioproctic position. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Proximal tubular receptaculum seminis. Moderately long vas deferens widened distally, prostate distinct, granulated. No external penial collar. Penis bluntly conical.

Luisella babai (Schmekel, 1972), comb. n. (original description in Schmekel 1972).

Samla annuligera Bergh, 1900

Body narrow. Notal ridge present, discontinuous. Cerata on low elevations. Single precardiac ceratal cluster. Rhinophores perfoliated, shorter than oral tentacles. Anterior foot corners present. Anus pleuroproctic. Rachidian teeth usually with relatively broad non-compressed cusp and distinct denticles, more rarely cusp compressed. Lateral teeth with attenuated process basally. Distal and proximal receptaculum seminis. Short vas deferens distally widens into non-granulated prostate. No external penial collar. Penis indistinct or conical.

Samla bicolor (Kelaart, 1858) (= Samla annuligera Bergh, 1900) (Fig. 46) (original description in Kelaart 1858; Bergh 1900b; redescription in Gosliner and Willan 1991), Samla bilas (Gosliner & Willan, 1991), comb. n. (original description in Gosliner and Willan 1991), Samla macassarana (Bergh, 1905), comb. n. (original description in Bergh 1905), Samla riwo (Gosliner & Willan 1991), comb. n. (original description in Gosliner and Willan 1991), Samla takashigei sp. n. (Fig. 47). Two more species are tentatively assigned to the genus Samla, but their placement needs to be refined using molecular data: Samla telja (Marcus & Marcus, 1967), comb. n. (original description in Marcus and Marcus 1967) and Samla rubropurpurata (Gosliner & Willan, 1991), comb. n. (original description in Gosliner and Willan 1991).

Holotype, ZMMU Op-530, 26 mm long (live), Japan, Osezaki, 11.09.2016, depth 10–15 m, coll. T.A. Korshunova, A.V. Martynov.

Osezaki, Japan.

Named in honour of Hiroshi Takashige (Tokyo), esteemed diver who is very fond of natural history and provided invaluable help during field collection in Osezaki, Japan.

Considerably reduced notal edge, forming several slightly elevated rows, background colour whitish with bluish hue, digestive gland in cerata light brownish, subapical parts of cerata orange-brownish, apical parts of cerata without white pigment, rachidian tooth with up to nine distinct denticles, slightly adpressed to central cusp, lateral teeth with up to eight denticles, penis conical.

External morphology (Fig. 47A–E). Body narrow. Foot and tail narrow, anterior foot corners long. Rhinophores ca. six times shorter than extremely long oral tentacles, annulated. Dorsal cerata finger-shaped to fusiform, forming eight slightly elevated rows along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosac. Distinct notal edge remains mostly below cerata clusters. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic on right side between first and second ceratal rows. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 47A). Background colour whitish with bluish hue. Digestive gland diverticula light brownish. Rhinophores background colour similar to body. Subapical parts of cerata brighter orange–brownish. Cerata covered with opaque white pigment throughout most of the length. Apical parts of cerata without opaque cap of white pigment.

Jaws (Fig. 47F, G). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears approximately 31 sharp denticles that form main single row of denticles on body of masticatory processes.

Radula (Fig. 47H). Radula formula: 19 × 1.1.1 (26 mm). Rachidian tooth elongate-triangular with short narrow cusp of less than 1/3 of tooth length (Fig. 47H). Rachidian tooth bears seven to nine well-defined separated long lateral denticles slightly adpressed towards cusp. Cusp is compressed by adjacent first lateral denticles. Lateral teeth (Fig. 47H) broadly triangular with obtuse and very attenuated posteriorly outer process, bear between six and eight sharp denticles. Some denticles can be forked or even triple.

Reproductive system (Fig. 47I, J). Diaulic. Hermaphroditic duct leads to convoluted ampulla of about two whorls. Vas deferens long, S-shaped, no distinct prostate. Penial sheath is narrow. Penis is narrow conical. Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Proximal receptaculum seminis oval, swollen. Distal receptaculum seminis present, small.

Shallow waters, stony habitats.

Pacific side of middle Japan (Honshu).

From all known species of the genus Samla, S. takashigei sp. n. differs by colour pattern and details of the radular teeth and these morphological differences are robustly supported by molecular data (Fig. 2). The three specimens examined demonstrate significant uniformity in the body shape and colour. Our specimens from Vietnam (Fig. 46) are consistent morphologically with the type species of the genus Samla, S. bicolor (Kelaart, 1858) and its recognised synonym S. annuligera Bergh, 1900, according to the original descriptions (Kelaart 1858; Bergh 1900b) and differ considerably from the Japanese S. takashigei sp. n. However, more species in the S. bicolor species complex are clearly present in the Indo-West Pacific according to the present phylogenetic analysis (Fig. 1); these will need attention in a further study.

Uncorrected p-distances of the mitochondrial barcode marker (COI) between Luisella babai and Samla species range between 19.0–21.0%, supporting the genus Luisella as a separate genus from Samla within the family Samlidae.

Body narrow. Notum fully reduced. Cerata in separate rows, on elevations. Rhinophores perfoliated. Anus mixed, pleuroproctic in higher acleioproctic position. Distinct oral glands present. Radula formula 1.1.1. Rachidian teeth cusp compressed by adjacent lateral denticles. Lateral teeth smooth with attenuated process basally. Distal receptaculum seminis. Vas deferens moderately long, with indistinct prostate. External permanent penial collar absent. Penis conical, narrow, always internal unarmed.

Apata gen. n., ?Tularia Burn, 1966.

Another unexpected and novel result is the apparent phylogenetic relationship between Samlidae and a North Pacific species, Coryphella pricei MacFarland, 1966. In our analysis C. pricei appears either as sister to the Samlidaes. str. (i.e. Samla + F. babai) or as a separate clade basal to Samlidae, Eubranchidae, and Tergipedidae (Figs 1, 2). Morphologically C. pricei is also quite separate from any Flabellinidaes. l. since it possesses peculiar comb-shaped ceratal rows in combination with a relatively long and thick vas deferens and smooth lateral teeth. Thus, C. pricei deserves not only a new genus but also a family-level taxon. Despite its somewhat unstable position, a new genus and family are established for C. pricei in order to highlight obvious morphological and molecular differences from the Samlidae (Apata gen. n. and Apataidae, respectively).

Tularia bractea Burn, 1966 was described from southern Australia (Burn 1966) and possesses simple raised rows of cerata instead of clusters or stalks, a triserial radula with smooth lateral teeth, and a reproductive system without a supplementary gland at the penis and single distal receptaculum seminis. These characters are in agreement with the diagnosis of the family Apataidae, and we therefore included Tularia in this family until molecular data are available.

Coryphella pricei MacFarland, 1966

From the Russian form "apata" of the Ancient Greek Απατη, a deity of deceit, in reference to some deceptive features of the new genus and family, which are highly similar (especially the radular teeth) to the family Flabellinidae, but some other characters (e.g., comb-like instead of pedunculate ceratal rows) and molecular phylogenetic data place the new taxon in a very separate position from true flabellinids, making the traditional family Flabellinidae remarkably polyphyletic.

Body narrow. Notal ridge completely absent. Cerata in several distinct rows. Rhinophores perfoliated, shorter than oral tentacles. Anterior foot corners present. Anus mixed: pleuroproctic shifted towards a dorsal acleioproctic position. Rachidian teeth with narrow compressed cusp and distinct denticles. Lateral teeth with attenuated process basally. Moderately long vas deferens widened distally, prostate indistinct. No external penial collar. Penis bluntly conical.

Apata pricei pricei (MacFarland, 1966), comb. n. (original description in MacFarland 1966), Apata pricei komandorica subsp. n.

Holotype, ZMMU Op-533, 8 mm long (fixed), North West Pacific, Commander Islands, 13.08.2014, 55°12.2182'N 165°55.4992'E, depth 19.5 m, coll. N.P. Sanamyan. Two paratypes, ZMMU Op-599, 7 mm long, same locality and date as holotype.

North West Pacific, Commander Islands.

After the Commander Islands in the NW Pacific (after original Russian spelling Komandorskie Islands), type locality of the subspecies.

Completely reduced notal edge, comb-like ceratal rows, background colour whitish, digestive gland in cerata greenish at the base and brownish-reddish toward ceratal top, subapical parts of cerata with white pigment, apical parts of cerata without white pigment, rachidian tooth with up to seven distinct denticles, adpressed to central cusp, lateral teeth smooth, penis conical.

External morphology (Fig. 48A–D). Body narrow. Foot and tail narrow, anterior foot corners short. Rhinophores similar in length to oral tentacles, bear up to 15 annulations. Dorsal cerata finger-shaped to fusiform, forming up to ten comb-shaped rows on dorsal side. Apices of cerata gradually pointed, with elongate cnidosac. Distinct notal edge remains mostly below cerata clusters. Digestive gland diverticulum fills significant volume of the cerata. Anal opening almost acleioproctic (“pleuroproctic in higher acleioproctic position”) on right side between six and seven ceratal rows. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 48A, C). Background colour whitish and translucent. Digestive gland diverticula greenish at base and first half and light brownish-dark reddish toward top of cerata. Rhinophores oral tentacles, and subapical parts of cerata covered dorsally with white pigment. Apical parts of cerata translucent.

Jaws (Fig. 48E, F). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears ca. 30 broad flattened denticles that form a main single row of denticles on the body of the masticatory processes.

Radula (Fig. 48G). Radula formula: 20 × 1.1.1 (8 mm). Rachidian tooth elongate-triangular with short narrow cusp of less than 1/3 of tooth length (Fig. 48G). Rachidian tooth bears between five and seven well-defined separated long lateral denticles considerably adpressed towards cusp. Cusp considerably adpressed by adjacent first lateral denticles. Lateral teeth (Fig. 48G) completely smooth, form long narrow curved plate with innermost pointed strong denticle.

Reproductive system (Fig. 48H). Diaulic. Hermaphroditic duct leads to compact ampulla. Vas deferens is long, looped, no distinct prostate, but distal part considerably enlarged. Penial sheath narrow. Penis narrow conical. Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Proximal receptaculum seminis oval, swollen. Distal receptacle present, rounded, on a very long convoluted duct, which is expanded distally.

Intertidal to 20–30 m, stony and soft bottom.

NW Pacific, Commander Islands, Middle Kurile Islands.

The type locality of Apata pricei (MacFarland, 1966) is California. According to the present phylogenetic analysis at least two species can be clearly separated among “Apata pricei” in Californian waters (Fig. 1): both are molecularly distinct from our material from Commander Islands using the COI molecular marker, although to different degrees. One species is highly divergent at 12.98%, and the other one is closer but still different (1.83%) from the Commander Islands specimens. The Commander Islands specimens are therefore recognised as a separate subspecies Apata pricei komandorica subsp. n. Morphological differences of the new subspecies are the fewer number of ceratal rows (up to ten) compared to the original description of A. pricei pricei from California by MacFarland (1966) (up to at least 12 ceratal rows). We cannot definitively evaluate the taxonomic placement of A. cf. pricei (CAS 114776) according to the original description of MacFarland (1966) due to the lack of the morphlogical description for this specimen in Cella et al. (2016). Further study on the Apata pricei complex is necessary to clarify its species composition in the Eastern Pacific.

Coryphella cynara Marcus & Marcus, 1967

From the Greek word κινάρα , which means “artichoke”, in reference to the Latinised name of the type species “C.” cynara which was originally named after the peculiar shape of its body which appeared when the animal folded its cerata, so the general outline of the body became similar to an artichoke.

Body narrow. Notum discontinuous. Cerata on low elevations, in several groups. Rhinophores perfoliated, shorter than oral tentacles. Anterior foot corners present. Anus mixed: pleuroproctic shifted towards dorsal acleioproctic position. Rachidian teeth with narrow non-compressed cusp and distinct denticles. Lateral teeth with attenuated process basally. Moderately long vas deferens with indistinct prostate. No external penial collar. Penis large, globular, tuberculated.

Kynaria cynara (Marcus & Marcus, 1967), comb. n. (original description in Marcus and Marcus 1967).

Kynaria cynara possesses a very special large globular copulative apparatus which is unknown among species of traditional Flabellinidae (Marcus and Marcus 1967; Millen and Hermosillo 2007). In combination with the anus in a higher acleioproctic position this puts Kynaria cynara apart from any other families analysed here or genera of traditional Flabellinidae. Kynaria cynara also demonstrates peculiar swimming behaviour (Marcus and Marcus 1967). No molecular data is available for Kynaria cynara, and it is separated into a new genus Kynaria gen. n. based on morphological data; its family placement as incertae sedis remains until molecular data are available.