Amphorina viriola, Korshunova & Malmberg & Prkić & Petani & Fletcher & Lundin & Martynov, 2020

Korshunova, Tatiana, Malmberg, Klas, Prkic, Jakov, Petani, Alen, Fletcher, Karin, Lundin, Kennet & Martynov, Alexander, 2020, Fine-scale species delimitation: speciation in process and periodic patterns in nudibranch diversity, ZooKeys 917, pp. 15-50 : 15

Amphorina viriola sp. nov. Figs 1 , 2 , 3 , 5 , 7b

Material examined.

Holotype. NE Atlantic, Skagerrak, Sweden, Region Västra Götaland, Bohuslän county, Ide fjord, close to Svarte Jan lighthouse (59°06'30"N 11°19'30"E), 4-6 m depth, 21.XII.2016, coll. Klas Malmberg (GNM Gastropoda - 9393, 6 mm in length, live, preserved length 3 mm). Paratypes. NE Atlantic, Skagerrak, Sweden, Region Västra Götaland, Bohuslän county, town of Lysekil, public marina, Dock D (58°16'00"N 11°26'00"E), 0.1-0.5 m depth, a mix of algae on floating blocks, 09.V.2015, coll. Klas Malmberg, seven specimens (GNM Gastropoda - 9093, 6 mm in length, live, GNM Gastropoda - 9260, preserved length 5.5 mm, GNM Gastropoda -9261, 7 mm in length, live, preserved length 6.5 mm, GNM Gastropoda -9262, 8 mm in length, live, preserved length 6.5 mm, GNM Gastropoda -9263, 8 mm in length, live, preserved length 5 mm, GNM Gastropoda -9264, 6 mm in length, live, preserved length 5 mm, GNM Gastropoda -9265, 7 mm in length, live, preserved length 5.5 mm). NE Atlantic, Skagerrak, Sweden, Region Västra Götaland, Bohuslän county, town of Smögen, Kleven, Smögen Dyk och Upplevelse Dive centre (58°21'08.8"N 11°13'40.6"E), 3 m depth, 25.III.2017, one specimen (GNM Gastropoda -9341, 7 mm in length, live). NE Atlantic, Skagerrak, Sweden, Region Västra Götaland, Bohuslän county, town of Smögen, Kleven, Smögen Dyk och Upplevelse Dive centre (58°21'30.8"N 11°13'31.0"E), 4-4.5 m depth, 01.IV.2017, coll. Sebastian Spora, one specimen (GNM Gastropoda -9360, 7 mm in length, live, preserved length 5 mm). NE Atlantic, Skagerrak, Sweden, Region Västra Götaland, Bohuslän county, Ide fjord, close to Svarte Jan lighthouse, five specimens (59°06'30"N 11°19'30"E), 4-6 m depth, 21.XII.2016, coll. Klas Malmberg (GNM Gastropoda - 9394, 8 mm in length, live, preserved length 4 mm, GNM Gastropoda - 9395, 7 mm in length, live, preserved length 3 mm, GNM Gastropoda - 9396, 6 mm in length, live, preserved length 3.2 mm, GNM Gastropoda - 9397, 8 mm in length, live, preserved length 2 mm, GNM Gastropoda - 9398, 8 mm in length, live, preserved length 7 mm). NE Atlantic, Skagerrak, Sweden, Region Västra Götaland, Bohuslän county, Ide fjord, close to Svarte Jan lighthouse (59°06'30"N 11°19'30"E), depth unknown, 2018-2019, coll. Mats Larsson, Michael Lundin (GNM Gastropoda - 9936).

Diagnosis.

Body up to ca. 12 mm; large dorsal pigment spots, if present, yellow-orange, dull; in specimens with yellow-orange spots on body and cerata there is never any yellow-orange pigment spot or stripe on the tail, but there might be a median whitish line or broken line on the tail; completely pale specimens lack tail spot; light pinkish subapical ring on cerata present; absence of white punctuated line on external edge of foot; cerata commonly moderate in width without distinctly attenuated apices; digestive gland in cerata relatively broad without distinct short branches; up to four anterior rows of cerata; radular formula 31-47 x 1.1.1, copulative stylet relatively long and almost straight, at the top, seminal receptacle pear-shaped with short distinct stalk between reservoir and long base.

Etymology.

" viriola ", Lat. small bracelet, referring to the light pinkish subapical pigment ring on the cerata.

Description.

External morphology. The live length of the holotype is 6 mm (Fig. 5a ). The length of adult specimens may reach 10-12 mm. The body is narrow. The rhinophores are smooth and 1.5-2 times longer than the oral tentacles. The cerata are relatively long, swollen. Ceratal formula of the neotype: right (2, 4, 4; anus, 3, 3, 2, 2, 1) left (2, 3, 3; anus, 3, 2, 2, 1, 1). The foot is narrow, anteriorly without foot corners.

Colour. There are three main colour morphs with several subdivisions of the colour variations (Fig. 3 ), from completely pale body and cerata without orange-yellow pigment spots on the body, to specimens with dull brownish orange-yellow spots. In the specimens with such spots there is never any orange-yellow colouration on the tail, but there can be a median whitish line or broken line on the tail. Specimens with greyish surface pigmentation are sometimes found, but not with blackish, non-transparent pigmentation (Fig. 3 ). No specimens with uniformly orange colour have been observed. The tips of the cerata may have orange-yellow pigmentation or lack pigment, leaving the cnidosacs visible. A light pinkish subapical ring on the cerata is usually present, or at least noticeable by some pinkish pigment dots. Absence of a punctuated white line on the edge of the foot. The upper part of the rhinophores are commonly covered with brownish to dark orange pigment and dispersed small white dots. The oral tentacles are similarly coloured.

Anatomy. Digestive system (Fig. 5 , a4-a8, b3-b8, c3-c8, d4-d8). The jaws are triangularly ovoid. The masticatory processes of the jaws bear a single row of ca. 15-21 distinct denticles. The radular formula in four studied specimens is 31-47 x 1.1.1. The radular teeth are yellowish. The central tooth is narrow, with a low cusp and 4-6 lateral denticles, including smaller intercalated denticles that may occur in different parts of the tooth.

Reproductive system. (Fig. 7B ). The ampulla is moderate in length and swollen (Fig. 7B , am). The prostate is distinct, moderately long and wide (Fig. 7B , pr). The prostate transitions to a penial sheath, which contains a conical penis with a short, chitinous, almost straight stylet (Fig. 5 , b9, b10). A supplementary ( “penial”) gland is relatively short and inserts into the base of the penis (Fig. 7B , pg). The seminal receptacle is moderate in size, pear-shaped (Fig. 7B , rs) with a long base to which it transitions with a distinct stalk. The female gland mass includes mucous and capsular glands (Fig. 7B , fgm).

Distribution and habitats.

Swedish northwest Skagerrak coast, in the south from the town of Lysekil at the Gullmar fjord, onwards to Smögen and the Väderö Island archipelago, to the Ide fjord in the north by the border with Norway. It is always found very shallow and above the halocline (situated at 6-7 m depth within the fjords and 15 m outside the fjords), most often from 0.1 to 6 metres depth, commonly on wharf pontoons in the marina. Inhabits exclusively the brackish water layer, salinity-range: ordinarily ca. 24-25 ‰ but may vary from 12 to 30 ‰.

Remarks.

Morphologically the brackish water-living A. viriola sp. nov. differs from the closely related A. andra sp. nov. by the presence of light pinkish subapical rings on the cerata, the absence of forms with non-transparent blackish pigmentation, or any forms with uniform orange colour (Fig. 3 ), a larger range of the number of lateral denticles on central radular teeth, a considerably smaller ampulla and elongated and pear-shaped receptaculum seminis. From A. farrani , A. viriola sp. nov. differs by the absence of a yellow or orange median stripe on its tail, and the absence of forms with black surface pigmentation (Fig. 3 ). From A. linensis , A. viriola sp. nov. differs by the absence of a distinct white line (sometimes dotted) along the foot edge, orange-yellow and not reddish orange spots (in spotted forms), a smaller number of ceratal rows and the shape of the cerata, the shape and size of the ampulla and receptaculum seminis. From A. pallida , A. viriola sp. nov. differs by the larger size of dorsal spots (in spotted forms), and the smaller number of anterior ceratal rows, the shape and size of the ampulla and receptaculum seminis.

Minimum uncorrected p-distances of the COI marker which separate the A. viriola sp. nov. from A. farrani , A. andra sp. nov., A. linensis , and A. pallida are 8.92 %, 0.15 %, 9.15 %, and 14.08 % respectively.

Figures

Figure 1. Phylogenetic relationships of nudibranchs Amphorina based on COI + 16 S + H 3 concatenated dataset inferred by Bayesian Inference (BI). The posterior probabilities from BI / bootstrap values for Maximum Likelihood (ML) are shown.

Figure 2. The haplotype network based on cytochrome c oxidase subunit I (COI) molecular data showing genetic mutations occurring within species of the genus Amphorina (A). Statistical test of the reliability of the bathymetric distribution patterns (and correlated with depths of brackish and marine environments) of A. viriola sp. nov. (red bar) and A. andra sp. nov. (blue bar) in Swedish waters (B). All specimens of A. viriola sp. nov. occur strictly in a very shallow brackish water layer above the halocline (salinity usually ca. 24 - 25 ‰), whereas in the same geographic region A. andra sp. nov. occur only below the halocline (at ca. 15 m depth) in waters with more stable oceanic salinity at 34 - 35 ‰.

Figure 3. Periodic-like presentation of the colouration variation among all species of the genus Amphorina, representing vertical rows. Three main periods (horizontal rows), each with several subperiods, are recognised according to the principle of spotless body / colourless forms at the bottom to forms with the maximal number of spots / coloured body at the top. Note that different species display fundamentally similar colouration forms, but not all, so some morphs in particular species (e. g., forms with extensive surface pigmentation and dark body in A. farrani, A. linensis, and A. pallida) can either be eventually discovered or do not exist, by some further constraints of the developmental system. Non-observed forms for each particular species are indicated as " unkn " = " unknown ").

Figure 5. Amphorina viriola sp. nov., Sweden. (a) A. viriola sp. nov. GNM 9393, a 1, head; a 2, cerata; a 3, tail; a 4, posterior part of radula (30 μm); a 5, anterior part of radula (30 μm); a 6, jaw (light microscopy); a 7, jaw (100 μm); a 8, jaw details (30 μm). (b) A. viriola sp. nov. GNM 9360, b 1, head; b 2, cerata; b 3, posterior part of radula (10 μm); b 4, posterior part of radula (20 μm); b 5, anterior part of radula (50 μm); b 6, jaw (light microscopy); b 7, jaw (200 μm); b 8, jaw details (20 μm); b 9, stylet details (10 μm); b 10, stylet (100 μm). (c) A. viriola sp. nov. GNM 9263, c 1, head; c 2, cerata; c 3, apical part of lateral teeth with possible denticles (1 μm); c 4, posterior part of radula (20 μm); c 5, anterior part of radula (20 μm); c 6, jaw (light microscopy); c 7, jaw (SEM, 200 μm); c 8, jaw details (20 μm). (d) A. viriola sp. nov. GNM 9260, d 1, head; d 2, tail; d 3, cerata; d 4, posterior part of radula (30 μm); d 5, anterior part of radula (30 μm); d 6, jaw (light microscopy); d 7, jaw (300 μm); d 8, jaw details (30 μm).

Figure 7. Reproductive systems, schemes. (A) Amphorina farrani. (B) Amphorina viriola sp. nov.; (C) Amphorina andra sp. nov. (D) Amphorina linensis. (E) Amphorina pallida. Abbreviations: am ampulla, fgm female gland mass, pg penial gland, pr prostate, psh penial sheath, rs receptaculum seminis.