Cuthonella anastasia, EKIMOVA, GRISHINA, NIKITENKO, 2024

Ekimova, Irina A., Grishina, Darya Yu. & Nikitenko, Ekaterina D., 2024, Nudibranch molluscs of Sakhalin Island, Northwestern Pacific: new records and descriptions of two new species, Ruthenica, Russian Malacological Journal 34 (2), pp. 69-91 : 84-85

Cuthonella anastasia sp. nov.

( Fig. 9 )

Zoobank registration: urn:lsid:zoobank.org:act:C146AF09-1376-4C16-9FCB-FDE7143CFE64

Type material: MIMB48076 , the Sea of Okhotsk, Aniva Bay , Moguchi River, Hirano ridge, 46°04.978’N, 142°13.021’E, 15–18 m in depth, 19 August 2023, coll. A. Plaksin, A. Semenov. Paratypes : MIMB48075 , 1 specimen, dissected, same locality and collectors as holotype . MIMB48077 , 1 specimen, partly dissected, the Sea of Okhotsk , Aniva Bay , Moguchi River, Hirano ridge, 46°05.372’N, 142°13.612’E, 20 m in depth, 20 August 2023, coll. A. Plaksin, A. Semenov.

Type locality: The Sea of Okhotsk , Aniva Bay , Moguchi River, Hirano ridge, 46°04.978’N, 142°13.021’E, 15–18 m in depth.

External morphology ( Fig. 9A, B ): Body elongated, moderately wide, up to 5 mm in length (MIMB48077). Rhinophores and oral tentacles cylindrical, smooth, almost equal in size or rhinophores slightly shorter. Cerata cylindrical, with rounded tips, arranged in continuous rows. Anal opening cleioproctic. Reproductive opening on right side below first cerata groups.

Coloration ( Fig. 9A, B ): Background body color pale beige to light-orange. Rhinophores and oral tentacles with same color as body, with distinct opaque white spots arranged in discontinuous subapical band in rhinophores, or dorsal lines on oral tentacles. Opaque white spots on head region concentrated between eyes. Cerata reddish brown with distinct opaque white spots (commonly 5–10 on each ceras) and subapical ring of white speckles around cnidosac area.

Internal morphology ( Fig. 9C, D ): Jaws triangular-shaped with masticatory border bearing one row of small denticles. Radular formula 24 × 0.1.0. Triangular rachidian tooth with strong, protracted, non-compressed conical cusp and 5–7 denticles on each side. Reproductive system was not studied in detail because of very poor fixation of specimens.

Molecular data: Unfortunately, after numerous attempts we failed to amplify COI marker for this species using a large set of universal primers. Specimens of C. anastasia sp. nov. cluster together on the phylogenetic tree ( Fig. 10; PP = 0.94, BS = 86). This species is recovered sister to Cuthonella georgstelleri Korshunova et al., 2020 from Matua Is., middle Kurile Islands (PP = 0.89, BS = 65). The p- distance in 16S rRNA comprises 1.20%, which is in line with interspecific p- distance values within the genus Cuthonella [ Korshunova et al., 2020b]. Cuthonella anastasia sp. nov. and C. georgstelleri forms a large clade with other North-West Pacific Cuthonella species: Cuthonella ainu Korshunova et al., 2020 , Cuthonella benedykti Korshunova et al., 2020 , C. soboli , Cuthonella osyoro (Baba, 1940) (PP = 1; BS = 59).

Distribution: This species is known only from the type locality.

Remarks: Although we were not able to study the reproductive system of the new species due to improper preservation of a single mature specimen (paratype MIMB48077), C. anastasia sp. nov. is well characterized by a combination of available molecular and morphological data. In the phylogenetic trees, this species forms a monophyletic group, which is sister to C. georgstelleri . From the latter species, C. anastasia sp. nov. differs in external morphology: it has brown cerata with white spots and pale orange body, while C. georgstelleri has elongated orangebrownish to salmon brown cerata lacking additional pigmentation except white bands on tips, and whitish body with slight disperse white pigment [ Korshunova et al., 2020b]. Cuthonella georgstelleri has a larger body size than C. anastasia sp. nov. (14 mm vs 5 mm in length respectivelly). Finally, these species differ in radular characters: C. georgstelleri has more teeth (30) and more denticles on rachidian teeth (up to 10 on each side). No other described Cuthonella has numerous distinct opaque white spots on cerata [ Korshunova et al., 2020b]. Cuthonella soboli has similar radular morphology ( Fig. 8K ) but differs from C. anastasia sp. nov. in coloration, since C. soboli has orange to light brown cerata with white speckles arranged in indistinct ring at upper midline ( Fig. 8D, E ).

Etymology: The species name refers to the Cape Anastasia, the closest large cape in the Aniva Bay to the type locality of the new species.

Figures

FIG. 9. External and internal morphology of Cuthonella anastasia sp. nov. A. Paratype MIMB48077, living photo. B. Holotype MIMB48076, living photo. C–D. MIMB48075, radula. Scale bars: C, D = 50 µm; E = 20 µm. Photo credits: A, B. Anton Plaksin. РИС.9. ВнешнЯЯи внутреннЯЯ морфологиЯ Cuthonella anastasia sp. nov.A. Паратип MIMB48077.B.Голотип MIMB48076. C–D. паратип MIMB48075, радула. Масштабные линейки: C, D = 50 µm, E = 20 µm. Авторство фотографий: A, B. Антон Плаксин.

FIG. 8. External and internal morphology of studied representatives of the family Fionidae.A. Eubranchus alexeii, MIMB48067, living specimen. B. Eubranchus rupium, MIMB48068, living specimen. C. Eubranchus rupium, egg masses on Obelia longissima colonies.D. Cuthonella soboli, MIMB48071, living specimen.E. Cuthonella soboli, MIMB48073,living specimen. F, G. living specimen of Cuthonella soboli MIMB48071 (F) and its egg-mass (G) on Sertularia sp. colony. H. Eubranchus alexeii, MIMB48067, middle radular portion, SEM. I. Eubranchus rupium, MIMB48070, posterior radular portion, SEM. K. Cuthonella soboli, MIMB48073, anterior radular portion, SEM. Scale bars: H, K = 20 µm; I = 10 µm. Photo credits: A–C, E. Darya Grishina; D, F, G. Irina Ekimova. РИС. 8. ВнешнЯЯ и внутреннЯЯ морфологиЯ иЗученных представителей семейства Fionidae. A. Eubranchus alexeii, MIMB48067. B. Eubranchus rupium, MIMB48068. C. Eubranchus rupium, кладка на колонии Obelia longissima. D. Cuthonella soboli, MIMB48071. E. Cuthonella soboli, MIMB48073. F, G. Cuthonella soboli MIMB48071 (F) и ее кладка (G) на колонии Sertularia sp. H. Eubranchus alexeii, MIMB48067, среднЯЯ часть радулы, СЭМ. I. Eubranchus rupium, MIMB48070,ЗаднЯЯ часть радулы, СЭМ.K.Cuthonella soboli, MIMB48073, переднЯЯчасть радулы, СЭМ.Масштабные линейки: H, K = 20 µm; I = 10 µm. Авторство фотографий: A–C, E. ДарьЯ Гришина; D, F, G. Ирина Екимова.