Cuthonella soboli Martynov, 1992

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

Cuthonella soboli Martynov, 1992

( Fig. 8D–G, K )

Material studied: MIMB48071 , 1 specimen, the Sea of Okhotsk , Aniva Bay , Moguchi River, Hirano ridge, 46°05’06.5”N, 142°12’39.4”E, 0.1–1 m in depth, on Sertularia sp. colonies, 7 August 2023, coll. I. Ekimova, D. Grishina. MIMB48072 – MIMB48074 , 3 specimens, two dissected, the Sea of Okhotsk , Aniva Bay , Moguchi River, Hirano ridge, 46°05’06.5”N, 142°12’39.4”E, 0.1–1 m in depth, on Sertularia sp. colonies, 7 August 2023, coll. I. Ekimova, D. Grishina.

Diagnosis: Body elongated, narrow, up to 7 mm in length, yellowish semitransparent to light beige. Rhinophores and oral tentacles cylindrical, smooth, equal in size. Cerata cylindrical, with pointed tips, arranged in continuous rows. Cerata orange to light brown, with white speckles arranged in indistinct ring at upper midline. Jaws triangular-shaped with masticatory border bearing one row of small blunt denticles. Radular formula 21 × 0.1.0. Triangular rachidian tooth with strong, protracted, non-compressed conical cusp and 5–6 denticles on each side. Ampulla narrow, slightly convoluted. Vas deferens without prostatic part, supplementary gland long and narrow. Penis conical. Receptaculum seminis small, ovate, muscular.

Molecular data: A BLAST-n search of COI sequences resulted in 98.32–98.84% identity to sequences of C. soboli from GenBank thus confirming the distinctness of the studied specimens.At the same time, specimens of C. soboli do not form a monophyletic group on the phylogenetic trees ( Fig. 10).

Distribution: This species is known from the northern part of the Sea of Japan [ Korshunova et al., 2020b]; these authors also suggested it may be found in the southern Kurile Islands and Hokkaido. This is the first confirmed record of this species in the Sea of Okhotsk.

Figures

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.