Eubranchus rupium ( Møller, 1842 )

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 : 83-84

Eubranchus rupium ( Møller, 1842)

( Fig. 8B, C, I )

Material studied: MIMB48068 – MIMB48070 , 3 specimens, all dissected, 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 Zostera sp. with Obelia longissima colonies, 7 August 2023, coll. I. Ekimova, D. Grishina.

Diagnosis: Body elongate, narrow, up to 5 mm in length, yellowish semitransparent with small reddish-brown spots. Rhinophores and oral tentacles elongated, smooth. Cerata finger-shaped, with pointed tips, bearing small thickening in upper part, arranged in 5–7 groups with 1–2 cerata per group. Jaws triangular-shaped with masticatory border bearing one row of small conical denticles. Radular formula 18–22 × 1.1.1. Triangular rachidian tooth with depressed central cusp and 6-7 lateral denticles on each side. Lateral teeth with rectangular base and triangular cusp. Ampulla small, bean-shaped. Vas deferens without prostatic part. Penis conical. Receptaculum seminis bent in middle part, expanded.

Molecular data: A BLAST-n search of COI sequences resulted in 99.57% identity to sequences of E. rupium from GenBank thus confirming distinctness of the studied specimens.

Distribution: This species has a wide distribution, having been recorded from Greenland [type locality, see Møller, 1842], Norway, Sweden, the Barents Sea, and the White Sea [ Martynov, 1998; Cella et al., 2016], the Sea of Japan [ Martynov, 1998], Maine [ Cella et al., 2016]. This is the first record of this species from Sakhalin Is. (Aniva Bay), although it has been found from adjacent areas [ Martynov, 2013].

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.