Cirsotrema matugisiense (Ozaki, 1958)

Sirenko, Boris I. & Drobyazin, Evgeny N., 2020, New finding of the epitoniid Cirsotrema matugisiense (Ozaki, 1958) (Mollusca: Gastropoda) in the Sea of Japan, The Bulletin of the Russian Far East Malacological Society 24 (1 / 2), pp. 61-66 : 62-66

Cirsotrema matugisiense (Ozaki, 1958)

Figs. 1 , 2B–F

Epitonium (Boreoscala) matugisiensis Ozaki, 1958, p. 142 , pl. 15, fig. 25 (fossil); Brown, Neville,

2015, p. 102 (fossil and Recent).

Epitonium (Boreoscala) yokozunai Ozaki, 1958, p. 143 , pl. 15, fig. 26 (fide Nakayama [2003]) (fossil).

Cirsotrema matugisiense (Ozaki, 1958) : Nakayama, 2003, p. 29, pl. 4, figs. 23–27 (fossil and Recent); Tsushida, Hasegawa, 2017, p. 894, pl. 183, fig. 7 (fossil and Recent).

Ty p e m a t e r i a l. The holotype ( NSMT 4498 ) .

Ty p e l o c a l i t y. Cliff, 500 m south of Matugisi Railway Station, Tyosi City, Iioka Formation, Neogene.

M a t e r i a l e x a m i n e d. The Sea of Japan, near western Sakhalin, 47°16.4′– 47°15.9′ N, 141°47.3′– 141°47.0′ E, depth 386–388 m, mud, R / V Bukhoro, research trawl, 2 specimens ( ZISP 62489 ); 1 specimen ( FEFU XII 53121 /Ga-10171), 04.07.2018, coll. E.N. Drobyazin ; 47°16.5′– 47°15.9′ N, 141°45.2′– 141°44.6′ E, depth 521 m, mud, R / V Bukhoro, research trawl, 1 specimen, 28.05.07.2015, coll. I. Kornejchuk.

D i s t r i b u t i o n. Japan: Boso Peninsula (fossil) [ Nakayama, 2003; Tsuchida, Hasegawa, 2017], off Kunashir Island, Hokkaido, Japan [ Nakayama, 2003] and the Sea of Japan, near western Sakhalin (this study). Nakayama [2003] was the first to report the discovery of this species in the Recent fauna near Kunashir Id. and Hokkaido. Unfortunately he did not give more detailed information about locality and depths. Specimens collected from western Sakhalin significantly advance the boundaries of the area of this species to the north and are the first find of the species off the coast of Russia. Reports of the distribution of this species off Greenland and in the Arctic seas [ Tsuchida, 2000], appear to be associated with incorrect identifications. Kazunori Hasegawa (in e-mail message) informed that he has seen specimens of this species only from the north-western Pacific (eastern Hokkaido and northwards), Okhotsk Sea and northern Sea of Japan.

Due to some differences between western Sakhalin specimens and fossil type and other similar specimens, we found it useful to give a brief description and distinctive diagnosis .

D e s c r i p t i o n. Shell big for the genus, height up to 85.4 mm, high, thin but rather solid, grayish white. Protoconch damaged, teleoconch consist of 7 convex whorls separated by distinct narrow sutures. Axial sculpture of teleoconch whorls consisting of numerous, low ribs of different thickness especially on the last whorl, where there are 36 axial ribs. Spiral ribs rather low, flattened, wide, 6 spiral ribs on whole surface of each whorl excluding base. Axial and spiral ribs presenting weakly cancellated appearance. Umbilicus narrow, fissure-like. Aperture round, the outer edge of the aperture is thickened by a wide axial rib, columellar lip narrow, smooth, slightly erect, the inner surface of the aperture purple. Operculum brownish black, paucispiral, nucleus of operculum shifted to the lower left edge.

There is no information about the radula due to the lack of soft parts of the body.

R e m a r k s. The protoconchs of all studied specimens were destroyed, so the real height of the shell is a few millimeters more (see Table). Nakayama [2003] believes that the holotypes of Epitonium (Boreoscala) matugisiense Ozuka, 1958 ( Fig. 2F ) and E. (B). yokozunai Ozuki, 1958 ( Fig. 2B, E ) are two parts of the same shell, so he composed the characters.According to the new diagnosis, the holotype of C. matugisiense has 26 axial ribs and 9 spiral ribs, which is at odds with the number of ribs in western Sakhalin specimens. In addition, the last specimens have a slit-like umbilicus. Kasunori Hasegawa (in e-mail message) and we believe that this is the result of intraspecific variability.

C. matugisiense differs from the other species of the family Epitoniidae , having few low flattened, wide spiral ribs throughout the whole surface of each whorl, excluding the base. Most similar to C. matugisiense is Amaea iwaotakii Azuma, 1961 ( Fig. 2A ). A. iwaotakii differs from C. matugisiense in having the whorls with many distinct minute spiral striae except on the upper third of each whorl [ Azuma, 1961] (vs. a few low flattened, wide spiral ribs throughout the whole surface of each whorl excluding the base in C. matugisiense ); all axial ribs are rather similar in size (vs. the axial ribs of different thickness, especially on the last whorl, in C. matugisiense ).

Figures

Fig. 1. Cirsotrema matugisiense, A–C – specimen ZISP 62489/1, shell, height of shell 83.1 mm, diameter of the last whorl 34.0 mm; D – specimen ZISP 62490/2, operculum 17.1x13.9 mm.

Fig. 2. Shells of Epitoniidae: A – Amaea iwaotakii, after Tsushida [2000]; C, D – Cirsotrema matugisiense (Recent), after Nakayama [2003]; B, E – Epitonium (Boreoscala) yokozunai (the holotype, fossil, after Nakayama [2003]); F – Epitonium (Boreoscala) matugisiense (the holotype, fossil, after Nakayama [2003]).