Cylichnoides densistriatus ( Leche, 1878 )

Chaban, E. M., 2016, Opisthobranch molluscs of « Cylichna occulta group » (Gastropoda: Opisthobranchia: Cylichnidae) from the Chukchi Sea and adjacent waters, The Bulletin of the Russian Far East Malacological Society 20, pp. 5-26 : 13-14

Cylichnoides densistriatus ( Leche, 1878)

Figs 3B ; 6I–L ; 7K–L

Utriculopsis densi-striata Leche, 1878, p. 74 –75, Taf. 1, fig. 20.

Utriculopsis densistriata Leche, 1878 : Herzenstein, 1885, p. 707.

Diaphana densistriata ( Leche, 1878) : Aurivillius, 1887, p. 371.

Cylichna densistriata ( Leche, 1878) : Knipowitsch, 1896, p. 300.

Cylichna occulta densistriata ( Leche, 1878) : Lemche, 1948, p. 79, figs 40a, 40b (paratype); Lemche, 1956, p. 236–239, pl. 1, figs 9, 10, 11; pl. 4, figs 42, 44; pl. 6, fig. 63; pl. 7, figs 82, 84; pl. 42, fig. 348.

Cylichnoides densistriata ( Leche, 1878) : Chaban, 2001, p. 108; Chaban, 2004, p. 83 –84, fig. 5C, D; Chaban, 2010, p. 76, fig. 6.5.

Type locality. Kara Sea, 63º05′ N, 73º45′ E, 9–70 fms.

Type s p e c i m e n s. SMNH [ Lemche, 1956, p. 236].

Material studied. New Siberian Islands : Russian polar expedition, R / V «Zarya», 1903, Kotelny Il., coll. A. V. Kolchak, det. N. Knipowitsch – 5 specimens ; East-Siberian Sea : R / V «Ivan Kireev», 2004, station 87, 69º31′17′′ N, 170º25′97′′ E, 11 m depth – 1 specimen; station 90, 70º02′81′′ N, 170º04′62′′ E, 18 m depth – 2 specimens; station 108, 70.275º N, 168.376º E, 27 m depth – 1 specimen; station 110, 70.835º N, 162.877º E – 2 specimens; Laptev Sea : 24.08.1973, Kondrat’evsky Isl., 7 m depth, coll., det. by A.N. Golikov – 2 specimens ; R / V «Ivan Kireev», 1993, station 31/53, 75.0000º N, 129.5730º E, 40 m depth, mud – 3 specimens ; R / V «Yakov Smirnitstkiy», 1995, station 60, 74.5401º N, 135.0002º E, 23 m depth, clay – 2 specimens ; station 62, 72.5501º N, 134.0003º E, 17 m depth, clay – 1 specimens.

D e s c r i p t i o n. Shell ( Fig. 6I–L ) very thick and strong, almost globose, up to 6 mm, very wide at the top, apex umbilicated, columellar margin short, straight, often wide, almost parallel to axis of shell. Spiral sculpture ( Fig. 7L ) consists of alternating narrow deep wavy grooves and ribs.

Anatomy. Studied specimens 5–5.5 mm height are adult, their narrow twisted prostate joined with a lateral side of the penial sac ( Fig. 3B ). Radula is 2:1:1:1;2 ( Fig. 7K ), bilobate rachidian teeth with straight denticles.

D i s t r i b u t i o n. White, Kara, Laptev and East-Siberian seas from 5 to 170 m [ Leche, 1878; Herzenstein, 1885; Aurivillius, 1887; Knipowitsch, 1896; Chaban, 2001, 2004, 2010].

N o t e s. The type specimens of C. densistriatus have not been studied here but the specimens here described belong to this amazing species without doubt. The species is easily defined due to their almost globose thick shell and hard spiral sculpture, and according to figures given by Leche [1878] and Lemche [1956]. C. validus differs from C. densistriatus in shell shape, sculpture and columellar margin. C. densistriatus has a very thick shell with hard spiral sculpture. C. occulta from Jørgen Brønlund Fjord (North Greenland) was regarded by Schiøtte [1989, fig. 11C] as identical to C. densistriatus due to the shell shape, but it does not have the appropriate spiral sculpture and is determined not to be C. densistriatus . Radula of the type specimen was studied by Lemche and he noted that the denticulation on the rachidian tooth is continuous over the median incision [ Lemche, 1956, p. 238]. This characteristic and the shell morphology distinguish C. densistriatus from other species of the genus. The species is not found to the east of the East-Siberian Sea.

Figures

Fig. 3. Male copulatory system: Cylichnoides scalptus, Laptev Sea (A); Cylichnoides densistriatus, Russian Polar Expedition 1901–1903, no data (B); Cylichnoides occultus, Novaya Zemlya, Matochkin Strait (C); Cylichnoides validus, Laptev Sea (D) and Chukchi Sea, «Vega» expedition (dorsal view (E), ventral view (F)). Abbreviations: m – muscle fibers, p.f – folds of penial sheath, others like to Fig. 2. Scale bar: A, D–F – 1 mm; B, C – 0.5 mm.

Fig. 6. Cylichnoides scalptus, shell: Kara Sea, «Fyodor Litke», station 183 (A–E); Barents Sea, R/V «Persey», station 862 (F, G) and station 866 (H) (ventral view: A – 10.2 mm, B – 9.9 mm, C – 9.5 mm, D – 5.3 mm, F – 5.0 mm, H – 10 mm; apical view: E, G). Cylichnoides densistriatus, shell: Kotelny Isl., New Siberian Islands, 1903 (I, J); Laptev Sea, Kondrat’evsky Il., 1973 (K, L), ventral view (I – 5.6 mm, L – 4 mm), apical view (J, K). Scale bar: E, G, J, K – 1.0 mm.

Fig. 7. Cylichnoides scalptus: Kara Sea, 1948: radula (A–F), shell sculpture (G–J), (B–D – rachidian tooth, denticles of the internal lateral tooth, E – denticles of the internal lateral tooth, F – outer lateral teeth). Cylichnoides densistriatus (K, L): radula (K), shell sculpture (L). Scale bar: A – 100 µm; B – 40 µm; C, F, K – 50 µm; D – 30 µm; E – 10 µm; G – 500 µm; H, I, L – 200 µm; J – 400 µm.