Cylichnoides validus ( Leche, 1878 ) Chaban, 2016

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 : 8-13

Cylichnoides validus ( Leche, 1878) stat. nov.

Figs 1A–L ; 2A–L ; 3D–F

Cylichna insculpta Totten var. valida Leche, 1878, p. 72 ; Aurivillius, 1887, p. 370 –371; Odhner, 1907, p. 13.

Cylichna reinchardti var. insculpta ( Totten, 1835) : Odhner, 1915, Taf. 1, fig. 21 (non Totten).

? Cylichna occulta ( Mighels et Adams, 1842) : Lemche, 1948, fig. 38 (det. as « insculpta »).

Cylichna occulta ( Mighels et Adams, 1842) : Chaban, 2004, fig. 5A, B.

Cylichnoides sp. : Chaban, 2010, p. 77, fig. 6.3B.

Type locality. The Kara Sea, 68º20′ N, 73º53′ E, 18 m (10 famnar).

Type s p e c i m e n s. «Type-8589, syntypes, 7 specimens, dry, Arctic Ocean , Russia, Kara Sea, off Obfjord. 73°53′ N 68°20′ E. Sand. Leg. Jenissej Exp. 1875 sta. 166» ( SMNH) ( Figs 1A, B ) .

Material studied. Chukchi Sea: 1879, «Vega» expedition, no data, identified by Aurivillius as Cylichna insculpta var. valida Leche , – 1 specimen; 09.VIII.1929, icebreaker «Fyodor Litke», station 54, Wrangel Isl. , 69º19′ N, 175º58′ W, 53 m depth, collected by P. V. Ushakov – 2 specimens ; 09.IX.1929,icebreaker «Fyodor Litke», station 55, Wrangel Il., 69º19′ N, 176º56′ W, 53 m depth, collected by P. V. Ushakov – 2 specimens ; 09.VIII.1935, icebreaker «Krasin», station 44, Wrangel Il., 72º30′ N, 178º45′ W, 50 m depth, mud, clay, collected by P. V. Ushakov – 1 specimen ; «Rusalka-2009»: 08.IX.2009, station 119, 44 m depth, 69.49192º N, 182.014º E – 3 specimens; 10.IX.2009, station 138, 75 m depth, 172.40068º N, 177.419º E – 1 shell; 11.IX.2009, station 136, north of Wrangel Il. , 27 m – 13 shells, 4 specimens ; East-Siberian Sea: R / V « Alpha-Helix » , 27.VIII.1995, station 10, 71º00′ N, 170º49′ E – 1 specimen; 27.VIII.1995, station 12, 70º20′ N, 171º49′ E – 1 specimen; Laptev Sea : 21.VIII.1937, icebreaker «Sadko», Laptev Sea, station 21, 76º12′9′′ N, 133º50′ E, 47 m depth – 6 specimens; R / V « Ivan Kireev » , 13.IX.1993, station 39/84, 77º08′ N, 137º10′ E, 30 m depth. Barents Sea : R / V «Persey» , 11.VIII.1924, 70º11′ N, 56º30′ E, station 150, depth 140 m, mud.

Diagnosis. Shell widely oval, white, solid, with spiral sculpture consists of wide ribs and striae alternating (narrow and wide) in width; columellar margin with strong convexity. Outer lip much extended beyond the apex. Denticles on the lateral teeth are long, strong and closely spaced, almost equal in length, forming a plate on the base of the tooth. Rachidians bilobate, slightly convex, equipped with single regular row of very small cusps on cutting edge, lateral edges without notches, ventral surface without vertical crest.

D e s c r i p t i o n. Shell. Shell thick but sometimes fragile, from 3 to 11.8 mm height, consists of one whorl, oval, narrows considerably posteriorly, widest in the middle as a rule ( Fig. 1 ). Color milky white in recently collected specimens, but uniformly dirty white in long preserved specimens. An edge of the outer lip with a horny brown band often present. Apex not umbilicated, outer lip higher than the apex of shell, regularly convexed. Parietal margin without callus, columellar margin with strong convexity, columellar umbilicus closed without chink. Longitudinal sculpture absent, spiral sculpture consist of deep, broad and straight grooves mostly at regular distances from each other, 8–10 grooves per one cm of shell, alternating with broad flattened ribs, which usually carry shallow striae.

Anatomy. Preserved specimen light brown, foot broad with parapodia, head shield very compressed and completely hidden under the front edge of mantle. Radula formula 10x:2:1:1:1:2. Denticles (30–32) on lateral teeth long, strong and closely spaced, almost equal in length, forming a plate on tooth base ( Fig. 2A ). Rachidian tooth slightly convex, asymmetrical for one studied specimen, equipped with the row of small cusps on cutting edge, and with three small additional denticles on the back of some teeth; it consists of two parts that are separated with a deep notch ( Fig. 2I ). Lateral edges without notches; ventral surface without vertical crest; upper-lateral ends tapering, angular ( Fig. 2E, F ). Outer marginal teeth with very small cusps. Gizzard plates ( Fig. 2J ) 2 mm long for specimen with shell height 8.4 mm, semi pellucid, yellowish, inner surface smooth, plates of some specimens with brown circle on inner surface; plates of long-preserved specimens brown. Male copulatory system with long narrow transparent prostate connected with proximal end of small penial sac which filled with muscular folds ( Fig. 3D ). A prostate of the specimen collected during «Vega» expedition is extraordinary: it has an additional short and narrow outgrowth in its middle part ( Figs 2L , 3E, F ).

D i s t r i b u t i o n. Kara Sea [ Leche, 1878], Spitsbergen [ Odhner, 1915, as Cylichna reinchardti var. insculpta ], Laptev Sea ( ZISP collection), East-Siberian Sea [ Chaban, 2010 as Cylichnoides sp. ] and Chukchi Sea [ Aurivillius, 1887 and ZISP collection].

N o t e s. The original description of Cylichna insculpta var. valida by Leche [1878] is very brief. Leche regarded that valida is a variety of insculpta and has « tjocka, nästan ogenomskinliga skal » [shell thick, almost opaque] [ Leche, 1878, p. 72]. The syntypes of C. insculpta var. valida from the Swedish Museum of Natural History ( Fig. 1A, B ) have solid oval shells with narrowed apex, hard shell sculpture which consists of pairs of wide ribs and alternating wide and narrow spiral grooves, and columellar margin with a strong convexity. These characters show that the syntypes of C. insculpta var. valida and specimens from our material belong to the same species.

Shell variability of Cylichnoides validus is shown on Fig. 1 . The specimen of C. validus , collected during «Vega» expedition in 1879 ( Fig. 1D ) has a more cylindrical shell, but the same columellar margin and shell sculpture as other specimens of the species. A specimen from the Laptev Sea (collected in 1937, Fig. 1L ), has a more narrow shell and corresponds to Cylichna reinchardti var. insculpta sensu Odhner [1915 , Taf. 1, fig. 21]. Another specimen from the Laptev Sea (collected in 1993, Fig.1I ) has the thickest shell with a very hard spiral sculpture. A specimen that was collected in Chukchi Sea in 1935 ( Fig. 1K ) has a wide regularly oval shell. But all specimens have, as is typical for C. validus characteristics: thick oval shell with narrowed apex and columellar fold, outer lip much extended beyond the apex, hard spiral sculpture with broad ribs and grooves.

The specimen collected by «Vega» has an extraordinary prostate with an additional short and narrow outgrowth (a.pr – Fig. 3E, F ) in its middle part. This type of prostate is unknown for other members of Cylichnidae . But only one specimen with this prostate was found, and it could be a malformation as is one or four gizzard plates in the gizzard of Cylichna alba (unpublished data). Further study is needed for clarification of the species.

The illustration of C. reinchardti var. insculpta sensu Odhner [1915 , Taf. 1, fig. 21] contradicts the description of insculpta given by Totten [1835]. Totten noted his insculpta as « impressed at the top » and having concave columellar margin (see Totten [1835, fig. 4]).According to specimens that were collected near Greenland (presumably from the collections of the Zoological Museum of Copenhagen) and labeled as « Bulla insculpta (= Bulla reinhardi )», insculpta has thin dark colored periostracum and very fine sculpture ( Fig. 3F ). If B. insculpta is really a synonym of H. solitaria ( Haminoeidae ) or belongs to Cylichnidae , in both cases C. validus and B. insculpta are different species.

Figures

Fig. 1. Cylichnoides validus, shell: syntypes of Cylichna insculpta var. valida, SMNH, ventral view (A, B); «Vega» expedition, 1878, no data, 7.5 mm, (ventral view – D); R/V «Persey», Barents Sea, station 150, 8.5 mm (ventral view – H); Chukchi Sea, «Rusalka»-2009, station 119 (apical view (C) and ventral view (E – 5 mm; F – 4 mm; G – 7 mm)); R/V «Ivan Kireev», station 9/42, Laptev Sea, ventral view, 7.5 mm (I); «Fyodor Litke», Chukchi Sea, station 54, ventral view, 9 mm (J); «Krasin», Chukchi Sea, station 44, ventral view, 7.8 mm (K); «Sadko», Laptev Sea, station 21, identified by G.P. Gorbunov as Cylichna insculpta, ventral view, 8.5 mm (L). Scale bar: C – 2 mm.

Fig. 2. Cylichnoides validus: radula (K), lateral teeth (A, B, D) and rachidian teeth (C, E, F, I); gizzard plate (J); shell sculpture (G, H); penis (L). A, I – Laptev sea, «Sadko», station 21; D, E, G, J – Chukchi sea, «Fyodor Litke», station 55; B, C, F, H, K – Chukchi sea, «Fyodor Litke», station 54; L – «Vega» expedition.Abbreviations: a – atrium, a.pr – additional prostate, pr – prostate, p.s – penial sheath. Scale bar:A, C, D, J – 50 µm; B, K – 100 µm; G, H – 200 µm; I – 40 µm; E, F – 10 µm; L – 0.5 mm.

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.