Cylichnoides occultus ( Mighels et Adams, 1842 )

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 : 14-18

Cylichnoides occultus ( Mighels et Adams, 1842)

Figs 3C ; 4A–L ; 5A–I

Bulla occulta Mighels et Adams, 1842, p. 54 , pl. 4, fig. 11.

Cylichna occulta ( Mighels et Adams, 1842) : Pilsbry, 1893, p. 292 (part.), pl. 28, fig. 36; Minichev, 1977, p. 428, fig. 1; Golikov, 1994, p. 81 (part); Golikov, 1995, p. 58 (part.); Malutin, 2006, p. 182.

Cylichnoides occulta ( Mighels et Adams, 1842) : Chaban, 2001, p. 108; Chaban, 2008, p. 153 –154 (part); 2010, p. 74–75, fig. 6.3A.

Bulla reinchardti Møller, 1842, p. 6 ; Schiotte, Warén, 1992, p. 12, fig. 5 (syntype).

Cylichna reinhardti (Møller, 1842) : Leche, 1878, p. 73, pl. 1, fig. 21; Odhner, 1907, p. 51; Odhner, 1915, p. 227.

Cylichna solitaria (Say, 1822) : Herzenstein, 1885, p. 705 –706 (non Say, 1822).

Type locality. Westbrook in the vicinity of Portland, Maine, USA.

Type s p e c i m e n s. Lectotype of Bulla occulta Mighels et Adams, 1842 (fossil): MCZ 156452 [ Johnson, 1949]; 2 syntypes of Bulla reinhardi Møller, 1842 : ZMUC GAS- 84 (in alcohol) [ Schiøtte, Warén, 1992, p. 12, fig.5].

Material studied. Chukchi Sea: «Vega» expedition, 1876, Chukchi Sea, det. Kaszczenko as Cylichna reinhardi – 17 specimens; icebreaker «Vaygach», 1911, Chukchi Sea, no data, identified by G.P. Gorbunov as Cylichna insculpta var. reinhardti – 24 specimens; icebreaker «Fyodor Litke», 07.IX.1924, Wrangel Il., station 44, collected by P. V. Ushakov – 3 specimens; 22.VIII.1976, Wrangel Isl., Rodzhers Bay, station 4, depth 2–4 m, collected and identified by A.N. Golikov – 20 specimens; 22.VIII.1976, Wrangel Il, Rodzhers Bay, station 4, 3–4 m depth, collected and identified by A.N. Golikov – 25 specimens; Greenland: 4 specimens, collected near Greenland, labelled as Bulla insculpta (= Bulla reinhardi ); Franz-Iosiph Land, Heiss Isl., station 441, depth 5–7 m, 6.VIII.1981, collected by V. Averintsev – 11 specimens.

Diagnosis. Shell ovate-cylindrical, apex not umbilicated, columellar margin without fold, spiral sculpture consist of regularly spaced weak narrow spiral grooves and ribs. Lateral teeth with 22–24 uneven denticles, which do not descend in to the base of the tooth; rachidians equipped with 9–12 denticles (on one lobe), which have triangular 1–2 tips. Lateral sides of rachidian tooth rolled, upper-lateral ends with notch, sometimes ear-shaped. Male copulatory system consists of a narrow prostate joined with lateral side of the small penial sac, which does not reach to the end of the prostate.

D e s c r i p t i o n. Shell from 3 to 11.3 mm height; ovate-cylindrical, apex not umbilicated, columellar margin without fold, spiral sculpture consists of regularly alternating weak narrow spiral grooves and ribs (16–18 grooves per 1 mm of shell) ( Fig. 5I ). Shell variability is presented on Fig. 4A–L .

Anatomy. Inner lateral teeth with 22–24 uneven denticles, which do not form a plate on the base of the tooth; outer laterals with the fine serration. Bilobate convex rachidians equipped with 9–12 denticles (on one lobe), which have 1–2 triangular tips. Internal surface with median crest ( Fig. 5F ). Lateral sides of rachidian tooth rolled, upper-lateral ends with notches, sometimes ear-shaped ( Figs 5A–I ). Male copulatory system consists of a narrow prostate joined with lateral side of the small penial sac that is filled with muscular folds ( Fig. 3D ).

D i s t r i b u t i o n. Circumpolar.

N o t e s. Lectotype of B. oculta was designated by Johnson [1949] but this specimen was not figured; syntypes of B. reinhardi were designated and figured by Schiøtte and Warén, [1992]. Description and drawing of shell morphology, radula and male copulatory system of C. occultus from Frantz-Joseph Land is given by Minichev [1977]. Specimens from that locality have 26–32 denticles on rachidian tooth. C. validus differs from C.occultus in shell and radular morphology.

Specimens from the Chukchi Sea, collected during the «Vega» expedition (identified by Kaszczenko, as Cylichna reinhardi , Fig. 3D ) and during the expedition of the ZISP, 1976 (identified by Golikov as Cylichna occulta ) correspond to description of B. occulta by Mighels and Adams and to imaging of the syntype of B. reinhardi . They are represented by specimens 3–5 mm (as type of B. occulta ) – 8–8.5 mm in height. Mighels and Adams [1842] state «this shell is the analogue of, B. triticea Couth. It however differs from that species in being proportionately wider». Bulla triticea Couthouy, 1838 has a cylindrical shell [Couthouy, 1838, pl. II, fig. 8] but B. occulta have been figured by Mighels and Adams [1842. pl. 4, fig. 11] as oval. Unfortunately, the lectotype of B. occulta is in poor condition [ Clench, Turner, 1950]. Pilsbry [1893] considered scalpta and reinhardi as synonyms of occulta , but noted that the first may be distinct. We consider both B. reinhardi and B. scalpta to be different species and based on the illustrations of B. occulta [ Mighels, Adams, 1842] and of the syntype of B. reinhardi , we regard the first as a senior synonym of the second.

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. 4. Cylichnoides occultus, shell: Chukchi Sea, Wrangel Isl., «Fyodor Litke», station 44 (A – 8.5 mm, ventral view); Wrangel Isl., Rodzhers Bay, station 4 (8.0 mm – B, 7.0 mm – C, ventral view); Greenland, identified previously as Cylichna insculpta (=Cylichna reinhardti) (8.0 mm – E, 6.5 mm – F); «Vega» expedition, 1876 (H – 4.0 mm, G – 5.0 mm, ventral view and D – apical view); Frantz Joseph Land (I – 7.2 mm, ventral view and J – apical view); K, L – Chukchi Sea, De Long Strait (K – apical view and L – 8.0 mm, ventral view); Cylichnoides sp. 1: «Fyodor Litke», station 44, Chukchi Sea, Wrangel Isl. (M – 7.8 mm).

Fig. 5. Cylichnoides occultus: radula (A – internal lateral teeth, B – F, H – rachidian teeth, G – outer lateral teeth) and shell sculpture (I) of the specimens collected in the Chukchi Sea, Wrangel Isl. (A–E, I – 1976; F–H – 1924). Cylichnoides sp. 1: radula (J, K, N – rachidian teeth, L – outer lateral teeth, M – internal lateral teeth) and shell sculpture (O). Scale bar: A, G, K, L – 50 µm; B, C, H – 30 µm; D, E, N – 10 µm; F, J – 20 µm; I – 200 µm; M – 40 µm; O – 100 µm.