Cylichnoides sp. 1

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 : 21

Cylichnoides sp. 1 .

Figs 4M ; 5J–O

Material studied. Chukchi Sea : Wrangel Isl., icebreaker «Fyodor Litke», 01.IX.1929, station 44 – 1 specimen, collected by P. V. Ushakov .

D e s c r i p t i o n. This shell has an almost straight columellar margin ( Fig. 4M ), very fine spiral sculpture, pale yellow periostracum and unusual rachidians. Spiral sculpture ( Fig. 5O ) consists of the weak straight striae equally close over the whole shell, mostly at regular distances from each other. These striae alternate with two more weak striae, which can be seen more clearly at the electron microscopy images. The height of the shell is 7.8 mm. Radula ( Fig. 5J–N ) has formula 10x2:1:1:1:2, lateral teeth with 20–24 regularly spaced curved denticles, which descend to the base of the tooth. Rachidian teeth equipped with the long curved denticles tapering with 1–4 filiform ends. Cutting edge is a simple rounded form. Lateral edges not rolled.

N o t e s. The species differs from other species of Cylichnoides in shell sculpture and rachidian teeth morphology. Rachidian tooth is equipped with long curved denticles tapering with 1–4 thread ends.

Figures

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.