Lepidozona acostata Sirenko, 2016

Sirenko, B. I., 2016, New and rare species of the genus Lepidozona (Mollusca: Polyplacophora) from the South China, East China and the Philippine seas, The Bulletin of the Russian Far East Malacological Society 20, pp. 28-46 : 36-40

Lepidozona acostata Sirenko sp. nov.

Figs. 8–10 , 15D, E urn:lsid:zoobank.org:act:12EAC1B4-B6C5-4506-BCA2-81FD6DFE50E0

T y p e m a t e r i a l. Holotype ( ZISP no. 2293), now disarticulated, consisting of mount of part of girdle and radula, vail with valves, part of radula and part of girdle, and 1 paratype ( ZISP 2294 ).

T y p e l o c a l i t y. South China Sea, 10 ° 33 ′ N, 109 ° 43 ′ E, depth 310 m.

E t y m o l o g y. The name is Latin for ‘without ribs’, in reference to the head valve which has no radial ribs.

M a t e r i a l e x a m i n e d. South China Sea ,near Vietnam, R / V Odissey, trawl 59, 10 ° 33 ′ N, 109 ° 43 ′ E, depth 310 m, holotype ( ZISP no. 2293), BL 8.0 mm, 1 paratype ( ZISP 2294 ), BL 4.5 mm, 24.09.1984, leg. B. Sirenko; Taiwan: TAIWAN 2001, Fishing Boat Chung Tung Long No. 26, stn CP 72, 24 ° 52.3 ′ N, 122 ° 04.5 ′ E, depth 760 m, 1 spm, BL 7 mm, 06.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 76, 24 ° 56.5 ′ N, 122 ° 01.5 ′ E, depth 115–170 m, 1 spm, BL 11 mm, 07.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 79, 24 ° 50.4 ′ N, 121 ° 59.9 ′ E, depth 145–200 m, 1 spm, BL 9 mm, 08.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 89, 24 ° 53.6 ′ N, 122 ° 01.4 ′ E, depth 310–420 m, 2 spms, BL 4.5–12.0 mm, 09.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 91, 24 ° 50.6 ′ N, 122 ° 01.4 ′ E, depth 400 m, 6 spms, BL 7–11 mm, 10.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 98, 24 ° 54.2 ′ N, 122 ° 02.9 ′ E, depth 362–400 m, 2 spms, BL 6.5–11 mm, 18.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 107, 24 ° 48.2 ′ N, 122 ° 11.3.0 ′ E, depth 335–420 m, 4 spms, BL 4–6 mm, 20.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 109, 24 ° 48.3 ′ N, 122 ° 84.0 ′ E, depth 246–256 m, 6 spms, BL 6–11 mm, 20.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 109, 24 ° 48.3 ′ N, 122 ° 84.0 ′ E, depth 246–256 m, 6 spms, BL 6–11 mm, 20.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 110, 24 ° 48.3 ′ N, 122 ° 04.0 ′ E, depth 316–350 m, 4 spms, BL 10–12 mm, 20.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan; stn CP 115, 24 ° 53.9 ′ N, 122 ° 02.0 ′ E, depth 381–440 m, 3 spms, BL 9–10 mm, 21.05.2001, leg. Ph. Bouchet, Richer, IRD and Chan .

D i s t r i b u t i o n. South China Sea , near Vietnam, and East China Sea, near Taiwan, 170–760 m.

D i a g n o s i s. Animal of small size, oval, moderately raised, carinated, valves not beaked. Head valve without radial ribs, sculptured with granules arranged quincuncially, lateral areas of intermediate valves sculptured like head valve and bearing up to 3 small rounded tubercles. Apophyses connected with rather long, not interapted jugal plate. Postmucronal slope of tail valve convex. Dorsal scales with 9–12 obsolete ribs and with a very short striated, nipple-like prolongation near the top. Central tooth of radula narrow, bulging at the base, narrowed in the middle, distally widening to a strong convex blade, head of major lateral tooth bidentate, outer denticle rather smaller than inner one.

D e s c r i p t i o n. Holotype 8.0x 4.6 mm, valves moderately elevated (dorsal elevation 0.56), carinated, not beaked. Color of tegmentum uniform cream to pale yellow, peppered with brown spots.

Head valve semicircular, slightly wider than tail valve, hind margin widely V-shaped, notched in the middle, tegmentum sculptured with very small, shallow pits arranged in a random manner. Intermediate valves broadly rectangular, front margin concave in the jugal part, convex at the pleural parts which are somewhat narrowing towards the sides, side margins slightly rounded, posterior margin about straight, central areas sculptured with small shallow pits arranged in a random manner in jugal part and in longitudinal rows in pleural parts, lateral areas weakly raised, sculptured with flattened diagonal rib ornamented with 2–3 round, elevated pustules. Tail valve with anterior mucro, antemucronal slope slightly convex, postmucronal slope little concave, antemucronal area sculptured like central area of intermediate valve, postmucronal area sculptured like head valve.

Articulamentum white, smooth, apophyses small, triangular, connected across the shallow sinus by a short, concave, distally slightly denticulated jugal plate, slit formula 10/1/9, slit rays indicated, not prominent, teeth short.

Girdle narrow (0.7 mm wide near valve V), dorsally covered with slightly bent, small, obsoletely longitudinally ribbed (9–12 ribs) scales (167x130) with a very short, striated nipple-like prolongation near the top. Marginal spicules of several kinds: long smooth needles (155x14 μm), flattened spicules, grooved in two directions (feather-lile) (80x18 μm), wedge-shaped, obliquely grooved spicules (58–60x23 μm), numerous, small, blunt-topped spicules (40x10 μm), small, narrow, smooth spicules (40x8 μm), bluntly pointed, smooth scales (60x20 μm) and triangle scales with one short rib on top. All marginal spicules embedded in a short chitinous sheath. Ventrally girdle covered with long rectangular scales (85x13 μm).

Radula of holotype 2.7 mm long with 31 transverse rows of mature teeth. Central tooth elongate, slightly pinched in the middle, widening to a strong blade, major lateral tooth with sharply pointed bidentate head, interior denticle the longest.

Fourteen gills per side arranged from valve IV to valve VII.

R e m a r k s. The new species is very similar to Lepidozona reevei Kaas et Van Belle, 1987 from « Japan », but differs from it by having tegmentum sculptured with very small, shallow pits arranged in a random manner (vs. tegmentum sculptured with numerous obsolete, radial riblets in L. reevei ), central areas sculptured with small shallow pits arranged in a random manner in jugal part and in longitudinal rows in pleural parts (vs. central areas with numerous, very fine, longitudinal, interrupted grooves in L. reevei ), flattened diagonal rib of intermediate valve ornamented with 2–3 round, elevated pustules (vs. no pustules in L. reevei ), anterior mucro (vs. central mucro in L. reevei ). Morover L. reevei is twice the size (up to 24 mm) of L. acostata sp. nov. (up to 12 mm).

An intermediate valve of a specimen from the Suruga Bay, illustrated in Saito [1997] ( Fig. 13 ) is very similar to L. acostata sp. nov. and may be belong to it. In that case the type locality of L. reevei will be in question; the vague locality « Japan » was provided at the commercial purchase of the type material by the original authors and was considered with reservation [ Kaas, Van Belle, 1987].

Figures

Fig. 8. Lepidozona acostata, holotype, BL 8 mm, south Vietnam, R/V Odissey, trawl 59, 310 m, on sunken wood; A – valve I, dorsal view; B – valve V, dorsal view, C – valve VIII, dorsal view; D – valve V, ventral view; E – valve V, detail of tegmentum in central area; F – valve VIII, lateral view; G – valve IV, rostral view.

Fig. 9. Lepidozona acostata, holotype, BL 8 mm, south Vietnam, R/V Odissey, trawl 59, 310 m, on sunken wood; A, C – dorsal scales; B – dorsal scales, marginal spicules and scales, ventral scales; D – radula.

Fig. 10. Lepidozona acostata, holotype, BL 8 mm, south Vietnam, R/V Odissey, trawl 59, 310 m, on sunken wood; A, B – dorsal scales; C–I – marginal needle, scales and spicules; J – ventral scale; K – central and lateral teeth of radula; L – head of major lateral tooth of radula. Scale bar 100 µm.

Fig. 15. Color images of species of genera Lepidozona. A – Lepidozona bisculpta, BL 8 mm, Vietnam, Tonkin Bay, 6–7 m, on old corals; B – Lepidozona bisculpta, with 5 valves, BL 8 mm, Vietnam, Tonkin Bay, 6–7 m, on old corals; C – Lepidozona bisculpta, with 7 valves, BL 8 mm, Vietnam, Tonkin Bay, 6–7 m, on old corals; D – Lepidozona acostata, holotype, BL 8 mm, south Vietnam, R/V Odissey, trawl 59, 310 m, on sunken wood; E – Lepidozona acostata, paratype, BL 8 mm, south Vietnam, R/V Odissey, trawl 59, 310 m, on sunken wood; F – Lepidozona excellens, holotype, BL 18.0 mm, Philippine Sea, R/V Odissey, stn 37, 380–420 m.

Fig. 13. Lepidozona excellens, holotype, BL 18.0 mm, Philippine Sea, R/V Odissey, stn 37, 380–420 m; A, B – radula.