Notoplax conica Is. & Iw. Taki, 1929

Sirenko, Boris I. & Saito, Hiroshi, 2017, New species of chitons of the superfamily Cryptoplacoidea (Mollusca: Polyplacophora) from Vietnamese waters, Zootaxa 4299 (4), pp. 451-506 : 453-455

Notoplax conica Is. & Iw. Taki, 1929

Figs 1–4 , 43 A

Notoplax (Ikedaëlla) conicus Is. & Iw. Taki, 1929: 46 –50, pl. 2, figs 7–9, textfigs 1–6. Notoplax (Ikedaella) conica: Bergenhayn, 1933: 51 , pl. 1, fig. 15, textfig. 15a–c; Is. Taki, 1962: 38; Iw. Taki, 1964: 413; Higo & Goto, 1993: 10.

Notoplax conica: Kaas & Van Belle, 1980: 30 ; 1998: 50; Saito, 1998: 158, fig. 2K; 2000b: 21, pl. 10, fig. 3; 2006a: 216; Higo et al., 1999: 30; Slieker, 2000: 100, pl. 38, fig. 29.

Type material. Not located:? ” Shanghai Science Institute”, Shanghai, China ( Taki, 1962).

Type locality. Near Kashima, Tanabe Bay, Kii Peninsula, in a crevice of a massive coral, water depth 1.5–1.8 m (about 1 fathom).

Material examined. Southern Vietnam, Nha Trang Bay, Tre Island, 12°07.387’N, 109°00.189’E, 0–0.5 m, on oysters and barnacles,1 spm, BL 10 mm, 0 4.05.2015, leg. B. Sirenko.

Description. Animal small, oblong in outline. Valves small, rather low. Color of tegmentum light brown with greenish tint on jugum and radial ribs on valves I, V–VII, dark brown with light brown jugum on valves II–IV and VIII, pinkish tint on all apices. Girdle ivory with buff brown maculation.

Tegmentum small, width almost same in valves IV–VII. Head valve semicircular with five radiating rows of large convex pustules; posterior margin widely V-shaped. Intermediate valves roughly pentagonal in outline, wider than long, with rather low, round dorsum; lateral areas separated from pleural areas by radiating rows of large convex fused pustules; front margin straight between apophyses, straight to slightly convex in pleural areas; hind margin slightly concave; side slope straight; jugum wedge-shaped in valve II, nearly parallel sided in valves III– VIII, with rather irregular longitudinal riblets of fused pustules and pustular side margins. Tail valve round in outline; mucro raised, located slightly posterior to the center; posterior area with radiating ribs; posterior slope slightly convex.

Jugal macraesthetes arranged on each riblet. Each macraesthete accompanied by several micraesthetes that are also distributed in the grooves between the riblets. Pustules on pleural area droplet-shaped, flat or slightly concave, those on lateral areas and diagonal ribs apparently convex. Each pustule with 1–2 macraesthetes and several micraesthetes around each macraesthete. Tegmental plain with many fine, commarginal wrinkles and micraesthetes.

Articulamentum well developed, moderately thick, white in color. Apophyses large, separated by widely Vshaped sinus; anterior margin round in intermediate valves, truncate in tail valve. Insertion plates long in head valve, moderately long in remaining valves. Slits U-shaped, each accompanied by shallow groove, extending from the edge of the tegmentum. Slit formula 6/1/6.

Girdle rather wide, dorsally densely covered with tiny flattened pointed spicules, 30–40 µm x 10 µm, scattered straight or often curved needles, 65–115 µm x 10 µm. Sutural tufts with long needles up to 600 µm x 17 µm. Marginal needles similar to sutural tuft needles but smaller, 200 µm x 15 µm. Ventral side beset with flattened pointed spicules, 80–94 µm x 15-18 µm.

Gills extending from valves VII to IV, composed of 6 ctenidia on each side.

Radula 3.3 mm long with 29 transverse rows of mature teeth. Central tooth large, asymmetrically squarish, shallowly concaved, bilobed at base. First lateral (centro-lateral) tooth with thin, weakly notched antero-dorsal corner. Major lateral tooth large, tricuspid; cusps sharply pointed, median one larger than others. Major uncinual tooth with narrow blade.

Distribution. Reported only from southern Japan and now Nha Trang Bay, southern Vietnam.

Remarks. Taki (1962) mentioned that he heard his collection of chiton specimens was deposited in the former “ Shanghai Science Institute” after the World War II in 1953. The building is now used as the Shanghai Institute for Biological Science, Chinese Academy of Sciences. We have located neither the collection nor the type material.

Figures

FIGURE 1. Notoplax conica, Southern Vietnam, Nha Trang Bay, Tre Island, BL 10 mm: A. Valve I, dorsal view; B. Valve II, dorsal view; C. Valve V, dorsal view; D. Valve VIII, dorsal view; E. Valve IV, ventral view; F. Valve V, detail of tegmentum in jugal and lateropleural areas; G. Valve II, rostral view; H. Valve V, rostral view; I. Valve VIII, lateral view.

FIGURE 2. Notoplax conica, Southern Vietnam, Nha Trang Bay, Tre Island, BL 10 mm: A. Valve II, detail of tegmentum in jugal and lateropleural areas; B. Sutural tufts; C, D. Tuft, dorsal needles and spicules.

FIGURE 3. Notoplax conica, Southern Vietnam, Nha Trang Bay, Tre Island, BL 10 mm: A, C. Dorsal spicules; B. Ventral spicules; D. Radula.

FIGURE 4. Notoplax conica, Southern Vietnam, Nha Trang Bay, Tre Island, BL 10 mm: A. Needles of tufts; B. Dorsal needles; C. Dorsal spicules; D. Marginal needle; E. Ventral spicules. F. Central and first lateral teeth of radula; G. Head of major lateral tooth of radula; H. Pustule of lateropleural areas of tegmentum with aesthete pores (not to scale). Scale bars: 100 µm.

FIGURE 43. Images of species of genera Notoplax and Leptoplax: A. Notoplax conica, Southern Vietnam, Nha Trang Bay, Tre Id, BL 10 mm; B. Notoplax odysseyi n. sp., Southern Vietnam, Off Phan Rang, 95 m, on old corals, holotype, BL 51 mm; C. Leptoplax nhatrangi n. sp., Nha Trang Bay, Dat Id., 7 – 12 m, on shells of Malleus malleus, holotype, BL 5.2 mm; D. Leptoplax doederleini, Vietnam, Nha Trang Bay, Dat Id., intertidal, under stones, BL 15 mm; E. Leptoplax tongkingi n. sp., Gulf of Tongking, Cat Ba Id., 3 – 4 m, on shells, paratype, BL 5 mm.