Notoplax odysseyi, Sirenko & Saito, 2017

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 : 455-459

Notoplax odysseyi n. sp.

Figs 5–8 , 43 B

Type material. Holotype, ZISP 2240, now disarticulated consisting of mounts of shell, perinotum and radula and 2 paratypes, ZISP 2241.

Type locality. Off Phan Rang , southern Vietnam, 11°26´N, 109°15´E, 95 m, on dead coral skeleton.

Etymology. Named after the R/V Odyssey of the Russian Academy of Science.

Material examined. Southern Vietnam, off Phan Rang, 11°26´N, 109°15´E, 95 m, dead coral skeleton, #53 cruise of R/ V Odyssey, trawl st. 48, holotype, BL 51 mm and two paratypes, BL 15–60 mm, 19.09.1984, leg. B. Sirenko.

Diagnosis. Large chiton with fleshy girdle completely encroaching between small valves. Tegmentum of intermediate valves greatly extended forward, with very narrow jugum. Color of tegmentum light brown with maculation of light gray and brown. Dorsal side of girdle densely covered with fine, sharply pointed needles which give shiny and hairy appearance to the girdle.

Description. Animal large, oval, moderately elevated. Valves small, completely encroached by fleshy girdle. Color of tegmentum light brown with maculation of light gray and brown. Girdle buff with shine from dense spicules.

Head valve more than semicircular with five radiating rows of large pustules; anterior margin concave between radial ribs; posterior margin nearly straight. Intermediate valves roughly elongate-pentagonal, moderately elevated, subcarinated; anterior margin round at anterior end of jugum, slightly concave between jugum and distal end of diagonal line; hind margin almost straight or slightly convex at both sides of hardly projecting apex; jugum very narrow wedge-shaped, raised, smooth on surface except for fine growth lines, with serrated side margins; rather wide lateral areas separated from pleural areas by raised ribs on diagonal line. Tail valve droplet-shaped, wider than head valve, with subcentral, raised mucro; posterior slope convex, with five weak radiating ribs.

Pustules on tegmentum droplet-shaped or elongate oval, densely packed, often larger on radial ribs; top of pustules flat or slightly concave; each pustule with 1–3 macraesthete pores and no micraesthete pores on top, several minute micraesthete pores in front of prepustular slope; no micraesthete pores on other area of tegmental plain.

Articulamentum well developed, white with rose in middle part, with transverse callus in posterior part, minute pores under jugum. Apophyses large, long, rounded at anterior margin in intermediate valves, roughly truncated in tail valve. Insertion plate exceedingly long, with rather wide slits; outer surface forming ridges from distal end of radial ridges to slits. Slit formula 5/1/4.

Girdle fleshy, very wide, ca. 11 mm near valve V (width of tegmentum 5.6 mm). Dorsal side of girdle, densely beset with long, curved, smooth, sharply pointed needles, 328–670 µm x 16–28 µm. Sutural tufts of up to 40 straight, smooth needles, attaining 730 µm x 40 µm. Ventral spicules flat, smooth, bluntly pointed, 85–210 µm x 16 µm.

Gills extending from valve VII to valve IV, composed of 22 ctenidia on each side.

Radula 13 mm long with 33 transverse rows of mature teeth. Central tooth rectangular, asymmetrical with bilobed base. First lateral (centro-lateral) tooth with thin, weakly notched antero-dorsal corner. Major lateral tooth with tricuspid head; cusps sharply pointed; central cusp slightly longer than others. Major uncinal tooth long, narrow.

Distribution. Only known from the type locality, off Phan Rang, Southern Vietnam.

Remarks. This species resembles ' Notoplax hilgendorfi ' (misidentified, not the species reported by Thiele 1909) reported from Hyotan-se bank, northern Izu Islands, the Pacific coast of central Japan ( Wu & Okutani 1995), which appears to be identical with Notoplax sp. from Sagami Bay, the Pacific coast of central Japan ( Saito 2006a) but the present species differs from the Japanese species by having wider ventral spicules and longer major uncinal teeth of the radula.

Figures

FIGURE 5. Notoplax odysseyi n. sp., Southern Vietnam, Off Phan Rang, holotype, BL 51 mm: A. Valve I, dorsal view; B. Valve V, dorsal view; C. Valve VIII, dorsal view; D. Valve VIII, lateral view; E. Valve IV, detail of tegmentum in jugal and lateropleural areas; F. Valve V, rostral view; G. Valve VI, ventral view.

FIGURE 6. Notoplax odysseyi n. sp., Southern Vietnam, Off Phan Rang, holotype, BL 51 mm: A, C. Valve IV, detail of tegmentum in jugal and lateropleural areas; B, D. Valve IV, detail of tegmentum in lateropleural area.

FIGURE 7. Notoplax odysseyi n. sp., Southern Vietnam, Off Phan Rang, holotype, BL 51 mm: A. Pustules on the front edge of valve IV; B. Needles of tuft; C. Dorsal needles; D. Radula.

FIGURE 8. Notoplax odysseyi n. sp., Southern Vietnam, Off Phan Rang, holotype, BL 51 mm: A. Needle of tufts; B. Dorsal needles, C. Ventral spicules, D. Head of major lateral tooth of radula; E. Central and first lateral teeth of radula; F. Pustule of lateropleural areas of tegmentum. 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.