Cryptoplax brunoi Saito, 2023

Sirenko, Boris I., Saito, Hiroshi & Nguyen, Tai-Tu, 2024, Chitons of the genus Cryptoplax (Mollusca: Polyplacophora) from the Spratly Islands, South China Sea, Zootaxa 5492 (1), pp. 52-70 : 58-61

Cryptoplax brunoi Saito, 2023

( Figures 2A , 6–8 )

Cryptoplax burrowi : Haddon 1886: 42 (in part), pl. 3 fig. 11; Pilsbry 1893: 54 (in part), pl. 9 fig. 7–10; Bednall 1897; 158 (in part, as doubtful record from South Australia); Thiele 1909: 56 (in part); Iredale & Hull 1925: pl. 12, fig. 32; Slieker 2000: 54, pl. 15, fig. 11; Schwabe 2005: 54, pl. 2, fig. 12. [all not of Chiton (Chitonellus) burrowi E. A. Smith 1884 ]

Cryptoplax brunoi Saito 2023: 48 , figs 1–4, 5A, B.

Cryptoplax plana : Granpoder et al. 2023: 75 (not of Cryptoplax plana Ang 1967 ).

Type material. Holotype, NSMT-Mo 82405

Type locality. Kuroshima Island , Yaeyama Islands, Ryukyu Archipelago, Japan, on reef .

Material examined. South China Sea, Spratly Islands, 10°10′17.0″N, 114°21′59.2″E, depth 3–30 m, SCUBA, washing off old corals, sample 17, 1 spm, ( ZIN 2450 ) BL 35.0 mm, B. Sirenko leg. 29.11.2018 .

Description. Based on young specimen (BL 35. 0 mm, ZIN 2450): Anterior four valves in contact, remaining valves separated from each other. Color of tegmentum pink with white streaks in terminal valves, brown in intermediate valves. Girdle light brown with brownish orange and white marginal fringe.

Head valve bell-shaped; tegmentum longer than wide, widest and shortest of all valves, sculptured with densely packed elongate pustules which are occasionally fused with neighboring ones. Valve II roughly oval, widest among intermediate and tail valves. Valves III–VIII narrow, spindle-shaped, of which valve VIII is the longest and valves VI is the shortest. Width of valves IV–VI almost same, narrower than other valves. Jugum wide wedge-shaped in valve II, narrow wedge-shaped in valves III and IV, almost parallel sided in remaining valves, nearly smooth on both surface and side margins. Pleurolateral area sculptured with longitudinal series of round to rectangular pustules, which are gradually increasing in size and fused into ribs anteriorly, and arranged in slightly divergent 6 rows in valves II, 3–5 rows in valves III–VIII. Tail valve with terminal mucro with very short post-mucronal area. Each pustule with 1–2 macraesthetes on top. Micraesthetes sparsely distributed along inner basal portion of riblets and prepustular area of pustules; no micraesthete on top of pustules.

Articulamentum of valves II–VII extending outward in anterior 4/5–5/6 of tegmentum in dorsal view. Insertion plates of head valve rather short, about 1/3 length of tegmentum. Insertion plate of tail valve wide, flared posteroventrally, with weak radial grooves on posterior surface. Slit formula 3/0/0. Color of articulamentum white with longitudinal rose stripe from jugum to apex in intermediate valves, white with rose spot in the middle in head valve, white in tail valve.

Girdle width moderate for genus. Dorsal side of girdle beset with minute slightly curved, strongly ribbed (7–9 double ribs) spicules, up to 90 μm x 30 μm, intermingling with large, club-shaped, finely grooved spicules, attaining 400 μm x 100 μm, and slender, parallel sided, finely grooved needles. Sutural tufts of up to 10–12 slightly curved, smooth or occasionally finely grooved blunt-tipped needles, up to 500 μm x 36 μm. Marginal needles numerous, similar to those of sutural tufts, but wider, up to 550 μm x 70 μm. Ventral spicules long, narrow with 8–9 ribs, up to 100 μm x 13 μm.

Gills extending from valve VI to valve VIII, composed of 20 ctenidia on each side.

Radula 7.2 mm long with 46 transverse rows of mature teeth. Central tooth small, narrow; posterior surface concaved in distal half, sharply keeled in basal one third, weakly angulate at top. Centro-lateral tooth with shallow groove at inner surface of antero-dorsal corner. Head of major lateral tooth with three denticles of nearly equal length, which have weak transverse ridgeline at the proximal portion of the cusps, and obtusely pointed. Major uncinal tooth narrow with obtuse tip, weakly keeled at posterior surface.

Distribution. Ryukyu Archipelago, southwestern Japan ( Saito 2023), Spratly Islands (present study), and Port Molle, North Queensland, Australia (E.A. Smith, 1884). Perhaps widespread in tropical and subtropical West Pacific.

Remarks. C. brunoi has long been confused with C. burrowi (E. A. Smith 1884) ( Saito 2023) , however, it differs from C. burrowi by having the tegmentum of the head valve being shortest of all valves (valves V–VII are clearly shorter than the head valve in C. burrowi ), narrower valves, especially obvious for valves II and IV, the flared articulamentum of the tail valve, brownish girdle lacking greenish maculation, and club-shaped larger dorsal girdle spicules (flat scales in C. burrowi ).

The sculpture of the two types of the dorsal girdle spicules is stronger in the present specimen than in the holotype.

Figures

FIGURE 2. Cryptoplax brunoi, Spratly Islands. A. (ZIN 2450), BL 35.0 mm. Cryptoplax burrowi, Spratly Islands. B. (ZIN 2451), BL 21.0 mm. Cryptoplax acerocostata n. sp., Spratly Islands. C. holotype (ZIN 2453), BL 15.0 mm. D. paratype (ZIN 2452), BL 12.0 mm. Scale: 2 mm for A–D.

FIGURE 6. Cryptoplax brunoi, Spratly Islands. A–K. (ZIN 2450), BL 35.0 mm. A. Valve I, dorsal view. B. Valve II, dorsal view. C. Valve III, dorsal view. D. Valve IV, dorsal view. E. Valve V, dorsal view. F. Valve VI, dorsal view. G. Valve VII, dorsal view. H. Valve VIII, dorsal view. I. Valve V, detail of tegmentum in jugal and pleurolateral areas. J. Valve V, rostral view. K. Valve VIII, lateral view.

FIGURE 7. Cryptoplax brunoi, Spratly Islands. A–D. (ZIN 2450), BL 35.0 mm. A. Marginal and ventral needles. B. Ventral needles. C. Dorsal spicules. D. Marginal needle.

FIGURE 8. Cryptoplax brunoi, Spratly Islands. A, B. (ZIN 2450), BL 35.0 mm. A. Radula. B. Central and first lateral teeth of radula.