Acanthochitona lanae, 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 : 484-489

Acanthochitona lanae n. sp.

Figs 30–32 , 44 D

Acanthochitona sp. Sirenko 2012: 98, pl. 14B, fig. 33.

Type material: Holotype, ZISP 2233, now disarticulated consisting of mounts of shell, perinotum and radula, 30 paratypes, ZISP 2234, BL 2–13 mm and 1 paratype, NSMT-Mo 78924, BL 5 mm.

Type locality. Near Da Nang, central Vietnam, 16°11.802´N, 108°10.593´E, intertidal, on barnacles.

Etymology. After the first author’s colleague Dr. Chan Than Lan who organized and led our field trip and was always thinking of the members of expeditions like her own children.

Material examined. Northern Vietnam, Gulf of Tongking , Cat Ba Id., 20°46.042´N, 107°05.800´E, intertidal– 1.5 m, rocks, 2 spms, BL 6–8 mm, 30.04.2012, leg. B. Sirenko ; 20°44.497´N, 107°04.098´E, 5–6 m, SCUBA, on shells of Pinna sp. or Isognomon sp., 1 spm, BL 7 mm, 0 1.05.2012, leg. B. Sirenko; 20°44.497´N, 107°04.098´E, 2 m, SCUBA, on red crustose calcareous algae, 2 spms, BL 5–6 mm, 0 1.05.2012, leg. B. Sirenko; 20°47.090´N, 107°06.103´E, 1–1.5 m, SCUBA, on shells of bivalve, 1 spm, BL 3 mm, 0 1.05.2012, leg. B. Sirenko; 20°45.445´N, 107°04.693´E, 0.5–1 m, SCUBA, on shells of bivalves with red crustose calcareous algae, 4 spms, BL 6–7 mm, 0 3.05.2012, leg. B. Sirenko; 20°43.675´N, 107°03.373´E, intertidal, under stones, 5 spms, BL 5–6 mm, 10.05.2014, leg. B. Sirenko. Central Vietnam, near Da Nang, 16°11.802´N, 108°10.593´E, intertidal, on barnacles, 32 spm: holotype, BL 8 mm and 31 paratypes, BL 2–13 mm, 16.05.2012, leg. O. Savinkin ; 16°09.332´N, 108°15.057´E, 7–8 m, SCUBA, on shells with barnacles, 1 spm, BL 5.5 mm, 19.05.2012, leg. O. Savinkin and E. Mekhova ; Son Cha Id. , 16°12.658´N, 108°12.105´E, 2–3 m, SCUBA, on small barnacles, 2 spm, BL 3–8 mm, 20.05.2012, leg. O. Savinkin ; 16°12.887´N, 108°11.906´E, 0–1 m, on barnacles, 1 spm, BL 14 mm, 16.04.2013, leg. B. Sirenko;16 °12.779´N, 108°11.938´E, 0–1 m, on barnacles, 2 spms, BL 6–7 mm, 19.04.2013, leg. B. Sirenko; 16 °12.649´N, 108°11.633´E, 0–1 m, on barnacles, 12 spms, BL 6–9 mm, 20.04.2013, leg. B. Sirenko; Me Id. , 19°22´59.9´´N, 105°54´52.2´´E, 6–10 m, SCUBA, on shells and stones, 1 intermediate valve, 14.04.2014, leg. O. Savinkin ; 19°23´02.8´´N, 105°55´36.7´´E, 4 m, SCUBA, on shells of Pinna sp., 13 spms, BL 4–7 mm, 14.04.2014, leg. P. Dgebuadze; 19°21´42.7´´N, 107°19´19.7´´E, 6 m, SCUBA, on barnacles, 1 spm, BL 11 mm, 16.04.2014, leg. S. Grebelny; 19°19´11.7´´N, 105°54´30.3´´E, 2 m, SCUBA, on barnacles and oysters, 9 spms, BL 3–9 mm, 17.04.2014, leg. S. Grebelny; Son Duong Id., 18°06´23.6´´N, 106°27´35.7´´E, 1–3 m, SCUBA, on barnacles, 14 spms, BL 8–12 mm, 21.04.2014, leg. S. Grebelny. Southern Vietnam, near Dat Id., 13°41.410´N, 109°13.577´E, intertidal, on oysters, 6 spms, BL 2–4 mm, 25.04.2013, leg B. Sirenko ; 13°41.037´N, 109°15.193´E, intertidal, on oysters, 2 spms, BL 3–7 mm, 28.04.2013, leg B. Sirenko.

Diagnosis. Small chitons with rather wide, low intermediate valves. Jugum of longitudinal rows of fused pustules. Tail valve small, semicircular, with central, low mucro. Pustules on lateropleural areas droplet-shaped or roughly diamond-shaped, quincuncially arranged; top of pustule flat, with single macraesthete pore, 0–2 micraesthete pores around macraesthete pore and 0–2 micraesthete pores on pre-pustular slope. No micraesthete pores on tegmental plain. Dorsal side of girdle beset with minute spicules which have rather strong riblets near the tip. Sutural tufts prominent, of thick, slightly curved, smooth needles.

Description. Animal small, elongate oval, low in profile. Color of tegmentum light green with brownish maculation or flecks on lateral and pleural areas; jugum white on midline bound with brown streaks at both sides. Girdle light brown with dark brownish bands around terminal valves and at sides of intermediate valves.

Head valve semicircular, posterior margin nearly straight; anterior slope slightly convex; no radial ribs. Intermediate valves rather wide, roughly rectangular, low, round-backed, beaked; front margin almost straight; hind margin slightly concave at both sides of beak; jugum wedge-shape, comprising of longitudinal rows of fused pustules; lateral areas slightly raised. Tail valve oval, with central, low mucro; width of tegmentum equal or less than half width of valve IV; posterior slope slightly convex.

Pustules on tegmentum rather densely distributed, arranged in quincunx order on all areas except for jugum. Each pustule flat or slightly concave at top with single macraesthete pore located slightly off centre towards prepustular slope, 0–2 micraesthete pores around macraesthete pore and 0–2 micraesthete pores on prepustular slope. No micraesthete pores on tegmental plain.

Articulamentum rather thin, white throughout except two small light brown spots on jugal part of intermediate valves, with transverse callus in middle of valves, porous under jugum: pores arranged in 10–12 longitudinal rows which are corresponding to longitudinal rows of fused pustules on the jugum. Apophyses well projecting forward, round, widely separated from each other in intermediate valves, truncated in tail valve. Insertion plate short with short, narrow slits. Slit formula 5/1/2.

Girdle rather wide, about 1.2 mm near valve V (width 2.7 mm), smooth in appearance. Dorsal side of girdle covered with minute spicules, 28–40 µm x 10–15 µm, somewhat flattened, with strong riblets at tip. Sutural tufts prominent, of up to 13 thick, sharply pointed, smooth or finely striate needles, which are up to 540 µm x 15 µm, surrounded by slenderer, sharply pointed, smooth spicules. Marginal needles lanceolate, depressed, up to 262 µm x 38 µm, smooth or finely ribbed. Ventral spicules small, 30–80 µm x 10–12 µm, flat, smooth, blunt at tip.

Gills extending from valve VII to valve IV, composed of 15 ctenidia on each side.

Radula 2.3 mm long, with 29 transverse rows of mature teeth. Central tooth with wide, almost straight cusp at top and keel at basal half. First lateral (centro-lateral) tooth with thick nodulous antero-dorsal corner. Major lateral tooth with tricuspid head; central cusp longest; cusps pointed, somewhat flattened near tips.

Distribution. Northern to southern Vietnam, from 20°47.090´N to 13 °41.037´N, intertidal– 7 m.

Remarks. This species differs from other Acanthochitona in the Indo-West Pacific area by the wide, rectangular intermediate valves which are sculptured with irregular rows of longitudinally fused pustules on the jugum, single macraesthete pore on each pustule top and the perinotum which is uniformly covered with minute, somewhat flattened spicules.

Figures

FIGURE 30. Acanthochitona lanae n. sp., Vietnam, near Da Nang, holotype, BL 8 mm: A. Valve I, dorsal view; B. Valve V, dorsal view; C. Valve VIII, dorsal view; D. Valve IV, ventral view; E. Valve V, detail of tegmentum in lateropleural area; F. Valve V, rostral view; G, Valve VIII, lateral view.

FIGURE 31. Acanthochitona lanae n. sp., Vietnam, near Da Nang, holotype, BL 8 mm: A. Valve VIII, detail of tegmentum in antemucronal area; B. Dorsal, marginal and ventral spicules, needles and spicules; C. Tufts, dorsal spicules, marginal needles and spicules and ventral spicules; D. Radula.

FIGURE 32. Acanthochitona lanae n. sp., Vietnam, near Da Nang, holotype, BL 8 mm: A. Needles of tufts; B. Dorsal spicules; C. Marginal needle and spicules; D. Ventral spicules; E. Head of major lateral tooth of radula; F. Central and first lateral teeth of radula; G. Pustule of lateropleural areas of tegmentum with aesthete pores. Scale bars: 100 µm.

FIGURE 44. Images of species of genus Acanthochitona and Cryptoplax: A. A. achates, near Da Nang, intertidal, on barnacles, BL 15 mm; B. A. biformis, Southern Vietnam, Cau Id., 13 – 17 m, on old shells, BL 11 mm; C. A condaoi n. sp., Gulf of Thailand, Vang Id., 9 – 11 m, on old shells, paratype, BL 6 mm; D. A. lanae n. sp., near Da Nang, intertidal, on barnacles, paratype, BL 12 mm; E. A. ostreaphila n. sp., Nha Trang Bay, Tre Island, Dambay Inlet, intertidal, mangrove community, on oysters, paratype, BL 12 mm; F. A. ostreaphila n. sp., Gulf of Tongking, Cat Ba Island, 0.5 m, on oysters, paratype, BL 5.5 mm; G. Cryptoplax burrowi, South China Sea, Macclesfield Bank, 21 m, BL 29 mm.