Leptoplax duongae (Carpenter MS) Dall, 1882

Sirenko, B. I., 2024, Molluscs of the genus Leptoplax (Mollusca: Polyplacophora) from Spratly Islands, South China Sea, Ruthenica, Russian Malacological Journal (Stockholm, Sweden: 1987) 34 (1), pp. 7-14 : 11-13

Leptoplax duongae sp. n.

( Figs 5–7)

Zoobank registration: urn:lsid:zoobank.org:act: 7D2A0A51-5708-47D8-AFC3-FBB93EA086A1

Type material. Holotype, ZIN 2570, now disarticulated consisting of mounts of shell, perinotum and radula.

Type locality. South China Sea, Spratly Islands, 10°10’17’’N, 114°21’59’’E, 10 m, on old corals.

Etymology. Named after Hoang Thuy Duong, the leader of the expeditions to Spratly Islands who helped me to collect this material.

Material examined. South China Sea, Spratly Islands, 11°23’45’’N, 114°35’15’’E, 14–15 m, SCUBA, sand, 1 head and 1 intermediate valves, ZIN 2571 , 25.11.2018, leg. B. Sirenko ; Spratly Islands, 10°10’17’’N, 114°21’59’’E, 10 m, SCUBA, on old corals, holotype ZIN 2570 , BL 4.0 mm, 05.12.2018, leg. B. Sirenko.

Diagnosis. Small oblong-oval chiton, moderately elevated, with distinctly elevated broad jugum. Pleural areas sculptured with roundish to less often oval small convex pustules arranged irregularly quincuncially. Intermediate valves carinated, beaked. Tail valve with central mucro. Girdle dorsally densely clothed with sharply pointed short and long ribbed spicules. Central tooth of the radula is markedly expanded in the lower half and with a relatively narrow blade above, major lateral tooth with a tridentate cusp, the median denticle largest.

Description. Animal small, elongate oval, moderately elevated (dorsal elevation 0.32). Color of tegmentum dirty-white with brown spots on pleural areas, jugal area olive-colored.

Head valve semicircular with roundish, small, convex pustules (about 50 µm) arranged irregularly quincuncially. Intermediate valves roughly rhombic, moderately elevated, carinated, beaked; jugum more or less smooth, wedge-shaped, broad and distinctly elevated, front margin concave between apophyses in valve II and straight in other intermediate valves; hind margin concave at both sides of strong beak.Tail valve oval, narrower than head valve, with central, low mucro; antemucronal area straight, posterior slope concave.

Top of each pustule with 1 megalaesthete and 2–3 micraesthetes. Micraesthete pores sparsely distributed also on tegmental plain.

Articulamentum moderately developed, white, with transverse callus in middle of valves, several large pores under anterior margin of jugum, numerous minute pores under remaining part of jugum. Apophyses wide, long, rounded at anterior margin in intermediate valves, truncated in tail valve. Insertion plate short with short, rather wide slits; slit formula 5/1/3.

Girdle dirty-white, rather wide. Dorsal side of girdle densely clothed with sharply pointed, short and long, ribbed spicules (40–90 µm x 8–14 µm). Sutural tufts of up to 10 straight, smooth needles (200–800 μm x 8–10 μm) surrounded by thick, smooth pointed spicules (35 μm x 15 μm). Marginal needles sharply pointed, distinctly ribbed (120 μm x 17 μm). Ventral spicules flat, with 1–2 riblets on a lower side (65 μm x 25 μm).

Radula 1.4 mm long with 31 transverse rows of mature teeth. Central tooth of the radula is markedly expanded in the lower half and with a relatively narrow blade above, major lateral tooth with a tridentate cusp, the median denticle largest.

Distribution. Only known from the Spratly Islands.

Remarks. The present species closely resembles Leptoplax nhatrang i Sirenko et Saito, 2017, L. tongkingi Sirenko et Saito, 2017, L. richardi (Kaas, 1990) and L. doederleini (Thiele 1909) in shell morphology, such as outline of the valves.

The new species differs from L. nhatrangi by the jugum, which in the new species is broader and less sharply separated from the pleurolateral areas; rounded rather than oval pustules on the pleurolateral areas; absence of a notch on the anterior margin of the apophyses in the tail valve.

L. duongae sp. nov. differs from L. tongkingi by rounded rather than oval pustules on the pleurolateral areas; absence of a notch on the anterior margin of the apophyses in the tail valve; less ribbed and shorter ventral spicules; slit formula 5/1/3 (vs. 5/1/ 9 in L. tongkingi ).

New species differs from, L. richardi by rounded rather than oval pustules on the pleurolateral areas; absence of a notch on the anterior margin of the apophyses in the tail valve; long and narrow dorsal spicules (vs. two kinds of spicules in L. richardi : short, ribbed with a very sharp top and long, bent, smooth).

L. duongae sp. nov. differs from L. doederleini by having round pustules (vs. elongate-oval in L. doederlein i); straight anterior margin of apophyses in the tail valve (deep concave anterior margin in L. doederleini ); ribbed dorsal spicules (vs. smooth dorsal spicules in L. doederleini ); slit formula 5/1/3 (vs. 5/1/ 8 in L. doederleini ).