Lucilina nemirkoae Sirenko, 2019

Sirenko, Boris I., 2019, New chitons (Mollusca: Polyplacophora) of the genera Rhyssoplax, Lucilina and Onithochiton from shallow waters of Papua New Guinea, The Bulletin of the Russian Far East Malacological Society 23 (1 / 2), pp. 63-81 : 70-74

Lucilina nemirkoae Sirenko sp. nov.

Figs. 6–8

urn:lsid:zoobank.org:act:04BE4B58-AFE5-4F27-B020-5B570A1B25F8

Ty p e m a t e r i a l. Holotype (ZISP 2304) now disarticulated, consisting of mount of part of girdle and radula, vial with valves, part of radula and part of girdle.

Ty p e l o c a l i t y. Papua New Guinea, Bismarck Archipelago, Manus Island, Silver Sound , 02°01′ S, 146°53′ E, 1 m ( R / V Dmitriy Mendeleev, 18 cruise, sample 4, 27.01.1977) .

E t y m o l o g y. Named in honour of my wife Alena Nemirko who help me to live and to work.

D i s t r i b u t i o n. Only known from the type locality.

D i a g n o s i s. Animal of small size, shell rounded. Intermediate valves sinuate in anterior margin, concave in the jugal area, convex at side margins, evenly convex, not beaked in posterior margin. Tail valve slightly narrower than head valve. Tegmentum of head valve, lateral area of intermediate valves, and postmucronal area of tail valve smooth, only with growth line. Pleural areas with 8–9 very short and deep longitudinal, sometimes interrupted grooves along diagonal line. Insertion plates very short and smooth. Dorsal spicules small, blunt-topped, with 8–10 ribs around. Ventral scales more or less rectangular, ornamented around 8–10 distally converging riblets. Major lateral tooth bearing a cusp with 4 denticles.

D e s c r i p t i o n. Holotype of small size, BL 7.0 mm, elongate oval. Valves low (dorsal elevation 0.37), back rounded, side slopes convex, not beaked. Tegmentum light yellow with white spots.

Head valve semicircular, front slope convex, posterior margin widely V-shaped, shallowly notched in the middle. Intermediate valves more than twice as wide as long, anterior margin sinuate, concave in the jugal area, convex at the pleurae, posterior margin evenly convex not beaked, lateral areas slightly raised. Tail valve slightly narrower than head valve, anterior margin slightly concave, hind margin evenly convex, mucro posterior, hind slope almost steep, convex, antemucronal slope straight.

Tegmentum of head valve, lateral area of intermediate valves, and postmucronal area of tail valve smooth, only with well noticeable growth line. Pleural areas with 8–9 very short and deep longitudinal, sometimes interrupted grooves along diagonal line on each side.

Articulamentum white, apophyses triangular with rounded top in intermediate valves, and trapezoidal in tail valve, separated by a wide, deep, slightly concave, delicately dentate sinus (10–11 denticles in valves IV– VI). Slit formula 9/1/11, slit rays hardly or not indicated, teeth rather long, not pectinated, those of the tail valve much deformed, eaves narrow, porous.

Girdle dorsally covered with close-set small (45x21 µm), blunt-topped spicules, with 10–11 ribs around, and scattered curved needles (39–42x5 µm). Marginal spicules slightly ribbed, round-topped up to 79x17 µm. Ventral side of girdle clothed with more or less rectangular scales (25x21 µm), ornamented around 12–13 distally converging riblets.

Radula of the holotype was damaged, only the head of major lateral tooth is preserved, It has four denticles.

Due to the fact that the holotype was damaged, it was not possible to calculate the number of gills.

R e m a r k s. Despite the fact that this new species has a small size it looks like an adult chiton. Suffice it to recall a related species Tonicia disalvoi (Dell Angelo, Raines et Bonfitto, 2004) whose body length is two millimeters less. The present new species is most similar to Tonicia disalvoi that also has similar sculpture of tegmentum and not pectinated insertion plates, but differs from the latter in having ribbed ventral scales (vs. smooth scales in T. disalvoi ), posterior mucro (vs. anterior mucro in T. disalvoi ), jugal and most part of central area smooth (vs. with small pits in T. disalvoi ), and curved shape of intermediate valves (vs. broadly rectangular in T. disalvoi ).