Leptochiton marshalli, Sirenko, 2020

Sirenko, Boris, 2020, New Zealand and Australian species of the genus Leptochiton (Mollusca Polyplacophora), Zootaxa 4851 (3), pp. 401-449 : 422-426

Leptochiton marshalli n. sp.

( Figures 24–27 , 44C, D )

Type material. Holotype ( NMNZ M 117376 ) and paratype ( NMNZ M 117439 ).

Type locality. New Zealand, Three Kings Islands, Tasman Bay, Great Island , 34°10.00’S, 172°9.00’E, 6 m.

Etymology. Named in honor of Bruce Marshall (NMNZ) who made a major contribution to the knowledge of molluscs.

Material examined. New Zealand, Three Kings Islands, NE Point of Great Island , 33°8.50’S, 172°9.00’E, 4–6 m, paratype, BL 8.0 mm, ( NMNZ M 117439 ), 04.02.1993, leg. F.J. Brook ; Three Kings Islands, Tasman Bay, Great Island , 34°10.00’S, 172°9.00’E, 6 m, holotype, BL 10.0 mm, ( NMNZ M 117376 ), 06.02.1993, leg. F.J. Brook.

Distribution. Only known from the type material.

Diagnosis. Animal of small size, valves moderately elevated, rounded, not beaked. Intermediate valves broadly rectangular, tail valve wider than head valve, with slightly anterior mucro. Tegmentum sculptured with weakly raised, oval granules arranged in longitudinal rows in central areas of intermediate valves and antemucronal area of tail valve and in radial rows in other areas. Each granule with one megalaesthete and eight micraesthetes. Girdle dorsally covered with rather wide, obtusely pointed scales with seven wide, flattened ribs. Major lateral teeth with bidentate cusps, inner denticle much smaller than outer one. Tegmentum beige with irregular white maculation.

Description. Holotype 10.0 mm long. Valves moderately elevated (elevation ratio 0.49 in valve V), slightly rounded, not beaked. Color of tegmentum beige with irregular white maculation.

Head valve semicircular. Intermediate valves broadly rectangular, anterior and posterior margins of intermediate valves straight, lateral areas slightly raised, lateral margins rounded. Tail valve slightly wider than head valve, antemucronal slope convex, postmucronal slope concave, mucro slightly anterior.

Tegmentum sculptured with weakly raised, more or less roundish granules arranged in longitudinal rows on central areas of intermediate valves (about 80 rows on valve V) and antemucronal area of tail valve, and in radial rows on other areas. Head valve with about 100 rows, lateral areas with 20 rows and antemucronal area with about 80 rows. Each granule with one megalaesthete and eight micraesthetes around it.

Articulamentum well developed, apophyses small, jugal sinus rather wide, ratio width of jugal sinus to width of apophyses 1.28 in valve V.

Girdle narrow (about 0.7 mm wide near valve V), dorsally, covered with wide obtusely pointed scales (82 x 63–74 μm) with seven wide, flattened ribs. Intersegmental area with long, smooth needles (220 x 22 μm). Marginal elements of three types: some similar to intersegmental needles (290 x 28 μm), elongate spicules with eight wide ribs (118 x 25 µm) and elongate, bluntly pointed scales with three ribs (130 x 38 μm). Ventrally girdle covered with elongate, obtusely pointed, smooth scales (67 x 25 μm), near the margin one row of longer ventral scales (114 x 30 μm).

Radula of holotype 6.0 mm long with 52 transverse rows of mature teeth. Central teeth long and narrow, first lateral tooth with a narrow cusp and an outward projecting wing, major lateral tooth with bidentate cusp, inner denticle much smaller than outer one.

Twelve gills per side arranged from valve VI to anus.

Remarks. Leptochiton marshalli n. sp. is very similar to L. inquinatus but differs from the latter by having 80 longitudinal rows of granules in the central areas of the intermediate valves (vs. 60 rows in L. inquinatus ), seven wide, flattened ribs in dorsal girdle scales (vs. nine narrow, sharp ribs in L. inquinatus ), 52 transverse rows of mature teeth of radula (vs. 34 rows in L. inqunatus ) and in the beige tegmentum coloration with irregular white maculation (vs. yellowish-white in L. inquinatus ). According to Kaas & Van Belle (1985) the tegmentum of L. inquinatus is yellowish brown to chestnut, but it seems that this color is caused by bottom deposits. The specimens of L. inquinatus stored in the ZISP have a yellowish-white color.

Figures

FIGURE 24. Leptochiton marshalli n. sp., holotype, BL 10.0 mm, (NMNZ M 117376). A. Valve I, dorsal view; B. Valve II, dorsal view; C. Valve V, dorsal view; D. Valve VIII, dorsal view; E. Valve V, tegmentum sculpture in central area; F. Valve V, rostral view; G. Valve VIII, lateral view.

FIGURE 25. Leptochiton marshalli n. sp., holotype, BL 10.0 mm, (NMNZ M 117376). A. Dorsal and ventral scales and marginal spicules; B. Dorsal scales near suture and sutural needle; C. Dorsal scales; D. Marginal needles and spicules and dorsal and ventral scales.

FIGURE 26. Leptochiton marshalli n. sp., holotype, BL 10.0 mm, (NMNZ M 117376). A. Central portion of radula from anterior part; B. Central and first lateral tooth of radula.

FIGURE 27. Leptochiton marshalli n. sp., holotype, BL 10.0 mm, (NMNZ M 117376). A. Sutural needle; B. Dorsal scales; C. Marginal needle; D, E. Marginal spicules; F. Ventral scale near margin; G. Ventral scale from mid-girdle; H. Central and first lateral teeth; I, J. Heads of major lateral teeth; K. Aesthete group in central area. Scale bar 100 μm (A–J).

FIGURE 44. Images of species of genus Leptochiton from New Zealand and Australia: A, B. L. cf. opiparus, New Zealand, Kermadec Islands, R/V Acheron, stn 1973312, 1188-1225 m, BL 16 mm, (NMNZ M 222132); C, D. L. marshalli n. sp., holotype, New Zealand, Three Kings Islands, Tasman Bay, Great Island, 6 m, BL 10.0 mm, (NMNZ M 117376); E, F. L. subantarcticus, New Zealand, Head of Pegasus Canyon, Pegasus Bay, 446 m, mud, BL 5.5 mm, (NMNZ M 152576); G, H. L. cf. laurae, New Zealand, South Island, SSE of Kaikoura, R/V James Cook, stn 1986020, 927–995 m, BL 10.5 mm, (NMNZ M 319764).