Leptochiton finlayi (Ashby, 1929)

(Figures 10–13, 45B)

Lepidopleurus finlayi Ashby 1929a: 367, pl. 32: figs. 57 (nom. nudum); 1929b: 372; Beu 1977: 37, fig. G.

Terenochiton finlayi; Iredale & Hull 1930: 157, pl. 16: figs. 2–5; Powell 1979: 21.

Leptochiton (Leptochiton) finlayi; Kaas & Van Belle 1985: 159, fig. 72, map 28.

Leptochiton finlayi; Beu & Maxwell 1990: 330, pl. 43, figs. a, c, e (holotype).

Type material. Holotype (AM C95165). Type locality. New Zealand, off Otago Heads, 108 m.

Material examined. New Zealand, North Island, 33°9’50’’S, 173°47’20’’E, 141 m, 3 spms, BL 5–7 mm, (NMNZ M.283635) 20.02.1989 , leg. R. Stewart; Head of Pegasus Canyon, Pegasus Bay, R / V Acheron, stn 1976558, 446 m, mud, 1 spms, BL 6.0 mm, (NMNZ M 328331), 27.09.1976 ; N of Cavalli Islands, 34°52.75’S, 173°55.03’E, R / V Tangaroa, stn TAN0906/ 81, 115 m, 1 spm, BL 8.0 mm, (NMNZ M 314504), 08.07.2009 .

Distribution. All around New Zealand and Stewart Island, from 115 to 446 m. There is a fossil occurrence of this species in the Pleistocene of New Zealand (Beu & Maxwell 1990).

Remarks. Two specimens were studied by SEM: a specimen with a BL of 7.0 mm (NMNZ M.283635) and a specimen with BL 6.0 mm (NMNZ M 328331). The specimen with BL 7.0 mm has 9 gills per side arranged from valve VI to the anus and a radula 3.1 mm long with 29 transverse rows of mature teeth. The second specimen differs from the first one by having dorsal scales with 5–7 ribs instead 5–9 ribs. These specimens are characterized by having subcarinated valves, longitudinal rows of granules in central areas of intermediate valves and in the antemucronal area of the tail valve, radial rows of granules on the head valve and granules arranged in a random manner in other areas, 9 aesthetes on each granule, sutural tufts of 13–14 long needles, dorsal scales with 5–9 narrow longitudinal ribs, marginal elements of three kinds: long, smooth needles, long ribbed spicules and short flattened spicules with ribs on both sides, central teeth of radula short and wide, major lateral teeth with bidentate sharply pointed cusps, inner denticle much smaller than outer one. As noted by Kaas & Van Belle (1985) “at the posterior margin of the lateral areas, there are three or more equi-spaced protuberances standing up about four times the height of the larger grains, a most characteristic feature of this species.”