Stenosemus albus ( Linnaeus, 1767 )

Stenosemus albus ( Linnaeus, 1767) View in CoL

Fig. 74 View FIGURE 74

Chiton albus Linnaeus, 1767, p. 1107 , n° 8; Dodge 1952, p. 22

Lophyrus albus View in CoL ; Antevs 1917, p. 368 –381, 416; Grønlie 1927, p. 2, 17, 26; Antevs 1928, p. 689.

Ischnochiton ( Trachydermon) albus View in CoL ; Pilsbry 1892, p. 70, pl. 7, figs 37–38; Pilsbry 1893, p. 64.

Trachydermon albus View in CoL ; Feyling-Hanssen 1955, p. 126.

Ischnochiton albus View in CoL ; Hägg 1951, p. 235, 236, 244.

Ischnochiton ( Lepidopleuroides) albus View in CoL ; Šulc, p. 24.

Ischnochiton ( Stenosemus) albus View in CoL ; Kaas & Van Belle 1990, p. 60, fig. 24, map 8.

Type material. The Linnean Society of London ( Dodge 1952) .

Type locality. “ In O. Islandico ” .

Material examined. No fossil material available, only descriptions and illustrations from the literature. Recent: N. Atlantic: Europe: Barents Sea, Greenland, Iceland, Norway, Denmark ( BD 255, Figs 74A–H View FIGURE 74 ); America: Canada ( Nova Scotia), Maine ( BD, ca 20 spm). Maximum width of the valves: 4 / 4.5 / 3.4 mm (measured on recent valves).

Description. Head valve semicircular, posterior margin widely V-shaped, weakly notched in middle, front slope straight. Intermediate valves broadly rectangular, carinate in anterior profile, rather elevated (H/W = 0.40–0.50), anterior margin slightly angular, side margins rounded, posterior margin about straight, apex hardly or not indicated, lateral areas scarcely raised. Tail valve semicircular, length aboul half width. mucro central, slightly elevated, not prominent, antemucronal slope slightly convex, postmucronal slope straight to weakly concave.

Tegmentum uniformly microgranulose, smooth and glossy to naked eye. HV, LA and PMA with several concentrical, low growth wrinkles, continuing, though less strongly, across CA and AMA.

Articulamentum with apophyses short, very wide, rounded, almost coalescing across small, shallow sinus, slit formula 13–14 / 1 (2) / 10–12, slits inequidistant, slit rays hardly or not indicated, teeth short, sharp, upper side and outer edge decidedly roughened, eaves narrow, solid.

Remarks. The fossil record of Stenosemus albus ( Linnaeus, 1767) is limited to the upper Pleistocene of

Scandinavia ( Norway and Sweden). Comparisons. See Tab. 12 for a comparison with the Stenosemus spp . considered in the present study. Distribution. Pleistocene: N Atlantic: Norway ( Grønlie 1927; Hägg 1951; Feyling-Hanssen 1955); Sweden

( Antevs 1917, 1928). Recent: Northern Atlantic Ocean, from Spitsbergen to Vigo ( Spain) and near the Azores ( Kaas

& Van Belle 1990; Van Belle 1984; Urgorri et al. 2017); Northern Pacific Ocean, SE to San Diego, California, and SW to the Okhotsk Sea and the Sea of Japan ( Dall 1921; Kaas & Van Belle 1990).