Tonicella marmorea ( Fabricius, 1780 )

Tonicella marmorea ( Fabricius, 1780) View in CoL

Fig. 131 View FIGURE 131

Chiton marmoreus Fabricius, 1780, p. 420 View in CoL ; Harder et al. 1949, p. 42.

Chiton ( Boreochiton) marmoreus View in CoL ; Knipowitsch 1900, p. 33, 35, 39, 44.

Boreochiton marmoreus View in CoL ; Brøgger 1901, p. 653; Holmboe 1904, p. 34, 35; Hoel 1907, p. 47; Hoel 1914, p. 33; Antevs 1917, p. 340 –353, 412, 416; Grønlie 1927, p. 2, 26; Antevs 1928, p. 646, 666–674, 677.

Tonicella marmorea View in CoL ; Knipowitsch 1902, p. 427, 439, 446; Feyling-Hanssen & Jørstad 1950, p. 18 –23, 27, 33–37, 57–61, 66, 68, 79; Hägg 1950, p. 339, 343; Hägg 1951, p. 231, 235, 236, 238, 239, 244; Feyling-Hanssen 1955, p. 125, pl. 17, figs 1–3; Ferreira 1982, p. 116, figs 60–68; Kaas & Van Belle 1985b, p. 139, fig. 64, map 27; Funder et al. 2002; p. 278; Petersen 2004, p. 25; Sirenko & Dell’Angelo 2023, p. 278, fig. 3.

Type material. ZMK: Five well preserved specimens, dry, strongly curled, one selected as lectotype (the largest specimen, estimated length 4 cm) and the other four as paralectotypes by Ferreira (1982) .

Type locality. Greenland and Kragere ( Norway) ( Ferreira 1982: 117) .

Material examined. No fossil material available, only descriptions and illustrations from the literature. Recent: N. Atlantic: Europe: White Sea ( BD 959, Figs 131A–H View FIGURE 131 ), Barents Sea, Greenland, Iceland, Norway, Denmark; America: Canada ( Nova Scotia), Maine (ca 25 spm). Maximum width: 4.2 / 4.5 / 3 mm.

Description. Head valve less than semicircular, posterior margin widely V-shaped, notched in the middle, slope slightly convex. Intermediate valves broadly rectangular (W/L = 2.73–2.75), moderately elevated (H/W = 0.37– 0.44), semicarinate in anterior profile, anterior margin straight, except in valve ii where it is somewhat anteriorly produced, side margins more or less rounded, posterior margins about straight, apex decidedly perceptible, lateral areas hardly raised, separated from the central area by a shallow, diagonal depression, Tail valve small, semielliptical more than twice as broad as long (W/L = 2.43–2.71), very short, anterior margin evenly convex, posterior margin usually with a very shallow caudal sinus, mucro subcentral, not prominent, antemucronal slope almost straight, postmucronal slope about straight or slightly convex.

Tegmentum uniformly, finely granulated in quincunx, growth lines relatively numerous, easily visible, concentrically crossing central areas, aesthetes very dense, each megalaesthete accompanied by many micraesthetes.

Articulamentum with apophyses wide, short, anteriorly rounded, separated by a rather narrow, straight sinus, insertion plates short, slit formula 7–12 / l / 5–11, teeth slightly thickened at the edges, rugose on the outside, slit rays not indicated, eaves finely porous.

Remarks. Tonicella marmorea ( Fabricius, 1780) has a long and rather complex nomenclatural history, summarized by Ferreira (1982) and Kaas & Van Belle (1985b). Specimens from the East coast of the U.S.A. differ slightly from European specimens in being higher elevated, relatively narrower, their back more rounded ( Kaas & Van Belle 1985b).

Our treatment of Tonicella marmorea is limited to the Pleistocene of the North Atlantic, based solely on citations of loose valves, without descriptions or figures, which could be questionable.

Comparisons. Tonicella marmorea is very similar to Boreochiton ruber ( Linnaeus, 1767) .

Distribution. Pleistocene: North Europe: Russia: Barents Sea ( Knipowitsch 1900), White Sea ( Funder et al. 2002); Greenland: Harder et al. 1949; Norway ( Brøgger 1901; Knipowitsch 1902; Holmboe 1904; Hoel 1907, 1914; Grønlie 1927; Hägg 1950, 1951; Feyling-Hanssen 1955); Sweden ( Antevs 1917, 1928); Denmark ( Petersen 2004). Recent: Arctic Ocean (Barents Sea, White Sea, The Kara Sea, near Spitzbergen and Franz Josef Land, and N. Canada); N. Atlantic Ocean, as far south as Massachusetts Bay on the western side, and the western coast of France on the eastern side; N. Pacific Ocean (Sea of Japan, the Okhotsk Sea and the Bering Sea, and near the Kurile, the Commander and the Aleutian Islands) ( Ferreira 1982; Kaas & Van Belle 1985b).