Leptochiton sarsi Kaas, 1981

Leptochiton sarsi Kaas, 1981 View in CoL

Fig. 21 View FIGURE 21

Leptochiton sarsi Kaas, 1981, p. 225 View in CoL figs 4, 9, 10C–D; Dell’Angelo et al. 2007b, p. 141; Dell’Angelo et al. 2009, p. 77, figs 2a–2n, 3a–3i; Dell’Angelo et al. 2013, p. 74.

Leptochiton ( L.) sarsi View in CoL ; Kaas & Van Belle 1985a, p. 60, fig. 25, map 12.

Lepidopleurus ( Leptochiton) sarsi ; Dell’Angelo & Palazzi 1989, p. 77, pl. 21, 25 figs 1–3; Dell’Angelo & Bonfitto 2005, p. 1.

Lepidopleurus View in CoL cfr. sarsi ; Giovine & Dell’Angelo 1993, p. 168, pl. 1, figs 4–5.

Lepidopleurus sarsi ; Palazzi & Villari 1994, p. 76.

Lepidopleurus cancellatus View in CoL [non Leptochiton cancellatus ( Sowerby, 1840) View in CoL ]; G.O. Sars 1878, pl. 7, figs 6a–6h ( fide Kaas 1981).

non Lepidopleurus ( Leptochiton) sarsi ; Dell’Angelo & Giusti 2000, p. 54, figs 5–10.

Type material. Holotype KNVSM, specimen 7.7 x 3.9 mm . Paratypes: KNVSM ( 2 paratypes) ; ZMO, type collection D 33690 ( 1 paratype) ; K 4914 ( 1 paratype).

Type locality. Asfjorden , Trondheimsfjord ( Norway) .

Material examined. Pleistocene: Italy: Calabria: Archi: 4 valves ( BD 390 , Figs 21B–D View FIGURE 21 ), Bovetto: 1 valve ( BD 391 ), Cannitello : 1 valve ( FG), San Procopio: 3 valves ( BD 392 , Figs 21G–H View FIGURE 21 ), Venetico Marina : 1 valve ( BD 393 , Fig. 21A View FIGURE 21 ); Sicily: Pezzo: 1 valve ( BD 394 ), Salice: 17 valves ( BD 395 , Figs 21E–F View FIGURE 21 ). Recent : Italy: Tuscan Archipelago, S. Lucia Bank: 2 specimens ( BD 396 , Figs 21I–L View FIGURE 21 ). Maximum width of the valves: - / 4 / 3.4 mm .

Description. Head valve semicircular, posterior margin widely V-shaped. Intermediate valves broadly rectangular (W/L = 1.90–2.12), rounded in anterior profile, elevated (H/W = 0.46–0.55), anterior margin slightly convex, side margins rounded, posterior margin almost straight, apex not evident, lateral areas slightly raised with concentric lines of growth. Tail valve almost semicircular (W/L = 1.84–1,90), anterior margin almost straight or slightly convex, mucro not prominent, subcentral or a little anterior, antemucronal slope convex, postmucronal slope concave directly behind the mucro.

Tegmentum rough, space between striae of granules large. HV, LA, PMA sculptured with small elliptical granules randomly arranged, with 2–3 stems in apical part. CA and AMA sculptured with more roundish and more compact granules arranged in longitudinal series (CA 50–60, AMA ca 45), with a regular quincuncial pattern displayed by granules of neighbouring rows. Each granule with a variable number of aesthetes, normally three lined up along diameter, a central megalaesthete and two micraesthetes at extremities in HV, LA and PMA, and six with a central megalaesthete and two or more micraesthetes on two sides in CA and AMA.

Articulamentum without insertion laminae, weakly developed, apophyses small, triangular, wide apart in intermediate valves, trapezoid in tail valve.

Remarks. Leptochiton sarsi Kaas, 1981 was described by Kaas (1981) in his revision of Leptochiton living along the Scandinavian coasts. By studying a lot of specimens, identified as L. cancellatus ( Sowerby, 1840) , Kaas found that specimens described and figured by G.O. Sars (1878: 111, pl. 7, figs 6a–6h) as L. cancellatus , did not agree with the species described by Sowerby (1840a: figs 104, 104a–104b, 105; 1840b: 4), and these were described as the new species L. sarsi Kaas, 1981 , along with an elaboration of the differences between the two taxa (Kaas 1981: table 2). The distribution of L. cancellatus was restricted to the British Isles, the Atlantic coasts of France, Spain and Portugal, and the Mediterranean Sea, while L. sarsi appeared to be continuously distributed along the Scandinavian coast, from Bohuslän ( Sweden) up to Finmark ( Norway) at a depth of 40 to over 700 m.

Leptochiton sarsi has been recently found in the Mediterranean Sea, on the basis of two specimens from S. Lucia Bank, 500 m depth ( Dell’Angelo et al. 2009). The species was already previously reported as loose valves, considered subfossil (Giovine & Dell’Angelo 1993: an intermediate valve from biogenic sands at Cannitello, Reggio Calabria, at 150m depth. The citation of Dell’Angelo & Giusti (2000: many valves from the Southern Ligurian Sea, between Capraia Island. and Capo Corso, 350/ 500 m depth) should be referred Leptochiton corticellii sp. nov.). Moreover, the species was already reported as a fossil in bathyal Pleistocene outcrops of S. Italy: Archi (figured by Dell’Angelo & Palazzi 1989: pl. 21, figs 1–2), San Procopio (figured by Dell’Angelo & Palazzi 1989: pl. 25, figs 1–3), Salice ( Dell’Angelo & Palazzi 1989), and Venetico Marina ( Palazzi & Villari 1994) .

Comparisons. Leptochiton sarsi differs from L. cancellatus ( Sowerby, 1840) mainly by the different sculpture, the more spaced rows of granules on CA and AMA, the granules larger and not connected. Leptochiton sarsi is also closest to Leptochiton corticellii sp. nov.

Distribution. Pleistocene: central Mediterranean, S. Italy: Archi, Bovetto, Cannitello, Pezzo, San Procopio, Salice, Venetico Marina ( Dell’Angelo & Palazzi 1989; Giovine & Dell’Angelo 1993; Palazzi & Villari 1994; this study). Recent: N. Atlantic Ocean, along the Scandinavian coast from Sweden to Norway ( Hansson 1998; Kaas 1981; Kaas & Van Belle 1985a), and Mediterranean Sea: Tuscan Archipelago: S. Lucia Bank ( Dell’Angelo et al. 2009).