Leptochiton josei, Dell'Angelo, Sosso, Prudenza & Bonfitto, 2013

Leptochiton josei View in CoL Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013

Fig. 17 View FIGURE 17

Leptochiton josei View in CoL Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013, p. 73, pl. 2, figs M–R; Dell’Angelo et al. 2020b, p. 52, tab. 9.

non Leptochiton View in CoL cf. L. josei View in CoL ; Dell’Angelo et al. 2018a, p. 17, fig. 3M–N (= Leptochiton sp. , fide this study).

Type material. Holotype: MZB 49985, one intermediate valve ( Figs 17A–C View FIGURE 17 ), width 2.08 mm. Paratypes: MZB 49984 (tail valve from Bussana, Fig. 17H View FIGURE 17 ), MSNG 56535 (intermediate valve from Caranchi), BD (tail valve from Bussana, BD 377, Figs 17E–G View FIGURE 17 ), MP (intermediate valve from Rio S. Antonino, Fig. 17D View FIGURE 17 ), MS (tail valve from Rio S. Antonino).

Type locality. Genova Sestri ( Liguria, Italy) .

Type stage. Lower Pliocene (Zanclean) .

Material examined. Lower Pliocene: Italy: type material plus Bussana: 4 valves ( BD 379 ), Genova Sestri: 1 valve ( BD 380 ), Rio S. Antonino: 2 valves ( MP), Rio Torsero : 1 valve ( BD 381 ). Maximum width of the valves: -- / 2.1 / 3 mm .

Description. Valves small. Head valve not available. Intermediate valve broadly rectangular, width greater than 3 times the length, rounded in anterior profile, not much elevated (H/W = 0.24), anterior margin straight, side margins slightly rounded, posterior margin almost straight, apex indistinct, lateral areas scarcely differentiated, with some concentric growth lines. Tail valve elliptical (W/L = 1.66), anterior margin slightly convex, mucro central, prominent, antemucronal slope slightly convex, postmucronal slope concave just underneath mucro.

Tegmentum rough, space between striae of granules large, growth lines always evident. LA and PMA sculptured with rather irregular roundish- subquadrangular granules, well separate from each other, arranged in irregular radial series (LA 5–6, PA 50–52). CA and AMA sculptured with rather irregular roundish- subquadrangular granules, well separate from each other, arranged in irregular longitudinal series (CA ca. 30–33, one or two tending to bifurcate, AA ca. 38–40, gradually converging posteriorly, some bifurcate), irregular stem structure between granules. Each granule with a central megalaesthete and several micraesthetes irregularly disposed along margin, more or less of same size.

Articulamentum without insertion laminae, apophyses wide, triangular in intermediate valves, trapezoidal in tail ones, apical area expanded with straight anterior margin.

Remarks. No additional material has been found since the original description.

Dell’Angelo et al. (2018a) attributed tentatively to Leptochiton josei a single tail valve from the lower Miocene of Noaillan ( France). Despite the existing similarity with L. josei , it is not possible to identify with certainty this valve, that is discussed and figured in the section dedicated to the “Species of unclear taxonomic position”, and it is left in open nomenclature as Leptochiton sp.

Comparisons. This species has a certain resemblance to Leptochiton scabridus ( Jeffreys, 1880) , with which it shares the well separated granules, but which differs from L. josei in having a different and characteristic sculpture, the tegmentum presents a rough surface, on which the granules are extended into a body usually formed by two or three longitudinal varices that become unified or merge together along the external margin of the valve (see above).

Distribution. Lower Pliocene: central Mediterranean, Italy: Liguria: Bussana, Genova Sestri, Rio S. Antonino, Rio Torsero ( Sosso & Dell’Angelo 2010; Dell’Angelo et al. 2013).