Lepidopleurus benoisti (de Rochebrune, 1882 )

Lepidopleurus benoisti (de Rochebrune, 1882) View in CoL

Fig. 2 View FIGURE 2

Chiton cinereus [non Lepidochitona cinerea ( Linnaeus, 1767) View in CoL ]; Bonelli 1824, n° 2648; Sismonda 1842, p. 24 ( fide Sacco,

1897). Chiton cajetanus [non Lepidopleurus cajetanus ( Poli, 1791) View in CoL ]; Sismonda 1847, p. 25 ( fide Sacco 1897). Chiton subcajetanus d’Orbigny, 1852, p. 94 , n° 1746 ( nomen nudum, fide Dell’Angelo et al. 2015a). Gymnoplax benoisti de Rochebrune, 1882, p. 64 , pl. 1, fig. 8. Callochiton benoisti ; Benoist 1882, p. xxix. Middendorffia subcajetana ; Sacco 1897, p. 90, pl. 7, figs 21–25; Ferrero Mortara et al. 1984, p. 299, pl. 55, fig. 6. Chiton miocaenicus [non Rhyssoplax miocenica ( Michelotti, 1847) ]; Cossmann & Peyrot 1919, p. 32, pl. 2, figs 21–22 ( fide

Dell’Angelo & Palazzi 1989). Chiton benoisti ; Cossmann & Peyrot 1919, p. 33, pl. 2, figs 23–27; Forli & Guerrini 2022, fig. 11.18 (6). Lepidopleurus subcajetanus ; Laghi 1977, p. 99, pl. 1, fig. 21. Lepidopleurus benoisti ; Dell’Angelo et al. 2015a, p. 222, pl. 2, figs 1–13, 18–20; Dell’Angelo et al. 2018a, p. 12, figs 2J–U,

3A–F; Dell’Angelo et al. 2020b, p. 52, tab. 9; Stein et al. 2021, p. 55, textfig. 6, pl. 6, fig. 4.? Lepidopleurus sp. ; Moths et al. 2010, p. 30, pl. 4, fig. 3; Stein et al. 2016, p. 176 ( fide Stein et al. 2021).

Type material. Syntypes MHNBx 2009.TY.P.306.0, two tail valves from the Benoist’s collection (width respectively 13.63 and 7.04 mm).

Type locality. Mérignac ( Gironde, France) .

Type stage. Lower Miocene , Aquitanian / Burdigalian .

Material examined. Upper Oligocene: France, Aquitaine Basin (Chattian): Abesse: 15 valves ( AC, JVC, Fig. 2A–D View FIGURE 2 ). Lower Miocene: France, Aquitaine Basin (Aquitanian): Maïnot: 1 valve (PR); Aquitaine Basin (Burdigalian): Cabanes: 1 valve ( JFL), Carrière Vives: 5 valves ( AC, BD 261, JFL, PR), Gamachot: 3 valves ( AC, JFL), la Flotte: 1 valve ( AC), Lahitet: 1 valve ( AC), Lorient: 7 valves ( AC, JFL, PR), Peloua: 33 valves ( AC, JFL, JVC, PR, Fig. 2E–F View FIGURE 2 ), Petit Bargues: 1 valve (PR), Pont St Martin: 23 valves ( JFL, PR, Fig. 2G–H View FIGURE 2 ). Italy: Torino Hills (Burdigalian): Valle Ceppi: 5 valves ( PMRSN BS.105.02.001–003, MZB 32008–32009). Middle Miocene:

France, Aquitaine Basin (Langhian): Carrière Gélis : 1 valve ( JFL) ; Aquitaine Basin (Serravallian): Orthez : 1 valve ( BD 262 ). Maximum width of the valves: 15.7 / 18 / 18 mm .

Description. Valves solid. Head valve large, semicircular, posterior margin widely V-shaped, slope almost straight or slightly convex, interrupted by profile of concentric, terraced ribs. Intermediate valves wide, broadly rectangular (W/L = 2.45), rounded in anterior profile, moderately elevated (H/W = 0.33–0.36), anterior and posterior margins straight, side margins rounded, apex inconspicuous, lateral areas not very raised. Tail valve semicircular (W/L = 1.64–1.76), elevate, mucro flat, in anterior position, antemucronal slope almost straight or slightly convex, postmucronal slope almost straight or slightly concave.

Tegmentum coarse, space between striae of granules reduced. HV, LA and PMA sculptured with numerous and very irregular radial chains of roundish granules, tending to branching and anastomosing, intersected by many and well evident concentric terraced ribs (up to 5–6 in LA). CA and AMA sculptured with many longitudinal chains of roundish granules (ca 100 or more in CA), almost regular in central part, much irregular and tending to branching and anastomosing in lateral parts, near side margins, with concentric ribs inconspicuous, barely visible (and not terraced).

Articulamentum without insertion laminae, apophyses narrow, rounded-triangular, widely projected in intermediate valves, larger but not completely preserved in tail valves.

Remarks. Dell’Angelo et al. (2015a) examined Chiton subcajetanus d’Orbigny, 1852 sensu Sacco 1897 and the related species ( Gymnoplax orbignyi de Rochebrune, 1882 and G. benoisti de Rochebrune, 1882 ); they consider Chiton subcajetanus a nomen nudum [no diagnosis, nec figuration in Bonelli (1824), Sismonda (1842, 1847) and d’Orbigny (1852)], and Lepidopleurus benoisti (de Rochebrune, 1882) the correct taxon to attribute to this species (including the large valves of L. decoratus of Šulc). Šulc considered a tail valve (width of 18 mm) from the Middle Miocene of Pötzleinsdorf, Austria and the valves illustrated by Sacco (as Middendorffia subcajetana ) as a very large form of Lepidopleurus decoratus ( Reuss, 1860) . In the Šulc collection housed at the NHMW, large tail valves— reported in the “Material Examined” section for Lepidopleurus cajetanus ( Poli, 1791) —are absent. We concur with Laghi (1977), Bałuk (1984), Studencka & Dulai (2010), and other authors in considering L. decoratus conspecific with L. cajetanus . Accordingly, we believe that records of “ subcajetanus ” or “ decoratus ” from the Paratethys should be attributed to the morphospecies Lepidopleurus cajetanus .

Many valves of Lepidopleurus benoisti were described by Dell’Angelo et al. (2018a) from the Aquitaine Basin of France, in sediments from upper Oligocene to Middle Miocene, and this has allowed the redescription of this species, first known only for few valves from the lower Miocene of France (de Rochebrune 1882; Cossmann & Peyrot 1919) and Italy (Turin hills: Sacco 1897; Dell’Angelo et al. 2015a).

The valves examined from the Aquitaine Basin of France mainly include tail valves, and it is possible to see a certain range of variability. The mucro is more pronounced in juvenile specimens, and the postmucronal slope decidedly concave ( Dell’Angelo et al. 2018a: fig. 3F, width 4.2 mm), while the position of the mucro remains in anterior position in fully developed specimens, on the contrary of what happens for Lepidopleurus cajetanus . In fact tail valves of Lepidopleurus benoisti are similar to those of L. cajetanus at the second stage of growth (see above), but with larger dimensions, larger than those reached by L. cajetanus at the last stage of growth, the mucro in anterior position, and less evident concentric terraced ribs in the postmucronal area (real concentric folds in L. cajetanus ).

The report of Chiton miocenicus Michelotti, 1847 by Cossmann & Peyrot (1919: 32, pl. 2, figs 21–22) can be attributed to Lepidopleurus benoisti , as already indicated by Dell’Angelo & Palazzi (1989: 55). Cossmann & Peyrot found three tail valves from Salies-de-Béarn (coll. Degrange-Touzin), one of which figured in Cossmann & Peyrot (1919: pl. 2, figs 21–22); Dell’Angelo et al. (2018a) examined these valves preserved at MHNBx and confirmed the attribution to L. benoisti .

Comparisons. This species is superficially similar to the recently described Lepidopleurus pseudobenoisti Dell’Angelo et al., 2018 (see below), from which it differs by the different shape of the tail valve with the very pronounced mucro (compare Figs 2F, 2H View FIGURE 2 with Figs 5B, 5L View FIGURE 5 ), and also by the coarser and very variable sculpture and the much more raised lateral areas of intermediate valves in L. pseudobenoisti . These two species cannot be separated based on their head valve (shape or sculpture). Another similar species is Lepidopleurus virgifer (Sandberger, 1859) from the Middle Oligocene (Rupelian) of Waldböckelheim, Germany (see below). The shape and the ornamentation of the valves are similar, but the sculpture is coarser in L. benoisti , with more pronounced growth lines, and the size of the valves is greater.

Distribution.Upper Oligocene: northeastern Atlantic (Chattian): Aquitaine Basin, France:Abesse ( Dell’Angelo et al. 2018a). Upper Oligocene to lower Miocene: North Europe, Germany: Neetze ( Stein et al. 2021). Lower Miocene: North Europe, Germany: Werder ( Moths et al. 2010; Stein et al. 2016); Northeastern Atlantic (Aquitanian-Burdigalian): Aquitaine Basin, France: Cabanes, Carrière Vives, Gamachot, la Flotte, Lahitet, Lorient, Maïnot, Peloua, Petit Bargues, Pont St Martin ( Cossmann & Peyrot 1919; Dell’Angelo et al. 2018a); Proto-Mediterranean Sea (Burdigalian): N. Italy: Torino Hill ( Sacco 1897; Dell’Angelo et al. 2015a). Middle Miocene: northeastern Atlantic, France, Aquitaine Basin: Carrière Gélis (Langhian), Orthez (Serravallian) ( Dell’Angelo et al. 2018a).