Stenosemus dolii (Van Belle & Dell'Angelo, 1998)

Stenosemus dolii View in CoL ( Van Belle & Dell’Angelo, 1998)

Fig. 75 View FIGURE 75

Ischnochiton dolii Van Belle & Dell’Angelo, 1998, p. 77 View in CoL , figs 1–5; Dell’Angelo et al. 2001a, p. 150; Dell’Angelo & Silva 2003, p. 11; Dell’Angelo et al. 2004, p. 34; Schwabe 2005, p. 94; Puchalski et al. 2008 (database: chiton fossil records).

Ischnochiton ( Stenosemus) dolii View in CoL ; Dell’Angelo & Smriglio 1999, p. 115, pls 36–38, fig. 53; Dell’Angelo & Giusti 2000, p. 55 ( pars); Dell’Angelo et al. 2001b, p. 55, fig. 1.

Stenosemus dolii View in CoL ; Dell’Angelo et al. 2012, p. 58, figs 4A, 4E, 4G ( pars); Dell’Angelo et al. 2013, p. 82, pl. 5, fig. A ( pars); Dell’Angelo et al. 2018b, p. 53, tab. 17; Dell’Angelo et al. 2020b, p. 8, 52, tab. 9; Dell’Angelo et al. 2021b, p. 415, figs 70–77 ( pars).

non Stenosemus dolii View in CoL ; Dell’Angelo et al. 2012, figs 4B–D, 4F, 4H–I; Dell’Angelo et al. 2013, figs B–I (= Stenosemus juliuspisai , fide this study); Dell’Angelo et al. 2015a, p. 235, pl. 6, fig. 1–9 (= Stenosemus praedolii , fide this study); Dell’Angelo et al. 2018a, p. 27, fig. 6D–F (= Stenosemus sp. , fide this study).

Lepidozona dorsuosa [non Ischnochiton dorsuosus ( Haddon, 1886) View in CoL ]; Laghi 1977, p. 105, pl. 2, fig. 3a–3b ( pars); Zanaroli 1985, p. 111, pl. 2, fig. 1 ( pars) ( fide this study).

Ischnochiton exaratus View in CoL [non Ischnochiton exaratus ( Sars, 1878) View in CoL ]; Dell’Angelo & Giusti 1997, p. 51, fig. 4 ( pars) ( fide this study).

Ischnochiton vanbellei View in CoL [non Stenosemus vanbellei (Kaas, 1985) View in CoL ]; Smriglio et al. 1989, p. 126, figs 3, 4a–b ( fide Dell’Angelo & Smriglio 1999).

Ischnochiton ( Stenosemus) aff. vanbellei View in CoL [non Stenosemus vanbellei (Kaas, 1985) View in CoL ]; Dell’Angelo et al. 2004, p. 34 ( pars).

Type material. Holotype: MZB 11302, intermediate valve, width 7.5 mm. Paratypes: MZB 11303 (5 valves), IRSN IG 28523 (4 valves), MNHN (3 valves), and private collections (320 valves): BD P151F/01 (90 valves, Figs 75A–H View FIGURE 75 ), FG (80 valves), RA (138 valves), VB F1003a (12 valves) .

Type locality. Tyrrhenian Sea , off Civitavecchia ( Italy), within a Roman amphora ( Latin: dolium) at a depth of 550 m ( 42°04’04”N, 11°45’31”E) GoogleMaps .

Type stage. Subfossil (“ the correct geological age of I. dolii cannot be established with any degree of certainty ”).

Material examined. Lower Pliocene: Italy: Liguria: Borzoli : 15 valves ( BD 544 , MZB 45720 ) . Pliocene : Spain: Estepona : 1 valve ( BD 545 ) . Italy: Piedmont: Valle Botto: 5 valves ( BD 546 ) ; Emilia-Romagna: Cava di Campore : 2 valves ( BD 547 ) ; Sicily: Altavilla : 110 valves ( AG, AR, Fig. 75L View FIGURE 75 , BD 548 , DGUP). Pleistocene : Italy: Tuscany: Capraia Island-Capo Corso -350/ 500m: 12 valves ( BD 549 , Figs 75I–K View FIGURE 75 ); Emilia-Romagna: Torrente Stirone: 1 valve ( BD 550 ) ; Latium: off Civitavecchia: type material; Calabria: Pecoraro : 1 valve ( BD 551 ) . Maximum width of the valves: 7 / 8 / 6.7 mm .

Description. Head valve semicircular, posterior margin widely V-shaped, with a rounded notch at apex. Intermediate valves broadly rectangular (W/L = 2.54–2.57), carinate in anterior profile, moderately elevated (H/ W = 0.34–0.49), anterior margin consisting of three segments, two lateral ones straight or slightly concave, and one between the apophyses straight or slightly convex, side margins almost straight or slightly rounded, posterior margin practically straight with mucro not very visible, lateral areas moderately elevated. Tail valve semicircular (W/L = 1.75–1.88), depressed, anterior margin as in intermediate valves, mucro in slightly anterior position and little elevated, antemucronal and postmucronal slopes almost straight.

Tegmentum rough. HV, LA and PMA sculptured with rather flat radial ribs (HV 17–26 at apex, splitting near anterior margin, LA 4–8 tending to become obsolete near lateral margins, PMA 18–20, sometimes barely conspicuous around mucro), separated by rather narrow spaces, and with well-evident and numerous growth lines, which intersect the radial ribs forming more or less elongated quadrangular granules. CA and AMA sculptured with 11–23 longitudinal grooves on each side, normally all reaching anterior margin with JA smooth, only in some valves 2–4 more internal grooves may not reach margin and converging towards jugum or become very irregular.

Articulamentum with apophyses short and wide, rounded, jugal sinus not very wide, weakly convex, insertion lamina divided into short and rough denticles of irregular width, slit formula 9–10 / 1 / 6–10.

Remarks. The fossil record of Stenosemus dolii ( Van Belle & Dell’Angelo, 1998) is limited to the Mediterranean Pliocene ( Italy and Spain) and Pleistocene ( Italy).

Stenosemus dolii was described on the basis of many loose subfossil valves found in a Roman amphora off Civitavecchia, at a depth of 550 m ( Van Belle & Dell’Angelo 1998); additional material pertains to a taphocoenosis from the South Ligurian Sea, between Corsica and Capraia Island, collected at a depth of 350/ 500 m ( Dell’Angelo & Giusti 1997, 2000). Living specimens have been found in the Tyrrhenian Sea between 150 and 480 m ( Smriglio et al. 1989); originally classified as Ischnochiton vanbellei Kaas, 1985 ( Dell’Angelo & Smriglio 1999; Dell’Angelo et al. 2001b), these specimens have been transferred to the genus Stenosemus based upon the girdle’s conic scales.

Dell’Angelo et al. (2018a) attributed tentatively to Stenosemus dolii a unique tail valve from the upper Miocene of Moulin Pochas ( France). Despite the existing similarity with S. dolii , 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 Stenosemus sp.

An in-depth reconsideration of the abundant material from the Pliocene of Altavilla Milicia ( Sicily), attributed to Stenosemus dolii by Dell’Angelo et al. (2012), suggests that two undescribed species are, in fact, present which we formalize here as S. juliuspisai sp. nov. and S. praedolii sp. nov. (see below). We consider Stenosemus dolii as a species with a radial sculpture (HV, LA, PMA) consisting of flat radial ribs intersected by well-evident and numerous growth lines, forming more or less elongated quadrangular granules, different from the real granulose sculpture characteristic of the two new species described below.

Laghi (1977: pl. 2, figs 1–4) recorded some valves from the Pliocene (Zinola, Valle Andona and Castell’Arquato) under the name Lepidozona dorsuosa ( Haddon, 1886) . These valves were later considered to fall in the range of variability of Stenosemus dolii by Dell’Angelo et al. (2018a). One of the valves illustrated by Laghi (1977: pl. 2, fig. 3a–3b), from the Pliocene of Castell’Arquato, agree with the attribution to S. dolii , but the other valves figured can be attributed to Stenosemus juliuspisai sp. nov. (see below).

The same partial attribution to both Stenosemus juliuspisai sp. nov. and S. praedolii sp. nov. has also been considered for the material, before attributed to S. dolii , from the upper Miocene of Northern Apennines [Dell’Angelo et al. 1999, as Ischnochiton ( Simplischnochiton) exaratus ( Sars, 1878) ; Dell’Angelo et al. 2015 a, 2016, as Stenosemus dolii ], the Pliocene of Liguria, Italy ( Dell’Angelo et al. 2013, 2021b, as Stenosemus dolii ), the Pliocene of Estepona, Spain [Dell’Angelo et al. 2004, as Ischnochiton ( Stenosemus) aff. vanbellei ], the Pleistocene of Capraia Island-Capo Corso, Italy ( Dell’Angelo & Giusti 1997, 2000, as Ischnochiton exaratus ).

The valves show a certain variability with regard to the sculpture, e.g., the number of longitudinal grooves on each side of the central areas of intermediate valves (varying from 11 to 23), the number of flat radial ribs of the lateral areas of intermediate valves (varying from 4 to 8 or more) the jugum normally smooth ( Fig. 70J View FIGURE 70 ), but with a sculpture of grooves converging towards the apex visible on the upper part ( Fig. 70D View FIGURE 70 ) when the more internal longitudinal grooves are converging towards it (normally in valve ii).

Comparisons. See Tab. 12 for a comparison with the Stenosemus spp . considered in the present study.

Distribution. Lower Pliocene: central Mediterranean, Italy: Liguria: Borzoli ( Dell’Angelo et al. 2013, 2021b). Pliocene: western Mediterranean, Estepona Basin, Spain (Dell’Angelo et al. 2004); central Mediterranean, Italy: Altavilla Milicia ( Dell’Angelo et al. 2012), Castellarquato ( Laghi 1977), Valle Botto, Cava di Campore (this study). Pleistocene: central Mediterranean, Italy: off Civitavecchia ( Van Belle & Dell’Angelo 1998), Capraia Island-Capo Corso, -350/ 500 m ( Dell’Angelo & Giusti 1997, 2000), Pecoraro, Torrente Stirone (this study). Recent: Mediterranean Sea, off the Latium coast and in Tuscan Archipelago, between 150 and 560 m, and in association with white coral biocoenosis ( Dell’Angelo & Smriglio 1999; Dell’Angelo et al. 2001b).