Stenosemus juliuspisai, Dell’Angelo & Sosso & Taviani, 2025

Stenosemus juliuspisai sp. nov.

Fig. 76 View FIGURE 76

Ischnochiton ( Stenosemus) dolii View in CoL [non Stenosemus dolii View in CoL ( Van Belle & Dell’Angelo, 1998)]; Dell’Angelo & Giusti 2000, p. 55 ( pars).

Stenosemus dolii View in CoL [non Stenosemus dolii View in CoL ( Van Belle & Dell’Angelo, 1998)]; Dell’Angelo et al. 2012, p. 58, fig. 4A–K ( pars); Dell’Angelo et al. 2013, p. 82, pl. 5, fig. B–I ( pars); Dell’Angelo et al. 2016, p. 96 ( pars); Dell’Angelo et al. 2021b, p. 415 ( pars).

Lepidozona dorsuosa [non Ischnochiton dorsuosus ( Haddon, 1886) View in CoL ]; Laghi 1977, p. 105, pl. 2, figs 1–2, 4 ( pars); Zanaroli 1985, p. 111, pl. 2, figs 2–6 ( pars) ( fide this study).

Ischnochiton exaratus View in CoL [non Stenosemus exaratus ( Sars, 1878) View in CoL ]; Dell’Angelo & Giusti 1997, p. 51, figs 6, 9 ( pars) ( fide this study).

Ischnochiton ( Simplischnochiton) exaratus View in CoL [non Stenosemus exaratus ( Sars, 1878) View in CoL ]; Dell’Angelo et al. 1999, p. 268, pl. 3, fig. 6 ( pars) ( fide this study).

Ischnochiton ( Stenosemus) aff. vanbellei View in CoL [non Stenosemus vanbellei (Kaas, 1985) View in CoL ]; Dell’Angelo et al. 2004, p. 34, pl. 7, figs 2, 5–6 ( pars).

Ischnochiton vanbellei View in CoL [non Stenosemus vanbellei (Kaas, 1985) View in CoL ]; Dell’Angelo & Giusti 1997, p. 52, fig. 3; Dell’Angelo et al. 2001a, p. 150, fig. 24; Puchalski et al. 2008 (database: chiton fossil records).

Type material. Holotype: MSNG 62650 View Materials , intermediate valve, width 5.7 mm ( Figs 76A–C View FIGURE 76 ) . Paratype 1: MSNG 62651 View Materials , head valve ( Figs 76D–E View FIGURE 76 ) . Paratype 2: MSNG 62652 View Materials , tail valve ( Figs 76F–H View FIGURE 76 ) . Paratype 3: MNHN.F.A98474, intermediate valve, width 4.8 mm . Paratype 4: MGGC 23374 , tail valve, width 3.9 mm . Paratype 5: MSNG 62653 View Materials , intermediate valve, width 3.4 mm ( Figs 76J–K View FIGURE 76 ), from Capraia Island-Capo Corso - 350 m, Pleistocene (presumably last glacial) .

Type locality. Altavilla Milicia ( Sicily, Italy) .

Type stage. Pliocene-Pleistocene (upper Piacenzian to lower Gelasian) ( Dominici et al. 2020).

Etymology. This species honors the Italian geologist and paleontologist Giulio Pisa (1936-1976), expert in Triassic ammonites, for his role in stimulating the malacological research of one of the Authors (MT) on the Pleistocene deposits of the Stirone river, rich in polyplacophoran remains.

Material examined. Lower Pliocene: Italy: Liguria: Borzoli: 115 valves ( BD 552, MZB 45723–45724), Bussana: 3 valves ( BD 553), Rio Sant’ Antonino: 39 valves ( MP, MZB 45721–45722), Zinola: 7 valves ( BD 554).

Pliocene. Spain: Estepona : 4 valves ( BD 555 ) . Italy: Piedmont: Valle Botto: 1 valve ( BD 556 ) ; Emilia-Romagna: Cava di Campore : 1 valve ( BD 557 ) , Rio Merli : 2 valves ( CT) ; Sicily: Altavilla ( type material plus 25 valves, BD 558, Fig. 76I View FIGURE 76 ). Pleistocene . Italy: Tuscany: Capraia Island-Capo Corso -350/ 500m: 7 valves ( BD 559 ) , Calabria: San Procopio : 2 valves ( BD 560 , Fig. 76L View FIGURE 76 ). Recent. Mediterranean Sea : Spain: Alboran Island -80/ 150 m (1 valve, BD 561, Figs 76M–N View FIGURE 76 ) ; Italy: Alghero - 180 m (3 valves, BD 562, Figs 76O–P View FIGURE 76 ). Maximum width of the valves: 4 / 5.7 / 8 mm .

Diagnosis. Head valve semicircular, intermediate valves broadly rectangular, carinate in anterior profile, moderately elevated, mucro inconspicuous, tail valve semicircular, mucro subcentral and little elevated. Tegmentum rough, sculptured with radial striae of quadrangular, elevated, more or less elongated and dense nodules in HV, LA, PMA, very few splitting, and longitudinal riblets on each side in CA, AMA, JA smooth. Articulamentum with apophyses short and wide, slit formula 7 / 1 / 8–10.

Description. Head valve semicircular, posterior margin widely V-shaped, with a rounded notch at apex. Intermediate valves broadly rectangular (W/L = 2.94–3.26), carinate in anterior profile, moderately elevated (H/ W = 0.34–0.48), 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 elevated. Tail valve semicircular, width about twice length (W/L = 1.90–2.04), anterior margin as in intermediate valves, mucro subcentral and little elevated, antemucronal slope slightly convex, postmucronal slope slightly concave.

Tegmentum rough. HV, LA and PMA sculptured with radial striae of quadrangular, elevated, more or less elongated and dense nodules (HV 16–22 at apex, very few splitting, LA 2–4, one of which can split, PMA 16–22, a few splitting), a few growth lines, little evident. CA and AMA sculptured with 11–16 longitudinal riblets on each side, normally all reaching anterior margin, more irregular and converging towards jugum, JA generally smooth, or in some cases irregularly covered by converging longitudinal riblets.

Articulamentum with apophyses short and wide, rounded, jugal sinus not very wide, almost straight to slightly concave, insertion lamina divided into short and rough denticles of irregular width, slit formula 7 / 1 / 8–10.

Remarks. The fossil record of Stenosemus juliuspisai sp. nov. appears limited to the Mediterranean Pliocene ( Italy and Spain) and Pleistocene ( Italy). Dell’Angelo et al. (1999), in their study of the chitons from the Miocene (Tortonian) of Borelli ( Italy), described some valves of the genus Stenosemus [as Ischnochiton ( Simplischnochiton) exaratus ] now attributed to S. praedolii sp. nov. (see below), illustrating also an intermediate valve from Altavilla Milicia (Dell’Angelo et al. 1999: pl. 3, fig. 6) which is attributable to S. juliuspisai sp. nov.

The studied material could also be attributed to the genus Ischnochiton Gray, 1847 , the generic attribution to Ischnochiton or Stenosemus is mainly based on the characters of the soft parts, e.g., the dorsal girdle covered with conical scales in Stenosemus , with imbricating, generally striated scales in Ischnochiton ( Kaas & Van Belle 1990) . The attribution to the genus Stenosemus is tentative, based on the great similarity of the valves here discussed with valves pertaining to Stenosemus [e.g., S. dolii ( Van Belle & Dell’Angelo, 1998), S. vanbellei (Kaas, 1985) , S. exaratus (G.O. Sars, 1878) ].

The nodules present along the radial striae of the lateral areas on intermediate valves are highly variable in shape, size, and density; however, they are consistently distinct, elevated, and well separated from one another. We also provisionally include the intermediate valve from the Pliocene/Pleistocene of Estepona, Spain —figured in Dell’Angelo et al. (2004: pl. 7, figs 2, 5, 6) as Ischnochiton ( Stenosemus) aff. vanbellei Kaas, 1985 —within the morphological range of Stenosemus juliuspisai sp. nov. Although the sculpture of the lateral areas appears different at first glance, we consider this variation to fall within the species’ variability and await additional material to confirm the precise taxonomic attribution. Some extant single intermediate valves of Stenosemus juliuspisai sp. nov. are present in the BD collection (currently under study, unpublished), in samples of debris collected by fishing boats, from Alghero (- 180m, coral bottom) and Alboran Island (-80/ 150m). Some of these valves are illustrated for comparison ( Figs 76M–P View FIGURE 76 ). No significant differences were found between the fossil and extant valves described in this study.

Comparisons. The intermediate valves of Stenosemus juliuspisai sp. nov. with only two radial striae of nodules present in the lateral areas show at first sight some similarities with S. vanbellei (a rare species randomly found in the Mediterranean Sea, not known as fossil), but differ mainly in the sculpture of the central area (11–16 longitudinal riblets on each side, normally all reaching anterior margin, vs. 7–9 longitudinal sulci in S. juliuspisai sp. nov., a little sinuous, the three or four innermost sulci not reaching the anterior margin).

Distribution. Lower Pliocene: central Mediterranean, Italy: Liguria: Borzoli, Bussana, Rio Sant’Antonino, Zinola ( Laghi 1977; Dell’Angelo et al. 2013, 2021b; this study). Pliocene: western Mediterranean, Estepona Basin, Spain: Estepona (Dell’Angelo et al. 2004); central Mediterranean, Italy: Altavilla Milicia ( Dell’Angelo et al. 2012), Valle Botto, Cava di Campore, Rio Merli (this study). Pleistocene: central Mediterranean, Italy: Capraia Island-Capo Corso 350-500 m ( Dell’Angelo & Giusti, 1997), San Procopio (this study). Recent: Mediterranean Sea, Italy: single valves from Alghero and Alboran Island (this study).