Ischnochiton ligusticus, Dell'Angelo, Sosso, Prudenza & Bonfitto, 2013

Ischnochiton ligusticus View in CoL Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013

Fig. 57 View FIGURE 57

Ischnochiton ligusticus View in CoL Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013, p. 78, pl. 4, figs B–M; Dell’Angelo et al. 2015a, p. 234, pl. 5, figs 10–11; Dell’Angelo et al. 2016, p. 96; Dell’Angelo et al. 2018a, p. 24; Dell’Angelo et al. 2018b, p. 53, tab. 17; Dell’Angelo et al. 2020b, p. 52, tab. 9; Dell’Angelo et al. 2021b, p. 414, figs 62–69.

Ischnochiton ulivii View in CoL (non Ischnochiton ulivii View in CoL Dell’Angelo & Forli, 1996); Sosso & Dell’Angelo 2010, p. 14, fig. p. 16.

Type material. Holotype: MZB 49983, an intermediate valve from Bussana ( Figs 57B–D View FIGURE 57 ). Paratypes: MZB 49981–49982 (tail and head valves from Caranchi and Zinola, Fig. 57A View FIGURE 57 ); MSNG 56536 (intermediate valve from Rio Torsero); MGPT PU 109800–109801 (intermediate and tail valves from Rio Torsero and Caranchi), and private collections: BD (3 valves, 2 from Bussana and 1 from Zinola), MS (1 tail valve), MP (1 tail valve from Rio S. Antonino).

Type locality. Bussana ( Liguria, Italy) .

Type stage. Lower Pliocene (Zanclean) .

Material examined. Upper Miocene: Italy: Montegibbio: 2 valves ( BD 448 , MZB 32051 ), Rio di Bocca d’Asino: 3 valves ( BD 449 , MZB 32028–32029 ). Lower Pliocene : Italy: Liguria: type material plus Borzoli: 9 valves ( BD 450 , Figs 57G–H View FIGURE 57 ), Bussana: 20 valves ( BD 451 ); Caranchi : 5 valves ( BD 452 , MP), Garlenda: 20 valves ( MP), Genova Sestri: 4 valves ( BD 453 ), Rio Sant’ Antonino : 40 valves ( MP, Fig. 57E View FIGURE 57 ), Rio Torsero : 2 valves ( BD 454 , Fig. 57F View FIGURE 57 ), Zinola: 4 valves ( BD 455 ). Maximum width of the valves: 3.2 / 3.8 / 3.6 mm .

Description. Head valve semicircular, posterior margin widely V-shaped, front slope straight. Intermediate valve broadly rectangular (W/L = 2.34–2.50), anterior margin straight, moderately elevated (H/W = 0.33), rounded to semicarinate in anterior profile, side margins slightly rounded, posterior margin practically straight, apex not very visible, lateral areas scarcely differentiated. Tail valve semicircular (W/L = 1.68–1.98), anterior margin almost straight, mucro central, not prominent, antemucronal slope practically straight, postmucronal slope slightly concave just behind mucro.

Tegmentum uniformly sculptured with very irregular granules, arranged in segments of various size and shape, slightly overlapping each other, forming rugosities. HV, LA and PMA sculptured with some rugosities acquiring vaguely concentrical zig-zag pattern, producing undulating macrosculpture. CA and AMA sculptured with rugosities sometimes giving impression of very irregular longitudinal chains of granules, or sinuose and intersecting each other, as a network of irregular, elongate pits. Each granule with many aesthetes of same size irregularly distributed.

Articulamentum with large apophyses, teeth of irregular width, deeply incised, slit formula 12 / 1 / 10–12.

Remarks. The fossil record of Ischnochiton ligusticus Dell’Angelo, Sosso, Prudenza & Bonfitto, 2013 is limited to the Miocene (Tortonian) of N. Italy (Po Basin) and the Pliocene (Zanclean) of N. Italy ( Liguria). The studied material is represented by valves sometimes incomplete and poorly preserved, especially the characters of the articulamentum are scarcely visible.

Comparisons. Ischnochiton ligusticus is superficially similar to Ischnochiton ulivii Dell’Angelo & Forli, 1996, from which it differs mainly by the very irregular sculpture, while I. ulivii is by contrast characterized by small granules quincuncially arranged on HV, LA and PMA, and by a decidedly pitted sculpture on CA and AMA.

Distribution: Upper Miocene: Proto-Mediterranean Sea (Tortonian): Po Basin, North Italy: Montegibbio, Rio di Bocca d’Asino ( Dell’Angelo et al. 2015a). Lower Pliocene: central Mediterranean, Italy: Liguria: Borzoli, Bussana, Caranchi, Garlenda, Genova Sestri, Rio S. Antonino, Rio Torsero, Zinola ( Sosso & Dell’Angelo 2010; Dell’Angelo et al. 2013, 2021b).

“ Ischnochiton ” luquei Dell’Angelo, Sosso & Taviani, 2024

Fig. 58 View FIGURE 58

“ Ischnochiton ” luquei View in CoL Dell’Angelo, Sosso & Taviani, 2024, p. 199 View Cited Treatment , fig. 4.

Type material. Holotype: MZUB 60343 View Materials , intermediate valve, width 2.5 mm ( Figs 58A–D View FIGURE 58 ) . Paratype 1: ( MZUB 60344 View Materials ), intermediate valve, width 2.8 mm ; Paratype 2: MZUB 60345 View Materials , intermediate valve, width 2.5 mm ; Paratype 3: MZUB 60346 View Materials , intermediate valve, width 2.8 mm ; Paratype 4 (MNHN-IM-2022-2405), intermediate valve, width 3.1 mm; Paratype 5 SMF 376793 About SMF , intermediate valve, width 2.8 mm ; Paratype 6 ( MZUB 60347 View Materials ), intermediate valve, width 3 mm .

Type locality. Capraia Island-Capo Corso, sediments–350/ 500 m by fishermen.

Type stage. Pleistocene, presumably last glacial.

Material examined. Pleistocene, presumably last glacial: Italy: Tuscany: Capraia Island-Capo Corso -350/ 500 m: type material plus 9 intermediate valves ( BD 251 ). Maximum width of the valves: 3.4 mm (intermediate valves) .

Description. Head and tail valve unknown. Intermediate valve broadly rectangular (W/L = 1.72–1.96), semicarinate in anterior profile, elevated (H/W = 0.45–0.50), anterior margin convex, side margins almost straight or little rounded, posterior margin almost straight at both sides of protruding apex, lateral areas raised.

Tegmentum smooth. LA smooth with some weak concentric growth lines. CA smooth, with some weak concentric growth lines, continuing from LA.

Articulamentum with large, triangular apophyses, insertion plate short with 1 slit, slit rays well visible, a second slit ray is almost always visible near posterior margin.

Remarks. “ Ischnochiton” luquei Dell’Angelo, Sosso & Taviani, 2024 is only known from the Tuscan Archipelago, Mediterranean Sea, offshore Capraia Island-Capo Corso at -350/ 500 m. Only intermediate valves are known to date.

Also, the generic attribution is difficult, many extant species with a smooth or microgranulose tegmentum are attributed to the genera Ischnochiton Gray, 1847 , Stenosemus von Middendorff, 1847 or Lepidochitona Gray, 1821 , mainly based upon the soft parts. We attribute provisionally the material studied to Ischnochiton .

Comparisons. “ Ischnochiton“luquei is superficially similar to Boreochiton ruber ( Linnaeus, 1767) , a species with an arctic-circumboreal distribution (Kaas & Van Belle 1985; Sirenko & Dell’Angelo 2023), with whom it shares the smooth tegmentum, and from which it differs by the different shape of the intermediate valves (much more elongate in B. ruber ), and the weaker concentric growth lines, more prominent in B. ruber .

Distribution. Pleistocene: central Mediterranean, Italy: Capraia Island-Capo Corso, sediments 350/ 500 m ( Dell’Angelo, Sosso & Taviani 2024).