Ischnochiton lesporti, Dell’Angelo & Sosso & Taviani, 2025

Ischnochiton lesporti sp. nov.

Fig. 65 View FIGURE 65

Ischnochiton rissoi View in CoL [non Ischnochiton rissoi ( Payraudeau, 1826) View in CoL ]; Dell’Angelo et al. 2018a, p. 22, figs 5A–I.

“ Chiton View in CoL ” sp. Lesport & Cahuzac, 2005, p. 86, 96, tab. 1 ( pars).

Type material. Holotype, MSNG 62644 View Materials , tail valve, width 3.5 mm ( Figs 65I–L View FIGURE 65 ) . Paratype 1, MSNG 62645 View Materials , intermediate valve, width 3.3 mm ( Figs 65F–H View FIGURE 65 ) . Paratype 2, MSNG 62646 View Materials , head valve, width 3.7 mm ( Figs 65A–B View FIGURE 65 ) . Paratype 3, MNHN.F.A98472, intermediate valve, width 5 mm ( Figs 65C–E View FIGURE 65 ) from Maureilhan ( France) . Paratype 4, MHNBx 2024.3.1, intermediate valve, width 4.3 mm, from Coupe du fossé près de La Solitude ( France) .

Type locality. Noaillan , Gamachot ( France) .

Type stage. Lower Miocene (Burdigalian) .

Etymology. The name honors Jean-François Lesport ( Sainte-Hélène, France), who collected part of the material here discussed. for his contribution to the knowledge of the malacofauna of the Aquitaine Basin.

Material examined. Lower Miocene (Burdigalian): France: type material plus Carrière Vives: 12 valves ( JFL, PR), Coupe du fossé près de La Solitude: 1 valve ( JFL), Gamachot: 63 valves ( AC, BD 531 , JFL, PR), Lahitet: 1 valve ( PR), Maureilhan: 8 valves ( BD 532 ). Middle Miocene (Serravallian) : France: Carré : 1 valve ( DA). Maximum width of the valves: 7.5 / 6.2 / 4.7 mm .

Diagnosis. Head valve semicircular, intermediate valves broadly rectangular, elevated, rounded, without trace of apex, tail valve semicircular, mucro subcentral to slighty anterior, swollen but not prominent. Tegmentum sculptured with concentric, large and irregular ribs in HV, LA, PMA, ribs continuing longitudinally in CA, AMA, someone joined together, others splitting, tegmentum fully covered by aesthetes, both on nodular elevations and between them. Articulamentum with apophyses small, slit formula: 12–13 / 2 / 12–14.

Description. Head valve semicircular, posterior margin widely V-shaped. Intermediate valves broadly rectangular (W/L = 2.35–3.00), moderately to highly elevated (H/W = 0.40–0.51), regularly rounded in anterior profile, anterior margin straight on jugal side, side margins slightly rounded, posterior margin straight, without trace of apex, lateral areas poorly elevated. Tail valve semicircular (W/L = 1.50–1.76), mucro subcentral to slighty anterior, swollen but not prominent, antemucronal slope almost straight, postmucronal slope almost straight or slightly concave just under mucro.

HV, LA and PMA sculptured with concentric, large and irregular ribs, very close to each other; ribs continue longitudinally on CA and AMA, more irregular, someone joined together, others splitting in various areas, mainly near anterior margin and towards LA. Tegmentum fully covered by megalaesthetes and micraesthetes, both on nodular elevations and between them.

Articulamentum with apophyses small, rounded, trapezoidal in tail valve, jugal sinus wide, insertion lamina divided into irregular teeth, slit formula: 12–13 / 2 / 12–14.

Remarks. The fossil record of Ischnochiton lesporti sp. nov. is limited to the lower and Middle Miocene of the Aquitaine Basin ( France). A lot of valves from the Burdigalian and Serravallian of the Aquitaine Basin has been attributed to Ischnochiton rissoi ( Payraudeau, 1826) by Dell’Angelo et al. (2018a), and really the two species ( I. rissoi and I. lesporti sp. nov.) are very similar.

Ischnochiton lesporti sp. nov. shows LA sculptured with concentric, almost longitudinal ribs, which continue longitudinally in CA, arranged more irregularly than in I. rissoi . This difference in the sculpture is considered sufficient to warrant separation of I. lesporti sp. nov. from I. rissoi .

Comparisons. The species is close to Ischnochiton sigwartae sp. nov. (see above and Tab. 9). Ischnochiton lesporti sp. nov. is superficially similar to I. striolatus ( Gray, 1828) , a living species from the western Atlantic frontage (from North Carolina to Brazil); it differs from I. lesporti sp. nov. mainly by the different sculptures of CA and AMA and the geographic/stratigraphic distribution ( Kaas & Van Belle 1990).

Distribution. Lower Miocene: northeastern Atlantic (Burdigalian): Aquitaine Basin, France: Carrière Vives, Coupe du fossé près de La Solitude, Gamachot, Lahitet, Maureilhan ( Dell’Angelo et al. 2018a; this study). Middle Miocene: northeastern Atlantic (Serravallian): Aquitaine Basin, France: Carré ( Dell’Angelo et al. 2018a; this study).