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

Ischnochiton sigwartae sp. nov.

Fig. 61 View FIGURE 61

Type material. Holotype: MSNG 62639 View Materials , tail valve, width 3.6 mm ( Figs 61I–K View FIGURE 61 ) . Paratype 1: MSNG 62640 View Materials , head valve, width 4.6 mm ( Figs 61A–C View FIGURE 61 ) . Paratype 2: MSNG 62641 View Materials , intermediate valve, width 4.2 mm ( Figs 61D–F View FIGURE 61 ) . Paratype 3: MNHN.F.A98470, intermediate valve, width 3 mm ( Figs 61G–H View FIGURE 61 ) . Paratype 4: MNHN.F.A98471, tail valve, width 3 mm ( Fig. 61L View FIGURE 61 ) . Paratype 5: SMF 380819 About SMF , intermediate valve, width 3 mm ).

Type locality. Archi S. Francesco, Reggio Calabria ( Calabria, Italy) .

Type stage. Upper Pleistocene .

Etymology. The specific name honors Julia Sigwart (Senckenberg Research Institute and Museum Frankfurt and Queen’s University Belfast), for her prominent contributions to the study of Recent and fossil chitons.

Material examined. Upper Pleistocene: Italy: Archi S. Francesco: type material plus 17 valves ( BD 519 ). Maximum width of the valves: 4.6 / 5.8 / 4.5 mm .

Diagnosis. Head valve semicircular, intermediate valves broadly rectangular, moderately elevated, rounded, without trace of apex, Tail valve semi-circular, mucro centrally swollen but not prominent. Tegmentum sculptured with concentric, large and irregular ribs in HV, LA, PMA, continuing longitudinally in CA and AMA, someone joined together, others splitting, tegmentum fully covered by aesthetes, both on nodular elevations and between them. Articulamentum with apophyses rounded, slit formula: 12 / 2 / 9–10.

Description. Head valve semicircular, posterior margin widely V-shaped. Intermediate valves broadly rectangular, moderately elevated (H/W = 0.28–0.37), rounded in anterior profile, anterior margin almost straight, side margins slightly rounded, posterior margin straight, without trace of apex, lateral areas not very elevated. Tail valve semicircular, mucro centrally swollen but not prominent, antemucronal slope slightly convex, postmucronal slope slightly concave.

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 aesthetes, both on nodular elevations (without a clearly recognizable structure of megalaesthetes and micraesthetes) and between them.

Articulamentum with apophyses rounded, trapezoidal in tail valve, jugal sinus wide, insertion lamina divided into irregular teeth, slit formula: 12 / 2 / 9–10.

Remarks. The fossil record of Ischnochiton sigwartae sp. nov. is limited to the upper Pleistocene of Archi S. Francesco ( Calabria, Italy). The material is quite well preserved, although all the intermediate valves are somewhat incomplete.

Comparisons. Ischnochiton sigwartae sp. nov. is similar to I. lesporti sp. nov., from which it shares the sculpture of the valves, but differs by the more flattened intermediate valves (H/W = 0.28–0.37 vs. 0.40–0.51 in I. lesporti sp. nov.), the slit formula (12 / 2 / 9–10 vs. 12–13 / 2 / 12–14 in I. lesporti sp. nov.), and the different geographic/stratigraphic distribution (upper Pleistocene of S. Italy vs. lower/Middle Miocene of the Aquitaine Basin for I. lesporti sp. nov.).

Distribution. Upper Pleistocene: central Mediterranean, Italy: Archi S. Francesco (this study).