Ischnochiton crovatoi, Dell'Angelo, Sosso & Bonfitto, 2019

Ischnochiton crovatoi View in CoL Dell’Angelo, Sosso & Bonfitto, 2019

Fig. 56 View FIGURE 56

Ischnochiton crovatoi View in CoL Dell’Angelo, Sosso & Bonfitto, 2019a, p. 45, figs 2.A–O.

Type material. Holotype MZB 50513 (tail valve, width 5.3 mm, Figs 56E–H View FIGURE 56 ). Paratypes: MZB 50514 (head valve, Figs 56A–B View FIGURE 56 ), MZB 50515 (intermediate valve, Fig. 56C View FIGURE 56 ).

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

Type stage. Upper Pleistocene .

Material examined. Lower Pleistocene: Italy: Archi, Fornace Aloi ( lower Pleistocene ): 1 valve ( BD 446 ). Upper Pleistocene : Italy: Archi S. Francesco: type material plus 19 valves ( BD 447 , Fig. 56D View FIGURE 56 ). Maximum width of the valves: 6.8 / 5.5 / 5.3 mm .

Description. Head valve semicircular, posterior margin widely V-shaped, front slope straight. Intermediate valves broadly rectangular, anterior margin slightly convex, side margins rounded, posterior margin straight, apex inconspicuous, lateral areas not raised, separated from central area by different sculpture. Tail valve semicircular (W/L = 1.71), anterior margin slightly convex, mucro subcentral, swollen but not prominent, antemucronal slope slightly convex, postmucronal slope slightly concave just behind mucro.

HV, LA and PMA sculptured with radial nodulose riblets ( HV 34–42 , 34 in paratype; LA 5; PA 38 in holotype), some of which tending to split near outer margins, roundish to squarish nodules become larger towards periphery. CA and AMA sculptured with nodulose longitudinal riblets ( CA ca. 20–30 on half valve, some more irregular near side margin; AMA 42 in holotype), with granules come nearer to each other, not distinctly separated .

Articulamentum with teeth irregular, slit formula: 12 / 1 / 9, slit rays well visible.

Remarks. The fossil record of Ischnochiton crovatoi Dell’Angelo, Sosso & Bonfitto, 2019 is limited to the Pleistocene of S. Italy. The material examined is in some case not well preserved or complete (especially the intermediate valves, none of them complete), and show a certain variability regarding the number of radial nodulose riblets on HV, ranging between 34 and 42, counting only the riblets without splitting (ca. 37–47 counted on the anterior margin).

Comparisons. The characteristic ornamentation of Ischnochiton crovatoi , formed by radial nodulose riblets on HV, LA and PMA, distinguishes it from the common Mediterranean species I. rissoi ( Payraudeau, 1826) ; in this latter species the sculpture consisting of concentric wavy lirae often crossed by fine radiating grooves, that gives to the tegmentum a granular outlook.

Distribution. Pleistocene: central Mediterranean, Italy: Archi S. Francesco, Archi Fornace Aloi ( Dell’Angelo et al. 2019a).