Rhyssoplax garillii, Dell’Angelo & Sosso & Taviani, 2025

Rhyssoplax garillii sp. nov.

Fig. 91 View FIGURE 91

Chiton sp. Dell’Angelo, Garilli, Germanà, Reitano, Sosso & Bonfitto, 2012, p. 61, figs 5A–K.

Chiton miocenicus Var. [non Rhyssoplax miocenica ( Michelotti, 1847) ]; Seguenza 1876, p. 264.

Type material. Holotype MSNG 62661 View Materials , tail valve, width 4.4 mm ( Figs 91J–L View FIGURE 91 ) . Paratype 1: MSNG 62662 View Materials , head valve, width 2.8 mm ( Figs 91A–B View FIGURE 91 ) . Paratype 2: MSNG 62663 View Materials , intermediate valve, width 3.5 mm ( Figs 91E–G View FIGURE 91 ) . Paratype 3: MNHN.F.A98476, intermediate valve, width 5.2 mm ( Figs 91C–D View FIGURE 91 ) . Paratype 4: MNHN.F.A98477, tail valve, width 4.2 mm ( Figs 91H–I View FIGURE 91 ) . Paratype 5: SMF 380821 About SMF , intermediate valve, width 5.8 mm . Paratype 6: SMF 380822 About SMF , tail valve, width 4.2 mm ).

Type locality. Altavilla Milicia ( Sicily, Italy) .

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

Etymology. The specific name honors Vittorio Garilli, for his contribution to the study of Recent and fossil mollusks of the Mediterranean basin.

Material examined. Upper Pliocene: Italy: Altavilla : type material plus 37 valves ( AG, AR, BD 742 ). Maximum width of the valves: 7.3– 6–6.7 mm .

Diagnosis. Head valve semi-oval, intermediate valves broadly rectangular, moderately elevated, carinate, apex small, sharp-pointed, tail valve more or less triangular, mucro in anterior position. Tegmentum smooth in HV, LA, PMA, sculptured with up to 12 longitudinal folds at both sides of smooth jugum, aesthetes very dense.Articulamentum with apophyses wide, rounded, connected by a short, dentate jugal plate, teeth pectinate,slit formula: 9 / 1 / 9–12.

Description. Head valve semi-oval, front slope straight, posterior margin widely V-shaped. Intermediate valves broadly rectangular (W/L = 2.76–2.94), moderately elevated (H/W = 0.35–0.47), carinate in anterior profile, anterior margin straight between apophyses, side margins truncated, posterior margin straight but for the small, sharp-pointed apex, lateral areas somewhat raised, clearly defined. Tail valve more or less triangular, W/L = 1.76–2.10, anterior margin straight between apophyses, mucro in anterior position, antemucronal slope straight to slightly convex, postmucronal slope slightly concave.

HV, LA and PMA smooth, concentric growth lines well marked. CA and AMA sculptured with up to 12 longitudinal folds at both sides of smooth jugum, innermost folds narrow, not reaching valve’s front margin. Aesthetes very dense, each megalaesthete accompanied by many micraesthetes.

Articulamentum with apophyses wide, rounded, connected across narrow, shallow sinus by a short, dentate jugal plate, slit formula: 9 / 1 / 9–12, slits shallow, inequidistant, slit rays finely indicated, teeth short, pectinate, eaves narrow, porous.

Remarks. The known fossil record of Rhyssoplax garillii sp. nov. is limited thus far to the Pliocene of Altavilla Milicia, in Sicily. The material examined belongs to the group of Rhyssoplax spp . characterized by the smoothness of HV, LA and PMA. These features are shared by Rhyssoplax corallina ( Risso, 1826) , one of the most common species of the Italian Pliocene, R. phaseolina ( Monterosato, 1879) , R. etrusca (Dell’Angelo & Forli, 1995), R. assurrecta Dell’Angelo et al., 2018 and R. capecchii ( Chirli, 2004) . However, the valves from Altavilla Milicia differ from R. corallina for a series of fairly constant characters (constants within the broad range of variability known for R. corallina ), and such as to justify the establishment of a new species.

Rhyssoplax garillii sp. nov. has already been reported by Seguenza (1876) as “ Chiton miocenicus Michelotti, 1847 Var. ” with a short diagnosis: “ Questa forma pliocenica differisce dal tipo della Superga per le linee d’accrescimento impresse e meglio distinte ”. Seguenza underlined the presence of marked growth lines as a distinctive character from C. miocenicus , and his short description was most probably based on material conspecific with the present one.

Comparisons. Rhyssoplax garillii sp. nov. differs from R. corallina ( Risso, 1826) by the more or less triangular shape of the tail valves (more semicircular in R. corallina ), the mucro in anterior position (subcentral in R. corallina ), the anterior profile of the intermediate valves decidedly carinate (semicarinate and tending to be more rounded in R. corallina ), the presence of concentric growth lines well marked (vaguely indicated in R. corallina ).

Distribution. Upper Pliocene: central Mediterranean, Italy: Altavilla Milicia ( Dell’Angelo et al. 2012; this study).