Acanthochitona plana ( Šulc, 1934 )

Acanthochitona plana ( Šulc, 1934)

Fig. 140 View FIGURE 140

Acanthochiton planus Šulc, 1934, p. 19 , pl. 2, fig. 33; Sieber 1953, p. 184; Sieber 1959, p. 275; Laghi 1977, p. 111. Acanthochiton aff. planus ; Stancu & Andreescu 1968, p. 459.

Acanthochitona plana ; Van Belle 1981, p. 56; Dell’Angelo et al. 2018b, p. 41, 49, 53, tab. 17; Dell’Angelo et al. 2020b, p. 37, tab. 9.

Type material. Holotype NHMW 2010/0256/0001, intermediate valve, width 4.18 mm, Figs 140 A–E View FIGURE 140 .

Type locality. Pötzleinsdorf ( Austria) .

Type stage. Middle Miocene.

Material examined. Middle Miocene: Central Paratethys: Austria: Pötzleinsdorf: type material, plus 1 valve ( NHMW 2010 /0256/0008), width 3.2 mm, Figs 140 F–H View FIGURE 140 ; Hungary: Letkés: 2 valves ( BD 1157 ), Figs 140 K–L View FIGURE 140 ; Romania: Lăpugiu de Sus : 2 valves ( BD 1156 ), Figs 140 I–J View FIGURE 140 . Maximum width: 7.4 mm .

Description. Head and tail valves unknown. Intermediate valves broadly rectangular (W/L = 1.94), scarcely elevated (H/W = 0.29–0.36), semicarinate in anterior profile, posterior margin slightly concave on both sides of pronounced apex, jugal area longitudinally striated, not raised, neatly separated from lateropleural area.

Whole tegmentum (except JA) sculptured with densely packed roundish granules, rather elevated, irregularly arranged along arched lines, with flat surface, JA longitudinally striated; granules small, widely separated from each other, roundish (diameter 46–57 µm), extended with a short longitudinal rib, more oval in LA (up to 65 µm), with a central megalaesthete generally surrounded by 2–3 irregularly arranged micraesthetes.

Articulamentum well developed, apophyses quadrangular and very protruding, delimiting a wide jugal sinus, one slit in intermediate valves.

Remarks. Acanthochitona plana ( Šulc, 1934) was described based on a single intermediate valve from

Pötzleinsdorf ( Austria), flatter and with an ornamentation identical with that of A. faluniensis (de Rochebrune, 1882) . The material present at NHMW is represented by the holotype (the intermediate valve figured by Šulc, Figs 140A–E View FIGURE 140 ) and two other valves (intermediate and tail) from the same type locality, Pötzleinsdorf, of which the tail valve is here attributed to A. sandeciana Bałuk, 1965 (see below).

Comparisons. Acanthochitona plana is morphologically close to A. faluniensis , from which it differs mainly by the smaller granules and the rather flattened valves.

Distribution. Middle Miocene: Central Paratethys (Langhian-Serravallian): Austria: Pötzleinsdorf ( Šulc 1934; Sieber 1953, 1959; this study); Hungary: Letkés (this study); Romania: Delineşti ( Stancu & Andreescu 1968), Lăpugiu de Sus (this study).