Acanthochitona faluniensis (de Rochebrune, 1882 )

Acanthochitona faluniensis (de Rochebrune, 1882)

Fig. 135 View FIGURE135

Acanthochites faluniensis de Rochebrune, 1882, p. 60 .

Acanthochiton faluniensis ; Šulc 1934, p. 17, pl. 1, fig. 29, pl. 2, figs 30–32, textfig. 2; Ashby & Cotton 1935, p. 391; Toth 1942, p. 504; Sieber 1959, p. 275; Stancu & Andreescu 1968, p. 459.

Acanthochiton (?) faluniensis ; Ashby & Cotton 1935, p. 391.

Acanthochiton falunensis (sic); Rado & Mutiu 1970, p. 144, 148, pl. 7, figs 6, 8–10; Rado 1971, p. 178; Macioszczyk 1988, p. 55, pl. 3, figs 8–9.

Acanthochiton falunesis (sic); Rado 1969, p. 193, pl. 2, figs 32–34.

Acanthochitona faluniensis ; Bałuk 1971, p. 463, pl. 2, figs 10–15; Jakubowski & Musiał 1977, p. 78, pl. 3, fig. 3; Laghi 1977, p. 111; Bałuk & Radwanski 1979, p. 231; Van Belle 1981, p. 37; Bałuk 1984, p. 291, pl. 8, figs 1–5; Studencka & Studencki 1988, p. 41, pl. 4, fig. 3; Dell’Angelo & Giusti 1997, p. 56; Ruman in Kováč et al. 1999, pl. 2, figs 1–2; Dell’Angelo et al. 1999, p. 273, 285; Dulai 2001, p. 43, pl. 2, figs 1–3; Kroh 2002, p. 10; Kroh 2003, p. 134, pl. 1, figs 6–7; Dulai 2005, p. 39, pl. 4, figs 5–10, pl. 5, figs 1–4; Zágoršek 2006, p. 96, fig. 1; Dulai & Studencka 2007, p. 17; Koskeridou et al. 2009, p. 322; Studencka & Dulai 2010, p. 268, text-fig. 7A–F; Dell’Angelo et al. 2013, p. 96; Ruman & Hudácková 2015, p. 164, figs 4.5–4.10; Dell’Angelo et al. 2016, p. 86, 98; Dell’Angelo et al. 2018b, p. 41, 49, 53, tab. 17; Dell’Angelo et al. 2020b, p. 37, tab. 9; Dulai & Katona 2024, p. 42, figs 30–38.

Chiton ( Acanthochites) fascicularis var. [non Acanthochitona fascicularis ( Linnaeus, 1767) View in CoL ]; Reuss 1860, p. 260, pl. 8, figs 4–6.

Chiton fascicularis var. [non Acanthochitona fascicularis ( Linnaeus, 1767) View in CoL ]; Procházka 1895, p. 99 ¸ Procházka 1900, p. 117.

Acanthochitona fascicularis View in CoL [non Acanthochitona fascicularis ( Linnaeus, 1767) View in CoL ]; Tomašových 1998, p. 360, 362, pl. 1, figs 1–6 ( fide Dulai 2005); Vetters 1910, p. 157; Dell’Angelo et al. 2007a, p. 44, fig. 4e.

Acanthochiton aff. fascicularis View in CoL [non Acanthochitona fascicularis ( Linnaeus, 1767) View in CoL ]; Sieber 1958, p. 144; Sieber 1959, p. 275.

Acanthochitona communis View in CoL ; Jakubowski & Musiał 1979, p. 51, pl. 2, fig. 3 ( fide Ruman & Hudácková 2015).

Acanthochiton sp. I Šulc, 1934, p. 19, pl. 2, fig. 34; Van Belle 1981, p. 71.

Acanthochiton sp. II Šulc, 1934, p. 20, pl. 2, fig. 35.

Acanthochiton sp. IV Šulc, 1934, p. 20, text-fig. 3.

Cryptoconchus ( Pseudoacanthochiton) steinabrunensis Šulc, 1934, p. 16 , pl. 1, figs 25–28, textfig. 1; Van Belle 1981, p. 73; Dell’Angelo et al. 1999, p. 284.

Cryptoconchus ( Pseudoacanthochiton) steinabrunnensis (sic); Sieber 1958, p. 143; Van Belle 1981, p. 73.

Acanthochiton View in CoL ( A.) steinabrunensis ; Marinescu 1964, p. 182, pl. 3, fig. 3a–c.

Acanthochiton View in CoL ( A) steinarbunensis (sic); Stancu & Andreescu 1968, p. 459.

Acanthochitona steinabrunensis : Puchalski 2008

Craspedochiton steinabrunensis ; Studencka & Studencki 1988, tab. 2, 3.

Type material. Location currently unknown; not in NHMW.

Type locality. Rudoltice (Czech Republik).

Type stage. Middle Miocene.

Material examined. Middle Miocene: Central Paratethys : Austria: Gainfarn: 2 valves ( BD 1010 , NHMW 1859 /0027/0193), Niederleis: 2 valves ( NHMW 2002 /0087/0001); Czech Republic: Kninice: 1 valve ( NHMW 1868 /0001/0119), Lysice: 3 valves ( NHMW 1865 /0015/0162), Portzeich: 4 valves ( NHMW 1871 /0010/0211); Romania: Bujtur: 1 valve ( NHMW 2010 /0256/0022), Kostej: 10 valves ( BD 1011 , NHMW 2010 /0256/0023, Figs 135I–L View FIGURE135 ), Lăpugiu de Sus: 20 valves ( BD 1012 , NHMW 1868 /0001/0602, 2010/0256/0015, 2010/0256/0019, Figs 135A–B View FIGURE135 ); Hungary: Bánd: 33 valves ( BD 1013 ) , Borsodbóta : 1 valve ( BD 1014 ) , Letkés : 31 valves ( BD 1015 ) , Várpalota : 8 valves ( BD 1016 ) ; Eastern Paratehys : Ukraine: Horodok: 42 valves ( BD 1017 ) , Kupin : 42 valves ( BD 1018 ) , Varovtsy : 500+ valves ( BD 1019 , Figs 135C–H, 135M–N View FIGURE135 ), Velyka Levada: 30 valves ( BD 1020 ) , Zalistsi : 2 valves ( BD 1021 ) .

Acanthochitona sp. I : Czech Republic: Hrusovany : NHMW 1861/0011/0202, intermediate valve ( Figs 135O–P View FIGURE135 , type figured by Šulc). Maximum width of the valves: 6 / 7 / 5 mm.

Description. Head valve semicircular, posterior margin straight, apex scarcely evident. Intermediate valves broadly rectangular (WT/LT = 1.45–1.89), moderately elevated (H/W = 0.37–0.64), semicarinate in anterior profile, posterior margin slightly concave on both sides of pronounced apex, jugal area generally narrow, longitudinally striated, raised, neatly separated from lateropleural area. Tail valve elliptical to circular, just straighter in jugal area (WT/LT = 1.20–1.70), jugal area longitudinally striated, raised, neatly separated from lateropleural area, mucro well evident in central position, antemucronal slope slightly convex, postmucronal slope concave behind the mucro.

Whole tegmentum (except JA) sculptured with densely packed roundish to oval granules, rather elevated, irregularly arranged along arched lines, with flat or slightly concave surface, sometimes with a characteristic incision on surface, JA longitudinally striated; granules small, widely separated from each other, of variable size, maximum diameter 110 μm, with a central megalaesthete generally surrounded by 1 to 4 irregularly arranged micraesthetes.

Articulamentum well developed, apophyses quadrangular and very protruding, delimiting a wide jugal sinus, expanded and completely surrounding tail valve, except for jugal margin, slit formula 5 / 1 / 2+.

Remarks. Acanthochites faluniensis de Rochebrune, 1882 was described with the following diagnosis: “ Chiton ( Acanthochites) fascicularis Lin. var. Reuss, loc. cit., p. 260, n° 110, Tag. VIII, fig. 4, 6. A. --- Testa elongata , augusta; valvis intermediis, summitate sulcatis, sulcis latis profundis, utrinque longitudinaliter granatis; granis secessis; valva postica, lata , rotundata, intense rostrata, antice radiatim, postice concentrice granosa. Long. 0,002. Lat. 0,001. Hab. Sables de Rudelsdorf ”. And de Rochebrune adds: “ Reuss ne voit aucune différence essentielle, entre cette espèce et l’A. fascicularis Lin. et il la réunit provisoirement à elle… Une grande confusion règne danse le détermination des Acanthochites , compris dans le groupe du fascicularis de Linné ”.

Considered conspecific with A. fascicularis ( Linnaeus, 1767) by some Authors (e.g., Laghi 1977; Dell’Angelo et al. 1999, 2004, 2007a), A. faluniensis differs from the extant species on some morphological characters ( Bałuk 1971, 1984; Dulai 2001, 2005; Kroh 2003; Zágoršek 2006; Ruman & Hudácková 2015).

The noteworthy variability of outlines of intermediate and tail valves, and of postmucronal slopes of tail valves of A. fascicularis is documented by Leloup (1941: figs 2–3; 1968: figs 4–6) and Dell’Angelo & Smriglio (1999: fig. 9) for Recent Mediterranean specimens.

The putative differences between the two taxa are summarized in Studencka & Dulai (2010):

• the tegmentum outline (the lateral margin of the tegmentum which usually is arched, rarely falciform in the posterior part in A. faluniensis , compared to more or less concave near the jugal area in A. fascicularis );

• the ornamentation, with small, rounded and very crowded granules arranged in curved series in two directions, parallel to the jugum and radiating from it towards the outer margin in A. fascicularis ; compared with finer granulation consisting of smaller numbers of distinctly larger rounded granules, each with 1–4

micraesthetes, arranged along orderly arched lines in A. faluniensis . The curved series of granules in in two directions in A. fascicularis is taken verbatim from the description of neotype of A. fascicularis designated by Kaas (1985a: 585, figs 1–6);

• the “gentle” postmucronal slope of the almost circular to more ellipsoidal tail valve of A. faluniensis ,

compared to deeply concave directly behind the sharp mucro in A. fascicularis .

In our opinion, it is somehow subjective to identify the arrangement of granules in curved series radiating from the jugum as postulated; instead, while one or more series of granules may appear parallel to the jugum, other granules are disposed without any apparent order. Furthermore, SEM images do not seem to clearly document any distinct arrangement in striae of the granules in A. fascicularis ( Fischer & Renner 1979) . About the “finer granulations” of A. faluniensis, Fischer & Renner (1979) reported a granules’ width of 50–80 μm, with 0–3 micraesthetes for each central megalaesthete. Thus, a convincing separation between A. faluniensis and A. fascicularis based upon unquestionable morphological characters of loose valves seems extremely difficult at present. We prefer, however, to keep them provisionally distinct mainly because of their different paleobiogeographic domains.

Cryptoconchus ( Pseudoacanthochiton) steinabrunensis Šulc, 1934 , has been described upon three valves from the Middle Miocene of Steinabrunn ( Austria), and recorded also from Romania ( Marinescu 1964; Stancu & Andreescu 1968). This species shows a tegmentum sculpture closest to that of Acanthochitona faluniensis , but with the tail valve characterized by larger number of slits, of which two, better developed, correspond to the slits in the genus Acanthochitona View in CoL , and the other ones are located between them. Šulc (1934) described the new genus Pseudoacanthochiton based on this character (see below). We consider that the greatest number of slits in the tail valve may fall in the intraspecific variability of the Acanthochitona spp , as already evidenced by Bałuk (1984), Dell’Angelo et al. (1999) and this study [see below for Craspedochiton ( Pseudoacanthochitona) ambiguus Laghi, 1977 considered as a synonym of A. fascicularis ], and we, therefore, consider Cryptoconchus ( Pseudoacanthochiton) steinabrunensis a junior synonym of A. faluniensis .

Acanthochitona sp , I was described by Šulc (1934) on the basis of a single intermediate valve (incomplete, width 2.5 mm, ca 5.2 mm after completion) from Hrušovany ( Czech Republic), and differs from A. faluniensis by its ornamentation, with granules which are twice as large and separated by larger intervals. The material at NHMW is represented by the intermediate valve figured by Šulc ( Figs 135O–P View FIGURE135 ), and we can therefore confirm that Acanthochitona sp. I View in CoL must be considered a synonym of A. faluniensis .

Also Acanthochiton sp. II Šulc, 1934 [a single tail valve from Rudoltice “ that is conspicuously elongated transversally and which shows more strongly developed folds of the side regions ” ( Šulc 1934, p. 20, translated by A. Kroh)], and Acanthochiton sp. IV Šulc, 1934 (a single tail valve from Steinabrunn with a slightly different shape) could be considered as junior synonyms of A. faluniensis .

Schmidt-Petersen et al. (2015) described a new recent species of Acanthochitona View in CoL from the Mediterranean ( France) and gave a comparison of the morphological differences between the new species ( A. pilosa View in CoL ) and the other three Mediterranean living species, A. fascicularis , A. crinita View in CoL and A. oblonga View in CoL ( Schmidt-Petersen et al. 2015: figs 5–6, tab. 1). They considered a distinctive feature of A. fascicularis the presence of a distinct incision in all the granules (e.g., Bonfitto et al. 2011: fig. 1), a character not always present in hundreds of valves of A. fascicularis examined ( pers. obs.). This incision is well visible in the valves from Rovinj (Adriatic Sea) illustrated by Fischer & Renner (1979: figs 4–5), but the structure of granules is not well made explicit in the description and figures of the Neotype of A. fascicularis designated by Kaas (1985a: 585–588, figs 1–6).

As discussed above, the morphology of valves of Acanthochitona fascicularis and A. faluniensis is rather close, with respect to the shape of valves and granules. The shape of the valves of A. faluniensis shows a great variability, e.g., the head valve, more frequently with apex scarcely evident, but that can sometimes be very pronounced (see Ruman & Hudácková 2015: fig. 4.9). The shape of granules is variable, sometimes the surface shows a characteristic incision on the surface, as well figured by Fisher & Renner (1979: fig. 4–6) and Bonfitto et al. (2011: fig. 1) on living specimens of A. fascicularis . In some cases, the granules show a narrow ridge pointing roughly towards the apex of the valves ( Figs 135D, 135P View FIGURE135 ). We prefer at present to keep the two species distinct, pending future confirmation or otherwise of their possible synonymy, considering A. faluniensis a species restricted to the Paratethys.

Comparisons. Acanthochitona faluniensis is morphologically close to A. fascicularis ,

Distribution. Middle Miocene: Central Paratethys (Langhian-Serravallian): Austria: Gainfarn, Niederleis, Steinabrunn ( Šulc 1934; Kroh 2003; this study), Czech Republic: Drnovice, Knínice, Lysice, Rudoltice, Portzeich, Sudice, Vranovice, Židlochovice ( Šulc 1934; Kroh 2003; Zágoršek, 2006; this study), Slovakia: Kúty, Rohožník, Devínska Nová Ves ( Tomašových 1998; Kováč et al. 1999; Ruman & Hudácková 2015), Hungary: Bánd, Borsodbóta, Letkés, Szokolya, Várpalota ( Studencka & Studencki, 1988; Dulai 2001, 2005; Dulai & Katona 2024; this study), Poland: Korytnica, Lychów, Miasteczko, Monastyrz, Navodzice, Rybnica, Trzesiny, Węglini, Weglinek ( Bałuk 1965, 1971, 1984; Jakubowski & Musiał, 1977, 1979; Studencka & Studencki, 1988; Macioszczyk, 1988), Romania: Bujtur, Lăpugiu de Sus ( Zilch 1934; Dell’Angelo et al. 2007a; this study), Bulgaria: Trnienie (Jakubowski & Musiał, 1979); Eastern Paratehys: Ukraine: Horodok, Kupin, Olesko, Szuszkowce, Varovtsi, Velyka Levada, Zalistsi ( Studencka & Dulai 2010; this study).