Hanleya multigranosa ( Reuss, 1860 )

Hanleya multigranosa ( Reuss, 1860) View in CoL

Fig. 45 View FIGURE 45

Chiton multigranosus Reuss, 1860, p. 259 , pl. 8, figs 8a–b ( partim, non fig. 9a–b); Procházka 1895, p. 99 ( partim); Procházka 1900, p. 72, 117 ( partim).

Acanthopleura multigranosa ; de Rochebrune 1882, p. 61 ( partim).

Hanleya multigranosa View in CoL ; Šulc 1934, p. 9, pl. 1, figs 7–12; Ashby & Cotton 1935, p. 389; Malatesta 1962, p. 153, fig. 10; Laghi 1977, p. 100; Bałuk & Radwanski 1979, p. 230; Bałuk 1984, p. 287, pl. 5, fig. 1a–b; Studencka & Studencki 1988, p. 43; Bellomo & Sabelli 1995, p. 202; Dell’Angelo & Smriglio 1999, p. 90; Louwye et al. 2010, p. 275; Sirenko 2014, p. 2930, 2943; Ruman & Hudácková 2015, p. 160, figs 5.2–5.3; Dell’Angelo et al. 2016, p. 98; Dell’Angelo et al. 2018a, p. 22; Dell’Angelo et al. 2018b, p. 20, 22, 25, 52, tab. 17; Dell’Angelo et al. 2020b, p. 52, tab. 9.

Hanleya? multigranosa View in CoL ; Bałuk 1971, p. 456, pl. 1, figs 5–7; Van Belle 1981, p. 52.

non Hanleya multigranosa View in CoL ; Sabelli & Taviani, 1979, p. 158, pl. 1, fig. 4 (= H. mediterranea View in CoL , fide Sirenko 2014).

Type material. Unknown, not present in NHMV.

Type locality. Rudoltice ( Czech Republic) .

Type stage. Middle Miocene.

Material examined. Middle Miocene: Central Paratethys : Czech Republic: Porzteich: 1 valve ( NHMV 2010 /0256/0014, Figs 45E–H View FIGURE 45 ). Maximum width of the valves: 2.6 / 4.2 / 2.7 mm .

Description. Head valve semicircular, quite narrow and strongly arched. Intermediate valves broadly rectangular, semicarinate in anterior profile, side margins rounded, posterior margin almost straight, except for well developed apex in middle, lateral areas not raised. Tail valve elliptical, mucro subcentral, clearly indicated.

Tegmentum surface smooth, deprived of aesthetes among granules. HV, LA and PMA uniformly sculptured with numerous roundish granules, more irregularly arranged and more variable in shape in LA. PA and AMA sculptured with elliptical granules (up to 170 x 70 µm), arranged in longitudinal very irregular striae, granules smaller (up to 130 x 50 µm) and more closely spaced in JA, transition from small to larger granules not gradual, but rather abrupt. Each granule contains 1 megalaesthete and up to 25 microaesthetes or more, megalaesthete slightly larger in some cases, but almost same width, no aesthetes among granules.

Articulamentum with apophyses wide, rounded, insertion plates well developed both on head and tail valves, slightly pectinated on head valve.

Remarks. Hanleya multigranosa ( Reuss 1860) is a rare and poorly known species. Reuss (1860) described it on the basis of two valves from Rudoltice, a head valve ( Fig. 45A View FIGURE 45 ) and a tail one, this last ( Reuss 1860: pl. 8, figs 9a–b) with a sculpture not matching any of the species known from the Oligocene to Pleistocene of Europe, and probably not attributable to the genus Hanleya (see the discussion in Šulc). Šulc (1934) described a few valves (head, intermediate and tail, Figs 45B–D View FIGURE 45 ) from Rudoltice, indicating also two other sites for this species, Kostej ( Romania) and Porzteich ( Czech Republic), and noted that the tail valve illustrated by Reuss differs considerably from the tail valves attributed by him to Hanleya multigranosa . De Rochebrune (1882) and Procházka (1900) do not figure this species but refers to the illustrations of Šulc (1934). Bałuk (1971, 1984) described many valves from Korytnica ( Poland), attributed to H. multigranosa following the Šulc’s descriptions and illustrations, also regarding the tail valve, and therefore not the one figured by Reuss (1860: pl. 8, figs 9a–9b). The last known record of H. multigranosa is that of Ruman & Hudácková (2015), a few valves from Rohožník ( Slovakia).

A single incomplete intermediate valve of Hanleya multigranosa from Porzteich ( Czech Republic), is preserved at NHMW in the Šulc collection ( Figs 45E–H View FIGURE 45 ), but not registered as the type material. The sculpture of the tegmentum is consistent with the attribution to the genus Hanleya , also if the articulamentum’s features are not visible: the granules are elevated, well separated, with a high number of micraesthetes around a megalaesthetes, arranged in irregular rows longitudinally oriented in the median area, and irregularly covering the jugal area. The sculpture of this valve corresponds to that described by Šulc (1934), apart for the shape of the granules. Šulc’s description says “ Some ( granules, on the median valve) are elongated in longitudinal direction, but they usually have a circular cross section ”. The granules in the examined valve are all of elliptical form, but in Hanleya spp . (e.g., H. hanleyi ) the granules in intermediate valves tend to be more elongated than the roundish granules predominant in HV and PA (see Dell’Angelo et al. 1998a: pl. 2, figs 1–2 and Dell’Angelo & Smriglio 1999: pl. 25, figs A, C, E, pl. 26, figs I, J). The Šulc’s figures of intermediate valve are not so clear to resolve the doubts, and also the description of intermediate valves by Ashby & Cotton (1935) does not give any supplementary information. Notwithstanding, there are no other species of Hanleya described for the Miocene of Paratethys, and the locality (“Porzteich”) is one of those reported by Šulc, so we attribute the examined valve to H. multigranosa .

Some authors consider Hanleya multigranosa to be the ancestral species of the Recent species Hanleya hanleyi (Bean in Thorpe, 1844) ( Šulc 1934; Malatesta 1962; Laghi 1977). In fact, the two species are rather similar). Unfortunately we were unsuccessful in locating the type material of H. multigranosa , which is not in the NHMW, the description given by Reuss (1860) is incomplete, and also the subsequent integration by Šulc (1934), as important diagnostic information is missing and his tail valve do not correspond to that described by Reuss, and for these reasons, and the conspicuous difference in stratigraphic and geographic distribution, we consider H. multigranosa and H. hanleyi as distinct species.

The elliptical granules of the valve figured from Porzteich ( Figs 45E–H View FIGURE 45 ) are variable in length, up to 170 μm, while the granules of intermediate valves of H. hanleyi range up to 100 μm ( Sirenko et al. 2016: figs 2E, 5E). Also, the number of micraesthetes around the megalaesthete is different, 8–12 for H. hanleyi ( Dell’Angelo & Smriglio 1999: 86; Sirenko et al. 2016: figs 2E, 5E) vs. up to 25 or more in the valve of H. multigranosa examined (but up to 14 in the valves from Korytnica studied by Bałuk 1984). The longitudinal rows of granules in the pleural areas of intermediate valves of H. hanleyi are more regular than in the valve examined, the granules are closer to one another and give a different look to the sculpture of the valve (see Sirenko et al. 2016: figs 2B, 5B–C).

Comparisons. Hanleya multigranosa differs from H. mediterranea Sirenko, 2014 in having a shorter insertion plate on the head valve, a differently shaped tail valve, and smaller and more numerous granules with a larger number of micraesthetes (up to 25 or more vs. 12–13 in H. mediterranea ).

Distribution. Lower-Middle Miocene: North Europe: Belgium: Antwerp ( Louwye et al. 2010). Middle Miocene: Central Paratethys (Langhian-Serravallian): Czech Republic: Rudoltice, Porzteich ( Reuss 1860; Procházka, 1900; Šulc 1934; this study), Slovakia: Rohožník ( Ruman & Hudácková 2015), Romania: Coştei ( Šulc 1934), Poland: Korytnica ( Bałuk 1971, 1984).