Pseudunio Haas, 1910

Lyubas, Artem A., Obada, Teodor F., Gofarov, Mikhail Y., Kriauciunas, Vidas V., Vikhrev, Ilya V., Nicoara, Igor N. & Bolotov, Ivan N., 2019, A taxonomic revision of fossil freshwater pearl mussels (Bivalvia: Unionoida: Margaritiferidae) from Pliocene and Pleistocene deposits of Southeastern Europe, Ecologica Montenegrina 21, pp. 1-16 : 11-15

Genus Pseudunio Haas, 1910

Type species: Unio sinuata Lamarck, 1819 [= Unio auricularius Spengler, 1793 ]

Pseudunio flabellatiformis ( Grigorowitch-Beresowski, 1915) comb. rev.

Unio flabellatiformis Grigorowitch-Beresowski (1915) .

Unio flabellatiformis var. levata Bogatchev (1961): 229 , plate XXIX, figs. 3-4.

Margaritifera (Pseudunio) moldavica Chepalyga (1964): 38 , plate IV, fig. 1.

Margaritifera (Pseudunio) robusta Chepalyga (1964): 40 .

Margaritifera (Pseudunio) robusta robusta Chepalyga (1964): 42 , plate III, fig. 1.

Margaritifera (Pseudunio) robusta speensis Chepalyga (1964): 42 , fig. 1б.

Margaritifera (Pseudunio) robusta tirassica Chepalyga (1964): 43 , plate IV, fig. 2.

Figs. 4 , 8C , 9

Types. Whereabouts unknown.

Type strata and locality. Upper Pliocene , Prut River valley near Slobozia Mare village, Danube Basin, Moldova [45.6067° N, 28.1656° E] .

Differential diagnosis. This species is conchologically similar to P. auricularius and P. homsensis ( Figs. 4- 8 ). Moreover, clear conchological features to distinguish the recent Pseudunio taxa from each other are lacking ( Araujo et al., 2009; Lopes-Lima et al., 2018). P. flabellatiformis and the recent Pseudunio species clearly differs from P. flabellatus by the lack of strong corrugate plication of the shell, although a weakly developed plication can be found in some specimens ( Chepalyga, 1967; Bolotov et al. 2016; Vikhrev et al. 2017; Lopes-Lima et al., 2018).

Phylogenetic position. Extinct lineage related to P. auricularius and P. homsensis . We assume that this extinct species was originated in a distinct isolate (Danube and Dniester paleo-basins) simultaneously with the two terminal species ( P. auricularius in Southern Europe and P. homsensis in Orontes Basin) since the Middle Miocene.

Stratigraphic and geographic range. Late Miocene – Late Pleistocene, Danube and Dniester paleo-basins, Black Sea drainage, Eastern Europe.

Paleoenvironment. Available data ( Chepalyga, 1964, 1965, 1967; this study) indicates that P. flabellatiformis inhabited the main channels of large rivers with sandy-gravel and sandy-pebble bottom substrate ( Fig. 2 ). It often co-occurred with Unio crassus Retzius, 1788 (or its stem lineages).

Pseudunio flabellatus ( Goldfuss, 1837) comb. rev. Unio flabellatus Goldfuss (1837): 182 .

Types. Lectotype and paralectotype STIPB-Goldfuss-822, Steinmann Institute for Mineralogy , Geology and Palaeontology (formerly Goldfuss Museum), University of Bonn, Bonn, Germany ( Schneider and Prieto, 2011) .

Type strata and locality. Upper Freshwater Molasse (Middle Miocene), Käpfnach, southern shore of Lake Zürich, Switzerland [approx. 47.2546° N, 8.6160° E] ( Schneider and Prieto, 2011) .

Differential diagnosis. This species differs from the other Pseudunio taxa by a strong corrugate plication of the shell. Furthermore, it seems to be the most ancient lineage among European Pseudunio ( Schneider and Prieto, 2011) .

Phylogenetic position. This species appears to be a stem lineage and the MRCA of a clade that contains the terminal species P. auricularius and P. homsensis , and the extinct species P. flabellatiformis .

Stratigraphic and geographic range. Miocene, Danube Paleo-Basin, Black Sea drainage, Western and Eastern Europe.

Paleoenvironment. This species is known from a variety of riverine and lacustrine paleo-environments ( Nesemann, 1993; Scholz et al., 2007; Schneider and Prieto, 2011).

Taxonomic comments. Schneider and Prieto (2011) provided a full redescription of this taxon with a nearly complete list of synonyms.

Figures

Figure 2. Subfossil riverbed substrate with a Pseudunio flabellatiformis shell, Sucleia outcrop, paleo-Dniester River valley, Middle Pleistocene, Moldova. Scale bar = 100 mm. Photo: Teodor F. Obada.

Figure 4. Subfossil shells of Pseudunio flabellatiformis (Grigorowitch-Beresowski, 1915) comb. rev. from the outcrop of the Middle Pleistocene riverine deposits near Sucleia village, paleo-Dniester River valley, Transnistria, Moldova: A) specimen no. 1 (RMBH); B) specimen no. Sc1 (RMBH); C) specimen no. Sc5 (RMBH); D) specimen no. Sc8 (RMBH); E) specimen no. Sc12 (RMBH); F) specimen no. Sc13 (RMBH). Scale bar = 20 mm. Photos: Artem A. Lyubas.

Figure 5. Scatter plot of PCA based on the shell measurements of our Pseudunio sample from the Sucleia locality and the type series of fossil nominal taxa from the Speya and Blizhniy Khutor localities (Chepalyga, 1964, 1965). The component 1 and component 2 accounted for 98.8% and 1.0% of the total variance, respectively.

Figure 6. Shells of the recent Pseudunio auricularius (Spengler, 1793): A) Indre River near Huismes commune, Loire Basin, France (SMF, voucher no. 307623); B) Ebro River near Cenicero, La Rioja, Spain (MNCN, voucher no. 15.07/197); C) Loire River upstream of Champtoceaux commune, Maine-et-Loire, France (SMF, voucher no. 307850); D) Garonne River, France (MNCN, voucher no. 15.07/178); E) Indre River near Huismes commune, Loire Basin, France (SMF, voucher no. 307623); F) Ebro River near Amposta city, Tarragona, Spain (MNCN, voucher no. 15.07/10366). Scale bar = 20 mm. Photos: Artem A. Lyubas & Ilya V. Vikhrev.

Figure 7. Shells of the recent Pseudunio homsensis (Lea, 1865): A) Orontes River near Homs, Syria (SMF, voucher no. 4450); B) Orontes River near Homs, Syria (SMF, voucher no. 345464); C) Orontes River near Homs, Syria (SMF, voucher no. 15263); D) Nahr al-Kabir al-Janoubi River near Harida, Syria (SMF, voucher no. 83160) E) Nahr al-Kabir al-Janoubi River near Tell Kalat, Syria (SMF, voucher no. 5156); F) Orontes River near Homs, Syria (SMF, voucher no. 4548). Scale bar = 20 mm. Photos: Ilya V. Vikhrev.

Figure 8. Teeth morphology of recent and fossil Pseudunio taxa: A) P. auricularius from the Indre River near Huismes commune, Loire Basin, France (SMF, voucher no. 307623); B) P. homsensis from the Nahr al-Kabir al-Janoubi River near Harida, Syria (SMF, voucher no. 83160); C) P. flabellatiformis comb. rev. from the Sucleia outcrop, paleo- Dniester River valley, Middle Pleistocene, Moldova (RMBH, voucher no. Sc1). Scale bars = 10 mm. Photos: Artem A. Lyubas and Ilya V. Vikhrev.

Figure 9. Mantle attachment scars on the inner side of subfossil shell of Pseudunio flabellatiformis comb. rev. from the Sucleia outcrop, paleo-Dniester River valley, Middle Pleistocene, Moldova (RMBH, voucher no. Sc5). Scale bar = 10 mm. Photo: Artem A. Lyubas.