Range map of <i>Margaritifera middendorffi</i> (Rosén, 1926) and <i>Margaritifera togakushiensis</i> (Kondo and Kobayashi, 2005).

<p>Circles—<i>M</i>. <i>middendorffi</i> locations, squares—<i>M</i>. <i>togakushiensis</i> locations. Green circles and squares are representing recent viable populations (observed since 2000), white circles—old records (until 2001), yellow squares—records without exact dates. Grey areas indicate approximate modern species ranges (showing only the large river systems). Species locality numbers on the map correspond to numbers in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s003" target="_blank">S3 Table</a>.</p

Range map of <i>Margaritifera dahurica</i> (Middendorff, 1850).

<p>Green circles are representing recent viable populations (observed since 2000), white circles—old records (until 2000). Question mark is indicated an uncertain record from the Langry River [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.ref069" target="_blank">69</a>], [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.ref026" target="_blank">26</a>]. Grey areas are indicated an approximate modern species range (it is shown only for the large river systems). Species locality numbers on the map correspond to numbers in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s002" target="_blank">S2 Table</a>.</p

Shells of <i>Margaritifera togakushiensis</i> (Kondo and Kobayashi, 2005) and <i>Margaritifera middendorffi</i> (Rosén, 1926).

<p>A—Holotype of <i>M</i>. <i>togakushiensis</i> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.ref018" target="_blank">18</a>]: 137, figs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.g005" target="_blank">5</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.g008" target="_blank">8</a>. B—Lectotype of <i>M</i>. <i>middendorffi</i> (ZISP: no. 6). Photo by I. V. Vikhrev. Scale bar—2 cm.</p

Map of location of the field study areas.

<p>1—Kamchatka Peninsula (2012, I. Bolotov, Y. Bespalaya, I. Vikhrev, M. Gofarov), 2—Central Sakhalin (2012, same team), 3—southern Sakhalin (2011–2012, same team & Y. Kolosova, O. Aksenova), 4—Kunashir Island (2011, same team & Y. Kolosova, O. Aksenova), 5—Primorye (2012, same team), 6—Transbaikalia (2004–2011, O.K. Klishko). Data on the studied river sites are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s001" target="_blank">S1</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s004" target="_blank">S4</a> Tables.</p

Shells of <i>Margaritifera dahurica</i> (Middendorff, 1850).

<p>A—Lectotype (ZISP: no. 7a). B—specimen from Komarovka River, Razdolnaya River basin, Primorye. Photos by I.V. Vikhrev. Scale bar—2 cm.</p

Shells of <i>Margaritifera laevis</i> (Haas, 1910).

<p>A—Sennaya River, Kunashir Island. B—Tym’ River, Sakhalin Island. Photos by I. V. Vikhrev. Scale bar—2 cm.</p

Range map of <i>Margaritifera laevis</i> (Haas, 1910).

<p>Green circles are representing recent viable populations (observed since 2000), white circles—old records (until 2001), yellow circles—records without exact dates. Grey areas indicate the approximate modern species range (showing only the large river systems). Species locality numbers on the map correspond to numbers in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s004" target="_blank">S4 Table</a>.</p

Teeth morphology of three Far Eastern margaritiferid species.

<p>A—<i>Margaritifera dahurica</i> (Middendorff, 1850). B—<i>M</i>. <i>middendorffi</i> (Rosén, 1926). C—<i>M</i>. <i>laevis</i> (Haas, 1910). Scale bar—1 cm.</p

General plan of soft tissue of three Far Eastern margaritiferid species.

<p>A—<i>Margaritifera dahurica</i> (Middendorff, 1850). B—<i>M</i>. <i>laevis</i> (Haas, 1910). C—<i>M</i>. <i>middendorffi</i> (Rosén, 1926). Scale bar—1 cm.</p

Typical habitats of the Eastern Asian margaritiferid species.

<p>A—<i>Margaritifera dahurica</i> (Middendorff, 1850): the Ilystaya River, Primorsky Kray. B—<i>M</i>. <i>middendorffi</i> (Rosén, 1926): the Nachilova River, Kamchatka. C—<i>M</i>. <i>middendorffi</i> (Rosén, 1926) & <i>M</i>. <i>laevis</i> (Haas, 1910): the Golovnina River, Kunashir Island. Photos by Y.V. Bespalaya, Y.S. Kolosova & I.V. Vikhrev.</p