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<mods:title id="3CB6305C8EC1995E313CD0BEF31FBC0C">Revision of the Bivalvia from the Upper Jurassic Reuchenette Formation, Northwest Switzerland — Ostreoidea</mods:title>
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<mods:namePart id="963D46B27A9537880329F8A0963D34FC">Koppka, Jens</mods:namePart>
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<treatment id="039087D7C015462EFF68FC36FABF36BC" ID-DOI="http://doi.org/10.5281/zenodo.6102686" ID-GBIF-Taxon="127377112" ID-Zenodo-Dep="6102686" LSID="urn:lsid:plazi:treatment:039087D7C015462EFF68FC36FABF36BC" httpUri="http://treatment.plazi.org/id/039087D7C015462EFF68FC36FABF36BC" lastPageId="14" lastPageNumber="15" pageId="12" pageNumber="13">
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<paragraph id="8B8636C1C015462CFF68FC36FE6E370C" blockId="12.[151,413,1013,1039]" box="[151,413,1013,1039]" pageId="12" pageNumber="13">
<heading id="D0CE81ADC015462CFF68FC36FE6E370C" bold="true" box="[151,413,1013,1039]" fontSize="11" level="1" pageId="12" pageNumber="13" reason="1">
<emphasis id="B94DEAD3C015462CFF68FC36FE6E370C" bold="true" box="[151,413,1013,1039]" pageId="12" pageNumber="13">
Classification
<taxonomicName id="4C394D42C015462CFEB8FC36FE6E370C" box="[327,413,1013,1039]" class="Bivalvia" family="Ostreidae" genus="Actinostreon" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="species" species="outline">outline</taxonomicName>
</emphasis>
</heading>
</paragraph>
<paragraph id="8B8636C1C015462CFF68FBFFFDD137E6" blockId="12.[151,1437,1084,1973]" pageId="12" pageNumber="13">
Molecular phylogenetics seems to be the only method capable of providing some invariant anchor points to oyster systematics which necessarily needs to be interwoven with morphological data from both living and fossil taxa. Hence, the starting point for the current classification scheme is based on the most comprehensive molecular analyses currently available and complemented by the paleontological approach of Carter
<emphasis id="B94DEAD3C015462CFB6EFB6AFB3237C3" box="[1169,1217,1191,1216]" italics="true" pageId="12" pageNumber="13">et al</emphasis>
. (2011) (see
<bibRefCitation id="EFA84B30C015462CFAA8FB64FEFD37E7" author="Bieler" pageId="12" pageNumber="13" refString="Bieler, R., Carter, J. G. &amp; Coan, E. V. (2010) Classification of bivalve families. In: Bouchet, P. &amp; Rocroi, J. - P. (Eds.), Nomenclator of bivalve families with a classification of bivalve families. Malacologia, 52 (2), pp. 113 - 184. [total page number: 184 pp.]" type="book chapter" year="2010">
Bieler
<emphasis id="B94DEAD3C015462CFF68FB0EFF3B37E6" box="[151,200,1228,1253]" italics="true" pageId="12" pageNumber="13">et al</emphasis>
. 2010
</bibRefCitation>
for an alternative view).
</paragraph>
<paragraph id="8B8636C1C015462CFF38FB2CFEF93676" blockId="12.[151,1437,1084,1973]" pageId="12" pageNumber="13">
According to the genetic data of
<bibRefCitation id="EFA84B30C015462CFDBCFB2CFC40360B" author="Giribet" box="[579,947,1263,1288]" pageId="12" pageNumber="13" refString="Giribet, G. &amp; Distel, D. (2003) Bivalve phylogeny and molecular data. In: Lydeard, C. &amp; Lindberg, D. R. (Eds.), Molecular Systematics and Phylogeography of Molluscs. Smithsonian Books, Washington D. C., pp. 45 - 90." type="book chapter" year="2003">Giribet &amp; Distel (2003, fig. 3.5)</bibRefCitation>
and
<collectingCountry id="F32E7651C015462CFC11FB2CFBF1360B" box="[1006,1026,1263,1288]" name="Iceland" pageId="12" pageNumber="13">Ó</collectingCountry>
Foighil &amp; Taylor (2000, figs. 2–5),
<taxonomicName id="4C394D42C015462CFF68FAD7FEF2362E" box="[151,257,1300,1325]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Lophinae">Lophinae</taxonomicName>
oysters appear either as a sister taxon to, or some species also nested within,
<taxonomicName id="4C394D42C015462CFB94FAD7FB25362E" box="[1131,1238,1300,1325]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Ostreinae">Ostreinae</taxonomicName>
rather than being basal to them. Hence, the two subfamilies form a crown group which is here synonymized with the Family
<taxonomicName id="4C394D42C015462CFF68FA9FFEF53676" box="[151,262,1372,1397]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">Ostreidae</taxonomicName>
.
</paragraph>
<paragraph id="8B8636C1C015462CFF38FABCFD2D3506" blockId="12.[151,1437,1084,1973]" pageId="12" pageNumber="13">
<taxonomicName id="4C394D42C015462CFF38FABCFE99369B" box="[199,362,1407,1432]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Crassostreinae">Crassostreinae</taxonomicName>
essentially form a sister taxon to this “restricted” family
<taxonomicName id="4C394D42C015462CFC12FABCFBA8369B" box="[1005,1115,1407,1432]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">Ostreidae</taxonomicName>
, and either a
<taxonomicName id="4C394D42C015462CFB0FFA43FA993694" box="[1264,1386,1408,1431]" class="Bivalvia" family="Ostreidae" genus="Saccostrea" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C015462CFB0FFA43FA993694" box="[1264,1386,1408,1431]" italics="true" pageId="12" pageNumber="13">Saccostrea</emphasis>
</taxonomicName>
or a
<taxonomicName id="4C394D42C015462CFF68FA66FEEE36BF" box="[151,285,1445,1468]" class="Bivalvia" family="Ostreidae" genus="Crassostrea" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C015462CFF68FA66FEEE36BF" box="[151,285,1445,1468]" italics="true" pageId="12" pageNumber="13">Crassostrea</emphasis>
</taxonomicName>
species appears at the base. Consistent in all analyses, Recent
<taxonomicName id="4C394D42C015462CFC0AFA67FB7736BE" box="[1013,1156,1444,1469]" class="Bivalvia" family="Gryphaeidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">Gryphaeidae</taxonomicName>
form the sister taxon of
<taxonomicName id="4C394D42C015462CFF68FA04FEF136E3" box="[151,258,1479,1504]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">Ostreidae</taxonomicName>
plus
<taxonomicName id="4C394D42C015462CFEBEFA04FE1436E3" box="[321,487,1479,1504]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Crassostreinae">Crassostreinae</taxonomicName>
, and the superfamily of Recent Ostreoidea appears very robustly as a monophylum:
<taxonomicName id="4C394D42C015462CFF68FA2FFED53506" box="[151,294,1516,1541]" class="Bivalvia" family="Gryphaeidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">Gryphaeidae</taxonomicName>
(
<taxonomicName id="4C394D42C015462CFECBFA2FFE2A3506" box="[308,473,1516,1541]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Crassostreinae">Crassostreinae</taxonomicName>
(
<taxonomicName id="4C394D42C015462CFE17FA2FFDAB3506" box="[488,600,1516,1541]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Ostreinae">Ostreinae</taxonomicName>
,
<taxonomicName id="4C394D42C015462CFD9CFA2FFD213506" box="[611,722,1516,1541]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Lophinae">Lophinae</taxonomicName>
).
</paragraph>
<paragraph id="8B8636C1C015462CFF38F9D3FAEA35BB" blockId="12.[151,1437,1084,1973]" pageId="12" pageNumber="13">
In the present context, these genetic results suggest that Mesozoic
<taxonomicName id="4C394D42C015462CFC4AF9CCFC0E352B" box="[949,1021,1551,1576]" class="Bivalvia" family="Ostreidae" genus="Lopha" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C015462CFC4AF9CCFC0E352B" box="[949,1021,1551,1576]" italics="true" pageId="12" pageNumber="13">Lopha</emphasis>
</taxonomicName>
-like oysters, here represented by the Jurassic genus
<taxonomicName id="4C394D42C015462CFEBCF9F7FE223548" box="[323,465,1588,1611]" class="Bivalvia" family="Ostreidae" genus="Actinostreon" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C015462CFEBCF9F7FE223548" box="[323,465,1588,1611]" italics="true" pageId="12" pageNumber="13">Actinostreon</emphasis>
</taxonomicName>
, are convergent to Recent
<taxonomicName id="4C394D42C015462CFCF9F9F7FC83354E" box="[774,880,1588,1613]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Lophinae">Lophinae</taxonomicName>
justifying the placement of these Mesozoic taxa outside
<taxonomicName id="4C394D42C015462CFF0EF994FEA83573" box="[241,347,1623,1648]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Lophinae">Lophinae</taxonomicName>
and outside
<taxonomicName id="4C394D42C015462CFE0FF994FDAD3573" box="[496,606,1623,1648]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">Ostreidae</taxonomicName>
, that is, in
<taxonomicName id="4C394D42C015462CFD1EF994FBE13573" authority="Vialov, 1983" authorityName="Vialov" authorityYear="1983" box="[737,1042,1623,1648]" class="Bivalvia" family="Arctostreidae" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">
Arctostreidae
<bibRefCitation id="EFA84B30C015462CFC7EF994FBE13573" author="Vialov" box="[897,1042,1623,1648]" pageId="12" pageNumber="13" refString="Vialov, O. S. 1983. Zagal'na klasifikatsii ustrits. [General classification of oysters]. Dopovidi Akademiyi Nauk Ukrayins'koyi RSR, ser. B, Heolohichni, Khimichni ta Biolohichni Nauky [= Doklady Akademii Nauk Ukrainskoi SSR], Series B, 11, 6 - 8. [in Ukrainian]" type="journal article" year="1983">Vialov, 1983</bibRefCitation>
</taxonomicName>
(Carter
<emphasis id="B94DEAD3C015462CFB8CF99AFB543573" box="[1139,1191,1623,1648]" italics="true" pageId="12" pageNumber="13">et al</emphasis>
. 2011, p. 8;
<bibRefCitation id="EFA84B30C015462CFAC3F994FF233597" author="Malchus" pageId="12" pageNumber="13" refString="Malchus, N. (1990) Revision der Kreide-Austern (Bivalvia: Pteriomorphia) Agyptens (Biostratigraphie, Systematik). Berliner Geowissenschaftliche Abhandlungen, Reihe A, 125, 1 - 231." type="journal article" year="1990">Malchus 1990</bibRefCitation>
) (see
<bibRefCitation id="EFA84B30C015462CFEEDF9BEFE3B3597" author="Hautmann" box="[274,456,1660,1684]" pageId="12" pageNumber="13" refString="Hautmann, M. (2001) Taxonomy and phylogeny of cementing Triassic bivalves (families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae). Palaeontology, 44 (2), 339 - 373. http: // dx. doi. org / 10.1111 / 1475 - 4983.00183" type="journal article" year="2001">Hautmann 2001</bibRefCitation>
, for a contrasting view). In addition, as a consequence of excluding
<taxonomicName id="4C394D42C015462CFB43F9BFFAAC3596" box="[1212,1375,1660,1685]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="subFamily" subFamily="Crassostreinae">Crassostreinae</taxonomicName>
from
<taxonomicName id="4C394D42C015462CFF68F95CFEF635BB" box="[151,261,1695,1720]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">Ostreidae</taxonomicName>
, this subfamily is included in the Family Flemingostreidae
<bibRefCitation id="EFA84B30C015462CFC61F95CFBC635BB" author="Stenzel" box="[926,1077,1695,1720]" pageId="12" pageNumber="13" refString="Stenzel, H. B. (1971) Oysters. In: Moore, R. C. (Eds.), Treatise on Invertebrate Paleontology. Part N, Mollusca 6 (Bivalvia). Vol. 3. Geological Society of America, University of Kansas, Boulder, pp. N 953 - N 1124." type="journal article" year="1971">Stenzel, 1971</bibRefCitation>
(Carter
<emphasis id="B94DEAD3C015462CFB6CF962FB3735BB" box="[1171,1220,1695,1720]" italics="true" pageId="12" pageNumber="13">et al</emphasis>
. 2011).
</paragraph>
<paragraph id="8B8636C1C015462CFF38F907FBB234B6" blockId="12.[151,1437,1084,1973]" pageId="12" pageNumber="13">
Indirectly, the genetic results also suggest that brooding evolved only once in Recent oysters, converting this character in a potential autapomorphy of the stem species of
<taxonomicName id="4C394D42C015462CFC7EF924FC1E3403" box="[897,1005,1767,1792]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">Ostreidae</taxonomicName>
(see
<collectingCountry id="F32E7651C015462CFBCAF924FBBA3403" box="[1077,1097,1767,1792]" name="Iceland" pageId="12" pageNumber="13">Ó</collectingCountry>
Foighil &amp; Taylor 2000, for anatomical arguments). The time when this happened cannot be ultimately fixed. However, current evidence from fossil larval shells hints towards the Tertiary (Eocene, Miocene) (
<bibRefCitation id="EFA84B30C015462CFC6AF8ECFA92344B" author="Malchus" box="[917,1377,1839,1864]" pageId="12" pageNumber="13" refString="Malchus, N. &amp; Sartori, A. (2013) Part N, Revised, Volume 1, Chapter 4: The early shell: ontogeny, features and evolution. Treatise Online, 61, 1 - 114." type="book chapter" year="2013" yearSuffix="p">Malchus &amp; Sartori 2013, p. 78, 84, 86</bibRefCitation>
). All pertinent results from the present study are consistent with this view [e.g., Pl. 9.10c–e, Pl. 10.1–2 (
<taxonomicName id="4C394D42C015462CFB0AF896FA96346F" box="[1269,1381,1877,1900]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="12" pageNumber="13" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C015462CFB0AF896FA96346F" box="[1269,1381,1877,1900]" italics="true" pageId="12" pageNumber="13">Nanogyra</emphasis>
</taxonomicName>
), Pl. 6.5, 10.3a (
<taxonomicName id="4C394D42C015462CFEE2F8BAFE5D3493" box="[285,430,1913,1936]" class="Bivalvia" family="Gryphaeidae" genus="Praeexogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="12" pageNumber="13" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C015462CFEE2F8BAFE5D3493" box="[285,430,1913,1936]" italics="true" pageId="12" pageNumber="13">Praeexogyra</emphasis>
</taxonomicName>
), Pl. 19.4a–d (
<taxonomicName id="4C394D42C015462CFD9FF8BBFD1D348C" box="[608,750,1912,1935]" class="Bivalvia" family="Ostreidae" genus="Actinostreon" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C015462CFD9FF8BBFD1D348C" box="[608,750,1912,1935]" italics="true" pageId="12" pageNumber="13">Actinostreon</emphasis>
</taxonomicName>
)].
<collectingCountry id="F32E7651C015462CFCEDF8BBFCC23493" box="[786,817,1912,1936]" name="American Samoa" pageId="12" pageNumber="13">As</collectingCountry>
of today, it appears therefore likely that none of the Jurassic
<emphasis id="B94DEAD3C015462CFF09F85EFEB934B7" box="[246,330,1949,1972]" italics="true" pageId="12" pageNumber="13">Ostrea-</emphasis>
or
<taxonomicName id="4C394D42C015462CFE8FF85EFE0534B7" box="[368,502,1949,1972]" class="Bivalvia" family="Ostreidae" genus="Crassostrea" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C015462CFE8FF85EFE0534B7" box="[368,502,1949,1972]" italics="true" pageId="12" pageNumber="13">Crassostrea</emphasis>
</taxonomicName>
-like taxa belongs to the
<taxonomicName id="4C394D42C015462CFCF4F85FFC8534B6" box="[779,886,1948,1973]" class="Bivalvia" family="Ostreidae" kingdom="Animalia" order="Ostreoida" pageId="12" pageNumber="13" phylum="Mollusca" rank="family">Ostreidae</taxonomicName>
as defined above.
</paragraph>
<caption id="DF466649C014462DFF82FDDDFB97316D" pageId="13" pageNumber="14">
<paragraph id="8B8636C1C014462DFF82FDDDFB97316D" blockId="13.[125,1899,542,622]" pageId="13" pageNumber="14">
<emphasis id="B94DEAD3C014462DFF82FDDDFF143137" bold="true" box="[125,231,542,564]" pageId="13" pageNumber="14">TABLE 1</emphasis>
. Main shell features for the eight oyster species from the Swiss Reuchenette Formation. “Convex-concave” RV refers to the nomenclature of Malchus (1990) (see also Malchus &amp; Aberhan 1998). Microstructure data refer to the left valve (LV) except for
<taxonomicName id="4C394D42C014462DFBE4FDF8FB6F3153" box="[1051,1180,571,592]" class="Bivalvia" family="Ostreidae" genus="Actinostreon" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreoida" pageId="13" pageNumber="14" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C014462DFBE4FDF8FB6F3153" box="[1051,1180,571,592]" italics="true" pageId="13" pageNumber="14">Actinostreon</emphasis>
</taxonomicName>
(LV+RV). The outermost simple prismatic (SP) or cross foliated (CF) shell layer are probably eroded in some species. Abbrevations see under “Methods: Terminology”.
</paragraph>
</caption>
<paragraph id="8B8636C1C014462DFF82FD5AF8BE31AC" blockId="13.[125,1875,665,1650]" box="[125,1869,665,687]" pageId="13" pageNumber="14">
Species LV
<taxonomicName id="4C394D42C014462DFE87FD5AFE4D31AC" box="[376,446,665,687]" class="Bivalvia" family="Ostreidae" genus="Actinostreon" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreoida" pageId="13" pageNumber="14" phylum="Mollusca" rank="species" species="outline">outline</taxonomicName>
LV convexity LV sculpture RV convexity RV sculpture Resilifer Posterior Chomata Microstructure
</paragraph>
<paragraph id="8B8636C1C014462DFA7AFD06F9FE31D8" blockId="13.[125,1875,665,1650]" box="[1413,1549,709,731]" pageId="13" pageNumber="14">adductor scar</paragraph>
<paragraph id="8B8636C1C014462DFF82FD31FA183088" blockId="13.[125,1875,665,1650]" pageId="13" pageNumber="14">
<taxonomicName id="4C394D42C014462DFF82FD31FF173004" box="[125,228,754,775]" class="Bivalvia" family="Arctostreidae" genus="Circunula" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreida" pageId="13" pageNumber="14" phylum="Mollusca" rank="genus" status="gen. nov.">
<emphasis id="B94DEAD3C014462DFF82FD31FF173004" box="[125,228,754,775]" italics="true" pageId="13" pageNumber="14">Circunula</emphasis>
</taxonomicName>
<taxonomicNameLabel id="A27E57A8C014462DFF15FD30FEDC300B" box="[234,303,755,776]" pageId="13" pageNumber="14" rank="genus">n. gen.</taxonomicNameLabel>
round low, ventral margin dorsally with weakly faint radial curved round only in SP,
<collectingCountry id="F32E7651C014462DF91FFD30F8F2300B" box="[1760,1793,755,776]" name="Russia" pageId="13" pageNumber="14">RF</collectingCountry>
, CCF
<taxonomicName id="4C394D42C014462DFF82FCDDFF133030" box="[125,224,798,819]" class="Bivalvia" family="Arctostreidae" genus="Circunula" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreida" pageId="13" pageNumber="14" phylum="Mollusca" rank="species" species="cotyledon">
<emphasis id="B94DEAD3C014462DFF82FCDDFF133030" box="[125,224,798,819]" italics="true" pageId="13" pageNumber="14">cotyledon</emphasis>
</taxonomicName>
upturned radial furrows inflated threads juveniles
<taxonomicName id="4C394D42C014462DFF82FC89FF10305C" box="[125,227,842,863]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C014462DFF82FC89FF10305C" box="[125,227,842,863]" italics="true" pageId="13" pageNumber="14">Nanogyra</emphasis>
</taxonomicName>
(
<emphasis id="B94DEAD3C014462DFF0EFC89FEF1305C" box="[241,258,842,863]" italics="true" pageId="13" pageNumber="14">N</emphasis>
.) oval capacious smooth convex- commarginal exogyrate dorsally absent SP,
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<taxonomicName id="4C394D42C014462DFF82FCB5FF433088" box="[125,176,886,907]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="species" species="nana">
<emphasis id="B94DEAD3C014462DFF82FCB5FF433088" box="[125,176,886,907]" italics="true" pageId="13" pageNumber="14">nana</emphasis>
</taxonomicName>
concave growth crests biconcave
</paragraph>
<paragraph id="8B8636C1C014462DFF82FC61FB3830E1" blockId="13.[125,1875,665,1650]" pageId="13" pageNumber="14">
<taxonomicName id="4C394D42C014462DFF82FC61FF1030B4" box="[125,227,930,951]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C014462DFF82FC61FF1030B4" box="[125,227,930,951]" italics="true" pageId="13" pageNumber="14">Nanogyra</emphasis>
</taxonomicName>
(
<emphasis id="B94DEAD3C014462DFF0EFC61FEF330B4" box="[241,256,930,951]" italics="true" pageId="13" pageNumber="14">P</emphasis>
.) kidney weakly inflated smooth flat, weakly smooth, faint exogyrate round present
<collectingCountry id="F32E7651C014462DF949FC61F92430B4" box="[1718,1751,930,951]" name="Russia" pageId="13" pageNumber="14">RF</collectingCountry>
, lenses?
<taxonomicName id="4C394D42C014462DFF82FC0EFF1530E1" box="[125,230,973,994]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="species" species="reniformis">
<emphasis id="B94DEAD3C014462DFF82FC0EFF1530E1" box="[125,230,973,994]" italics="true" pageId="13" pageNumber="14">reniformis</emphasis>
</taxonomicName>
convex radial threads
</paragraph>
<paragraph id="8B8636C1C014462DFF82FC3AFA183792" blockId="13.[125,1875,665,1650]" pageId="13" pageNumber="14">
<taxonomicName id="4C394D42C014462DFF82FC3AFF10370D" box="[125,227,1017,1038]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C014462DFF82FC3AFF10370D" box="[125,227,1017,1038]" italics="true" pageId="13" pageNumber="14">Nanogyra</emphasis>
</taxonomicName>
(
<emphasis id="B94DEAD3C014462DFF0EFC3AFEF3370D" box="[241,256,1017,1038]" italics="true" pageId="13" pageNumber="14">P</emphasis>
.) comma capacious numerous radial convex- faint radial exogyrate oval present
<collectingCountry id="F32E7651C014462DF949FC3AF924370D" box="[1718,1751,1017,1038]" name="Russia" pageId="13" pageNumber="14">RF</collectingCountry>
, lamellar
<taxonomicName id="4C394D42C014462DFF82FBE7FF35373A" box="[125,198,1060,1081]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="species" species="virgula">
<emphasis id="B94DEAD3C014462DFF82FBE7FF35373A" box="[125,198,1060,1081]" italics="true" pageId="13" pageNumber="14">virgula</emphasis>
</taxonomicName>
riblets concave threads lenses
<taxonomicName id="4C394D42C014462DFF82FB92FEF33765" box="[125,256,1105,1126]" class="Bivalvia" family="Gryphaeidae" genus="Praeexogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C014462DFF82FB92FEF33765" box="[125,256,1105,1126]" italics="true" pageId="13" pageNumber="14">Praeexogyra</emphasis>
</taxonomicName>
drop capacious commarginal flat, ventrally ventrally faint trigonal, dorsally absent SP,
<collectingCountry id="F32E7651C014462DF91FFB92F90C3765" box="[1760,1791,1105,1126]" name="Russia" pageId="13" pageNumber="14">RF</collectingCountry>
<taxonomicName id="4C394D42C014462DFF82FBB8FF2E3793" box="[125,221,1147,1168]" class="Bivalvia" family="Gryphaeidae" genus="Praeexogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="species" species="dubiensis">
<emphasis id="B94DEAD3C014462DFF82FBB8FF2E3793" box="[125,221,1147,1168]" italics="true" pageId="13" pageNumber="14">dubiensis</emphasis>
</taxonomicName>
growth lines, concave radial threads oblique biconcave
</paragraph>
<paragraph id="8B8636C1C014462DFD36FB64FC9737BE" blockId="13.[125,1875,665,1650]" box="[713,868,1191,1213]" pageId="13" pageNumber="14">weak swellings</paragraph>
<paragraph id="8B8636C1C014462DFF82FB17FAB23617" blockId="13.[125,1875,665,1650]" pageId="13" pageNumber="14">
<taxonomicName id="4C394D42C014462DFF82FB17FEF337EA" box="[125,256,1236,1257]" class="Bivalvia" family="Gryphaeidae" genus="Praeexogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C014462DFF82FB17FEF337EA" box="[125,256,1236,1257]" italics="true" pageId="13" pageNumber="14">Praeexogyra</emphasis>
</taxonomicName>
kidney capacious commarginal flat, ventrally faint radial trigonal, high-oval absent
<collectingCountry id="F32E7651C014462DF948FB17F92B37EA" box="[1719,1752,1236,1257]" name="Russia" pageId="13" pageNumber="14">RF</collectingCountry>
, CF
<taxonomicName id="4C394D42C014462DFF82FB3CFEDD3617" box="[125,302,1279,1300]" class="Bivalvia" family="Gryphaeidae" genus="Praeexogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="13" pageNumber="14" phylum="Mollusca" rank="species" species="monsbeliardensis">
<emphasis id="B94DEAD3C014462DFF82FB3CFEDD3617" box="[125,302,1279,1300]" italics="true" pageId="13" pageNumber="14">monsbeliardensis</emphasis>
</taxonomicName>
swellings concave threads oblique
</paragraph>
<paragraph id="8B8636C1C014462DFF82FAE9F8EB366F" blockId="13.[125,1875,665,1650]" pageId="13" pageNumber="14">
<taxonomicName id="4C394D42C014462DFF82FAE9FF0D363C" box="[125,254,1322,1343]" class="Bivalvia" family="Gryphaeidae" genus="Helvetostrea" kingdom="Animalia" order="Ostreoida" pageId="13" pageNumber="112" phylum="Mollusca" rank="genus" status="gen. nov.">
<emphasis id="B94DEAD3C014462DFF82FAE9FF0D363C" box="[125,254,1322,1343]" italics="true" pageId="13" pageNumber="14">Helvetostrea</emphasis>
</taxonomicName>
n. trapezoid, capacious, thick irregular growth flat unknown ostreoid, high-oval absent
<collectingCountry id="F32E7651C014462DF948FAE8F92B3643" box="[1719,1752,1323,1344]" name="Russia" pageId="13" pageNumber="14">RF</collectingCountry>
, CCF, large gen.
<taxonomicName id="4C394D42C014462DFF51FA94FEF0366F" box="[174,259,1367,1388]" class="Bivalvia" family="Gryphaeidae" genus="Helvetostrea" kingdom="Animalia" order="Ostreoida" pageId="13" pageNumber="14" phylum="Mollusca" rank="species" species="sequana">
<emphasis id="B94DEAD3C014462DFF51FA94FEF0366F" box="[174,259,1367,1388]" italics="true" pageId="13" pageNumber="14">sequana</emphasis>
</taxonomicName>
tube-like shelled squamae massive chambers
</paragraph>
<paragraph id="8B8636C1C014462DFB0AFA42FAA93694" blockId="13.[125,1875,665,1650]" box="[1269,1370,1409,1431]" pageId="13" pageNumber="14">bourrelets</paragraph>
<paragraph id="8B8636C1C014462DFF82FA6DFAA93571" blockId="13.[125,1875,665,1650]" pageId="13" pageNumber="14">
<taxonomicName id="4C394D42C014462DFF82FA6DFF0C36C0" box="[125,255,1454,1475]" class="Bivalvia" family="Ostreidae" genus="Actinostreon" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreoida" pageId="13" pageNumber="14" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C014462DFF82FA6DFF0C36C0" box="[125,255,1454,1475]" italics="true" pageId="13" pageNumber="14">Actinostreon</emphasis>
</taxonomicName>
broadly convex plicae (5–35) convex plicae (5–35) weakly round, present
<collectingCountry id="F32E7651C014462DF949FA6DF92436C0" box="[1718,1751,1454,1475]" name="Russia" pageId="13" pageNumber="14">RF</collectingCountry>
, CCF,
<emphasis id="B94DEAD3C014462DFF82FA19FF0A36EC" box="[125,249,1498,1519]" italics="true" pageId="13" pageNumber="14">greagareum</emphasis>
crescentic convex dorsally flat to hollow (RV), weakly chambers (both massive concave valves) bourrelets
</paragraph>
<paragraph id="8B8636C1C017462EFF38FF54FE6F321E" blockId="14.[151,1436,151,1472]" pageId="14" pageNumber="15">
These &quot;cornerstones&quot; apart, the evolution of Jurassic oysters, especially the phylogenetic relationships between
<taxonomicName id="4C394D42C017462EFF68FF7FFEFB33D6" box="[151,264,188,213]" class="Bivalvia" family="Arctostreidae" genus="Circunula" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreida" pageId="14" pageNumber="112" phylum="Mollusca" rank="genus" status="gen. nov.">
<emphasis id="B94DEAD3C017462EFF68FF7FFEFB33D6" box="[151,264,188,213]" italics="true" pageId="14" pageNumber="15">Circunula</emphasis>
</taxonomicName>
n. gen,
<taxonomicName id="4C394D42C017462EFE8CFF7FFDF233D6" box="[371,513,188,213]" class="Bivalvia" family="Gryphaeidae" genus="Helvetostrea" kingdom="Animalia" order="Ostreoida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus" status="gen. nov.">
<emphasis id="B94DEAD3C017462EFE8CFF7FFDF233D6" box="[371,513,188,213]" italics="true" pageId="14" pageNumber="15">Helvetostrea</emphasis>
</taxonomicName>
<taxonomicNameLabel id="A27E57A8C017462EFDF2FF7FFD9133D6" box="[525,610,188,213]" pageId="14" pageNumber="15" rank="genus">
<emphasis id="B94DEAD3C017462EFDF2FF7FFD9133D6" bold="true" box="[525,610,188,213]" pageId="14" pageNumber="15">n. gen.</emphasis>
</taxonomicNameLabel>
,
<taxonomicName id="4C394D42C017462EFD89FF7EFCF433D7" box="[630,775,189,212]" class="Bivalvia" family="Gryphaeidae" genus="Praeexogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C017462EFD89FF7EFCF433D7" box="[630,775,189,212]" italics="true" pageId="14" pageNumber="15">Praeexogyra</emphasis>
</taxonomicName>
, and
<taxonomicName id="4C394D42C017462EFCAFFF7EFC3333D7" box="[848,960,189,212]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C017462EFCAFFF7EFC3333D7" box="[848,960,189,212]" italics="true" pageId="14" pageNumber="15">Nanogyra</emphasis>
</taxonomicName>
described herein and the true origin of
<emphasis id="B94DEAD3C017462EFF68FF22FDF233FB" box="[151,513,223,248]" italics="true" pageId="14" pageNumber="15">
<taxonomicName id="4C394D42C017462EFF68FF22FF0533FB" box="[151,246,225,248]" class="Bivalvia" family="Gryphaeidae" genus="Liostrea" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus">Liostrea</taxonomicName>
,
<taxonomicName id="4C394D42C017462EFEFEFF1CFE9533FB" box="[257,358,223,248]" class="Leotiomycetes" family="Pezizellaceae" genus="Catinula" higherTaxonomySource="CoL" kingdom="Fungi" order="Helotiales" pageId="14" pageNumber="15" phylum="Ascomycota" rank="genus">Catinula</taxonomicName>
,
<taxonomicName id="4C394D42C017462EFE8FFF22FDF233FB" box="[368,513,225,248]" class="Bivalvia" family="Gryphaeidae" genus="Praeexogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus">Praeexogyra</taxonomicName>
</emphasis>
, and
<taxonomicName id="4C394D42C017462EFDC1FF23FD3733F4" box="[574,708,224,247]" class="Bivalvia" family="Ostreidae" genus="Crassostrea" kingdom="Animalia" order="Ostreoida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C017462EFDC1FF23FD3733F4" box="[574,708,224,247]" italics="true" pageId="14" pageNumber="15">Crassostrea</emphasis>
</taxonomicName>
remain a puzzle. Therefore, the presently proposed classification is necessarily tentative.
</paragraph>
<paragraph id="8B8636C1C017462EFF38FEE4FD1532D3" blockId="14.[151,1436,151,1472]" pageId="14" pageNumber="15">
<emphasis id="B94DEAD3C017462EFF38FEE4FD9B3243" bold="true" box="[199,616,295,320]" pageId="14" pageNumber="15">Important morphological features.</emphasis>
Classical characters examined in this approach are shell shape, external ornament, phenotypic variation, coiling, muscle-scar shape and position, chomata, microstructure (e.g.
<bibRefCitation id="EFA84B30C017462EFAD1FE8FFF21328B" author="Aqrabawi" pageId="14" pageNumber="15" refString="Aqrabawi, M. (1993) Oysters (Bivalvia-Pteriomorphia) of the Upper Cretaceous rocks in Jordan. Palaeontology, stratigraphy and comparison with the Upper Cretaceous oysters of Northwest Europe. Mitteilungen des geologisch-palaontologischen Instituts der Universitat Hamburg, 75, 1 - 135." type="journal article" year="1993">Aqrabawi 1993</bibRefCitation>
; Carter &amp; Malchus in Carter
<emphasis id="B94DEAD3C017462EFDE0FEB2FDAB328B" box="[543,600,367,392]" italics="true" pageId="14" pageNumber="15">et al.</emphasis>
2011;
<bibRefCitation id="EFA84B30C017462EFD58FEB3FCAC328B" author="Hautmann" box="[679,863,368,392]" pageId="14" pageNumber="15" refString="Hautmann, M. (2001) Taxonomy and phylogeny of cementing Triassic bivalves (families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae). Palaeontology, 44 (2), 339 - 373. http: // dx. doi. org / 10.1111 / 1475 - 4983.00183" type="journal article" year="2001">Hautmann 2001</bibRefCitation>
;
<bibRefCitation id="EFA84B30C017462EFC93FEACFBFC328B" author="Malchus" box="[876,1039,367,392]" pageId="14" pageNumber="15" refString="Malchus, N. (1990) Revision der Kreide-Austern (Bivalvia: Pteriomorphia) Agyptens (Biostratigraphie, Systematik). Berliner Geowissenschaftliche Abhandlungen, Reihe A, 125, 1 - 231." type="journal article" year="1990">Malchus 1990</bibRefCitation>
, 1998;
<bibRefCitation id="EFA84B30C017462EFB9CFEACFB0B328B" author="Stenzel" box="[1123,1272,367,392]" pageId="14" pageNumber="15" refString="Stenzel, H. B. (1971) Oysters. In: Moore, R. C. (Eds.), Treatise on Invertebrate Paleontology. Part N, Mollusca 6 (Bivalvia). Vol. 3. Geological Society of America, University of Kansas, Boulder, pp. N 953 - N 1124." type="journal article" year="1971">Stenzel 1971</bibRefCitation>
), and as far as possible the larval shell (
<bibRefCitation id="EFA84B30C017462EFE4CFE57FDAB32AE" author="Malchus" box="[435,600,404,429]" pageId="14" pageNumber="15" refString="Malchus, N. (1995) Larval shells of Tertiary Cubitostrea Sacco 1897, with a review of larval shell characters in the subfamilies Ostreinae and Crassostreinae (Ostreoidea, Bivalvia). Bulletin de l'Institut royal des Sciences naturelles de Belgique, Sciences de la Terre, 65, 187 - 239." type="journal article" year="1995">Malchus 1995</bibRefCitation>
,
<bibRefCitation id="EFA84B30C017462EFD9AFE57FD5332AF" author="Malchus" box="[613,672,404,428]" pageId="14" pageNumber="15" refString="Malchus, N. (2000) Evolutionary significance of fossil larval shell characters: a case study from the Ostreoidea (Bivalvia: Pteriomorphia). In: Harper, E. M., Taylor, J. D. &amp; Crame, J. A. (Eds.), Evolutionary Biology of the Bivalvia. Geological Society of London, Special Publications, 177, 303 - 312." type="journal article" year="2000">2000</bibRefCitation>
,
<bibRefCitation id="EFA84B30C017462EFD53FE57FD0032AF" author="Malchus" box="[684,755,404,428]" pageId="14" pageNumber="15" refString="Malchus, N. (2004 a) Shell ontogeny of Jurassic bakevelliid bivalves and its bearing on bivalve phylogeny. Acta Palaeontologica Polonica, 49 (1), 85 - 110." type="journal article" year="2004" yearSuffix="a">2004a</bibRefCitation>
;
<bibRefCitation id="EFA84B30C017462EFCFFFE57FBEA32AF" author="Malchus" box="[768,1049,404,429]" pageId="14" pageNumber="15" refString="Malchus, N. &amp; Sartori, A. (2013) Part N, Revised, Volume 1, Chapter 4: The early shell: ontogeny, features and evolution. Treatise Online, 61, 1 - 114." type="book chapter" year="2013">Malchus &amp; Sartori 2013</bibRefCitation>
). For comparison of characteristic shell features of the Reuchenette oysters see
<tableCitation id="C6BB037AC017462EFD73FE74FD1332D3" box="[652,736,439,464]" captionStart="TABLE 1" captionStartId="13.[125,211,542,564]" captionText="TABLE 1. Main shell features for the eight oyster species from the Swiss Reuchenette Formation. “ Convex-concave ” RV refers to the nomenclature of Malchus (1990) (see also Malchus &amp; Aberhan 1998). Microstructure data refer to the left valve (LV) except for Actinostreon (LV + RV). The outermost simple prismatic (SP) or cross foliated (CF) shell layer are probably eroded in some species. Abbrevations see under “ Methods: Terminology ”." pageId="14" pageNumber="15">Table 1</tableCitation>
.
</paragraph>
<paragraph id="8B8636C1C017462EFF38FE1EFBD63163" blockId="14.[151,1436,151,1472]" pageId="14" pageNumber="15">It was found, however, that many of the postlarval characters, which are generally accepted as diagnostic at various taxonomic levels, can vary with age (size). Although strongly limited by taphonomy and diagenesis, the present approach thus tried to include even the smallest specimens of each species to capture information on their earliest shell stage characters. Some relevant examples are briefly circumscribed:</paragraph>
<paragraph id="8B8636C1C017462EFF38FDAFFD533736" blockId="14.[151,1436,151,1472]" pageId="14" pageNumber="15">
Coiling—Early postlarval growth in oysters is almost intrinsically anterior-directed helicoidal thus producing an opisthogyrate, or at least opisthocline umbo. This appears to be due to a delayed offset of the larval coiling tendency (
<bibRefCitation id="EFA84B30C017462EFEF3FD77FE4131CF" author="Malchus" box="[268,434,692,717]" pageId="14" pageNumber="15" refString="Malchus, N. (2000) Evolutionary significance of fossil larval shell characters: a case study from the Ostreoidea (Bivalvia: Pteriomorphia). In: Harper, E. M., Taylor, J. D. &amp; Crame, J. A. (Eds.), Evolutionary Biology of the Bivalvia. Geological Society of London, Special Publications, 177, 303 - 312." type="journal article" year="2000">Malchus 2000</bibRefCitation>
, p. 308, text-figs. 1–4; 2004a, p. 99, characters E to I; 2004b, p. 1546, text-figs. 3b, 8). However, offset and even radical changes in coiling direction may occur very early after metamorphosis. This is, for example, the case in an unusually large number of individuals of
<taxonomicName id="4C394D42C017462EFC2BFD3FFBB63016" box="[980,1093,764,789]" class="Bivalvia" family="Arctostreidae" genus="Circunula" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus" status="gen. nov.">
<emphasis id="B94DEAD3C017462EFC2BFD3FFBB63016" box="[980,1093,764,789]" italics="true" pageId="14" pageNumber="15">Circunula</emphasis>
</taxonomicName>
<taxonomicNameLabel id="A27E57A8C017462EFBAEFD3FFB573016" box="[1105,1188,764,789]" pageId="14" pageNumber="15" rank="genus">
<emphasis id="B94DEAD3C017462EFBAEFD3FFB573016" bold="true" box="[1105,1188,764,789]" pageId="14" pageNumber="15">n. gen.</emphasis>
</taxonomicNameLabel>
<taxonomicName id="4C394D42C017462EFB4FFD3FFAEE3016" box="[1200,1309,764,789]" class="Bivalvia" family="Arctostreidae" genus="Circunula" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreida" pageId="14" pageNumber="15" phylum="Mollusca" rank="species" species="cotyledon">
<emphasis id="B94DEAD3C017462EFB4FFD3FFAEE3016" box="[1200,1309,764,789]" italics="true" pageId="14" pageNumber="15">cotyledon</emphasis>
</taxonomicName>
which are prosogyrate in early postlarval life. Another example is
<taxonomicName id="4C394D42C017462EFCBCFCE3FBAB303B" box="[835,1112,800,824]" class="Bivalvia" family="Ostreidae" genus="Actinostreon" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreoida" pageId="14" pageNumber="15" phylum="Mollusca" rank="species" species="gregareum">
<emphasis id="B94DEAD3C017462EFCBCFCE3FBAB303B" box="[835,1112,800,824]" italics="true" pageId="14" pageNumber="15">Actinostreon gregareum</emphasis>
</taxonomicName>
which is actually strongly exogyroid in earliest postlarval life (Pl. 16.6; Pl. 18.1b,c; Pl. 19.4a–d). But this potentially important feature is rarely preserved because the juvenile umbo becomes easily eroded. Generally speaking, later growth phases are mostly characterized by gradual changes in the degree of coiling rather than by radical re-orientation. Gradual changes may also be diagnostic, as discussed here for various species of
<taxonomicName id="4C394D42C017462EFC39FC72FBC530CB" box="[966,1078,945,968]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C017462EFC39FC72FBC530CB" box="[966,1078,945,968]" italics="true" pageId="14" pageNumber="15">Nanogyra</emphasis>
</taxonomicName>
. Coiling and changes of coiling direction also affect the orientation and width of the ligament area which are thus not independent diagnostic features (
<bibRefCitation id="EFA84B30C017462EFF00FC34FE563713" author="Malchus" box="[255,421,1015,1040]" pageId="14" pageNumber="15" refString="Malchus, N. (2000) Evolutionary significance of fossil larval shell characters: a case study from the Ostreoidea (Bivalvia: Pteriomorphia). In: Harper, E. M., Taylor, J. D. &amp; Crame, J. A. (Eds.), Evolutionary Biology of the Bivalvia. Geological Society of London, Special Publications, 177, 303 - 312." type="journal article" year="2000">Malchus 2000</bibRefCitation>
,
<bibRefCitation id="EFA84B30C017462EFE4EFC34FE0F3713" author="Malchus" box="[433,508,1015,1040]" pageId="14" pageNumber="15" refString="Malchus, N. (2004 a) Shell ontogeny of Jurassic bakevelliid bivalves and its bearing on bivalve phylogeny. Acta Palaeontologica Polonica, 49 (1), 85 - 110." type="journal article" year="2004" yearSuffix="a">2004a</bibRefCitation>
,
<bibRefCitation id="EFA84B30C017462EFDFEFC34FDE33713" author="Malchus" box="[513,528,1015,1040]" pageId="14" pageNumber="15" refString="Malchus, N. (2004 b) Constraints in the ligament ontogeny and evolution of pteriomorphian Bivalvia. Palaeontology, 47, 1539 - 1574. http: // dx. doi. org / 10.1111 / j. 0031 - 0239.2004.00419. x" type="journal article" year="2004" yearSuffix="b">b</bibRefCitation>
). These characters are often better visible in the free right valve (
<figureCitation id="13022A44C017462EFB07FC34FACE3713" box="[1272,1341,1015,1040]" captionStart="FIGURE 9" captionStartId="24.[151,250,929,951]" captionTargetBox="[174,1413,564,904]" captionTargetId="figure@24.[169,1418,555,908]" captionTargetPageId="24" captionText="FIGURE 9. Comparison of juvenile RVs of Gryphaea, Nanogyra, and Actinostreon. 1. Gryphaea ferruginea Terquem, 1855, Aalenian, Poland (redrawn after Pugaczewska 1971 b, fig. 1). 2. Nanogyra (Palaeogyra) virgula (Deshayes, 1831), Upper Kimmeridgian, Switzerland. 3. Nanogyra (N.) nana (J. Sowerby, 1822), Lower Kimmeridgian, Switzerland. 4. Actinostreon marshii (J. Sowerby, 1814), Callovian, Lithuania." httpUri="https://zenodo.org/record/288043/files/figure.png" pageId="14" pageNumber="15">Fig. 9</figureCitation>
) than in the attached and often xenomorphic left valve.
</paragraph>
<paragraph id="8B8636C1C017462EFF38FBFCFF1F360E" blockId="14.[151,1436,151,1472]" pageId="14" pageNumber="15">
Chomata—Malchus (1998) already mentioned that these denticle-like shell margin features of still unknown provenience (
<bibRefCitation id="EFA84B30C017462EFECEFBA7FDBD377F" author="Malchus" box="[305,590,1124,1149]" pageId="14" pageNumber="15" refString="Malchus, N. &amp; Sartori, A. (2013) Part N, Revised, Volume 1, Chapter 4: The early shell: ontogeny, features and evolution. Treatise Online, 61, 1 - 114." type="book chapter" year="2013">Malchus &amp; Sartori 2013</bibRefCitation>
) may disappear during ontogeny. It is again
<taxonomicName id="4C394D42C017462EFBA6FBA7FB39377E" box="[1113,1226,1124,1149]" class="Bivalvia" family="Arctostreidae" genus="Circunula" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus" status="gen. nov.">
<emphasis id="B94DEAD3C017462EFBA6FBA7FB39377E" box="[1113,1226,1124,1149]" italics="true" pageId="14" pageNumber="15">Circunula</emphasis>
</taxonomicName>
<taxonomicNameLabel id="A27E57A8C017462EFB2CFBA7FAD6377E" box="[1235,1317,1124,1149]" pageId="14" pageNumber="15" rank="genus">
<emphasis id="B94DEAD3C017462EFB2CFBA7FAD6377E" bold="true" box="[1235,1317,1124,1149]" pageId="14" pageNumber="15">n. gen.</emphasis>
</taxonomicNameLabel>
<taxonomicName id="4C394D42C017462EFAD0FBA7FA6F377E" box="[1327,1436,1124,1149]" class="Bivalvia" family="Arctostreidae" genus="Circunula" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreida" pageId="14" pageNumber="15" phylum="Mollusca" rank="species" species="cotyledon">
<emphasis id="B94DEAD3C017462EFAD0FBA7FA6F377E" box="[1327,1436,1124,1149]" italics="true" pageId="14" pageNumber="15">cotyledon</emphasis>
</taxonomicName>
providing a case in point where the character is deemed to be species (or genus) specific. Chomata also seem to leave antimarginal riblets on the shell exterior, at least in
<taxonomicName id="4C394D42C017462EFCE0FB6EFBDD37C7" authority="Palaeogyra" authorityName="Palaeogyra" box="[799,1070,1196,1221]" class="Bivalvia" family="Gryphaeidae" genus="Nanogyra" higherTaxonomySource="GBIF" kingdom="Animalia" order="Pterioida" pageId="14" pageNumber="15" phylum="Mollusca" rank="genus">
<emphasis id="B94DEAD3C017462EFCE0FB6EFC7C37C7" box="[799,911,1197,1220]" italics="true" pageId="14" pageNumber="15">Nanogyra</emphasis>
(
<emphasis id="B94DEAD3C017462EFC5FFB6FFBD037C6" box="[928,1059,1196,1221]" italics="true" pageId="14" pageNumber="15">Palaeogyra</emphasis>
)
</taxonomicName>
. Hence, the presence/absence of an apparently independent external ornamental feature may actually be linked to the onset/offset of an internal shell feature.
</paragraph>
<paragraph id="8B8636C1C017462EFF38FAD4FABF36BC" blockId="14.[151,1436,151,1472]" pageId="14" pageNumber="15">
Posterior adductor scar—Juvenile imprints may have a different shape, orientation and position compared with their adult pendants. The posterior adductor of juvenile
<taxonomicName id="4C394D42C017462EFCA9FAFFFB9D3657" box="[854,1134,1340,1364]" class="Bivalvia" family="Ostreidae" genus="Actinostreon" higherTaxonomySource="GBIF" kingdom="Animalia" order="Ostreoida" pageId="14" pageNumber="15" phylum="Mollusca" rank="species" species="gregareum">
<emphasis id="B94DEAD3C017462EFCA9FAFFFB9D3657" box="[854,1134,1340,1364]" italics="true" pageId="14" pageNumber="15">Actinostreon gregareum</emphasis>
</taxonomicName>
, for instance, leaves an “elongated” imprint (Pl. 18.3b) whereas that of the adult is round (Pl. 16.5b, 6a; Pl. 17.1b,c, 3b,c). In addition, the posterior border of the juvenile imprint corresponds to the ventral side of the adult adductor scar. It appears plausible to assume that this ontogenetic change largely corresponds to a rotational growth of the soft parts.
</paragraph>
</subSubSection>
</treatment>
</document>
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