Pixiechlamys Santelli & del Río, 2019
SANTELLI, M. B. & C. J. DEL RÍO. 2019. Neogene Pectinidae (Bivalvia) of tribe Chlamydini Teppner, 1922 in Patagonia (Argentina): Zygochlamys Ihering, 1907 and three new genera. Journal of Paleontology, 93 (2): 312-336, figs. 1-11. [p. 327]
«Pixiechlamys new genus
Type species.— Pecten quemadensis Ihering, 1897. Early Miocene, Monte Léon, San Julián, and Chenque formations, by monotype.
Diagnosis.— As for type species.
Occurrence.— Early Miocene of Austral and Golfo San Jorge Basins.
Etymology.— From pixie, a word of probable Celtic origin, meaning dwarf, mythical creatures, in reference to the small shells of the genus.
Remarks.— Pixiechlamys n. gen. is here proposed to include the small Miocene species P. quemadensis (Ihering, 1897) n. comb., well differentiated from other Patagonian taxa in having nonfolded shell, which is sculptured with ribs.
Pixiechlamys n. gen. is characterized by having shells with one or two growth ledges (Fig. 8.8, 8.11–8.13) sculptured with very fine ribs covered with low, closely packed scales instead of the ribbed plicae ornamented with prominent scaly ribs as in Zygochlamys. In addition, Pixiechlamys n. gen. has a smaller, more circular disc, more asymmetrical auricles, a smaller posterior auricle, a strongly sinuous free margin of the left anterior auricle, and a deeper byssal sinus than Zygochlamys. Pixiechlamys n. gen. differs from Chokekenia n. gen. in having smaller shells sculptured with primary and secondary ribs covered with scales that arise earlier in ontogeny, up to two growth ledges, a narrower umbonal angle, more asymmetrical auricles, and a markedly deeper byssal notch and byssal sinus. Pixiechlamys n. gen. is distinguished from Swiftopecten Hertlein, 1936 (type species Swiftopecten swiftii [Bernardi, 1858], Recent, Japan) in having more-circular shells, a deeper byssal sinus, valves ornamented with ribs of different orders that lack nodes, and weaker and less frequent growth ledges. This new genus could be confused with small Australian and New Zealand species of Talochlamys Iredale, 1929, which have more circular shells, sculptured with primary, secondary, and tertiary ribs in some species, and a deep byssal sinus. Beu and Darragh (2001, p. 97) also indicated the presence of shagreen microsculpture in some specimens of T. eyrei (Tate, 1886) as also happens in Pixiechlamys n. gen. However, remarkable differences separate the two genera, such as the presence in Pixiechlamys n. gen. of more-triangular, ledged shells and microsculpture represented by fine commarginal lirae at the beginning of the radial stage rather than by coarse commarginal lamellae as in Talochlamys. Pixiechlamys n. gen. also has a much shorter preradial stage, more-obvious and frequent bifurcations of ribs on the right valve, and many rib intercalations on both valves, and the interspaces are ornamented with secondary ribs from the initial radial stage; in Talochlamys, when present, secondary ribs appear in late ontogeny. Some specimens of T. eyrei have superimposed secondary ribs on the sides of the primary ribs, but they arise as intercalations on both valves and later in ontogeny than in Pixiechlamys n. gen.» MARÍA BELÉN SANTELLI & CLAUDIA JULIA DEL RÍO, 2019
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Pixiechlamys quemadensis (Ihering, 1897) n. comb.; M. B. Santelli & C. J. del Río, 2019, Neogene Pectinidae (Bivalvia) of tribe Chlamydini Teppner, 1922 in Patagonia (Argentina): Zygochlamys Ihering, 1907 and three new genera.figures 8.8-8.13.
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