Moirechlamys 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. 329]
«Moirechlamys new genus
Type species.— Pecten actinodes Sowerby, 1846. Late Miocene, Puerto Madryn, Gran Bajo del Gualicho and Barranca Final formations and ‘Cabo Buentiempo Beds.’
Included species.— Moirechlamys aurorae (Feruglio, 1954). Early Pliocene ‘Araucanense Beds.’
Diagnosis.— Shell large, left-convex, opisthocline, elongate anteriorly. Umbonal angle 90°–115°. Byssal notch deeper than in other Patagonian Chlamydini. Left anterior auricles with 21–30 radial ribs and posterior auricles with 13–25 radial ribs. Both valves sculptured with 24–44 simple plicae separated by interspaces narrower than those of Zygochlamys.
Occurrence.— Late Miocene from the Peninsula Valdés area (Chubut Province), Barranca Final and Salinas del Gualicho (Río Negro Province), and Río Gallegos area (Santa Cruz Province); early Pliocene from ‘Araucanense Beds’ (Santa Cruz Province).
Etymology.— From the Moiré optical effect in reference to the pattern of ornamentation.
Remarks.— Moirechlamys n. gen. develops very large and convex shells for the tribe Chlamydini, with subcircular or flabelliform, opisthocline adult discs, with a very narrow right anterior auricle and valves sculptured with a large number of single plicae, of variable height, covered with small, low scales that extend over the entire surface except for the umbonal area and rather frequent shagreen microsculpture on both valves. There is a trend toward the elongation of the anterior auricles from the late Miocene M. actinodes to the early Pliocene M. aurorae, which leads to the development of a deeper byssal notch and sinus in the Pliocene species.
The type species of this new genus, Pecten actinodes, has been assigned to Chlamys (Fleming, 1957; Beu, 1985) and to Zygochlamys (Ihering 1907; Waller, 1991; Beu, 1995; Jonkers; 2003; Griffin and Nielsen, 2008), but its distinctive characters show that it deserves to be included in a new genus. Moirechlamys n. gen. is separated from Chlamys s. str. (type species: Chlamys islandica [Müller, 1776], Arctic Sea and North Atlantic and North Pacific Oceans, early Pleistocene–Recent) in having nonfolded, larger, and left-convex shells, opisthocline discs that are elongated anteriorly, a longer hinge margin, and narrower and longer anterior auricles. In Chlamys, shagreen microsculpture is always present, at least on right valves; in Moirechlamys n. gen. it is present less frequently. Moirechlamys n. gen. can be distinguished from Zygochlamys by having more-inflated, left-convex shells, circular or flabelliform in shape, with opisthocline, anteriorly elongate adult discs, a narrower and longer right anterior auricle, a deeper byssal notch, posterior auricles ornamented with up to 25 riblets, and shagreen microsculpture more frequently extending to the ventral margin on right valves. Moreover, species of Moirechlamys n. gen. are sculptured with almost the same number of unpaired plicae covered with fewer and smaller scales, whereas those of Zygochlamys differ strongly in the number of plicae. Moirechlamys n. gen. differs from Pixiechlamys n. gen. in having larger, opisthocline shells without ledges, a shallower byssal sinus ornamented with lower and much more numerous plicae, covered with fewer ribs, and shagreen microsculpture extending further over the disc surface. Finally, Moirechlamys n. gen. differs from Chokekenia n. gen. in having larger shells without ledges, a larger byssal notch, and byssal sinus, sculptured with numerous plicae covered with narrower and lower ribs of different sizes. In addition, the shagreen microsculpture extends over more of the disc than in Chokekenia n. gen.» MARÍA BELÉN SANTELLI & CLAUDIA JULIA DEL RÍO, 2019
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Moirechlamys actinodes (Sowerby, 1846) n. comb.; M. B. Santelli & C. J. del Río, 2019, figures 10.1-10.11.
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