Mimachlamys Iredale, 1929
IREDALE, T. 1929. Mollusca from the continental shelf of eastern Australia. No .2. Records of the Australian Museum, 17: 157-189. [p. 162]
«Four very distinct series are at once noted, the asperrimus, lividus, bifrons and "hedleyi" groups, and it will clarify matters to designate these groups as genera, so I herewith propose Mimachlamys with P. asperrimus as type, Scaeochlamys with Pecten lividus as type, Equichlamys with P. bifrons as type and Mesopeplum with M. caroli as type.
In Mimachlamys the valves are both convex, but the left valve is more convex than the right, the auricles are unequal, the posterior being much smaller than the anterior. The byssal gape is deep and very strong, pectinidial teeth are present, a deeply furrowed fasciole occurring. The sculpture consists of closely scaled numerous radials flanked with subsidiary more delicate riblets, a deep gutter intervening between each group, which becomes filled up with such riblets as maturity is reached. The prodissoconch is smooth, with concentric growth lines, the succeeding sculpture being plain riblets with scratched intervals, the scales developing later. The sculpture on the two valves does not differ appreciably in design.» TOM IREDALE, 1929
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Pecten asperrimus Lamarck; L. A. Reeve, 1852-1853, Monograph of the genus Pecten. In: L. A. Reeve (Ed.), 1843-1878, Conchologia Iconica; or illustrations of the shells of molluscous animals, volume 8, plate 20, figure 75.
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H. H. Dijkstra & A. G. Beu, 2018, Living scallops of Australia and adjacent waters. Figures 88A, 88H: Mimachlamys asperrima (Lamarck); figures 188B-88D, 88F: Mimachlamys cloacata (Reeve); figures 88E, 88G: Mimachlamys funebris (Reeve); figures 88I, 88J: Mimachlamys gloriosa (Reeve).
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«Mimachlamys Iredale, 1929: 162. Type species (by original designation): Pecten asperrimus Lamarck, 1819. Recent, southwestern, southern and southeastern Australia.
Diagnosis. Medium-sized to large, byssate Mimachlamydini with chlamydoid shape, auricles highly unequal; a primitive hinge type with prominent resilial and dorsal teeth; macrosculpture of evenly spaced, undivided, solid radial plicae in most species, bearing spines, flanked with secondary costellae; antimarginal and/or divaricated interstitial microsculpture; byssal notch deep, ctenolium well-developed.
Distribution. Eocene–Recent (Waller, 1991: 32). Indo-West Pacific and eastern Atlantic, living in the intertidal to sublittoral zones, byssally attached to rocks or coral and amongst rubble.
Discussion. Hertlein (1969: N355) placed Mimachlamys in the synonymy of Chlamys Röding, 1798, as did Vaught (1989: 118). Waller (1991: 31; 1993: 200) established the morphological differences between Mimachlamys and Chlamys, and placed the former genus in Mimachlamydini.»
DIJKSTRA, H. H. & A. G. BEU. 2018. Living scallops of Australia and adjacent waters (Mollusca: Bivalvia: Pectinoidea: Propeamussiidae, Cyclochlamydidae and Pectinidae). Records of the Australian Museum, 70 (2): 113-330, figs. 1-102. [p. 275]
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«Diagnosis. — Medium-sized to large, byssate Mimachlamydini with chlamydoid shape, auricles highly unequal; a primitive hinge type with prominent resilial and dorsal teeth; macrosculpture of evenly spaced, solid radial costae in most species, bearing spines, flanked with secondary costellae; antimarginal and/or divaricated interstitial microsculpture; byssal notch deep, ctenolium well-developed.
Distribution. — Eocene to Recent (Waller, 1991: 32). Indo-West Pacific and eastern Atlantic; living intertidally to sublittorally. Remarks. — Hertlein (1969: N355) placed Mimachlamys in the synonymy of Chlamys Röding, 1798, as did Vaught (1989: 118). Waller (1991: 31; 1993: 200) established the morphological differences between Mimachlamys and Chlamys, and placed the former genus in Mimachlamydini.» DIJKSTRA, H. H. 2013. Pectinoidea (Bivalvia: Propeamussiidae and Pectinidae) from the Panglao region, Philippine Islands. Vita Malacologica, 10: 1-108, pls. 1-32 pls, 2 tabs.
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«Type species.— Pecten asperrimus Lamarck, 1819, by original designation.
Original diagnosis.— "In Mimachlamys the valves are both convex, but the left valve is more convex than the right, the auricles are unequal, the posterior being much smaller than the anterior. The byssal gape is deep and very strong, pectinidial teeth are present, a deeply furrowed fasciole occurring. The sculpture consists of closely scaled numerous radials flanked with subsidiary more delicate riblets, a deep gutter intervening between each group, which becomes filled up with such riblets as maturity is reached. The prodissoconch is smooth, with concentric growth lines, the succeeding sculpture being plain riblets with scratched intervals, the scales developing later. The sculpture on the two valves does not differ appreciably in design." (Iredale, 1929: 163).
Emended diagnosis.— Mimachlamydini with rib interspaces lacking commarginal lamellae, having instead divaricating, diagonal, or herringbone antimarginal microsculpture; rib crests smooth between scales. Primary ribs continuous from early dissoconch, with only minor intercalation or branching in early ontogeny; scaly secondary costae commonly present on ribs and interspaces.
Remarks.— The greatest species diversity of Mimachlamys in present-day oceans is in the western Pacific and Indian Oceans, there being only one species, M. varia (Linnaeus, 1758), occurring in the warm-temperate to cool-temperate regions of the eastern Atlantic (Waller, 1991: 30; 1993: 228). The two new species described below from the late Miocene and early Pliocene of the Dominican Republic and M. landi (Cooke, 1921) from the Pliocene La Cruz Formation of Cuba are the only known representatives of Mimachlamys thus far recognized in the tropical western Atlantic region. The genus apparently became extinct in this region in the Pliocene.
Geographic range.— In present-day seas, limited to tropical to cool-temperate eastern Atlantic and western Indo-Pacific, living off shore to mid-continental shelf depths.
Stratigraphic range.— Eocene to Recent in eastern Atlantic and Indo-Pacific regions; upper Miocene and Pliocene in the tropical western Atlantic.»
WALLER, T. R. 2011. Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae (Mollusca: Bivalvia: Pectinoidea) of the Cibao Valley. Bulletins of American Paleontology, 381: 1-197, pls. 1-18. [p. 34]
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«In Palaeontology it has been customary to consider Pectinidae with strongly developed radial ribs, unequal auricles and an elongated ovoid shape as belonging to the genus Chlamys.
GLIBERT & VAN DE POEL, 1965, considered this genus as containing only those species which show a thimble-microsculpture (pl. 1, fig. 1). With this characteristic it is easy to differentiate Chlamys-species from Mimachlamys-species. (Mimachlamys IREDALE, 1929 type-species Pecten asperrimus LAMARCK, 1819 O. D.). On Recent and Tertiary specimens the microsculpture makes it possible for us to differentiate both genera, but on Chlamys-species from Cretaceous or older deposits the microsculpture, due to the state of preservation, is almost never visible (exception: Chlamys faujasi (DEFRANCE) from Maastricht and C. dentata (NILSSON) from Ivö). Because of the absence of the microsculpture other characteristics must be found to differentiate in Chlamys s.l. the two genera. Such characteristics exists but numerically it seems impossible to express them. Chlamys-species are more elongated and have a narrower umbo than Mimachlamys-species; usually on Chlamys-species the ribs are broad, complex and few in number, whereas on Mimachlamys-species they are simple, very narrow and often very numerous.» DHONDT, A. V. 1973a. Systematic revision of the Chlamydinae (Pectinidae, Bivalvia, Mollusca) of the European Cretaceous. Part 3: Chlamys and Mimachlamys. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, 49 (1): 1-134, pls. 1-9. [p. 4]
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