Psychrochlamys Jonkers, 2003
JONKERS, H. A. 2003. Late Cenozoic-Recent Pectinidae (Mollusca: Bivalvia) of the Southern Ocean and neighbouring regions. Monographs of Marine Mollusca, 5: i-viii + 1-125 pp, 17 pls. Backhuys Publishers, Leiden. [p. 43]
Genus Psychrochlamys gen. nov.
Etymology. From the Greek ψυχρός, 'cold', 'cool', 'of cool water', and the generic name Chlamys. The name reflects the cold-water habitat of the genus' living species, and acknowledges the usefulness of the genus as a cold-water indicaior in Australia and New Zealand during latest Pliocene and Pleistocene.
Type species. Pecten patagonicus King & Broderip, 1832, from the Recent off southern South America.
Diagnosis. Small- to moderate-sized (mean VH 30-80 mm; Fig. 34) chlamydoids with acline to strongly opisthocline shells, changing strongly in shape during ontogeny (Fig. 35); disc nearly circular to highly asymmetrical (and then posterior part of disc longer than anterior part); umbonal angle 110"-115". Macrosculpture consisting of low, undulating plicae (often with distinctly angulate cross-secrion), carrying fascicles of fine scaly costae, with similar costellae in interspaces. Microsculpture in pre-radial stage of LV and on disc consisting of fine anrimarginal ridgelets, never shagreen (Plate 1, figs. a-c). Outer ligament compararively short; arcuare (never acute) byssal notch, shallow in most taxa (Fig. 29). Resilifer never oblique. Functional ctenolium present in all species, but weakly developed in some of the younger (Late Pliocene-Recent) species.
Remarks. The main differences with Zygochlamys are the generally smaller size, the mostly opisthocline shell shape, a shorter outer ligament, a shallower byssal notch, and the complete absence of shagreen microsculpture. Unlike species of Zygochlamys, all taxa show dramatic changes in shell morphology during ontogeny (Fig. 35). Juveniles have an almost identical chlamydoid shape, but the relative reduction in length of the outer ligament, together with a relative decrease in depth of byssal notch and an increase in width of the umbonal angle give rise to an aequipectinoid morphology in the adult of most taxa (particularly in Fig. 35h); in such, disc gapes are usually present.
Stratigraphical range and distrbution. Pliocene-Recent (Fig. 25). Living represenrarives of Psychrochlamys are found off Islas Juan Fernández (SE Pacific), in the $ords of sourhern Chile, on rhe Patagonian shelf off Argentina and the Falkland Islands, and off the east coast of South Island, New Zealand, and the sub-Antarctic islands to the south of New Zealand (Fig. 28). Fossil taxa occur in the Pliocene of southern and (rarely) central Chile (Fig. 20), and in the Pliocene of New Zealand's North Island and in the Chatham Islands; Pleistocene fossils are found off Tasmania and southeast Australia, and in the offshore New Zealand region as far north as the Three King Islands (Fig. 22).
Included species. Psychrochlamys patagonica (King & Broderip, 1832), Recent, off Patagonia, P. delicatula (Hutton, 1873), comprising the subspecies P. delicatula delicatula, Late Pliocene, New Zealand, P. delicatula instar (Iredale, 1925), Pleistocene, off SE Australia and New Zealand, and P. delicatula subantarctica (Hedley 1916), Recent, sourhern New Zealand region, and P. moerickei (Hertlein, 1936), Late? Pliocene, Chile, P. phalara (Roth, 1975) Recent, Islas Juan Fernández, SE Pacific Ocean, P. seymouri (Marwick, 1928), earliest Pliocene, Chatham Island, New Zealand, and P. whenuataruensis sp. nov., early Late Pliocene, Pitt Island, Chatham Islands, New Zealand.»
H. A. JONKERS, 2003
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Psychrochlamys patagonica (King & Broderip); H. A. Jonkers, 2003, Late Cenozoic-Recent Pectinidae (Mollusca: Bivalvia) of the Southern Ocean and neighbouring regions, plate 8, figures c-f.
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Psychrochlamys patagonica (King & Broderip); H. A. Jonkers, 2003, Late Cenozoic-Recent Pectinidae (Mollusca: Bivalvia) of the Southern Ocean and neighbouring regions, plate 9, figures e, f.
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«Zygochlamys differs from Psychrochlamys (type species: Pecten patagonicus King, 1832, Magellanic and Argentine Malacological provinces, Holocene–Recent; Jonkers, 2003, pl. 1, fig. 1, pl. 8, figs. c–f, pl. 9, figs. e, f) in having larger, thicker, and less prosocline shells that are higher than long or as high as long in adult stages, a narrower umbonal angle, a longer hinge margin with more asymmetrical auricles, the free margin of left anterior auricles inclined anteriorly, a deeper byssal notch, and a byssal sinus. Sculpture also separates the two genera because Zygochlamys species have higher plicae, interspaces are covered with scaly riblets of two or three orders, and the commarginal microsculpture is almost restricted to the umbonal area or, as happens in Z. sebastiani Morra, 1985, to certain narrow bands of the shells, while in Psychrochlamys coarse commarginal lamellae extend over the entire surface and it lacks the shagreen microsculpture that characterizes Zygochlamys.»
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. 317]
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«Iredale (1925: 253) and Beu (1995: 18) pointed out that the type material of Talochlamys pulleineana is closely similar to Pecten (Chlamys) dichrous and that Chlamys (Mimachlamys) taiaroa is a subjective junior synonym of the former. According to Beu (1995) and Beu & Darragh (2001), Zygochlamys and Talochlamys have different origins, and C. dichroa should be placed in Talochlamys. According to Jonkers (2003) circum-subantarctic Recent species, formerly placed in Zygochlamys, belong in a distinct genus Psychrochlamys, lacking the shagreen microsculpture present on some early species of Zygochlamys. However, in our opinion middle Eocene specimens observed (AGB, with M. Griffin, Museo de La Plata, Argentina) in the Rio Turbio Formation, southern Argentina, are typical of Zygochlamys as well as very similar to Recent specimens of Z. patagonica and Z. delicatula in all characters. This group merely lost shagreen microsculpture during its evolution, and these taxa all form one clade. We follow the opinion of Beu & Darragh (2001: 118) and Dijkstra & Marshall (2008: 63) and treat Psychrochlamys as a synonym of Zygochlamys.»
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. 273]
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H. A. Jonkers, 2003, Late Cenozoic-Recent Pectinidae (Mollusca: Bivalvia) of the Southern Ocean and neighbouring regions, figure 34.
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«Remarks
Jonkers (2003) introduced Psychrochlamys for taxa that differ from Zygochlamys species primarily as follows: smaller size, mostly opisthocline shape, shorter outer ligament, shallower byssal notch, complete lack of shagreen sculpture, and in that all species undergo a marked transformation in shell shape during ontogeny from a chlamydoid to an essentially aequipectinoid shape. Certainly all species referred by Jonkers to Psychrochlamys transform from chlamydoid to aequipectinoid shape, but the type species of Zygochlamys itself undergoes a similar transformation, the change being less pronounced in other Zygochlamys species. Jonkers reported that shagreen sculpture completely covers the disc in some Zygochlamys species, but that it occurs to a variable extent in early ontogeny in Z. geminata. It seems clear to us that all of these differences are simply grades, none of which are of great magnitude (see Jonkers 2003, figs 30, 34). Accordingly we interpret Psychrochlamys as a synonym of Zygochlamys.» DIJKSTRA, H. H. & B. A. MARSHALL. 2008. The recent Pectinoidea of the New Zealand region (Mollusca: Bivalvia: Propeamusiidae, Pectinidae and Spondylidae). Molluscan Research, 28 (1): 1-88, figs. 1-70. [p. 63]
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