Pascahinnites Dijkstra & Raines, 1999
DIJKSTRA, H. H. & B. K. RAINES. 1999. Pascahinnites n. gen. for "Pecten (Chalmys)" [sic] pasca Dall, 1908, a cemented Easter Island scallop (Bivalvia: Pectinidae). Basteria, 63 (4-6): 199-203, figs. 1, 2. [p. 200]
«Pectinidae Wilkes, 1810 [emend. Waller, 1978]
Chlamydinae von Teppner, 1922 Chlamydini von Teppner, 1922 Pascahinnites gen. nov.
Tlpe species.— Pecten (Chlamys) pasca Dall, 1908. Only one species known.
Diagnosis.— Byssate fiuvenile stage) or cemented (adult stage). With antimarginal microsculpture only in the preradial stage (between dissoconch and radial stage). Hexagonal (shagreen) or quadrangular microsculpture and radial macrosculpture present. Antimarginal and commarginal sculpture absent on disc.
Discussion.— Pascahinnites has a chlamydoid form with a Semipallium-llke sculpture in early stages, when the animals are attached to the substratum by byssus, and a Hinnites-like appearance in a later stage, when they are cemented to the hard substratum with the right valve. Specimens of Semipallium species are attached to the substratum by byssus throughout their life and are never cemented.
On shells of Chlamys species, antimarginal striae are more prominent and also present near the lateral margins and rib interspaces, whereas a shagreen microsculpture is more consistent and prominent ín Pascaltinnites. In Chlamys the animals are only byssally attached to the substratum, not cemented. Shells of Crassadoma species djffer frorn Pascahinnites by the absence of antimarginal and the presence of intercalated commarginal lirae in early stages. In Pascahinnites there are antimarginal striae in the preradial stage and a shagreen microsculpture on the radial rib interspaces. In Hinnites species, the shells have a more prominent antimarginal microsculpture and no shagreen microsculpture. Both genera are cemented in late stages. Distribution.— Pacific, Isla de Pascua [= Easter Island]; Recent, sublittoral.»
HENK H. DIJKSTRA & BRET K. RAINES, 1999
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Pascahinnites pasca. (Dall, 1908); H. H. Dijkstra & B. K. Raines, 1999, Pascahinnites n. gen. for "Pecten (Chalmys)" [sic] pasca Dall, 1908, a cemented Easter Island scallop (Bivalvia: Pectinidae), figures 1, 2.
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Pascahinnites coruscans coruscans (Hinds); H. H. Dijkstra & A. G. Beu, 2018, Living scallops of Australia and adjacent waters, figures 74E, 74F.
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Pascahinnites Dijkstra & Raines, 1999
Pascahinnites Dijkstra & Raines, 1999: 200. Type species (by original designation): Pecten (Chalmys) [sic] pasca Dall, 1908; living, Easter Island.
Diagnosis. Small subcircular chlamydoid shells up to c. 20 mm high. Some species (including the type species) byssate in juvenile stage, cemented to hard substrates after a height of c. 9–11 and growing irregularly thereafter; others living byssally attached to hard substrates throughout life, without cementation. External prismatic layer lacking from early right dissoconch; antimarginal microsculpture in early pre-radial stage; shagreen microsculpture and radial macrosculpture present throughout; commarginal sculpture lacking. Byssal notch and functional ctenolium prominent in juvenile stage, absent in cemented adults.
Distribution. Pleistocene (Oliver, 1911: 527; 1915: 554; Deyrell Islet, Kermadec Islands; Waller, 1972a: 234; Midway I., Hawaii; Taylor, 1978; Aldabra) and Recent. Tropical and temperate Indo-West Pacific; Kermadec Islands and Easter Island, at sublittoral depths.
Remarks. For several years the following species has been included in Semipallium, but Paulay (2003), following advice from T. R. Waller, included it in Pascahinnites. The similarity of “Pecten (Chlamys)” pasca Dall to “Chlamys” coruscans has been commented on previously by Rehder (1980: 109, pl. 13, figs 3–6) (again, following advice from T. R. Waller) and Bernard (1986: 71). The style of radial sculpture, with each pair of high, narrowly rounded costae separated by a single relatively wide secondary costa, the presence of shagreen microsculpture, the lack of a pre-radial external prismatic calcite layer in the right valve, and the relatively wide, acline shape confirm that Pecten coruscans Hinds, 1845 is related phylogenetically to Pascahinnites pasca (Dall) rather than to the dorsoventrally elongate, prosocline species included in Semipallium. See also Dijkstra & Marshall (2008: 51).
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. 251]
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