Capedopecten Dijkstra & Janssen, 1988
DIJKSTRA, H. H. & A. W. JANSSEN. 1988. Capedopecten anellus gen. et spec. nov. (Mollusca, Bivalvia: Pectinidae) from the Antewerp Sands (Miocene, Hemmoorian) in Belgium. Basteria, 52: 175-187, figs. 1-8. [p. 177]
«Description of Capedopecten gen. nov.
Diagnosis.— Shell moderately large, inaequivalve, orbicular and rather thin-walled. The anterior and posterior auricles are inequal and the hinge line is straight. External disc surface of both valves macroscopically smooth, but with fine irregular radial costae crossed by equally fine concentric lamellae near the umbo. On the entire shell surface a microscopic 'Camptonectes' sculpture is present. Concentric growth lines occur near the ventral margin. An inactive ctenolium is present.
Type species.— Capedopecten anellus spec. nov.
Derivatio nominis.— The genus is, according to its general form, named after capedo (Latin): a sacrificing dish.
Remarks.— Capedopecten resembles at first glance the associated genus Korobkovia; see descriptions of the type species Korobkovia woodi (Nyst, 1861) in e.g., Glibert (1945: 88, pl. 5, fig. 3a-c, s.n. Amusium woodi), Anderson [1964: 137 , text-frg. 9a-b, s.n. Amussium (Amussium) woodi], and Janssen ( 1984: 53, pl. 24, figs. 3a-b, 4a-b). The genus Korobkovia was introduced by Glibert & Van de Poel (1965:10).
Capedopecten differs from Korobkovia by the complete absence of radial sculpture on the inner surface ofthe left valve. The external surface bears a fine radial and concentric sculpture in the umbonal region, which is absent in Korobkovia. Also similar is the genus Lentipecten Marwick, 1928 [type species L. hochstetteri (Von Zittel, 1864) from the Early Miocene of New Zealand]. This generic name is also applied to North Sea Basin species, e.g. for the Eocene and Oligocene L. corneus (Sowerby, 1818). Lentipecten díffers basicly frorn Capedopecten by the absence of the complicated umbonal sculpture. A 'Camptonectes' microsculpture has never explicitly been mentioned for the type species of Lentipecten It was placed in the genus Pseudamussium by Park (1905: 485) and Von Ihering (1907: 85), and in Camptonectes by Suter (1914: 43), whereas Von Teppner (1922:95) classified this species with the genus Amussium. Such a microsculpture is present, however, in the species L. corneus. This was already described by Wood (1861-1871: 39): "Our shell, which is smooth to the naked eye, exhibits under a common hand-glass fine diverging striae, most distinct near the margins of the shell, and in well-preserved specimens they are plainly visible all over." We could corroborate this in specimens from the Eocene of Belgium (localities Bambrugge, Meldert and Balegem, age Ledian), in which, however, the microsculpture is extremely fine and only visible in low angle light. In this material of Lentipecten corneus the 'Camptonectes' sculpture is considerably finer than in Capedopecten. A further distinct difference between L. hochstetteri and L. corneus is the morphology of the posterior auricle, which is regularly rounded in L. hochstetteri. In L. corneus the transition between the dorsal and posterior margins of the same auricle is distinctly angular. For these reasons it might be necessary to reconsider the generic position of L. corneus. Also the anterior right valve auricle of L. hochstetteri demonstrates a similarly rounded outline. In L. corneus the transition between the dorsal and anterior margins of the right valve anterior auricle is somewhat rounded, but still slightly angular. In Capedopecten the right valve anterior auricle has a shape similar to that of L. corneus. Both Korobkovia and Lentipecten differ from Capedopecten by the morphology of the hinge line in the right valve. The upper margins of the anterior and posterior auricle are in line in both valves of Capedopecten, which therefore have a completely straight hinge line. These margins enclose an angle of some 125º in the right valve of the two other species, which therefore have a curved hinge line. Furthermore, both Korobkovia and Lentipecten possess auricular denticles, which are absent in Capedopecten. It is very difficult and, in our opinion, hardly useful to speculate on the relationship of the genus Capedopecten within the strongly radiated pectinid group. The absence of any indication of radial sculpture elements on the inside of the valves points to a quite remote relationship with the Amusium-group. The macro- and microsculpture, on the contrary, indicate a closer resemblance with the Camptonectes-group, but other characters, such as the size of the shells, the shallow byssal sinus and the rounded outer margin of the right anterior auricle rather suggest a close relationship with the Lentipecten-group (the indication 'group' here applied in the sense of Hertlein in Moore, 1969).» HENK H. DIJKSTRA & ARIE W. JANSSEN, 1988
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Capedopecten anellus spec. nov., holotype; H. H. Dijkstra & A. W. Janssen, 1988, Capedopecten anellus gen. et spec. nov. (Mollusca, Bivalvia: Pectinidae) from the Antewerp Sands (Miocene, Hemmoorian) in Belgium, figures 1a-1d.
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