Mizuhopecten mollerensis (MacNeil, 1967)
MACNEILL, F. S. 1967. Cenozoic pectinids of Alaska, Iceland, and other nothern regions. United States Geological Survey Professional Paper, 553: iv + 1-57, pls. 1-25. [p. 43, pl. 4, fig. 1; pl. 5, figs. 1, 6]
1967 Fortipecten mollerensis MacNeil, 1967
F. S. MacNeil, 1967, plate 5.
|
«Description. — Shell large, thick, medium inflated, slightly elongate anteroposteriorly, hinge line moderately long. Ears of left valve large and moderately elongate, the anterior ear slightly larger, terminal margins nearly vertical, anterior margin of anterior ear slightly sinuous. Sculpture of left valve consisting of about 16 low, rounded, moderately broad ribs, separated by shallow, rounded interspaces nearly twice as broad as the ribs. No secondary riblets or microsculpture discernible on type. Interior of left valve with moderately deep, rounded grooves oppmite ribs that extend only a short distance from the margin, probably being filled with callus centrally. Adductor muscle scar very large and deep, probably made deeper than originally by the solution of an aragonitic attachment layer. Pedal retractor scar also large and deep. Subumbonal callus area well defined and sunken. Right valve ears unknown. Sculpture consisting of moderately strong broad ribs that may range from rounded to flattened to medially grooved on the central part of the disc, and finer irregularly spaced ribs terminally ; some terminal interspaces have a moderate interstitial riblet. The central ribs of the right valve are broader than the interspaces.
Discussion. — This species has a shorter hinge than either F. takahashii or F. kenyoshiensis, the ribs are considerably stronger and broader, and there is no apparent tendency for every third or fourth rib to be stronger. There is no tendency for the ribs of F. mollerensis to form nodes or bumps at regular intervals as in the Japanese species and in F. hallae from Alaska. F. mollerensis and F. hallae both have wider and stronger ribs and a shorter hinge line than the Japanese species. If F. mollerensis has any fine radial markings between the primary ribs of the left valve, they are not visible on the type; it differs in this respect from the other known species of Fortipecten. The antecedents of this species, and, for that matter, the origin of the genus Fortipecten remains unknown. There is at least a superficial resemblance between F. mollerensis and some large pectinids from the Miocene of the Vienna basin. One such species, Amussiopecten gigas plana Schaffer (1910, pl. 22, figs. 1, 2) has very large ears and somewhat similar sculpture. The muscle scars are not figured. Relationship is suggested between Fortipecten and both Pecten and Amussiopecten by the fact that the dorsal marginal areas of the left valve of both F. takahashii and F. hallae are more swollen than the dorsal central part of the disc. An outside origin for Fortipecten is only a possibility at present, however, and an early Tertiary Japanese origin cannot be ruled out entirely. F. mollerensis occurs with Clinopegma cf. C. stantoni (Arnold), Turritella aff. T. sagai Kotaka, Acila cf. A. empirensis Howe, Cyclocardia, Siliqua, Spisula, Macoma, Panomya, and Mya. The fauna is dated, tentatively, as late Miocene. Types: The holotype (USNM 645047), a left valve, measures 118 mm in height and 125 mm in length. The paratype (USNM 645048) is a fragment of a right valve. Type locality: A small knob extending above the level of the Recent terrace on the south shore of Port Moller, approximately 3 miles southeast of Point Divide, USGS M2131.» FRANCIS STEARNS MACNEIL, 1967
|
«On the other hand, several species such as Fortipecten takahashii, F. pilutunensis, F. sachalinensis, and F. mironovi, have been described from North Sakhalin and Kamchatka (KHOMENKO, 1931; SLODKEWITSCH, 1938; ILYNA, 1963; KRISHTOFOVICH, 1964). And F. hallae (Dall) (MACNEIL, 1943) and F. mollerensis MacNeil (1967) have been described from Alaska. Therefore, the occurrence of Fortipecten in the Circum North Pacific is a result of migration from the Japanese Islands. However, those mentioned species are in need of further study to clarify their taxonomic relations. For example, according to the present writer's study based upon the holotype and topotype of F. mollerensis MacNeil, it is evident that MacNeil's mollerensis is different from Fortipecten and should be referred to Mizuhopecten.»
MASUDA, K. 1978. Neogene Pectinidae of the Nothern pacific. The Veliger, 21 (2): 197-202. [p. 199]
|