Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 11b): GS990, R14/f6012, coastal section between Gibson and Carter's beaches, near Whaingaroa Harbour, South-west Auckland, Waitakian (GNS)
Beu & Maxwell (1990): Chapter 10; p. 144; pl. 11 b.
Synonymy: Pecten athleta Zittel 1864, p. 49; Pecten (Patinopecten) marshalli Suter 1913b, p. 295; Athlopecten marshalli
Type species of Athlopecten Marwick, 1928
Description: Large for family (height 100-180 mm), robust, moderately to strongly inflated, apparently equivalve. Ears large, the anterior ones somewhat the larger, those on left valve separated from disc by deep channels; posterior ear on right valve with similar channel, anterior ear with deep, broad byssal notch in young shells, notch apparently shallower and less prominent in adults; ctenolium prominent in young shells, absent from adults. Radial sculpture on disc of 10 or 11 prominent costae, those on left valve remaining simple and convex throughout growth, though joined by secondary costae in some shells; those on right valve more flattened and subdivided by a longitudinal groove, which may arise near the beak or at some distance from it, and may divide the costae subequally or very unequally; secondary costae arising in interspaces during growth. Ears with prominent radial costae. Commarginal sculpture of imbricate, lamellar growth ridges, locally prominent, particularly on ears; present all over some unusually well-preserved specimens, suggesting it is usually abraded off. Well preserved shells with shagreen microsculpture on disc and ears. Resilifer large, distinctly oblique, directed posteroventrally, bounded by narrow ridges.
Comparison: This distinctive and spectacular pecten has no known close relatives in the New Zealand fauna nor, as far as can be judged from available literature, elsewhere. Apart from its large size (greater than any other New Zealand Cenozoic pecten), it is distinguished by its deep subaural channels, by having relatively few primary radial costae, by its rather coarsely lamellar commarginal sculpture and by the shagreen microsculpture, and in having an oblique resilifer bordered by tooth- like ridges. Pecten marshalli was not compared with A. athleta by its author, but apart from the relatively small size of the holotype (height 115 mm), it does not differ significantly from younger (Waitakian rather than Duntroonian) specimens, and is here regarded as a synonym of Athlopecten athleta. Waller (1991) pointed out that shagreen microsculpture is charactersistic of a group of primitive chlamidines, and the retention of extensive shagreen over much or all of the disc is a rare character. It is present also on the similarly "cryptogenetic" Australian genus and species Equichlamys bifrons (Lamarck, 1819) (late Pliocene-Recent, southern Australia; Beu & Darragh 2001, p. 55) as well as on the huge Argentinian Oligocene-early Miocene scallops assigned to Reticulochlamys and Jorgechlamys (Del Rio 2004). However, much the longest record of such shagreen-bearing scallops is in the North Pacific, particulrly Japan, where genera related to Patinopecten, Mizuhopecten and Fortipecten are highly diverse (e.g., Masuda 1962). It seems likely, therefore, that brief "cryptogenetic" appearances of these shagreen-bearing scallops in the Southern Hemisphere resulted from dispersal of larvae from the North Pacific.
Distribution: Duntroonian-Waitakian; Takaka Limestone, Motupipi, Northwest Nelson, Waitakian (type locality of P. athleta); Muddy Terrace, Waikaia, Southland, Duntroonian (type locality of P. marshalli); and from numerous localities in North and South Islands, mostly from limestone, greensand and calcareous sandstone.
Cite this publication as: "A.G. Beu and J.I. Raine (2009). Revised
descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990). GNS
Science miscellaneous series no. 27."
© GNS Science, 2009
(Included with a PDF facsimile file copy of New Zealand Geological Survey Paleontological Bulletin 58 in CD version from: Publications Officer, GNS Science, P.O. Box 30368 Lower Hutt, New Zealand)