Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 44j, k): GS4061, R22/f6392, Lower Kai Iwi Siltstone, Castlecliff, Wanganui, Castlecliffian (GNS) (right valve exterior, and left valve exterior of umbonal area and ears).
Beu & Maxwell (1990): Chapter 16; p. 336; pl. 44 j.k.
Synonymy: Pecten gemmulatus Reeve 1853 (in 1852-1853), pl. 27, fig. 111; Pecten radiatus Hutton 1873a, p. 82 (secondary homonym of Ostrea radiata Gmelin, 1791, = Pecten radiatus of Bosc 1802); Pecten (Chlamys) suteri Hertlein 1933, p. 63 (new name for Pecten radiatus Hutton, preoccupied); Chlamys (Mimachlamys) gemmulata; Chlamys gemmulata radiata; Chlamys gemmulata suteri; Chlamys (sensu lato) gemmulata, Beu & Maxwell 1990, p. 338, pl. 44g; Talochlamys gemmulata, Beu 1995, p. 18
Description: Moderate-sized for genus (to about 50 mm high, 65 mm in the suteri form), thin and brittle, very little-inflated (left valve more inflated than right), finely sculptured. About 25 low, narrow, closely spaced costellae on shells up to 10 mm high divide to form 35 or more major costae and many secondary and tertiary costellae over outer third of disc of adults, tending to be arranged in groups of 3 or more costae in increasing and then decreasing sizes, so that each primary costa is of low triangular section, with several orders of costellae on its flanks; all costal crests finely scaly or spinous; costal interspaces crowded with fine antimarginal microsculpture. Disc higher than long, extended slightly obliquely postero- ventrally; anterior ears much larger than posterior ones, anterior ear of right valve with deep, wide byssal notch and long, finely toothed ctenolium; simple pallial line and circular adductor scar visible in some specimens.
Comparison: Talochlamys gemmulata is a member of a group of very finely costate species recorded also in Landon to Taranaki Series rocks, but early forms are of uncertain status. T. araroensis (Kapitean, East Cape) possibly is part of the variation of T. gemmulata. The similar, highly varied species T. zelandiae (= dieffenbachi Reeve, 1853; = zeelandona Hertlein, 1931; = suprasilis Finlay, 1928) (Mangapanian-Recent) has fewer, wider, more prominent, and more coarsely scaly radial costae, and varies according to its ecological station; fossils are much less common than those of the ubiquitous T. gemmulata, and most are from moderately near-shore, high-energy environments (e.g., Tainui Shellbed, Castlecliff).
Distribution: Tongaporutuan-Kapitean?; Opoitian-Recent. Recent, New Zealand (types of Pecten gemmulatus and P. radiatus (non Bosc) = P. suteri). Common today all around New Zealand, byssally attached to hard substrates (canyon walls, worm tubes, boulders, other shells) from not far below low tide to the upper bathyal zone; abundant and ubiquitous in all New Zealand Pliocene and Pleistocene rocks, other than very shallow, near-shore deposits (e.g., terrace deposits). Specimens from Stewart Island (e.g., living in Paterson Inlet) are larger and less inflated than those from most of the rest of New Zealand, and the name suteri is available for the Stewart Island form, but most taxonomists now consider it to be an infrasubspecific variety of only ecological significance (e.g., Powell 1979, p. 378).
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)