Serripecten Marwick, 1928
MARWICK, J. 1928. The Tertiary Mollusca of the Chatham Islands including a generic revision of the New Zealand Pectinidae. Transactions and Proceedings of the New Zealand Institute, 58 (4): 432-506, figs. 1-148. [p. 455]
«6. Genus SERRIPECTEN nov.
Type: Pecten hutchinsoni Hutton. (1) Subgenus Serripecten s. str. Shell fairly large, equilateral; right valve more inflated than left; ears subequal, right anterior one slightly larger than posterior. Sculpture: right valve with over thirty strong, sharp, scaly, bevelled ridges, often with a scaly secondary thread in the interstices. Left valve with about seventy scaly threads, many of which have appeared during growth.
beethami (Hutton), enfieldensis (Marwick), hutchinsoni (Hutton), tiorioriensis n. sp.»
JOHN MARWICK, 1928
|
Serripecten hutchinsoni (Hutton, 1873); A. G. Beu & P. A. Maxwell, 1990, Cenozoic Mollusca of New Zealand, plate 17, figures f, g.
|
«Remarks. Serripecten yahliensis (= hutchinsoni) is a large, spectacular pectinid, up to c. 170 mm long, markedly longer than high, with a wide umbonal angle and radial sculpture of low, serrate costae, much fewer, wider and more prominent on the RV than on the LV. All Serripecten species have rather uniform LV radial sculpture of numerous low, closely spaced, finely scaly costae, and although there are specific differences in the LV sculpture, they are very much less marked than the differences in RV sculpture. The beautifully preserved specimens from Fyansford Formation near Melbourne were studied by SEM (Fig. 24A-H), and show that the LV preradial dissoconch, like the rest of the shell surface, is sculptured with very fine, closely spaced antimarginal ridgelets. These form the sole sculpture on the LV preradial dissoconch, which therefore closely resembles that of Zygochlamys delicatula (Fig. 41C, E). Auricles are low and long and, although the RV anterior auricle is elongated, with a moderately deep byssal notch and a functional ctenolium in specimens of S. yahliensis up to about half-grown, ie., juveniles presumably are byssally attached, the byssal notch is very shallow in large adults. In most species, auricles are separated from the disc by quite prominent grooves.
In S. yahliensis, the RV radial sculpture is of relatively few low, wide costae (most specimens have c. 30-40; ranging from 26-50; Boreham 1965: fig. 3). The few costae near the centre of the disc are of symmetrical section, but the others all have a sloping, bevelled section, with a low, wide, gentle slope facing towards the disc centre, a sharp crest, and a short, steeply sloping edge facing away from the disc centre. Many of the larger specimens have large, serrate spines along the steep edge of each costa, lying on the gently sloping face of the neighbouring costa. The RV dorsal margin of the auricles also bears large serrate spines. However, S. yahliensis is one of the more unusual species of Serripecten. The numerous (many still unnamed) small Eocene and Oligocene species in New Zealand (eg., Maxwell 1992: pl. 4) have different sculpture, with many finely scaly costae on the RV, and the Australian S. excultatus sp. nov. is a finely sculptured example of this type. The Australian S. squamocostatus sp. nov. (known to us only from Longfordian rocks) resembles a rather large version of the New Zealand Eocene species, with quite similar scaly costae on both valves, recalling the species described by Maxwell (1992). The trend in the S. yahliensis lineage towards longer and lower auricles at a large size is carried still further by its apparent descendent, the huge S. carteri sp. nov. in Mitchellian rocks of Gippsland; this species has the auricles fused with the disc in large adults, and the radial sculpture develops numerous fine costellae not seen in S. yahliensis. A final unexpected side branch of the evolutionary radiation of Serripecten is provided by S. semilaevis (McCoy) which, contrary to the coarsening RV sculpture trend seen in the evolution of S. yahliensis, has an almost completely smooth RV. Although it is concluded here that S. yahliensis is conspecific with the New Zealand S. hutchinsoni, so it is clear that there has been considerable trans-Tasman exchange of larvae in some Serripecten species, neither S. carteri nor S. semilaevis are known in New Zealand. These apparent absences are to be expected because the genus barely survived into the Late Miocene in New Zealand, and in Late Miocene rocks is recorded only from the Gisborne district in the northeastern North Island [Beu 1995: 75; three specimens of S. yahliensis recorded (as S. hutchinsoni) from the early Late Miocene Patutahi Limestone, near Gisborne]. Sea temperatures around much of New Zealand apparently were too low for Serripecten by Late Miocene time. The one pectinid genus from elsewhere in the world that appears to be similar to Serripecten is Batequeus Squires & Demetrion, 1990, based on Batequeus mezquitalensis gen. nov., sp. nov. from Middle Eocene (Lutetian) rocks of Baja California Sur, Mexico. This species closely resembles the Eocene Serripecten species from New Zealand described by Maxwell (1992) in size, shape and sculpture, but the RV has a deeper byssal notch and a more depressed byssal fasciole and the RV exterior is sculptured with more prominent, more elevated, square-edged, more subdivided, markedly smoother radial costae than in any New Zealand or Australian Serripecten species. Campbell (1995) added a second species, B. ducenticostatus, from the Eocene Santee Limestone of South Carolina, commenting on the similarity to Serripecten. The frequently subdivided and intercalated costae, the smooth interior lacking internal rib carinae, and the narrow resilial and dorsal hinge teeth show that Batequeus belongs in the Chlamydini, and it appears to be quite feasible that it is closely related phylogenetically to Serripecten, although the similarity is, on present knowledge, as likely to be convergent.» BEU, A. G. & T. A. DARRAGH. 2001. Revision of southern Australian Cenozoic fossil Pectinidae (Mollusca: Bivalvia). Proceedings of the Royal Society of Victoria, 113: 1-205, figs. 1-67. [p. 76, 77]
|