Austrochlamys marisrossensis Jonkers, 2003
JONKERS, H. A. 2003. Late Cenozoic-Recent Pectinidae (Mollusca: Bivalvia) of the Southern Ocean and neighbouring regions. Monographs of Marine Mollusca, 5: i-viii, 1-125 p., pls. 1-17. Backhuys Publishers, Leiden. [p. 63, pl. 2, fig.g; pl. 3, fig. a; pl. 15, figs. c-d]
2003 Austrochlamys marisrossensis Jonkers, 2003
H. A. Jonkers, 2003, plate 2.
H. A. Jonkers, 2003, plate 3.
H. A. Jonkers, 2003, plate 15.
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«Etymology. From the Latin for Ross Sea, currently the only region from which this species is known.
Type material. IGNS, TMB237 (?LV VH c. 30 mm festimated]; holorype; Plate 15, fig. d), from DSDP Site 272 (Leg 28), 77°07.62' S, 176°45.61 W, Ross Sea, water depth 629 m, core 33, section 2 (top), c. 309.5 mbsf, DSDP Leg28 Shipboard Party leg., 6 Feb. 1975 (latex peel in the BAS collections under AR.7.1). Material examined. 1 ?LV fragments, from Lower Miocene sequences in drill cores raken in the Ross Sea; lodged at BAS and IGNS (see Appendix). Description. (Based on LV only) Shell of moderate size (largest observed fragment estimared at c. 50 mm high), ar least 0.5 mm thick. Radial macrosculpture consisting of relatively widely spaced (1.0-3.2 mm apart) arcuate plicae, 0.8-1.8 mm in width, nor present on the posterior disc flank; rib number increases by simple intercalation; rib number unknown. Commarginal sculpture formed by closely spaced frills, continuous on rib crests and across rib interspaces. Microsculpture made up of regularly spaced antimarginal ridges that are interrupted by commarginals (Plate 3, fig. a). Auricles not known. Stratigraphical age and distribution. Early Miocene (c. 18 Ma in CRP-1 [Lavelle, 1998]; Fig. 25). This new species is currently known only from core material (DSDP Site272 and CRP-1) from the Ross Sea (Figs. 3, 10). Remarks. Austrochlamys marisrossensis sp. nov. is very imperfectly known from the incomplete holotype and from three fragments recovered from 62.19-62.25 mbsf in CRP-1 (water depth 153.2 m), McMurdo Sound, Ross Sea. The two best preserved fragments together represent the anteroventral disc part of a presumably left valve (Plate 15, fig. c). Although the posterior part of this valve is missing, and hence the nature of that part remaining unknown, both the DSDP and CRP-i fossils are considered to be conspecific, coming from the same general area and being of similar age. Radial macrosculpture of A. marisrossensis is very similar to that of A. natans, the chief difference being the absence of ribs on the posterior disc part. The comparatively narrower plicae and wider interspaces suggest a somewhat lower total rib number than in A. natans. Radial microsculpture on the disc of the latter is somewhat wider than in A. marisrossensis (compare Plate 2, figs. e and g, and Plate 3, fig. a). The absence of radial plicae on the posterior disc flank is a condition also seen in Adamussium colbecki (Smith, 1902) (see Plate 15, figs. f-i). However, the well-defined narrow radial plicae which are present on the anterodorsal part of the disc (Plate 15, fig. d), suggest that this new species belongs in Austrochlamys rarher than in Adamussium.» H. A. JONKERS, 2003
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