Leoclunipecten gazdzickii (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 pp, 17 pls. Backhuys Publishers, Leiden. [p. 63, pl. 1, fig. g; pl. 3, fig. c; pl. 12, figs. a-d]
2003 Austrochlamys gazdzickii Jonkers, 2003
H. A. Jonkers, 2003, plate 1.
H. A. Jonkers, 2003, plate 3.
H. A. Jonkers, 2003, plate 12.
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«Etymology. Named after Andrzej Gaździcki, Polish Academy of Sciences, Warszaw, Poland, in recognition of his contributions to the palaeontology of Antarctica, in particular that of King George Island.
Type material. BAS, P.2856.1 (LV VH 68.9 mm; holorype; PIate 12, fig. b), P.2856.38 (RV VH 45.6 mm; pararype; Plate 12, fig. a), from Battke Point, King George Island, South Shetland Islands, Antarctica, 62º08'20" S, 58º07'30" W, 30-35 m above sea level, H.A. Jonkers & S.L. White Ieg., 9 Feb. 1996. Material examined. 14 pairs (internal moulds), 85 LV 150 RV (valves mostly fragmented), from the Oligocene Polonez Cove Formation. Lions Rump area, King Georse Island. Sourh Shetland Islands; lodged at BAS (see Appendix). Description. Shell of moderare size (mean VH c. 53 mm: maximum observed VH 75.3 mm [P2854.21.2]) and very thin; slightly prosocline, with anterior part of disc longer than posterior part (VLA/VLP 1.04); weakly convex, with LV slightly more so than RV; umbonal angle c. 114º. Dorsal disc gapes absent (inferred from internal moulds). Radial macrosculpture of up to c. 75 narrow, shallow plicae in simple arrangement, increasing slightly in number by intercalation (LV) and bifurcation (RV). Prominent commarginal lamellae continuous across rib interspaces. Radial microsculpture of relatively wide antimarginal ridgelets. Auricles comparatively long (OL/VH 0.45), highly asymmetrical (OLA/OLP 1.62); LV anterior auricle with 7-8 costellae, anterior margin straight, forming an angle with hinge of c. 100º; RV anterior auricle with relatively deep, acute byssal notch; mean number of byssal teeth in functional ctenolium 4.8. Measuremernts and counts. VH 53.3 ± 1.3 mm (n = 49),VHA 27.0 ± 0.6 mm (n = 45),VHP 26.5 ± 0.8 mm (n = 45), VL 52.8 ± 1.5 mm (n = 49), VLA 26.5 ± 0.8 mm (n = 45), VLP 25.9 ± 0.9 mm (n= 45), C (LV) 9.4 ± 0.3 mm (n = 16), C (RV) 8.0 ± 0.3 mm (n = 14), OL 23.3 ± 0.6 mm (n = 37), OLA 15.0 ± 0.5 mm (n = 59), OLP 9.0 ± 0.2 mm (n = 53), AHA (LV) 10.6 ± 0.3 mm (n = 36), AHA (RV) 8.0 ± 0.2 mm (n = 65), AHP 8.4 ± 0.2 mm (n = 48), BND 5.0 ± 0.1 mm (n = 57), UA 114.3º ± 0.6 (n = 56), AAAD 99.8º ± 1.1 (n = 24), AAPD 118.6º ± 1.3 (n = 25), BT 4.8 ± 0.2 (n = 32). Stratigraphical age and distribution. Oligocene (30-28 Ma [Dingle et al.,1997];Fig.25). A. gazdzickii is the oldest known species of Austrochlamys, and is found only in the Lions Rump area of King George Island, South Shetland Islands, Antarctica (Figs. 3, 4), where it occurs together with rare Adamusium alanbeui sp. nov. There is a questionable record from CRP-1 drillhole, Ross Sea (Figs. 3, 10). Remarks. Austrochlamys gazdzickii sp. nov. is morphometrically similar to Recent A. natans (Philippi, 1845) in many respects (e.g. similar size, shell shape, umbonal angle, length of outer ligament, number of functional byssal teeth, similar number of costellae in LV anterior auricle), but its valves are relatively longer (Fig. 44) , but less convex, with a much higher number of ribs that are lower and narrower, commarginal frills are wider apart, auricular asymmetry is higher, and the byssal notch is deeper (Fig. 41); in addition, it lacks dorsal disc gapes. Differences between A. gazdzickii and A. anderssoni (Hennig, 1911), with which it was initially associated, are discussed below.» H. A. JONKERS, 2003
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«Distribution. Leoclunipecten gen. nov. gazdzickii is recorded only from the Lions Rump area of King George Island, from Polonez Cove Formation and possibly from Boy Point Formation, both of late Early Oligocene (Rupelian) age. The possible record by Jonkers (2003, p. 64) from the CRP-1 drillhole, Ross Sea, is based on equivocal small fragments.
Dimensions. Austrochlamys gazdzickii holotype (Jonkers 2003, pl. 12, fig. b): H 68.9, L 67.0 mm; paratype RV (Jonkers 2003, pl. 12, fig. a) H 45.6 mm, L 43.5 mm (Jonkers 2003, caption to pl. 12; lengths measured from figures).
Diagnosis. As for the genus, only the type species is included.
Description. Shell of moderate size (H 53–75 mm), disc relatively long (antero-posteriorly), almost equidimensional, at most weakly prosocline, very weakly inflated; umbonal angle c. 115 degrees. Macrosculpture of c. 65–75 low, even, flat-crested, sharply defined, closely spaced radial costae, most costae similar and not segregated into primary, secondary or lesser ranks; a few costae intercalated or subdivided to produce secondary costae in some specimens; with flat-bottomed interspaces each equal in width to or slightly narrower than one costa; microsculpture of widely spaced, prominent commarginal ridges, serrating the costal margins or riding over costal crests, and many very fine antimarginal ridgelets. Byssal notch wide, deep; RV anterior auricle long and narrow with subparallel dorsal and ventral margins; byssal notch and ctenolium functional in adults; LV anterior auricle tall, with anterior and dorsal margins meeting approximately at a right angle; posterior auricles short, with forward-sloping, concave posterior outline. Without internal rib carinae. Preradial microsculpture and internal characters unknown.
Remarks. The photograph of the RV paratype (Fig. 6A) supplied by P. Bucktrout (BAS) clearly reveals the characters of this genus and species. The Polish scientists who first collected Leoclunipecten gen. nov. gazdzickii on King George Island, from a formation then of unknown age, naturally assumed that it was the well-known, abundant, very widespread Antarctic species now identified as Austrochlamys anderssoni. However, the wider and much flatter shape and the much greater number of similar, even, primary radial costae in L. gazdzickii than in A. anderssoni readily distinguish these genera and species.»
BEU, A. & M. TAVIANI. 2014. Early Miocene Mollusca from McMurdo Sound, Antarctica (ANDRILL 2A drill core), with a review of Antarctic Oligocene and Neogene Pectinidae (Bivalvia). Palaeontology, 57 (2): 299-342, figs. 1-9. [p. 318, 319]
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Leoclunipecten gen. nov. gazdzickii (Jonkers, 2003); A. G. Beu & M. Taviani, 2014, Early Miocene Mollusca from McMurdo Sound, Antarctica (ANDRILL 2A drill core), with a review of Antarctic Oligocene and Neogene Pectinidae (Bivalvia), figure 6A.
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