Zygochlamys whenuataruensis 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. 54, pl. 10, figs. c-d]
2003 Psychrochlamys whenuataruensis Jonkers, 2003
H. A. Jonkers, 2003, plate 10.
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«"unnamed species intermediate between C. seymouri
and C. patagonica"; Beu, 1985, p. 7. Etymology. The name is taken from the Whenuataru Tuff on Pit s the type level of this species.
Type material. IGNS, TMS231 (LV, VH 52.1 mm; holorype; Plate 10, fig. d), from nofthern point of Pitt I., base of cliffs at SW side of Moutapu Point, at northern end of small beach separating Red Bluff Tuff of Flowerpot-Moutapu coast from Whenuataru Tuff of Moutapu Point, A.G. Beu, J.I. Beu, P.A. Maxwell & H.J. Campbell leg., 1977; TM8232 (RV, VH 56.3 mm; pararype; Fig. 34j), from northern Pitt I., low bluffs on hillside at NE end of Flowerpot Bay between bluff woolshed and c. 10 m uphill from the beach, A.G. Beu, J.L Beu & P.A. Maxwell, 1977;TMB235 (RV, VH 67.7 mm. [computed]; paratype: Plate 10, fig. c, from northern Pitt I., Whenuataru Tuff in cliff due north of bluff homestead, A.G. Beu, P.A. Maxwell & H.J. Campbell leg., 1977. Material examined. 1 pair, 18 LV, 29 RV (type series and topotypes), from the earliest Late Pliocene Whenuataru Tuff, Pitt Island, Chatham Islands, New Zealand; lodged at IGNS (see Appendix). Description. Shell of moderate size (mean VH 52 mm; maximum observed VH 61.8 mm [GS12161]; maximum calculated VH 67.7 m m [TM8235]): acline, with anterior part of valve much shorter than posterior part (WA/VLP 0.82); rather strongly convex; umbonal angle relatively narrow (c. 104º). Radial macrosculpture of c. 21 plicae carrying fascicles of distinctly tripartite costae, which are later flanked by smaller costellae; main costae on anterior RV with coarse scales; interspaces rather deep. Microsculpture of antimarginal striae. Auricles highly asymmetrical (OLA/OLP 1.75); LV anterior auricle comparatively high, with c. 6 scaly costellae, anterior margin straight or with shallow byssal sinus, angle between free margin and hinge c. 86º; RV anterior auricle with deep byssal notch; mean number of byssal teeth in functional ctenolium 5.3. Measurements and counts. VH 52.0 ± 1.9 mm (n = 16), VHA 28.0 ± 1.7 mm (n = 7), VHP 28.4 ± 1.0 mm (n =7),VL 49.6 ±.2.6 mm (n = 6), VLA 22.3 ± l.2 mm (n = 7), VLP 27.3 ± 1.1 mm (n = 7),OL 21.3 ± 1.0 mm (n = 10), OLA 13.4 ± 0.6 mm (n = 10), OLP 7.7 ± 0.3 mm (n = 15), AHA (LV) 10.9 ± 0.8 mm (n = 7), AHA (RV 8.4 ± 0.4 mm (n = 8), AHP 8.1 ± 0.5 mm (n = 14), BND 4.4 ± 0.2 mm (n = 7), UA 104.4º ± 1.0 (n = 12), AAAD 86.2º ± 1.4 (n = 5), AAPD 116.0º ± 1.4 (n = 13), BT 5.3 ± 0.3 (n = 4). Stratigraphical age and distribution. Earliest Late Pliocene (Waipipian; Fig. 25) (Beu, 1985). This new species is known only from the type locality on Pitt Island (Fig. 22), where it occurs together with Kaparachlamys hectori (Hutton, 1873), and a species of Talochlamys, similar to T. chathamensis (Hutton, 1873) (CampbeII et al.,1993). Remarks. Psychrochlamys whenuataruensis sp. nov. is similar to the older Pliocene P. seymouri in overall shell shape, both having acline, but strongly asymmetrical shells, with similar VH/VL. It differs from that species in having more convex shells, with coarser radial sculpture, a narrower umbonal angle, a much higher LV anterior auricle, more strongly asymmetrical auricles, and a deeper byssal notch (Fig.34). The next younger P. delicatula has a much higher valve symmetry, a wider UA, a higher angle between the free margin of the LV anterior auricle and hinge (>90º), a relatively longer outer ligament, a much higher auricular symmetry, a shallower byssal notch (Fig. 40), and a lower number of functional byssal teeth. The clearly fasciculate radial sculpture is more akin to that of P. delicatula delicatula than to that of P. seymouri. Beu (1985) considered this new species to be intermediate between P. seymouri and P. delicatula delicatula. However, although there seem to be "trends" in some measured parameters (e.g. in AAAD, AAPD, and OL/VH; Fig. 34), these are not seen in other measurements (i.e. UA, OLA/OLP, AHA/VH [LV], and BND/VH), and therefore P. whenuataruensis cannot be considered truly intermediate.» H. A. JONKERS, 2003
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