Annachlamys rhipidata Beu & Darragh, 2001
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. 148, figs. 53A, 54C-E]
2001 Annachlamys rhipidata Beu & Darragh, 2001
A. G. Beu & T. A. Darragh, 2001, figure 54.
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«Description. Moderate-sized for genus (to c. 60 mm long), length exceeding height significantly in all specimens, umbonal angle c. 125°; acline to very weakly prosocline; weakly inflated, LV umbonal area slightly less inflated than RV umbonal area. Anterior, ventral and posterior disc margins an even, regular curve. RV disc sculptured with 22-29 low, wide, rather weakly defined radial costae with narrow interspaces, each interspace about one third width of one costa; entire disc and auricles sculptured with fine, low, closely spaced commarginal lamellae, abraded off crests of costae near centre of disc on many specimens. LV disc sculptured with a corresponding number of narrow, widely spaced, narrowly rounded radial costae with shallowly concave sides, each costa about one-third width of one interspace; a few specimens with one or two secondary costae intercalated in one or two interspaces; closely covered with commarginal lamellae as on RV. RV anterior auricle with weakly sinuous anterior margin inclined slightly towards anterior, without byssal fasciole or ctenolium, byssal notch very shallow; row of small ctenolial teeth remaining in groove between RV anterior auricle and disc on well preserved specimens, indicating that ctenolium is functional until about third to half adult size; RV posterior auricle with slightly convex posterior margin inclined slightly towards anterior. LV auricles with lightly convex anterior and posterior margins, each slightly inclined towards umbo; each auricle sculptured with 4 — 5 low, narrow, widely spaced radial costae and many closely spaced commarginal lamellae. Interior with prominent rib carinae, arranged clearly in pairs on edges of internal expression of radial costae, in distal area of disc forming a thin, raised ridge on each carina. Hinge with low, narrow teeth, one pair of narrow dorsal teeth and one pair of intermediate teeth.
Type material. Holotype, NMV P300478, Jan Juc Formation (Janjukian), coastal section south of Bird Rock, Torquay, Victoria, coll. R. Wilkins; 2 paratypes, NMV P302135-6, Jan Juc Formation (Janjukian), ‘Bird Rock ledge’, coastal section at Torquay, Victoria, coll. F. A. Cudmore.
Other material examined. Janjukian: CALDER RIVER LIMESTONE: Aw3 and Aw4, anticline on Aire coast (1 specimen); Aw3, Aire coast (I specimen); Calder River, Horden Vale (2 specimens); Spud Point, Glenaire (2 specimens); CLIFTON FORMATION: Kawarren lime quarry (3 specimens); W of Princetown (4 specimens); base of limestone overlying conglomerate, 0.8 km NW of Point Ronald, Princetown (1 specimen); JAN JUC FORMATION: PL3024, Bird Rock, Torquay (17 specimens); PL3025, Fishermans Steps, Torquay (1 specimen); Spring Creek, Torquay (6 specimens); Torquay (7 Specimens); WAURN PONDS LIMESTONE: Waum Ponds (26 specimens); Ceres (1 specimen); PL3279, Blue Circle old pit (10 specimens); Point Addis Limestone: PL3227, Point Addis (10 specimens); Aireys Inlet (1 specimen); WAM 85.438, 50 m E of steps, SW corner of Point Addis (1 specimen). Longfordian: MANNUM FORMATION: PL3184, quarry at Taworri (13 specimens); PL3187, quarry at Younghusband (10 specimens); PL3192, road cutting, Punthari (2 specimens); PUEBLA FORMATION: Ad6, mouth of Spring Creek, Torquay (4 specimens); ZEALLY LIMESTONE: yellow polyzoal limestone between Torquay village and Jan Juc Creek (1 specimen). Occurrence and time range. Janjukian and Longfordian. Most records are from Torquay, Victoria, or from Mannum Formation, Murray Basin. As A. rhipidata is easily distinguished from A. murrayana, it is potentially of high biostratigraphic utility. Remarks. Annachlamys rhipidata sp. nov. differs markedly from A. murrayana in a number of prominent characters: its lesser inflation; its much less obvious flattening of the umbonal area of the LV; its equal inflation of the two valves, rather than the RV being much the more inflated, as in A. murrayana; its slightly less rectangular auricles; most clearly, in having discrepant sculpture on the two valves, rather than identical sculpture as in A. murrayana; and in having only the fine, close, low commarginal sculpture characteristic of the Decatopectinini, and not the much more prominent, high, widely spaced commarginal lamellae of A. murrayana. Annachlamys murrayana succeeds A. rhipidata abruptly in Batesfordian rocks and, possibly in Longfordian rocks, at one Gippsland locality. These two species are so dissimilar that an ancestordescendent relationship between them appears unlikely; ie., the abrupt replacement did not result from a speciation event. Rather than indicating that the replacement was diachronous, the few Longfordian records of A. murrayana in Gippsland seem more likely to suggest that the replacement of A. rhipidata by A. murrayana occurred during Longfordian time. Etymology. The specific name (Greek ‘rhipis’, a fan) refers to the unusual, discrepant radial costae of this species.» ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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