Zoila viathomsoni, Darragh, 2011

Darragh, Thomas A., 2011, A revision of the Australian fossil species of Zoila (Gastropoda: Cypraeidae), Memoirs of Museum Victoria 68, pp. 1-28 : 5-7

Zoila viathomsoni sp. nov.

Figures 1D , 2C , 5B–C, H, L

Description. Shell of small size for genus (19–28 mm in length), pyriform. Spire not visible on most specimens, projecting on one specimen. Posterior canal very short, slightly bent to left. Anterior canal very short, slightly deflected to right. Aperture slightly sinuous; outer lip with about 23–25 teeth present along entire lip; columella with about 23–26 teeth present along entire lip. Fossula well-developed, deep, elongate, projecting, bounded anteriorly by thickened ridge; very weak notch present in inner edge just posterior to anterior ridge; weak terminal ridge joining edge of fossula. First columellar tooth adjacent to terminal ridge, almost blocking shallow sulcus that extends into fossula parallel to terminal ridge.

Dimensions .

Type locality. PL3171 gravel scrape beside Thomson Highway, 23.5 km north of Highway l, north of Walpole , Western Australia. Grid ref. Deep River (l:100 000 series) 743487. Pallinup Siltstone , Aldingan , Late Eocene .

Type material. Western Australian Museum : Holotype WAM 72.296 , collected T. A. Darragh and G.W. Kendrick, 12–14 March 1969 ; paratype WAM 72.253 , collected G.W. and W.E. Kendrick, 25 January 1969 . Museum Victoria: Paratype P310193, collected T. A. Darragh & G.W. Kendrick, 12-14 March 1969 .

Time range. Aldingan, Late Eocene.

Occurrence and material. Type locality only (one undistorted specimen, four complete distorted specimens, nine fragments).

Remarks. This is one of the two oldest true cowries recorded from Australia and occurs only in southwest Australia, associated with Willungia ovulatella (Tate) and Semitrivia pompholugota (Tate) . Specimens from the type locality are preserved as silica replacements weathered out of the Pallinup Siltstone. The associated fauna comprises large numbers of siliceous sponges. The protoconch observed in cross-section (fig. 2C), is paucispiral and slightly deviated from the axis of the teleoconch, unlike the multispiral protoconchs of Cypraeorbis species. The general size and shape of the shell resembles that of Cypraeorbis medius , C. bartonensis and C. ventripotens ; however, the fossula (fig. 5L) is not the same as that present in these species. The fossula is very wide and prominent, projecting into the aperture. It is more elongate than that of these three species, does not have a prominent notch and the anterior border is not thickened. In general shape and concavity, it resembles those in Zoila friendii and Z. decipiens . Zoila viathomsoni bears a close resemblance to Z. chathamensis (Cernohorsky) , late Paleocene to early Eocene, Chatham Islands, New Zealand, but it is not as tumid, has much finer and more numerous apertural teeth, the posterior labral border of the posterior canal is more produced posteriorly and it is only about two-thirds the size. Given the similarities, Z. chathamensis is a possible ancestor of Z. viathomsoni sp. nov.; Z. chathamensis is the earliest known representative of the genus.

Zoila viathomsoni bears some resemblance in size and shape to Lyncina (Austrocypraea) onkastoma Yates, 2009 , recorded from the early Oligocene of South Australia, but lacks the well-defined anterior rostrum of L. (A.) onkastoma , as well as the prominent notch on the fossula.

Etymology. Latin via road.

Figures

Figure 1. A, Cypraeorbis medius (Deshayes,1835), × 5;B, Cypraeorbis sphaeroides (Conrad,1848),× 5; C, Cypraeorbis ventripotens (Cossmann, 1903), × 5; D, Cypraeorbis viathomsoni sp. nov. WAM 72.296, × 5; E, Zoila didymorhyncha sp. nov. P302687, × 2.6; F, Zoila campestris sp. nov. WAM 89.437, × 2.6; G, Zoila fodinata sp. nov. WAM 89.637, × 3; H, Zoila chathamensis (Cernohorsky, 1971) GNSTM 87922, × 2.3. Arrows indicate the location of the notch.

Figure 2. Protoconchs. A, Zoila platypyga (McCoy, 1876), P308781, × 7; B, Zoila gigas (McCoy, 1867), P308792, × 3.6; C, Zoila viathomsoni sp. nov., WAM × 10.

Figure 5. A, D–G, I–K, Zoila chathamensis; A, E, I, holotype, AIM 71325, Flower Pot Harbour, Chatham Islands; A, E, × 1.5; I, × 2; D, F–G, J–K, GNS TM8792, Taruwhenua Peninsula, Chatham Islands; D, F–G, K, × 1.5; J, × 2; B–C, H, L, Z. viathomsoni; B–C, H, holotype, WAM 72.296, Thomson Highway, Western Australia; L, fossula, P310194, Thomson Highway, × 3.

Dimensions