Zoila gigas McCoy, 1867

Darragh, Thomas A., 2011, A revision of the Australian fossil species of Zoila (Gastropoda: Cypraeidae), Memoirs of Museum Victoria 68, pp. 1-28 : 21-24

Zoila gigas McCoy, 1867

Figures 2B , 13E–H , 14A–H , 15A–E

Cypraea gigas McCoy, 1867a:18 .— McCoy, 1867b:194.— McCoy, 1867c:438.

Cypraea (Aricia) gigas McCoy. — McCoy, 1875:19, pl. 15; pl. 16, fig. 2; pls. 17–18, fig. 1; — McCoy, 1876, p. 35, pls. 28–29, fig. 1.

Cypraea dorsata Tate, 1890:212 .— Tate, 1892, pl. 10, fig. 4; pl. 11, fig.6.

Cypraea (Erosaria) gigas McCoy. — Harris, 1897:208.

Cypraea gabrieli Chapman, 1912:190 , pl. 13, figs 1–3.

Gisortia gigas (McCoy) .— Vredenburg, 1927:58.

Gisortia dorsata (Tate) .— Vredenburg, 1927:58.

? Gigantocypraea gigas (McCoy) .— Schilder, 1930:126, fig. 34-5 (cast).

Zoila (Gigantocypraea) gigas (McCoy) .— Schilder, 1935:337, 338, fig. 17. — Wilson and Clarkson, 2004:53, pl. 57.

Zoila (Gigantocypraea) dorsata (Tate) .— Schilder, 1935:337, 338.

Description. Shell solid, very large for genus, globose, covered with glaze, humped at dorsal midpoint of shell. Ventral surface flat to slightly concave on most specimens. Spire scarcely projecting, covered with thick callus. Four teleoconch whorls. Protoconch of two whorls, the first depressed, large, irregular, with finely granulated surface, coiled at an angle to axis of teleoconch whorls. Posterior canal bounded by very thick walls, deeply incised, strongly reflexed dorsally, deeply notched. Anterior canal short, about same length as posterior canal, narrow, deeply incised, strongly reflexed dorsally. Aperture very sinuous, widest at beginning of anterior canal; outer lip with 2–28 teeth, on most specimens only extending to midpoint of lip. Columellar lip edentulous. Fossula scarcely differentiated from columellar lip, relatively small, slightly depressed, somewhat rectangular, extending only slightly into aperture, bounded by very weak terminal ridge.

Dimensions.

Type locality. ‘ Blue clay of Muddy Creek, 10 miles south of Hamilton’ , (i.e. PL3082 Clifton Bank , Muddy Creek , 7 km west of Hamilton , Victoria) . AMG Coleraine WD 818225. Muddy Creek Formation. Balcombian, Middle Miocene .

Type material. Lectotype P12139, presented Lindsay Clarke. McCoy’s figured specimen chosen as lectotype.

Holotype of Cypraea dorsata Tate, SAM T849, Muddy Creek , Ralph Tate collection.

Holotype of Cypraea gabrieli Chapman, P12366, Bird Rock cliffs, presented by C.J. Gabriel, 3 April 1912.

Figured specimen P13060, presented W.H. Gregson 14 April 1919; figured specimen P308774, collected F.P. Spry 1922.

Time range. Janjukian–Bairnsdalian, Late Oligocene–Middle Miocene.

Occurrence and material. Janjukian. Jan Juc Formation: Bird Rock cliffs, Torquay (P308679, P308801, one specimen and one fragment); Deadmans Gully, Torquay (P315577, one specimen).

Batesfordian.

Gellibrand Formation: PL 3047 cutting Princetown-Simpson Road (P308786, one fragment).

Balcombian

Muddy Creek Formation : Muddy Creek (P12969, P219370, P61265, P308774, P308794, P308780, P308772-3, 11 specimens); PL3082 Clifton Bank (P308776, P308795, two specimens) .

Gellibrand Formation : Southeast of Gibson Beach (P54362, P308682, two specimens) .

Fyansford Formation : PL3078 Fossil Beach (P308677, 308779 two specimens) ; Balcombe Bay (P308683-5, three specimens) ; Mornington (P308782, one specimen) ; Schnapper Point (P24866, P30777-8, three specimens) ; Port Phillip (P308781, one specimen) ; Altona Bay Coal Shaft (P308787, one fragment); Batesford (P308790, one specimen) ; Overburden , Batesford Quarry (P303315, one specimen and one fragment); Orphanage Hill (P308784, one specimen) .

Morgan Limestone: Broken Cliffs opposite Waikerie, Murray River Cliffs , South Australia (private collection, Mannum) .

Bairnsdalian

Gellibrand Formation: Glenample Steps (P308771, one specimen); Princetown (P5288, one specimen).

Fyansford Formation : Grices Creek (P5286, P12968, P12970, P13060, P308681, five specimens) ; Middle beds, Grices Creek (P308680, one specimen) ; Murgheboluc (P308678, one specimen) .

Casts of a large cowry — which, due to their size, are almost certainly this species — have been found as follows:

Longfordian?

Gambier Limestone : Mount Gambier (P61262, one specimen, BM (NH) one specimen) .

Batesfordian.

Curlewis Limestone: Curlewis (P308806, one specimen).

Balcombian

Nullarbor Limestone: 5 km south of Watson Station , South Australia (P316748, one specimen) .

Fyansford Formation: Keilor (P58646, one specimen); sewerage excavation, Belmont (P308688, one specimen).

Gippsland Limestone: Newmerella Railway cutting (P308686, one specimen).

Morgan Limestone: Blanchetown (P316749, one specimen); ‘Brittan’, Murray River cliff 4.8 km downstream of Morgan (P316751, one specimen) .

Remarks. This is the largest known Australian cowry, living or fossil. Specimens over 190 mm in length are not uncommon. Specimens are quite common in the middle Miocene, but because of their size, complete or undamaged specimens are uncommon. Cypraea dorsata Tate is merely a small specimen of Zoila gigas . The general shape, fossula and aperture are the same. The main difference is that the anterior and posterior canals are more strongly developed in most large specimens of Z. gigas . Small specimens, like the type of C. dorsata , occur with larger specimens at Fossil Beach, Grices Creek, Muddy Creek and Batesford Quarry, and there are also gradations between the smallest and the largest specimens. For these reasons, C. dorsata is synonymised with Z. gigas .

Cypraea gabrieli Chapman was based on a crushed specimen from the Jan Juc Formation, which is very difficult to compare with other material. The main differences between it and the lectotype of Z. gigas McCoy are a depressed spire, the lack of callus covering the spire and the presence of a dimpled dorsum. Only one other specimen from the Jan Juc Formation is available. This is complete and uncrushed, but has a very chalky shell. There are well-developed teeth on the outer lip extending to about midway on the lip. On the columella there are some very low but distinct teeth situated over the fossula and about midway along the aperture. The dorsum is smooth and the base is rounded rather than flat or convex. Apart from the presence of the columellar teeth, this specimen closely matches a similarsized specimen from the Fyansford Formation at Grices Creek in all features including the spire and fossula. McCoy pointed out there were weak teeth just visible on the columella of the holotype of Z. gigas . The significance, if any, of the presence of the dimpled dorsum cannot be assessed as there are so few specimens. Because there are no consistent differences between the two specimens from the Jan Juc Formation and specimens of Z. gigas from the Fyansford Formation, Cypraea gabrielli is regarded as a further synonym of Z. gigas .

The protoconch of this species (figs 2B, 13E–F) is different from those of other species of Zoila and also from those of species of Umbilia . There are fewer whorls and the first is irregular in shape, suggesting that it might originally have been chitinous and subsequently calcified. Other species of Zoila are similar to species of Umbilia in that they have a smooth, regular protoconch of three whorls, and a coiling axis at an angle to that of the teleoconch.

Figures

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 13. A–C, Zoila platypyga, P304415, PL 3078, × 1; E–H, Z. gigas; E, protoconch, P308804, Muddy Creek, × 2.5; F, protoconch, P308807, Batesford Quarry, × 2; G–H, holotype of Cypraea dorsata Tate, SAM T849, Muddy Creek, × 1.

Figure 14. A–H, Zoila gigas; A–B, holotype of Cypraea gabrieli Chapman, P12366, Bird Rock cliffs, Torquay, × 0.5; C–E, P308679, Bird Rock cliffs, × 0.5; F–H, P13060, Grices Creek, 0.5.

Figure 15. A–E, Zoila gigas; A–B, P308774, Clifton Bank, × 0.5; C–E, lectotype, P12139, Muddy Creek, × 0.5.

Dimensions.